Caseasaur
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Caseasauria is one of the two main
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s of early
synapsids Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
, the other being the
Eupelycosauria 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 ...
. Caseasaurs are currently known only from the
Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...
and the
Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...
, and include two superficially different families, the small insectivorous or carnivorous
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 l ...
, and the large,
herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...
Caseidae Caseidae are an Extinction, extinct Family (biology), family of Basal (phylogenetics), basal synapsids that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the so ...
. These two groups share a number of specialised features associated with the morphology of the snout and external
naris A nostril (or naris , : 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 turbinates, ...
. The ancestor of caseasaurs can be traced back to an insect eating or an omnivorous
reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
-like
synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
from the Pennsylvanian time of the
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
, possibly resembling ''
Archaeothyris ''Archaeothyris'' is an extinct genus of ophiacodontid synapsid that lived during the Late Carboniferous and is known from Nova Scotia. Dated to 306 million years ago, ''Archaeothyris'', along with a more poorly known synapsid called ''Echinerpet ...
'', the earliest known synapsid. The caseasaurs were abundant during the later part of the
Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...
, but by 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 ± 0. ...
caseasaur diversity declined because the group was outcompeted by the more successful therapsids. The last caseasaurs became extinct at the end of the Guadelupian (Middle Permian).


Description

Among the most conspicuous characteristics uniting caseasaurs are an enlarged nostril and a snout tip that overhangs the tooth row. Early caseasaurs, including all eothyridids, were relatively small animals. However, most caseids reached larger sizes, and some caseids, such as ''Cotylorhynchus'' and ''
Alierasaurus ''Alierasaurus'' is an extinct genus of caseid synapsid that lived during the early Guadalupian, Middle Permian (Roadian) in what is now Sardinia. It is represented by a single species, the type species ''Alierasaurus ronchii''. Known from a ve ...
'', were among the largest terrestrial animals of the early Permian. These large herbivorous taxa reached a length of and a mass of .


Evolution

Caseasaurs first appear in the fossil record in the late
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
, alongside many other early amniote groups. The earliest known synapsid, ''
Asaphestera ''Asaphestera'' is an extinct genus of a synapsid described on the basis of fossils from the Carboniferous of the Joggins locality in Nova Scotia, Canada. It was originally described as an undetermined lepospondyl and subsequently classified as ...
'' from the
Bashkirian The Bashkirian is in the International Commission on Stratigraphy geologic timescale the lowest stage (stratigraphy), stage or oldest age (geology), age of the Pennsylvanian (geology), Pennsylvanian. The Bashkirian age lasted from to Mega annu ...
age, may be an eothyridid caseasaur. The earliest definitive caseasaur is '' Eocasea''. Caseids thrived during 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 Arti ...
age, and numerous large herbivorous caseids are known from the Kungurian of the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
. Caseasaurs are one of the two pelycosaur clades known to have survived into the
Guadalupian The Guadalupian is the second and middle Series (stratigraphy), series/Epoch (geology), 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 an ...
epoch, along with varanopids. Two caseasaur taxa are known from the Guadalupian of Russia, representing the geologically youngest known caseasaurs: the small, possibly omnivorous or insectivorous ''
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 Bash ...
'', and the large, herbivorous ''
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 ...
''.


Classification

Caseasauria is generally regarded as the most basal clade of synapsids, with all other synapsids being grouped in the clade
Eupelycosauria 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 ...
. However, not all studies have supported this position. In 2012, Roger Benson argued that most of the characters supporting a basal position for caseasaurs pertained to the skull, and presented a phylogenetic analysis incorporating more postcranial data that resolved a clade comprising ophiacodontids and varanopids as the basalmost synapsid clade. However, new postcranial data from eothyridids and basal caseids established that caseasaurs were more basal than ophiacodontids and varanopids after all, with the characters supporting a more derived position for caseasaurs being the result of convergent evolution between caseids and more derived synapsids. The
diadectomorphs Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional ...
, conventionally regarded as anamniote tetrapods, may prove to be synapsids even more basal than Caseasauria. Most caseasaurs are divided into two families,
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 l ...
and
Caseidae Caseidae are an Extinction, extinct Family (biology), family of Basal (phylogenetics), basal synapsids that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the so ...
. The affinities of the earliest definitive caseasaur, ''Eocasea'', are uncertain, with some phylogenetic analyses finding it to be a caseid and others finding it to be a basal caseasaur belonging to neither family. Three genera are typically regarded as belonging to the family Eothyrididae: ''Eothyris'', ''Oedaleops'', and ''Vaughnictis''. However, some phylogenetic analyses have failed to resolve the eothyridids as a clade, instead finding them to be paraphyletic with respect to Caseidae. ''Asaphestera'' has been provisionally regarded as an eothyridid as well, without being included in a phylogenetic analysis. The remaining caseasaurs belong to the family Caseidae.


List of species


Paleoecology

The paleoecology of caseids is debated. They are typically interpreted as terrestrial animals of dry, upland habitats. However, Caseids exhibit a similar bone microstructure to cetaceans and pinnipeds, which has led to the hypothesis that they led an aquatic lifestyle. This hypothesis has been challenged on the grounds that their bone microstructure specifically resembles fully pelagic animals, and is unlike the bone microstructure of semiaquatic animals, but that the body plan of caseids is inconsistent with a pelagic lifestyle. Moreover, caseid fossils are predominantly associated with arid upland deposits.


See also

*
Evolution of mammals The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian (geology), Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synaps ...
*
Vertebrate paleontology Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct vertebrates (animals with vertebrae and their descendants). It also t ...
*
Permian tetrapods Permian tetrapods were amphibians and reptiles that lived during the Permian Period. During this time, amphibians remained common, including various Temnospondyli and Lepospondyli. Synapsids became the dominant type of animal, represented by the ...


References


Bibliography

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External links


Palaeos Vertebrates 390.100 Synapsida
{{Taxonbar, from=Q131807 Pennsylvanian first appearances Guadalupian extinctions Taxa named by Samuel Wendell Williston