Tarjadia
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''Tarjadia'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of erpetosuchid
pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
n, distantly related to modern
crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
ns. It is known from a single species, ''T. ruthae'', first described in 1998 from the
Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...
Chañares Formation in
Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
. Partial remains have been found from deposits that are
Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...
-
Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...
in age. Long known mostly from
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...
s,
vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
e, and fragments of the skull, specimens described in 2017 provided much more anatomical details and showed that it was a fairly large predator. ''Tarjadia'' predates known species of
aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
s and
phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...
s, two
Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...
groups of crurotarsans with heavy plating, making it one of the first heavily armored archosaurs. Prior to 2017, most studies placed it outside
Archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...
ia as a member of Doswelliidae, a family of heavily armored and crocodile-like archosauriforms. The 2017 specimens instead show that it belonged to the Erpetosuchidae.


Etymology

The genus name ''Tarjadia'' is derived from Sierra de los Tarjados, the closest mountain range to the outcrops of the Los Chañares Formation where remains have been found. The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''T. ruthae'' was named in honor of Ruth Romer, wife of the American
paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Alfred 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 ...
, who led a
Harvard Harvard University is a private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher lear ...
expedition to Los Chañares in 1964 and 1965. Ruth went with Alfred on the expedition and was the first woman to work in the locality.


History

The first remains of ''Tarjadia'' from the Chañares Formation were mentioned by Alfred Romer in 1971. He recognized two types of osteoderms from the formation, which he tentatively attributed to the rauisuchian ''
Luperosuchus ''Luperosuchus'' (meaning "vexing" or "difficult crocodile") is an extinct genus of loricatan pseudosuchian reptile (historically known as a "rauisuchian") which contains only a single species, ''Luperosuchus fractus.'' It is known from the Cha ...
'' because of their large size and similar appearance to scutes of other rauisuchians. In 1990, more complete osteoderms were found from the formation, as well as associated vertebrae. Three years later, in Romer's collections at
Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...
, remains of a skull were found in association with an osteoderm that was similar to the ones described in 1971 and 1990. This allowed ''Tarjadia'' to be erected as a new genus, distinct from ''Luperosuchus''.


Specimens

The initial 1998 description of ''Tarjadia ruthae'' listed several specimens: * PULR (Museo de Paleontologia at Universidad de La Rioja) 603 (
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
): six complete
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...
s, three osteoderm fragments, and at least six fragmentary
vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
e. * MCZ 9319: A fragmentary skull roof and
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
, a fragment of the lower jaw, and an osteoderm fragment. * MCZ 4076: four osteoderms. In 2016, Ezcurra considered MCZ 4077 (a partial femur and osteoderm fragments), which had previously been referred to ''Luperosuchus'' and even used in a study of the histology of that genus, as actually referable to ''Tarjadia''. Additional specimens from various parts of the Chañares Formation were described in 2017, greatly expanding knowledge of the animal. These specimens include: * CRILAR
Centro Regional de Investigaciones y Transferencia Tecnológica de La Rioja, Paleontología de Vertebrados
-Pv 463b: six osteoderm fragments. * CRILAR-Pv 477: A partial skeleton, not including the skull. * CRILAR-Pv 478: A partial skeleton, including a partial skull. * CRILAR-Pv 479: The tip of a dentary, seven vertebrae, two osteoderms, and rib fragments. * CRILAR-Pv 495: A nearly complete skull and lower jaws. * CRILAR-Pv 564: two vertebrae, two teeth, and other fragments. * CRILAR-Pv 565: A partial skeleton including the rear part of a skull. * CRILAR-Pv 566: A partial braincase.


Description


Osteoderms

''Tarjadia'' has been diagnosed on the basis of its osteoderms, or bony
scute A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "Scutum (shield), shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of Bird anatomy#Scales, birds. The ter ...
s, the most common material that has been found of the genus. The paramedian osteoderms, which overlie the back to either side of the midline, are thick and rectangular. Their medial edges are serrated, allowing the two rows to suture tightly together. Smaller, more rounded osteoderms are thought to have been placed to the sides of the paramedians, although no articulated remains bearing these lateral osteoderms have been found to prove this. Both the paramedian and lateral osteoderms are deeply pitted. The paramedian osteoderms are thickest at the center and medial edges, with
spongy bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
between the
compact Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to: * Interstate compact, a type of agreement used by U.S. states * Blood compact, an ancient ritual of the Philippines * Compact government, a t ...
outer layers.


Skull

''Tarjadia'' is characterised by an extremely robust skull. The bones of the skull table are very thick. Like the osteoderms, they are covered in coarse pitting. The surfaces of these bones also bear perforations for blood vessels, especially around the edges of the
orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...
, or eye sockets. The
parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...
s, which lie between two openings on the skull table called
supratemporal fenestrae Temporal fenestrae are openings in the Temple (anatomy), temporal region of the skull of some Amniote, amniotes, behind the Orbit (anatomy), orbit (eye socket). These openings have historically been used to track the evolution and affinities of re ...
, have a distinctive
sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...
. On the underside of the parietals, there is a depression for the
olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
of the
brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
, responsible for the perception of smell. An olfactory channel leads up to this depression and can be seen on the underside of the
frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...
s. The fragmentary occipital area of the skull (the base of the skull) shows part of the boundary of the
foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...
(through which the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
enters the skull), channels for the
vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...
(part of the
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
responsible for balance), and holes for the
semicircular canal The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
(also part of the vestibular system). These holes and channels are found on the supraoccipital bone. The exoccipitals and opisthotics are also known in ''Tarjadia'', and form the paraoccipital processes, two projections for the attachments of muscles that horizontally rotate the skull. These processes form notches that may be tympanic fossae, grooves towards the eardrums.


Vertebrae

The
vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
e of ''Tarjadia'' have
centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the individual shops are all owned by individual franchisees. The chain has three ...
, or central bodies, that are about as long as they are high. The centra have concave ventral surfaces and depressed lateral surfaces. The
neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
that project upward from the centra are laterally compressed, but have distal portions that expand into a flattened table with a groove on its upper surface. Above the flat tables of the neural arches lie the paramedian osteoderms, which also form a flat surface. Thick
transverse processes Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
on some vertebrae suggest that they make up the
sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
, the area of the spine that attaches to the
pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
. The six vertebrae known from ''Tarjadia'' probably represent the posterior dorsals, sacrals, and first caudals, comprising the end of the back vertebrae and the beginning of the tail vertebrae.


Classification

Comparisons between ''Tarjadia'' and other Triassic archosaurs and archosauriforms were made in its initial 1998 description. The
archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles encompassing archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common anc ...
s '' Doswellia'' and ''
Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W. K. Parker) is an Extinction, extinct genus of archosauriform reptile from the Triassic of South Africa. ''Euparkeria'' is close to the ancestry of Archosauria, the reptile gro ...
'', as well as the archosauriform family Proterochampsidae, all have heavy armor over the dorsal vertebrae and existed around the same time as ''Tarjadia''. Proterochampsids do not have ornamented osteoderms like ''Tarjadia'', nor do they have two rows of osteoderms on either side of the back (most proterochampsids, with the exception of '' Cerritosaurus'' and '' Chanaresuchus'', have only a single row on either side). While ''Euparkeria'' has a pair of osteoderms overlying each vertebra, similar to the condition seen in ''Tarjadia'', its osteoderms aren't ornamented. Ornamented paired osteoderms are seen as derived conditions in ''Doswellia'' and crurotarsan archosaurs. Some studies have not considered ''Tarjadia'' to be a close relative of ''Doswellia'' because of differences in the structure of the vertebrae. Moreover, ''Tarjadia'' possesses a
prefrontal bone The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and ...
in the skull which is absent in ''Doswellia''. Among crurotarsans, vertebrae that are each overlain by a single row of pitted, paired osteoderms as in ''Tarjadia'' are seen in aetosaurs, phytosaurs, and
Crocodylomorpha Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...
. ''Tarjadia'' has been distinguished from aetosaurs by its apparent lack of an anterior articular lamina (a depressed region along the front of each osteoderm), and clear differences in the skull tables. ''Tarjadia'' differs from
sphenosuchia Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms ...
ns and
proterosuchia Proterosuchia is one of the suborders of the paraphyletic group Thecodontia, containing the most primitive and ancestral forms. These were primitive, vaguely crocodile-like, archosauriforms that mostly lived during the Early Triassic epoch. Th ...
ns, the two main Triassic crocodylomorph groups, in that its osteoderms lack any clear structures on the anterior edges of the osteoderms. In the case of sphenosuchians, the anterior edge of the osteoderm forms a process or "lappet", while in protosuchians, the anterior edge has a depressed band similar to those of aetosaurs. Out of all Triassic crurotarsans, the osteoderms of ''Tarjadia'' bear the closest resemblance to those of phytosaurs; they have a similar shape and are also heavily pitted. Moreover, the skull roof of is also pitted in phytosaurs. However, ''Tarjadia'' can be distinguished from all phytosaurs in that it has differently shaped parietal bones. The strong sagittal crest on the parietals of ''Tarjadia'' is not seen in any phytosaur. When it was first erected in 2011, the family Doswelliidae was proposed to include ''Doswellia'', '' Archeopelta'', and ''Tarjadia''.
Synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
, or unique features of the group, include coarsely pitted and incised osteoderms and an anterior articular lamina. The phylogenetic analysis conducted by Ezcurra ''et al.'' (2017) did not confirm a close relationship between ''Tarjadia'' and ''Doswellia''; instead, ''Tarjadia'' was recovered as an erpetosuchid
pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
n archosaur. The cladogram of the strict consensus tree from the study is given below.


References


External links


Supplementary data
for "Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea" (2017), including geological information, anatomical details on ''Tarjadia ruthae'', and details of a phylogenetic analysis. {{Taxonbar, from=Q7686222 Erpetosuchidae Middle Triassic pseudosuchians Middle Triassic reptiles of South America Anisian life Triassic Argentina Fossils of Argentina Chañares Formation Fossil taxa described in 1998 Prehistoric pseudosuchian genera