''Koilamasuchus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 indeterminate

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 ...

from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

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 ...

. It is based on an external mold of a partial postcranial skeleton from the

Quebrada de los Fósiles Formation Quebrada may refer to: Places Argentina * Quebrada de Las Flechas, a valley in the province of Salta in northern Argentina * Quebrada de Humahuaca, World Heritage, a valley in the province of Jujuy in northern Argentina * Quebrada de Luna, vill ...

. Due to its incomplete nature, the relationships of this reptile are difficult to establish. Originally described as a non-

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...

archosauriform, later studies tentatively considered it a doswelliid or a suchian archosaur.

Discovery

Remains have been found in the Quebrada de los Fósiles Formation of the Puesto Viejo Group in Argentina.''Koilamasuchus''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org This locality is probably

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). ...

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 ...

( Middle to

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 ...

) in age, although its exact age is debatable. ''Koilamasuchus'' is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word '''koilamas''' (which means cavity or pocket) and the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

suchus''' (which means crocodile). This is in reference to the lateral fossae (pits) on the type specimen's vertebrae. 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 ...

of ''Koilamasuchus, K. gonzalezdiazi'', refers to Dr. Emilio F. Gonzalez Diaz, the

paleontologist 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 ...

who discovered the holotype specimen. The fossil has been known since 1981 when it was first described by paleontologist

José Bonaparte José Fernando Bonaparte (14 June 1928 – 18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists . One of the best-known Argentine paleo ...

, but it was not described as a new genus and species until 2010. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen, MACN-Pv 18119, is an external mold of various parts of the postcranial skeleton, including dorsal

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e and a dorsal

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

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, a right ilium, a

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, an

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 ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual ...

, a

chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock ...

, a possible

gastralium Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...

, two

metapodial Metapodials are long bones of the hand (metacarpals) and feet (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. ...

s (either

metacarpal 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 ...

s or

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 ...

s), and several indeterminate bones including a possible

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

. The mold has several diagnostic features, such as an elongated illiac blade that is convex along its upper margin, that indicate that it is an archosauriform.

Description

In life, ''Koilamasuchus'' would have been a small reptile. Based on the proportions of ''

Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close ...

'', it would have been approximately 50 centimeters (20 inches) in total length. The dorsal vertebrae are tall, particularly the neural spines. The

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

part of the shaft of the rib curves outwards slightly, but also possesses a notch which forces the rib to strongly project outwards for a short distance and then gradually curve back inwards. A deep sulcus (groove) is also present on the shaft of the rib. The humerus is hourglass-shaped, with an expanded proximal end more than 3.5 times the width of the shaft. The distal end is also expanded to a slightly lesser degree. A wide, slanting ridge (or tuberosity) runs down the shaft of the humerus. The ilium possesses a completely closed

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...

with a triangular lower edge. The

pubic In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior r ...

and ischial peduncles are widely separated and the pubic peduncle is rather long while the ischial peduncle is short. One of MACN-Pv 18119's osteoderms is triangular, with a pointed front edge, a slightly rounded rear edge, and a pronounced longitudinal keel. Some other osteoderms are smaller and more oval-shaped.

Classification

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 was conducted in the 2010 paper which named and described the genus. ''Koilamasuchus'' was found to be closely related to Archosauria, a

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

that includes living

crocodilian 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 ...

s and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s. It was placed as the sister taxon to a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

containing Archosauria and

Erythrosuchidae Erythrosuchidae (meaning "red crocodiles" in Greek) are a family of large basal archosauriform carnivores that lived from the later Early Triassic (Olenekian) to the early Middle Triassic (Anisian). Naming The family Erythrosuchidae was named b ...

, a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of large basal archosauriforms. According to the resulting

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

, ''Koilamasuchus'' is more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

than ''

Osmolskina left, 210px, Fossil elements. ''Osmolskina'' is a genus of archosauriform reptile which lived during the Early Triassic in what is now Poland. The type species, ''Osmolskina czatkowicensis'', was described by Magdalena Borsuk−Białynicka and ...

'', ''

Sarmatosuchus ''Sarmatosuchus'' is an extinct genus of archosauriform reptile found in sediments of Middle Triassic age and known from the single species ''Sarmatosuchus otschevi''. It is one of the earliest stem-archosaur species known. The holotype and only ...

'', '' Fugusuchus'' (commonly thought to be an erythrosuchid), and

proterosuchid Proterosuchidae is an early family of basal archosauriforms whose fossils are known from the Latest Permian and the Early Triassic of Europe, Asia, Africa, Australia and possibly South America. The name comes from Greek πρότερο- ("first") ...

s (which were found to be

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 ...

). Being more derived than these other taxa, ''Koilamasuchus'' is closer to the crown group Archosauria. ''Koilamasuchus'' is considered more derived than proterosuchids and other early archosauriforms because it possesses an iliac preacetabular process, or a bony projection near the

(part of the hip joint). The pubic peduncle, a projection on the ilium that connects it to the pubis and forms part of the front edge of the acetabulum, is angled less than 45° from the bone's vertical axis. This is a derived feature not seen in more basal archosauriforms. ''Koilamasuchus'' had dorsal

s covering its back, which are also present in erythrosuchids and some archosaurs, but not in more basal archosauriforms such as proterosuchids. The 2016 description of ''

Teyujagua ''Teyujagua'' (named for Teyú Yaguá, a legendary beast from local Guaraní mythology) is an extinct genus of small, probably semi-aquatic archosauromorph reptile that lived in Brazil during the Early Triassic period. The genus contains the ty ...

'' placed ''Koilamasuchus'' in a polytomy with ''Fugusuchus'' and all other non-proterosuchid archosauriforms. A 2016 study on

Euparkeriidae Euparkeriidae is an extinct family of small carnivorous archosauriforms which lived from the Early Triassic to the Middle Triassic (Anisian). While most other early archosauriforms walked on four limbs, euparkeriids were probably facultative ...

included ''Koilamasuchus'' in its phylogenetic analysis, and found that it was a basal doswelliid. This classification was supported by the presence of a convex illiac blade with rounded anterior and posterior ends. Nevertheless, the authors noted that the large amount of missing data for the genus makes this assignment uncertain. In another 2016 analysis on archosauriforms, ''Koilamasuchus'' was classified as an

, specifically a basal member of

Suchia Suchia is a clade of archosaurs containing the majority of pseudosuchians (crocodilians and their extinct relatives). It was defined as the least inclusive clade containing '' Aetosaurus ferratus'', '' Rauisuchus tiradentes'', '' Prestosuchus ch ...

. Some of the features supporting this classification include the presence of a lateral fossa on each

vertebral centra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

, a humerus with a proximal end that is roughly symmetrical from the front, and a well-developed preacetabular process of the ilium which nevertheless does not extend further forward than the pubic peduncle. However, the osteoderms of MACN-Pv 18119 do not bend along their lateral edge, meaning that ''Koilamasuchus'' was more basal than advanced suchians such as members of

Paracrocodylomorpha Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorpha ...

References

{{Taxonbar, from=Q6426285 Prehistoric archosauriforms Early Triassic reptiles of South America Triassic Argentina Fossils of Argentina Fossil taxa described in 2010