Chanaresuchus
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''Chanaresuchus'' is an extinct
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
proterochampsia Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae (e.g. '' Proterochampsa'', '' Chanaresuchus'' and '' Tropidosuchus'') and probably also the Doswelliidae. Nesbitt (2011) defi ...
n
archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...
. It was of modest size for a proterochampsian, being on average just over a meter in length. Fossils are known from the Middle and
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 ...
of La Rioja Province,
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
and
Rio Grande do Sul Rio Grande do Sul (, , ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative_units_of_Brazil#List, fifth-most-populous state and the List of Brazilian st ...
(geoparque Paleorrota),
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. The
type species In 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 species that contains the biological type specimen ...
and only currently known species is ''Chanaresuchus bonapartei'' was named from the
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). ...
-age
Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones ...
in 1971. A second species ''C. ischigualastensis'' named in 2012 from the late
Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
-age
Ischigualasto Formation The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...
, was briefly assigned to ''Chanaresuchus'' before being moved to its own genus '' Pseudochampsa'' in 2014. ''C. bonapartei'' has recently been found in the Carnian
Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and oth ...
in Brazil. ''Chanaresuchus'' appears to be one of the most common archosauriforms from the Chanares Formation due to the abundance of specimens referred to the genus. Much of the material has been found by the La Plata-Harvard expedition of 1964-65. ''Chanaresuchus'' was originally classified in the family
Proterochampsidae Proterochampsidae is a family of proterochampsian archosauriforms. Proterochampsids may have filled an ecological niche similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now South America in the Mid ...
, although it has been placed in the family Rhadinosuchidae in more recent studies (both families belong to the larger group
Proterochampsia Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae (e.g. '' Proterochampsa'', '' Chanaresuchus'' and '' Tropidosuchus'') and probably also the Doswelliidae. Nesbitt (2011) defi ...
).


Description

''Chanaresuchus'' has a low, elongate skull that is characteristic of proterochampsians. The skull is quite broad posteriorly with a narrow snout, varying in length from around 165mm to 260mm in the largest individuals. The nares are slit-like and positioned away from the tip of the
rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...
, farther up the skull. 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 b ...
is slightly down-curved. The skull table is highly ornamented in larger specimens, with the
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including much of the skull, jaws, gill covers, shoulder girdle and fin spines rays (lepi ...
s well sculptured. The palate of ''Chanaresuchus'' has two elongate
choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...
e. Two small openings anterior to the choanae may be anterior palatine foramina that could have been used for access to
vomeronasal organ The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate) in various tetrapods. ...
s. The
secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...
formed between these two sets of openings may have been an adaptation for breathing through the snout while underwater. Unlike other proterochampsians and early archosaurs, ''Chanaresuchus'' had little body armor. The only
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 amp ...
s found are small and scale-like, forming a single row down the back. They run from the neck to the hip, ending at the last
presacral In human anatomy, the presacral space is inside the pelvis, behind the rectum and in front of the coccyx and sacrum. Normally it is empty, or it contains a pocket of fat. It is usually covered by sigmoid colon. Clinical significance The presacral ...
vertebra. They most likely continue down the tail, although tail osteoderms are not preserved in any specimens. There are roughly three osteoderms overlying each vertebra. The foot of ''Chanaresuchus'' differs from other related archosaurs in that the inner toes are inlarged, whereas other primitive archosaurs retain a more symmetrical pattern. The first digit is reduced but robust, the second digit is the thickest, and the third digit is the longest, although somewhat slender in comparison to the others. The fourth digit is very slim and the fifth consists of only a
metatarsal 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 ...
spur.


Paleobiology

A semiaquatic lifestyle similar to
phytosaur Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...
s and modern day
crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
ns has been proposed for ''Chanaresuchus'', as is suggested by the secondary palate and upward facing orbits and nostrils. However, some evidence, such as a lack of aquatic
amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s found from the Chañares Formation, suggests that the area was relatively dry during the time of deposition. A terrestrial lifestyle is possible for the genus, as extreme differences in the size of the forelimbs relative to the hind limbs in comparison to other "thecodonts" may be considered a characteristic of
bipedalism Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' a ...
. However, this is most likely not the case for ''Chanaresuchus'', and the evidence still remains in favor of a semiaquatic animal. The
depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...
of the locality from which specimens of ''Chanaresuchus'' have been found was in close proximity to an area of high
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...
activity, because it was in an active
rift basin In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben wi ...
. It is thought that all of the recovered specimens had died in a single event of mass mortality and may have been buried on a
fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...
strandline A high water mark is a point that represents the maximum rise of a body of water over land. Such a mark is often the result of a flood, but high water marks may reflect an all-time high, an annual high (highest level to which water rose that ...
. The mortality-causing event was most likely linked to regional volcanic activity. The locality from which specimens of ''C. bonapartei'' have been found is well known for its abundance of tetrapods. Theraspids include the
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, typicall ...
''
Dinodontosaurus ''Dinodontosaurus'' (meaning "terrible-toothed lizard") is a genus of dicynodont therapsid. It was medium to large dicynodont of the Triassic (with skull up to long) and had a beak corneum. It lived in the Middle Triassic but disappeared in the ...
'', and
cynodonts The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
such as ''
Probainognathus ''Probainognathus'' meaning “progressive jaw” is an extinct genus of cynodonts that lived around 235 to 221.5 million years ago, during the Late Triassic in what is now South America. ''Probainognathus'' is a member of the family Probainogna ...
'' and '' Massetognathus'', the latter being the most abundant taxon of the locality. However, the most common group of tetrapods present from the formation are the archosaurs.
Ornithodira Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinos ...
ns include ''
Lewisuchus ''Lewisuchus'' is a genus of archosaur that lived during the Late Triassic (early Carnian). As a silesaurid dinosauriform, it was a member of the group of reptiles most commonly considered to be the closest relatives of dinosaurs (possibly tr ...
'', ''
Lagerpeton ''Lagerpeton'' is a genus of lagerpetid avemetatarsalian, comprising a single species, ''L. chanarensis''. First described from the Chañares Formation of Argentina by A. S. Romer in 1971, ''Lagerpeton'' anatomy is somewhat incompletely kn ...
'', ''
Marasuchus ''Marasuchus'' (meaning " Mara crocodile") is a genus of basal dinosauriform archosaur which is possibly synonymous with ''Lagosuchus''. Both genera lived during the Late Triassic in what is now La Rioja Province, Argentina. ''Marasuchus'' cont ...
'', and ''
Pseudolagosuchus ''Lewisuchus'' is a genus of archosaur that lived during the Late Triassic (early Carnian). As a silesaurid dinosauriform, it was a member of the group of reptiles most commonly considered to be the closest relatives of dinosaurs (possibly tr ...
''. Other archosaurs include ''
Gracilisuchus ''Gracilisuchus'' (meaning "slender crocodile") is an extinct genus of tiny pseudosuchian (a group which includes the ancestors of crocodilians) from the Late Triassic of Argentina. It contains a single species, ''G. stipanicicorum'', which is pl ...
'' and ''
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 ...
''. Another proterochampsian, which was named alongside ''Chanaresuchus'' in 1971, is '' Gualosuchus''. It is very similar in appearance to ''Chanaresuchus'', differing only in size and cranial proportions.


References


External links


''Chanaresuchus''
in the
Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...
{{Taxonbar, from=Q744348 Proterochampsians Prehistoric reptile genera Middle Triassic reptiles of South America Late Triassic reptiles of South America Triassic Argentina Fossils of Argentina Santa Maria Formation Triassic Brazil Fossils of Brazil Fossil taxa described in 1971 Taxa named by Alfred Romer