Caseidae are an
extinct family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of
basal
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes rep ...
s that lived from the Late
Carboniferous to Middle
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...
between about 300 and 265 million years ago. Fossils of these animals come from the south-central part of the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
(
Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
,
Oklahoma, and
Kansas
Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to ...
), from various parts of
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
(
European Russia
European Russia (russian: Европейская Россия, russian: европейская часть России, label=none) is the western and most populated part of Russia. It is geographically situated in Europe, as opposed to the cou ...
,
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...
,
Germany
Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...
,
Sardinia
Sardinia ( ; it, Sardegna, label= Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, af ...
, and
Poland
Poland, officially the Republic of Poland, , is a country in Central Europe. Poland is divided into Voivodeships of Poland, sixteen voivodeships and is the fifth most populous member state of the European Union (EU), with over 38 mill ...
), and possibly from
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...
if the genus ''
Eunotosaurus
''Eunotosaurus'' (''Latin'': Stout-backed lizard) is an extinct genus of amniote, possibly a close relative of turtles. ''Eunotosaurus'' lived in the late Middle Permian (Capitanian stage) and fossils can be found in the Karoo Supergroup of So ...
'' is indeed a caseid as some authors proposed in 2021. Caseids show great
taxonomic
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. A ...
and morphological diversity. The most basal taxa were small
insectivorous
A robber fly eating a hoverfly
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
The first vertebrate insectivores were ...
and
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
forms that lived mainly in the Upper Carboniferous and Lower Permian, such as ''
Eocasea
''Eocasea'' is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas. It is known from a single type species, ''Eocasea martini''.
Description
''Eocasea'' is the oldest and most basal member of Caseidae, lacking many o ...
'', ''
Callibrachion
''Callibrachion'' is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen ( MNHN.F.AUT490) is represented by an almost complete postcranial skeleton asso ...
'', and ''
Martensius
''Martensius'' is an extinct genus of caseid synapsid from the Early Permian of Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after R ...
''. This type of caseid persists until the
middle Permian
The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ...
with ''
Phreatophasma
''Phreatophasma'' is an extinct genus of synapsids from the Middle Permian of European Russia. It includes only one species, ''Phreatophasma aenigmatum'', which is itself known from a single femur found in a mine near the town of Belebei in Bashk ...
'' and may be ''Eunotosaurus''. During the early Permian, the
clade is mainly represented by many
species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
that adopted a
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
diet. Some have evolved into gigantic forms that can reach in length, such as ''
Cotylorhynchus hancocki
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and possibly the early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. The large num ...
'' and ''
Alierasaurus ronchii'', making them the largest Permian synapsids. Caseids are considered important components of early terrestrial
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s in vertebrate history because the numerous herbivorous species in this family are among the first terrestrial
tetrapod
Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...
s to occupy the role of
primary consumer
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
. The caseids experienced a significant
evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rap ...
at the end of the early Permian, becoming, with the
captorhinid
Captorhinidae (also known as cotylosaurs) is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea.
Description
Ca ...
eureptiles
Eureptilia ("true reptiles") is one of the two major subgroups of the clade Sauropsida, the other one being Parareptilia. Eureptilia includes Diapsida (the clade containing all modern reptiles and birds), as well as a number of primitive Permo- ...
, the dominant herbivores of terrestrial ecosystems in place of the
edaphosaurids
Edaphosauridae is a family of mostly large (up to 3 meters or more) Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.
Characteristics
They were the earliest known herbivoro ...
and
diadectids
Diadectidae is an extinct family of early tetrapods that lived in what is now North America and Europe during the Late Carboniferous and Early Permian in Asia during the Late Permian. They were the first herbivorous tetrapods, and also th ...
.
In 2016 and 2022, paleontologists proposed a
semiaquatic
In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below.
Semiaquatic animals
Semi aquatic animals include:
* Ve ...
lifestyle for the most derived genera like ''Cotylorhynchus'' and ''Lalieudorhynchus'', but this hypothesis is disputed by other researchers.
With a fossil record spanning from the Late Carboniferous to the Middle Permian, caseids are one of the basal synapsids groups (formely known as “
pelycosaur
Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is now ...
”) having the largest
stratigraphic
Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostr ...
range. They also represent one of only two basal synapsid groups (along with the
Varanopidae
Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an ''Archaeothyris''-like synapsid in the Late Carbonifero ...
) to survive in
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...
-dominated terrestrial communities. Thus, the last known caseids come from the
strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...
of the
middle Permian
The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ...
(Upper
Roadian
In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian Epoch or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the K ...
-
Wordian
In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian Epoch or Series. The Wordian lasted between and million years ago (Ma). It was preceded by the Roadian and ...
) of France and European Russia, where they cohabited notably with
dinocephalia
Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinoceph ...
ns. These last caseids still show a certain morphological diversity with medium to large herbivores (''
Ennatosaurus
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
'' and ''
Lalieudorhynchus
''Lalieudorhynchus'' is an extinct genus of caseid synapsids that lived during the Guadalupian (= Middle Permian) in what is now the south of France. The genus is only known by its type species, ''Lalieudorhynchus gandi'', which was named in 20 ...
''), as well as small predatory or omnivorous forms such as ''Phreatophasma'' and possibly ''Eunotosaurus''. Caseids are so far unknown in Upper Permian strata and probably disappeared at the end of the Middle Permian. They were replaced by
pareiasaur
Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permia ...
s (with similar dentition) and
dicynodont
Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typica ...
s.
Description

Caseids measured from less than to in length.
They had a small head wider than high and with a forward-inclined snout, a very short neck, a long tail, robust forelimbs, and a body of variable proportions depending on their diet. Small insectivorous species like ''
Eocasea
''Eocasea'' is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas. It is known from a single type species, ''Eocasea martini''.
Description
''Eocasea'' is the oldest and most basal member of Caseidae, lacking many o ...
'' had an unexpanded trunk.
Others with an omnivorous diet like ''
Martensius
''Martensius'' is an extinct genus of caseid synapsid from the Early Permian of Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after R ...
'' had a barely enlarged rib cage, a more elongated skull, smaller
nostril
A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called t ...
s, and a snout less inclined forward than in herbivorous caseids.
The latter were characterized by their disproportionately small
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...
compared to the size of the body. The postcranial skeleton indeed shows a spectacular increase in the volume of the
rib cage
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi ...
, which becomes very wide and barrel-shaped, probably to accommodate a particularly developed
intestine
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans a ...
, necessary for the digestion of high-fiber rich plants. In these forms, the skull has very large external nostrils and a very short facial region with a strong forward inclination of the end of the snout which clearly overhangs the dental row. The
temporal fenestrae
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
are also relatively large (especially in ''
Ennatosaurus
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
''), the
supratemporals are large in size, and, on the
occipital
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cere ...
surface, the paroccipital
processes
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
are massively developed, establishing strong supporting contacts with the
squamosals.
The dorsal surface of the skull is covered with numerous small pits. These suggest the presence of large
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number ...
on the head of these animals.
Numerous
labial
The term ''labial'' originates from '' Labium'' (Latin for "lip"), and is the adjective that describes anything of or related to lips, such as lip-like structures. Thus, it may refer to:
* the lips
** In linguistics, a labial consonant
** In zoolo ...
running parallel to the ventral edge of the
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
and
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...
, as well as along the dorsal edge of the
dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, suggest the presence of scaly "lips" which must have concealed the dentition when the jaws were closed.
The
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...
, simply conical and pointed in insectivorous species, adopt in herbivorous species a leafy or spatulate morphology and are provided with more or less numerous cuspules. Numerous small teeth also adorned several bones of the palate. Herbivorous species do not show a simple evolutionary trend towards increasing tooth complexity.
Thus, the teeth of the basal taxa ''
Casea
''Casea'' is a genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, ''Casea broilii'', named by Samuel Wendell Willisto ...
'' and ''
Arisierpeton
''Arisierpeton'' is an extinct genus of synapsids from the Early Permian Garber Formation ( Sumner Group) of Richards Spur, Oklahoma. It contains a single species, ''Arisierpeton simplex''. Material was copied from this source, which is avail ...
'' have three cuspules
just like in the more derived forms ''
Cotylorhynchus
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) and possibly the early Middle Permian (Roadian) in what is now Texas and Oklahoma in the United States. The large number o ...
'' and ''
Caseopsis
''Caseopsis'' is an extinct genus of large pelycosaurs that was about long. ''Caseopsis'' lived in the late Early Permian epoch (Kungurian Age), before the pelycosaurs were replaced by the more advanced therapsids (in the next age). It was a li ...
''.
''Ennatosaurus'' and ''
Euromycter
''Euromycter'' is an extinct genus of caseid synapsids that lived in what is now southern France during the Early Permian (late Artinskian) about 285 million years ago. The holotype and only known specimen of ''Euromycter'' ( MNHN.F.MCL-2) in ...
'', which occupy an intermediate
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
position, have teeth bearing 5 to 7 cuspules and 5 to 8 cuspules respectively.
''
Angelosaurus
''Angelosaurus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) and early Middle Permian (Roadian) in what is now Texas and Oklahoma in the United States. Like other herbivorous caseids ...
'', one of the most derived caseids, has teeth with 5 cuspules.
In ''Angelosaurus'' the teeth have a bulbous morphology with very short and wide crowns. Their sturdiness and the significant wear they show, indicate that ''Angelosaurus'' must have fed on tougher plants than those on which most other herbivorous caseids fed.
Herbivorous caseids also show very different dietary adaptations from those seen in another group of basal synapsids, the
Edaphosauridae
Edaphosauridae is a family of mostly large (up to 3 meters or more) Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.
Characteristics
They were the earliest known herbivorous ...
. The latter had, in addition to the marginal dentition, a dental battery made up of numerous teeth located both on the
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly s ...
and on the inner surface of the lower jaws. In herbivorous caseids, the palatal teeth are smaller, and the inner surface of the lower jaws bears no teeth. Instead of a dental battery, they had a massive
tongue
The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste bu ...
(as indicated by the presence of a highly developed
hyoid apparatus
The hyoid apparatus is the collective term used in veterinary anatomy for the bones which suspend the tongue and larynx. It consists of pairs of stylohyoid, thyrohyoid, epihyoid and ceratohyoid bones, and a single basihyoid bone. The hyoid appar ...
found in ''Ennatosaurus'' and ''Euromycter'') perhaps rough, with which they had to compress food against the palatal teeth.

The forelimbs of caseids are often more robust than the hindlimbs. It has indeed been observed that the bones of the forelimbs gained in robustness from the beginning of the evolution of the group, before the appearance of large species, while the hindlimbs remained slenderer. These characteristics suggest that the initial strengthening of the forelimbs was probably related to a particular function such as digging, and that this trait was later
exapted
Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common ...
by more derived and larger caseids to support their weights of up to several hundred kilograms.
During their evolutionary history, caseids also show a reduction in their phalangeal formula. The most basal caseids like ''Eoasea'', ''
Callibrachion
''Callibrachion'' is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen ( MNHN.F.AUT490) is represented by an almost complete postcranial skeleton asso ...
'', and ''Martensius'' possessed the
plesiomorphic
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, an ...
condition of early
amniotes with a
phalangeal formula
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones ...
of 2-3-4-5-3 for
manus
Manus may refer to:
* Manus (anatomy), the zoological term for the distal portion of the forelimb of an animal (including the human hand)
* ''Manus'' marriage, a type of marriage during Roman times
Relating to locations around New Guinea
* Man ...
and 2-3-4-5-4 for
pes.
In ''Euromycter'' the manus has a formula of 2-3-4-4-3 (the pes is unknown).
In the more derived forms like ''Cotylorhynchus'' the manus and pes show a phalangeal formula of 2-2-3-3-2.
Along with this reduction in the number of phalanges, the proportions of the autopods also change in derived caseids with
metacarpals
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...
,
metatarsals
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...
, and
phalanges
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones ...
becoming shorter and broader. At the extreme of this specialization the genus ''Angelosaurus'' has short, broad, and smooth
ungual
An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulate
Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammal ...
phalanges which resemble
hooves
The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rum ...
rather than
claw
A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tars ...
s.
Footprints
Many vertebrate tracks have been proposed as belonging to Caseidae. In the early 2000s, large footprints known as ''
Brontopus giganteus'' from the Permian
Lodève
Lodève (; oc, Lodeva ) is a commune in the département of Hérault, in the Occitanie region in southern France. It is a sub-prefecture of the department. The derivation of the city's name is from Gaulish ''Luteva'', composed of lut-, swamp, m ...
basin in southern
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...
were considered to belong either to a caseid or
dinocephalia
Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinoceph ...
n
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...
.
In 2019, Lorenzo Marchetti and colleagues, however, determined that dinocephalians were most likely the trackmakers of the ichnogenus ''Brontopus''.
In 2012, Rafael Costa da Silva and colleagues proposed that the ichnogenus ''
Chelichnus
''Chelichnus'' is an ichnogenus of Permian tetrapod footprint. The name means ''tortoise traces'', because the shape of the prints was originally mistakenly thought to be produced by a tortoise. This is now known to be incorrect, as tortoises did ...
'', widely distributed in Permian desert facies (fossil
dune
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
s) of
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
,
North America and
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...
, could represent caseids footprints.
In 2019, Marchetti and colleagues, however, reinterpreted ''Chelichnus'' as a ''
nomen dubium
In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application.
Zoology
In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
'' and a
taphotaxon
A taphotaxon (from the Greek ταφος, ''taphos'' meaning ''burial'' and ταξις, ''taxis'' meaning ''ordering'') is an invalid taxon based on fossils remains that have been altered in a characteristic way during burial and diagenesis. The f ...
, this type of track showing false anatomical features generated by locomotion on sandy inclined paleosurface.
In 2014, Eva Sacchi and colleagues described the ichnotaxon ''
Dimetropus osageorum'' from about a hundred isolated footprints and several trackways from the early Permian
Wellington Formation
The Wellington Formation is an Early Permian geologic formation in Kansas and Oklahoma. The formation's Hutchinson Salt Member is more recognized by the community than the formation itself, and the salt is still mined in central Kansas. The Well ...
in
Oklahoma. The morphological study of these footprints and their comparison with tetrapod skeletons revealed that they probably belong to a large caseid comparable in size to ''
Cotylorhynchus romeri
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and possibly the early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. The large num ...
'' (the latter from more recent strata).
According to Sacchi and colleagues, some footprints from the Lodève Basin (unspecified geological formation) are similar to those from the Wellington Formation and these authors designate them as ''Dimetropus'' cf. ''osageorum''.
The study by Sacchi et al. also demonstrates that the ichnogenus ''Dimetropus'' exhibits great morphological variation and that its producers can be assigned to different zoological groups among non-therapsid synapsids and not just
Sphenacodontidae
Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian ...
as once thought.
In 2021, Rafel Matamales-Andreu and colleagues assigned footprints found in the Lower Permian (
Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of th ...
-
Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Art ...
) Port des Canonge Formation in
Mallorca
Mallorca, or Majorca, is the largest island in the Balearic Islands, which are part of Spain and located in the Mediterranean.
The capital of the island, Palma, is also the capital of the autonomous community of the Balearic Islands. The Bale ...
to a caseid. These footprints resemble those of ''D. osageorum'' but they also have differences. These footprints are left in open nomenclature as cf. ''Dimetropus'' sp.. They are, however, smaller than those of ''D. osageorum'' and would have been produced by a caseid of modest size with proportions comparable to ''
Ennatosaurus
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
''.
Paleobiology
Diets

During their evolutionary history, caseids shifted from faunivorous to herbivorous diet, a pattern that also occurred independently in other Carboniferous and Permian tetrapod groups such as
Captorhinida
Fossil of '' Labidosaurus hamatus''
Captorhinida (older name: Cotylosauria) is a doubly paraphyletic grouping of early reptiles. Robert L. Carroll (1988) ranked it as an order in the subclass Anapsida, composed of the following suborders:R. L. ...
e and
Edaphosauridae
Edaphosauridae is a family of mostly large (up to 3 meters or more) Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.
Characteristics
They were the earliest known herbivorous ...
. Earliest and most basal caseids, such as the late Carboniferous ''
Eocasea
''Eocasea'' is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas. It is known from a single type species, ''Eocasea martini''.
Description
''Eocasea'' is the oldest and most basal member of Caseidae, lacking many o ...
'' and the early Permian ''
Callibrachion
''Callibrachion'' is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen ( MNHN.F.AUT490) is represented by an almost complete postcranial skeleton asso ...
'' had an unexpanded rib cage and dentition composed of very small conical teeth suggesting an insectivorous diet. Another basal caseid, ''
Martensius
''Martensius'' is an extinct genus of caseid synapsid from the Early Permian of Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after R ...
'', has a slightly enlarged barrel-shaped trunk and dentition in which teeth indicative of an
insectivorous
A robber fly eating a hoverfly
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
The first vertebrate insectivores were ...
diet in juveniles have been
ontogenetically replaced in adults by teeth suggesting an
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
diet. In ''Martensius'', the adult was still able to feed on insects, but it also possesses a draft of the herbivorous diet specializations present in later caseids, such as a relatively short, slightly forward-inclined snout, and a dentition that is almost
homodont
In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology.
In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example ...
in the upper jaws and completely homodont in lower jaws. The sequence of dental trait acquisition in ''Martensius'' suggests that
intestinal
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans an ...
vegetation processing preceded
oral
The word oral may refer to:
Relating to the mouth
* Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid
**Oral administration of medicines
** Oral examination (also known as an oral exam or ora ...
processing in the evolution of caseid herbivory. A juvenile insectivorous diet would have provided the opportunity for successful introduction into the intestine of microorganisms capable of
endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...
cellulolysis
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
, particularly if the prey ingested were herbivorous insects which harbor such microorganisms in their
viscera
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...
. Subsequently, the caseids adopted a strictly herbivorous diet and evolved into gigantic forms. These herbivorous caseids had spatulate teeth equipped with more or less numerous cuspules and a very enlarged and barrel-shaped rib cage which must have housed highly developed intestines necessary for the digestion of plants with low nutritional value. This adaptation would partly explain the diversification and expansion of the group at the end of the Lower Permian and during the Middle Permian, because it allowed them to exploit a fiber-rich plant resource that had by then become abundant and widespread. Nevertheless, small probably faunivorous caseids like ''
Phreatophasma
''Phreatophasma'' is an extinct genus of synapsids from the Middle Permian of European Russia. It includes only one species, ''Phreatophasma aenigmatum'', which is itself known from a single femur found in a mine near the town of Belebei in Bashk ...
'' seem to have persisted until the Middle Permian.
Semiaquatic vs terrestrial lifestyle

Caseids are generally considered primarily terrestrial animals.
Everett C. Olson
Everett Claire Olson (November 6, 1910 – November 27, 1993) was an American zoologist, paleontologist, and geologist noted for his seminal research of origin and evolution of vertebrate animals.
Through his research studying terrestrial verte ...
in particular considered that the degree of ossification of the skeleton, the relatively short feet and hands, the massive claws, the limbs with very powerful extensor muscles, and the solid sacrum, strongly suggested a terrestrial lifestyle. Olson did not rule out that the caseids spent some time in water, but he considered locomotion on land to be an important aspect of their lifestyle.
It has been suggested that the very powerful forelimbs, with strong and very tendinous extensor muscles, as well as very massive claws, could be used to dig up roots or tubers.
However, the very short
neck
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
implied a low amplitude of vertical movements of the head which precluded the large species from feeding at ground level.
Another hypothesis suggests that the caseids could have used their powerful forelimbs to fold large plants towards them, which they would have torn off with their powerful claws.
Other hypotheses suggest that some caseids such as ''Cotylorhynchus'' used their limbs with powerful claws to defend themselves against predators, or during intraspecific activities linked in particular to
reproduction
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – " offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual o ...
. According to Olson, an interesting thing about this, is that almost all known specimens of the species ''
Cotylorhynchus hancocki
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and possibly the early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. The large num ...
'' have one to ten ribs broken and healed during life.
Finally, for some authors, the large derived caseids would have been
semiaquatic
In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below.
Semiaquatic animals
Semi aquatic animals include:
* Ve ...
animals that used their hands with large claws like
paddle
A paddle is a handheld tool with an elongated handle and a flat, widened distal end (i.e. the ''blade''), used as a lever to apply force onto the bladed end. It most commonly describes a completely handheld tool used to propel a human-powered ...
s, which could also be used to manipulate the plants on which they fed.
In 2016, Markus Lambertz and colleagues questioned the terrestrial lifestyle of large caseids like ''Cotylorhynchus''. These authors showed that the bone microstructure of the humerus, femur and ribs of adult and immature specimens of ''
Cotylorhynchus romeri
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and possibly the early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. The large num ...
'' resembled that of aquatic animals more than that of terrestrial animals, the bones having a very
spongy structure, an extremely thin
cortex
Cortex or cortical may refer to:
Biology
* Cortex (anatomy), the outermost layer of an organ
** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain''
*** Motor cortex, the regions of the cerebral cortex i ...
, and having no distinct
medullary canal
The medullary cavity (''medulla'', innermost part) is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow (adipose tissue) is stored; hence, the medullary cavity is also known as the marrow cavity.
Located in the ma ...
. This low bone density would have been a handicap for animals weighing several hundred kilos with a strictly terrestrial lifestyle. Lambertz et al. also argued that the joints between the vertebrae and the dorsal ribs allowed only small ranges of motion of the rib cage, thus limiting costal ventilation. To overcome this, they proposed that a proto-
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
was present to facilitate breathing, especially in aquatic environment. These authors also consider that the arid
paleoclimates to which the caseid deposits correspond are not incompatible with an aquatic lifestyle of these animals. These paleoenvironments in fact included a significant number of water bodies (rivers, lakes and lagoons). The arid conditions could have been the reason why the animals would sometimes congregate and eventually die. In addition, arid environments have a low density of plants, which would require even more locomotor effort to find food. Thus, for Lambertz et al., large caseids like ''Cotylorhynchus'' must have been mainly aquatic animals that only came on dry land for the purposes of reproduction or
thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
.
This hypothesis is however disputed by Kenneth Angielczyk and Christian Kammerer as well as by Robert Reisz and colleagues based on
paleontological
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
and
taphonomic
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...
data combined with the absence in these large caseids of morphological adaptations to an aquatic lifestyle. According to Angielczyk and Kammerer, the low bone density of caseids identified by Lambertz et al. does not resemble that of semiaquatic animals, which tend to have a more strongly ossified skeleton to provide passive
buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
control and increased stability against current and wave action. ''Cotylorhynchus'' bone microstructure is more similar to what is seen in animals living in the
open ocean
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
, such as
cetaceans and
pinniped
Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammal, marine mammals. They comprise the extant taxon, extant family (biology ...
s, which emphasize high maneuverability, rapid acceleration and hydrodynamic control of buoyancy. However, the caseid morphology was totally incompatible with a
pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
lifestyle. Thus, due to these unusual data, Angielczyk and Kammerer consider that the available evidence is still insufficient to question the more widely assumed terrestrial lifestyle of caseids.
Robert Reisz and colleagues also dispute the supposed semiaquatic lifestyle of the caseids on the fact that the latter possess no morphological adaptations to an aquatic lifestyle and, in the case of the species ''Cotylorhynchus romeri'', on the interpretation that this animal lived in a dry environment for part of the year as indicated by the presence of numerous skeletons of the amphibian ''
Brachydectes
''Brachydectes'' is an extinct genus of lysorophian amphibian that lived from the Carboniferous. It had a very small head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, an ...
'' preserved in
aestivation
Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and ...
and of the
lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
''
Gnathorhiza
''Gnathorhiza'' is an extinct genus of prehistoric lobe-finned fish (lungfish) which lived during the Permian period and Early Triassic epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the or ...
'', another well-known aestivator.
In 2022, Werneburg and colleagues proposed a somewhat different semiaquatic lifestyle, in which large caseids like ''
Lalieudorhynchus
''Lalieudorhynchus'' is an extinct genus of caseid synapsids that lived during the Guadalupian (= Middle Permian) in what is now the south of France. The genus is only known by its type species, ''Lalieudorhynchus gandi'', which was named in 20 ...
'' (whose bone texture is even more osteoporotic than in ''Cotylorhynchus'') would be ecological equivalents of modern
hippos, passing part of their time in the water (being underwater walkers rather than swimming animals) but coming on dry land for food.
Evolution


Caseids first appear in the fossil record at the end of the Carboniferous and are already present in both
North America and
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
with small predatory forms like ''
Eocasea
''Eocasea'' is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas. It is known from a single type species, ''Eocasea martini''.
Description
''Eocasea'' is the oldest and most basal member of Caseidae, lacking many o ...
'' and ''
Datheosaurus
''Datheosaurus'' is an extinct genus of caseasaur. It was at least in length. It lived during the Latest Carboniferous to Early Permian in Poland.
Discovery and history
It was originally described in 1905 on a basis of a specimen from late C ...
''.
These faunivorous caseids also exist at the beginning of the lower Permian, such as ''
Callibrachion
''Callibrachion'' is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen ( MNHN.F.AUT490) is represented by an almost complete postcranial skeleton asso ...
'',
and may have existed until the base of the middle Permian with ''
Phreatophasma
''Phreatophasma'' is an extinct genus of synapsids from the Middle Permian of European Russia. It includes only one species, ''Phreatophasma aenigmatum'', which is itself known from a single femur found in a mine near the town of Belebei in Bashk ...
''.
During the Permian, the representatives of the clade mainly evolved towards herbivory. These herbivorous caseids experienced an important
evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rap ...
during the second half of the lower Permian by becoming, with the moradisaurine
captorhinid
Captorhinidae (also known as cotylosaurs) is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea.
Description
Ca ...
eureptiles
Eureptilia ("true reptiles") is one of the two major subgroups of the clade Sauropsida, the other one being Parareptilia. Eureptilia includes Diapsida (the clade containing all modern reptiles and birds), as well as a number of primitive Permo- ...
, the main herbivores of terrestrial
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s instead of
edaphosaurids
Edaphosauridae is a family of mostly large (up to 3 meters or more) Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.
Characteristics
They were the earliest known herbivoro ...
and
diadectids
Diadectidae is an extinct family of early tetrapods that lived in what is now North America and Europe during the Late Carboniferous and Early Permian in Asia during the Late Permian. They were the first herbivorous tetrapods, and also th ...
. The decline of edaphosaurids and the propagation of caseids coincides with an aridification of the environment that occurred from the
Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of th ...
and which would have favored the caseid expansion.
Sedimentological
Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of mod ...
and
taphonomic
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...
data indicate that the majority of edaphosaurids favored humid habitats (their remains are found mainly in lacustrine and marshy deposits) while herbivorous caseids generally lived in drier
biotopes where ponds and streams water were ephemeral.
The last caseids date from the Middle Permian and are mainly known in Europe with ''Phreatophasma'' and ''
Ennatosaurus
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
'' from the
Roadian
In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian Epoch or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the K ...
-
Wordian
In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian Epoch or Series. The Wordian lasted between and million years ago (Ma). It was preceded by the Roadian and ...
of Russia,
''
Alierasaurus
''Alierasaurus'' is an extinct genus of caseid synapsid that lived during the early Middle Permian (Roadian) in what is now Sardinia. It is represented by a single species, the type species ''Alierasaurus ronchii''. Known from a very large par ...
'' from the Roadian-(Wordian?) of Sardinia,
and ''
Lalieudorhynchus
''Lalieudorhynchus'' is an extinct genus of caseid synapsids that lived during the Guadalupian (= Middle Permian) in what is now the south of France. The genus is only known by its type species, ''Lalieudorhynchus gandi'', which was named in 20 ...
'' from the late Wordian-early
Capitanian
In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian Epoch or Series. The Capitanian lasted between and million years ago. It was preceded ...
of southern France.
In North America, ''
Angelosaurus romeri'' and ''
Cotylorhynchus bransoni'' from the Chickasha Formation in Oklahoma probably date to the early Roadian, while the caseids from the San Angelo Formation in Texas are slightly older and may straddle the
Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Art ...
-Roadian boundary but it is not yet clear whether they date from the latest Kungurian or from the earliest Roadian.
Paleobiogeography
Caseid
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s have been found in the southern and central
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
(
Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
,
Oklahoma,
Kansas
Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to ...
),
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...
,
Germany
Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...
,
Poland
Poland, officially the Republic of Poland, , is a country in Central Europe. Poland is divided into Voivodeships of Poland, sixteen voivodeships and is the fifth most populous member state of the European Union (EU), with over 38 mill ...
,
Sardinia
Sardinia ( ; it, Sardegna, label= Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, af ...
, and
European Russia
European Russia (russian: Европейская Россия, russian: европейская часть России, label=none) is the western and most populated part of Russia. It is geographically situated in Europe, as opposed to the cou ...
. This geographical distribution corresponds to the paleoequatorial belt of
Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...
during the Carboniferous and the Permian, with the exception of the Russian localities which were located at the level of the
30th parallel north
The 30th parallel north is a circle of latitude that is 30 degrees north of the Earth's equatorial plane. It stands one-third of the way between the equator and the North Pole and crosses Africa, Asia, the Pacific Ocean, North America and th ...
where a more temperate climate prevailed. The absence in Russia of terrestrial vertebrate localities prior to the
Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Art ...
does not allow us to know the precise moment of the arrival of caseids in this region of the world.
According to Werneburg and colleagues, the presence of caseids at this
paleolatitude
Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.''
Certain magnetic minerals in rocks ...
suggests their possible existence in the temperate regions of
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...
.
A possible Gondwanan occurrence was proposed as early as the 1990s by Michael S.Y. Lee and in 2021 by Asher J. Lichtig and Spencer G. Lucas, who reinterpreted the middle Permian taxon ''
Eunotosaurus
''Eunotosaurus'' (''Latin'': Stout-backed lizard) is an extinct genus of amniote, possibly a close relative of turtles. ''Eunotosaurus'' lived in the late Middle Permian (Capitanian stage) and fossils can be found in the Karoo Supergroup of So ...
'' from
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...
as a small burrowing caseid.
Between these two dates, other researchers classified ''Eunotosaurus'' as a
parareptile
Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids (reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the ...
or a
pantestudines
Pantestudines or Pan-Testudines is the group of all reptiles more closely related to turtles than to any other living animal. It includes both modern turtles ( crown group turtles, also known as Testudines) and all of their extinct relatives (als ...
.
If the first three authors are correct, ''Eunotosaurus'' would be the first caseid found in the
Southern Hemisphere and the last known representative of the family with a latest
Capitanian
In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian Epoch or Series. The Capitanian lasted between and million years ago. It was preceded ...
age for the most recent specimens.
Elsewhere in Gondwana, the presence of the
ichnotaxon
An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...
''
Dimetropus'' in the Permian of
Morocco
Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria ...
suggests the future discovery of basal synapsids (including caseids) in the Permian basins of
North Africa
North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...
, which were also part of the paleoequatorial belt and constituted one of the main
migratory routes between the Northern and Southern Hemispheres.
Phylogeny
The family Caseidae was erected by
Samuel Wendell Williston
Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and paleontologist who was the first to propose that birds developed flight cursorially (by running), rather than arboreally (by leaping from ...
in 1911.
In 1940,
Alfred Sherwood Romer
Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution.
Biography
Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
and L.W. Price placed Caseidae and
Edaphosauridae
Edaphosauridae is a family of mostly large (up to 3 meters or more) Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.
Characteristics
They were the earliest known herbivorous ...
in the same suborder, which they named Edaphosauria.
This group is now abandoned, the edaphosaurids being closer to the
Sphenacodontia
Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes '' Haptodus baylei'', '' Haptodus garnettensis'' and ''Sphenacodon ferox'', but not '' Edaphosaurus pogonia ...
(with which they form the
clade Sphenacomorpha
Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308million years ago during the Early Pennsylvanian epoch, with the fo ...
) than to the caseids.
The latter are grouped with the
Eothyrididae
Eothyrididae is an extinct family of very primitive, insectivorous synapsids. Only three genera are known, ''Eothyris'', ''Vaughnictis'' and ''Oedaleops'', all from the early Permian of North America. Their main distinguishing feature is the large ...
in the clade
Caseasauria
Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small inse ...
, which represent the most
basal
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes rep ...
s.
The first
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis of caseids was published in 2008 by Hillary C. Maddin and colleagues. In this analysis, the genus ''
Oromycter
''Oromycter'' is an extinct genus of caseid synapsids from the Early Permian of Oklahoma. The sole and type species, ''Oromycter dolesorum'', was named in 2005 by Robert R. Reisz.Reisz, R. R. 2005. ''Oromycter'', a New Caseid from the Lower Per ...
'' occupies the most basal position within the clade. ''
Ennatosaurus
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
'' is the
sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
of a clade containing ''
Cotylorhynchus romeri
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and possibly the early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. The large num ...
'' and ''
Angelosaurus dolani
''Angelosaurus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. Like other herbivorous casei ...
''. This analysis reveals for the first time the
paraphyly of the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
''
Casea
''Casea'' is a genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, ''Casea broilii'', named by Samuel Wendell Willisto ...
'', the species ''“Casea” rutena'' representing a distinct genus which will be named in 2011 ''
Euromycter
''Euromycter'' is an extinct genus of caseid synapsids that lived in what is now southern France during the Early Permian (late Artinskian) about 285 million years ago. The holotype and only known specimen of ''Euromycter'' ( MNHN.F.MCL-2) in ...
''.
Below is the first
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
of caseids published by Maddin et al. in 2008.
Another phylogenetic analysis carried out in 2012 by Benson includes the genus ''
Trichasaurus'' which occupies an intermediate position between ''
Casea broilii
''Casea'' is a genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, ''Casea broilii'', named by Samuel Wendell Williston ...
'' and ''“Casea” rutena''. ''Ennatosaurus'' is identified as the sister group of a clade including ''Angelosaurus'' and the three species of ''Cotylorhynchus''. Within the latter genus, ''Cotylorhynchus romeri'' is the sister group of the two species ''C. hancocki'' and ''C. bransoni''.
Below is the cladogram of Caseasauria published by Benson in 2012.
In 2015, Marco Romano and Umberto Nicosia published the first cladistic study including almost all Caseidae (with the exception of ''
Alierasaurus ronchii'' from
Sardinia
Sardinia ( ; it, Sardegna, label= Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, af ...
, then considered too fragmentary). This study again resolves the genus ''Casea'' as paraphyletic, with the species ''“Casea” nicholsi'' representing a distinct unnamed genus. In their most parsimonious analysis, ''
Ruthenosaurus
''Ruthenosaurus'' is an extinct genus of caseid synapsids that lived in what is now southern France during the Early Permian (late Artinskian) about 285 million years ago. It is known from the holotype MNHN.F.MCL-1 an articulated partial po ...
'' is closely related to ''Cotylorhynchus hancocki''. ''Ennatosaurus'' occupies a higher position than in previous analyses, and is identified as more closely related to ''
Angelosaurus dolani
''Angelosaurus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian ( Kungurian) and early Middle Permian ( Roadian) in what is now Texas and Oklahoma in the United States. Like other herbivorous casei ...
''. However, the close relationship between ''A. dolani'' and ''Ennatosaurus'' may be biaised by the extreme incompleteness of the material from the North American species.
Below is the cladogram of caseids published by Romano and Nicosia in 2015.
A phylogenetic analysis published in 2016 by Neil Brocklehurst and colleagues includes for the first time the genera ''
Callibrachion
''Callibrachion'' is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen ( MNHN.F.AUT490) is represented by an almost complete postcranial skeleton asso ...
'' and ''
Datheosaurus
''Datheosaurus'' is an extinct genus of caseasaur. It was at least in length. It lived during the Latest Carboniferous to Early Permian in Poland.
Discovery and history
It was originally described in 1905 on a basis of a specimen from late C ...
'' which are identified as basal caseids occupying an intermediate position between ''Eocasea'' and ''Oromycter''.
Below is the phylogenetic analysis published by Neil Brocklehurst and colleagues in 2016.
In 2017 Romano and colleagues published the first phylogenetic analysis including the genus ''
Alierasaurus
''Alierasaurus'' is an extinct genus of caseid synapsid that lived during the early Middle Permian (Roadian) in what is now Sardinia. It is represented by a single species, the type species ''Alierasaurus ronchii''. Known from a very large par ...
''. The latter is recovered as the sister taxon of the genus ''Cotylorhynchus''.
Below is the phylogenetic analysis published by Romano and colleagues in 2017.
In describing the species ''
Martensius bromackerensis'' in 2020, Berman and colleagues published two
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
s in which ''Martensius'' is identified as one of the most basal caseids, and is positioned just above the Late Carboniferous ''
Eocasea martini
''Eocasea'' is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas. It is known from a single type species, ''Eocasea martini''.
Description
''Eocasea'' is the oldest and most basal member of Caseidae, lacking many of ...
''. In the first cladogram, the position of the remaining caseids is poorly resolved. In the second cladogram, ''
Casea broilii
''Casea'' is a genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, ''Casea broilii'', named by Samuel Wendell Williston ...
'' is positioned above ''Martensius bromackerensis'', and is followed by a
polytomy
An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
between ''
Oromycter dolesorum'', ''
Trichasaurus texensis'', and a clade of remaining caseid. Within these remaining taxa, a sequence of branching taxa begins with ''Casea nicholsi'', followed by ''
Euromycter rutenus
''Euromycter'' is an extinct genus of caseid synapsids that lived in what is now southern France during the Early Permian (late Artinskian) about 285 million years ago. The holotype and only known specimen of ''Euromycter'' ( MNHN.F.MCL-2) inc ...
'', then ''
Ennatosaurus tecton
''Ennatosaurus'' is an extinct genus of caseid synapsid that lived during the Middle Permian (late Roadian - early Wordian) in northern European Russia. The genus is only represented by its type species, ''Ennatosaurus tecton'', which was named ...
'', then ''
Angelosaurus romeri'', then an apical clade of the three ''
Cotylorhynchus
''Cotylorhynchus'' is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) and possibly the early Middle Permian (Roadian) in what is now Texas and Oklahoma in the United States. The large number o ...
'' species plus ''
Alierasaurus ronchii''. In this final clade, ''Cotylorhynchus hancocki'' and ''C. bransoni'' are sister taxa and the clade forms a polytomy with ''C. romeri'' and ''Alierasaurus ronchii''.
Below are the two caseid cladograms published by Berman and colleagues in 2020.
In 2022, Werneburg and colleagues described the genus ''
Lalieudorhynchus
''Lalieudorhynchus'' is an extinct genus of caseid synapsids that lived during the Guadalupian (= Middle Permian) in what is now the south of France. The genus is only known by its type species, ''Lalieudorhynchus gandi'', which was named in 20 ...
'' and published a phylogenetic analysis which concluded that the genera ''Angelosaurus'' and ''Cotylorhynchus'' are
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
and are represented only by their type species. In this analysis, ''Cotylorhynchus romeri'' is positioned just above the genus ''Angelosaurus'', and forms a polytomy with a clade containing ''Ruthenosaurus'' and ''
Caseopsis
''Caseopsis'' is an extinct genus of large pelycosaurs that was about long. ''Caseopsis'' lived in the late Early Permian epoch (Kungurian Age), before the pelycosaurs were replaced by the more advanced therapsids (in the next age). It was a li ...
'' and another clade containing ''Alierasaurus'', the two other species of ''Cotylorhynchus'' and ''Lalieudorhynchus''. Within this latter clade, ''Alierasaurus'' is the sister group of ''“Cotylorhynchus” bransoni'' and a more derived clade including ''Lalieudorhynchus'' and ''“Cotylorhynchus” hancocki''.
Below is the cladogram published by Werneburg and colleagues in 2022.
Notes
References
External links
Tree of Life
{{Taxonbar, from=Q132725
Caseasaurs
Prehistoric synapsid families
Taxa named by Samuel Wendell Williston