''Kwanasaurus'' is an extinct

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 silesaurid dinosauromorph reptiles from the

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 ...

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

. It is known from a single species, ''Kwanasaurus williamparkeri''. ''Kwanasaurus'' had a deeper, stronger skull and greater specialization for herbivory compared to other silesaurids. It also possessed many unique characteristics of the snout, ilium, and lower part of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

. It was described along with new specimens of ''

Dromomeron ''Dromomeron'' (meaning "running femur") is a genus of Lagerpetidae, lagerpetid Avemetatarsalia, avemetatarsalian which lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the South ...

'' from the Eagle Basin, the northernmost extent of the Chinle Formation.

Discovery

''Kwanasaurus'' hails from Triassic deposits in the Eagle Basin surrounding the town of Eagle, Colorado. This area contains the most northern exposures of the Chinle Formation, which is famous for its Late Triassic fossils of

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

and other

reptiles 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 ...

. Tentative terrestrial reptile

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

estimates that the Eagle Basin fossils, which were preserved in red

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

, belong to the Revueltian biozone of the mid to late

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

stage of the Triassic, 215-207 million years ago. The

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 ...

of ''Kwanasaurus'' is a partial silesaurid maxilla, DMNH EPV.65879. All other silesaurid maxillae recovered from the area seem to represent the same taxon, indicating that ''Kwanasaurus'' was likely the only silesaurid from the Eagle Basin. With this in mind, all other Eagle Basin fossils resembling those of silesaurids have been referred to the taxon. These include multiple dentaries, teeth, ilia, femora, and a

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

. Dinosauromorph-like tibia and scapulae from the area may also belong to ''Kwanasaurus'', though they have not been referred to the genus due to lacking any clear silesaurid features. ''Kwanasaurus'' was named in a 2019 paper by Jeffrey W. Martz and Bryan J. Small, along with the description of new ''

'' material. The genus name incorporates ''kwana'', the

Ute Ute or UTE may refer to: * Ute people, a Native American people of the Great Basin * Ute Indian Tribe of the Uintah and Ouray Reservation, Utah * Ute Mountain Ute Tribe, Colorado, New Mexico, and Utah * Southern Ute Indian Tribe of the Southern ...

name for eagle. The specific name commemorates paleontologist Bill Parker.

Description

Skull

The

maxilla In vertebrates, the maxilla (: maxillae ) 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 two maxil ...

is much deeper and more robust in ''Kwanasaurus'' than in any other silesaurid. There are replacement pits on the inner edge of the tooth row similar to those of

thyreophora Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of bod ...

ns, and smaller and more numerous pits on the outer surface of the maxilla. Five of the replacement pits at the midlength of the bone are set in a groove, a trait also present in '' Silesaurus'' and silesaurid skull material from the Ntawere Formation. The front of the maxilla is similar to that of '' Lewisuchus'' and ''Silesaurus'', with a triangular

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 mammals h ...

ry facet and thick, sharp

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

ine flange. The ascending process of the maxilla is a thin, anteroposteriorly wide, and steeply-rising prong, and the antorbital fossa has a concave lower edge, both like ''Silesaurus''. The inner surface of the maxilla has a thick medial flange, which droops down to the tooth row as a smooth triangular blade. This medial flange is unique to ''Kwanasaurus'' among silesaurids (and Triassic dinosauromorphs in general), and likely extended the maxilla's connection with 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 sep ...

behind the vomer. The rear portion of the

maxilla is characteristically complex and similar to that described for ''

Plateosaurus ''Plateosaurus'' (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Eu ...

''. These complex traits include a posterolateral flange which likely shielded part of the jugal, a pair of deep dorsomedial grooves (likely articulating with the lacrimal and jugal), and a broad groove behind the medial flange which likely articulated with the

palatine A palatine or palatinus (Latin; : ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman Empire, Roman times.

Lower jaw bones referred to ''Kwanasaurus'' include DMNH EPV.63136, one of the most complete dentaries found for any silesaurid. As in other sulcimentisaurians, the meckelian groove is positioned close to the lower edge of the jaw and the teeth are constricted at the root. The front tip of the dentary is pointed, toothless, and has a lateral groove akin to that of ''Silesaurus'' and '' Sacisaurus,'' along with several medial grooves. Further back, the dentary is relatively deep and develops a lateral ridge similar to one reported for ''

Diodorus Diodorus Siculus or Diodorus of Sicily (; 1st century BC) was an ancient Greek historian from Sicily. He is known for writing the monumental universal history '' Bibliotheca historica'', in forty books, fifteen of which survive intact, b ...

'' and '' Eucoelophysis''. The pattern of pitting and holes on the outer surface of the dentary also resembles those taxa. The tooth row is edged by a medial groove connecting a series of replacement pits; above the groove the bone is inset similar to the case in ''Silesaurus'', ''Eucoelophysis'', and '' Technosaurus''. ''Kwanasaurus'' is the only silesaurid to preserve data on the mandibular fenestra. This hole in the jaw was triangular, edged from below by a posteroventral process of the dentary which also overlapped a partial angular. The dentary's posterodorsal process is sharp along its upper edge and notched along its lower edge.

Teeth

Teeth of ''Kwanasaurus'' have been found both as isolated material and within maxillae and dentaries. Isolated teeth are leaf-shaped, with coarse denticles, slightly flattened sides, and crown tips more than halfway towards the rear of the tooth. The lingual (tongue) side of the tooth has a thick vertical ridge covered in striations. ''Sacisaurus'', ''Eucoelophysis'', and possibly ''Technosaurus'' are the only other silesaurids known to possess similar teeth, although leaf-shaped teeth are also common in various other herbivorous

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 ...

s. In some of the maxilla, the teeth are short and swollen (almost round in cross section) and become smaller towards the rear of the bone. The dentary teeth are similar but more asymmetrical. The middle of the dentary has the largest and most denticulate teeth in the jaw. There are 12 maxillary teeth and 14 dentary teeth. These teeth extend further back in the skull than most silesaurids, as is the case in ''Lewisuchus'', but they are not as numerous as those of that taxon. Like other silesaurids, ''Kwanasaurus'' has ankylothecodont tooth implantation, meaning the teeth are set in sockets but also fused to the surrounding bone. At least in the maxilla, ''Kwanasaurus'' has a complex pattern of tooth replacement. This pattern involves replacement teeth being formed along the lingual edge of the tooth row, shifting outwards (at which point the original tooth's attachment dissolves and the tooth detaches), fusing to the leftover socket and leaving behind a replacement pit. The tooth row has alternating empty and full sockets, indicating that adjacent teeth were never replaced at the same time. This contrasts with ''Silesaurus'' and ''Technosaurus'' (which sometimes have several adjacent teeth replaced at once), but resembles the condition in some specimens of ''Sacisaurus'', ''Diodorus'', and '' Asilisaurus''.

Forelimbs

A long and slender

is the only forelimb bone safely assigned to ''Kwanasaurus'', based on its similarity to that of ''Silesaurus'' and ''Diodorus''. The proximal portion is slightly expanded, but the humeral head is not as thick or straight as that of other silesaurids. Unlike

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s (but in line with other silesaurids), the deltopectoral crest is small and extends less than a third down the length of the shaft. The distal portion of the humerus is simple and barely expanded, twisted relative to the proximal portion (similar to ''Silesaurus''), but also with a groove running up its anterolateral surface (similar to ''Diodorus'').

Hip and hindlimbs

The hip is only represented by the ilium, which had a low, saddle-shaped upper blade like silesaurids such as ''Silesaurus'', ''Eucoelophysis'', and '' Ignotosaurus''. It also resembles these taxa in its elongated and expanded preacetabular process. ''Kwanasaurus'' takes this trend further, lengthening the preacetabular process so that it projects further forwards than the pubic peduncle, an adaptation otherwise only seen in several lineages of dinosaurs among dinosauromorphs. The postacetabular process is large and possesses a well-developed brevis shelf and brevis fossa, traits standard for sulcimentisaurians. Like many basal dinosauromorphs, the brevis shelf merges with the edge of the

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

and the rear edge of the postacetabular process has a small pointed extension. The acetabulum is deep and has a very thin and concave lower edge. This contrasts with other silesaurids, which have a straight lower edge to the acetabulum, and instead may suggest a partially perforated acetabulum akin to that of dinosaurs. The inner surface of the ilium has several facets for the sacral ribs. The second facet is twice as long as the first and may have encompassed two sacral ribs, suggesting that ''Kwanasaurus'' possessed three sacral vertebrae. Kwanasaurus distal femur

Multiple femora of various sizes and conditions have been referred to ''Kwanasaurus''. The

femoral head The femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the ...

was similar to that of other advanced silesaurids, according to several traits. These include a longitudinal groove on its upper surface, a straight (rather than rounded) articular facet on the medial surface, a distinct notch on its underside, and an overall triangular cross section due to the lack of a distinct posteromedial tuber. Directly below the head extends a ridge known as a dorsolateral trochanter. Adjacent to it is the anterior trochanter, a pronounced vertical crest characteristic of dinosauriforms (and a few ''

'' specimens). The crest was blade-like, triangular, and straight-edged, proportionally most similar to ''Silesaurus'' among dinosauriforms. Only one femur referred to ''Kwanasaurus'' (DMNH EPV.125924) possessed additional muscle attachment structures such as a trochanteric shelf and a swelling that likely represented the iliotrochanteris caudalis attachment site. ''Asilisaurus'' and ''Silesaurus'' are the only other silesaurids with trochanteric shelves, and its development is sometimes considered to be related to skeletal maturity. However, the largest ''Kwanasaurus'' femur (DMNH EPV.34579) lacks a trochanteric shelf, despite its presence in the smaller 125924 specimen. All specimens had a low

fourth trochanter The fourth trochanter is a shared characteristic common to archosaurs. It is a protrusion on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'', the m ...

, sometimes edged by an anterior depression as in ''Sacisaurus'' and ''Diodorus''. The distal portion of the femur possessed several unique features. The medial condyle was a sharp flange, notably thinner than the lateral condyle and crista tibiofibularis. This is similar to lagerpetids but in contrast to the broader medial condyle of all other silesaurids. ''Kwanasaurus'' also possesses a characteristic depression on the distal surface of the femur, in front of the crista tibiofibularis. Nevertheless, the notably deep and extensive sulcus present between the medial and lateral condyles is in line with that of other silesaurids.

Classification

''Kwanasaurus'' was added into a

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

to test its relationship to other silesaurids. The codings for the taxon were based on both all the Eagle Basin silesaurid material as well as the dinosauromorph tibiae and scapulae which may additionally belong to it. The strict consensus tree (average result of all most parsimonious trees) was poorly resolved, with practically all silesaurids in a polytomy along with

ornithischia Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...

ns and

sauropodomorphs Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

. The adams consensus tree (in which unstable taxa cluster at the base of the smallest group they are always within) has better resolution. In this tree, the highly unstable '' Ignotosaurus'' shifts to a polytomy with dinosaurs and other silesaurids, while Silesauridae starts with '' Lewisuchus'' at the base, followed by '' Soumyasaurus'' and '' Asilisaurus'', and finally a clade containing all other silesaurids. This

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 ...

was named Sulcimentisauria by the authors of the paper. Removing ''Ignotosaurus'', ''Soumyasaurus'', and '' Technosaurus'' led to higher resolution within Silesauridae. ''Kwanasaurus'' was found to be the

sister taxon 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 ...

to the other North American taxon, '' Eucoelophysis.'' Here is the consensus cladogram (specifically the portion focusing on dinosauromorphs) after the removal of the three unstable taxa:

Paleoecology

''Kwanasaurus'' was the northernmost and youngest silesaurid found in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. Its short, leaf-shaped, and heavily denticulated teeth were adapted for eating plants, a trait shared by several other advanced silesaurids. This diet represents the culmination of a series of adaptations within Silesauridae, starting with carnivory in '' Lewisuchus'' (evidenced by recurved and finely serrated teeth), leading to omnivory and/or insectivory in '' Asilisaurus'' and '' Silesaurus'' (conical teeth with few serrations), and eventually the evolution of a specialized herbivorous diet in advanced sulcimentisaurians. ''Kwanasaurus'' in particular had robust skull bones ornamented with ridges, indicating that it likely fed on tougher plants than other herbivorous silesaurids. The timing of silesaurid dietary evolution mirrors the acquisition of herbivory in

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

s, which diversified in southern and eastern portions of

Pangea 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 (continent), Siberia during the Carboniferous period ...

in the

stage. The absence of herbivorous dinosaurs in the Chinle Formation may indicate that they had not yet colonized the northwestern region of Pangea that would eventually become North America. This would leave herbivorous niches available for other

amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...

s, explaining the diversity of non-dinosaur herbivores in the Chinle Formation. These include allokotosaurs ('' Trilophosaurus''),

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 ...

ns ('' Revueltosaurus'',

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 shuvosaurids), and

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

s ('' Placerias''). ''Kwanasaurus'' was one of the silesaurids that was a part of this Norian herbivore guild, along with its relative '' Eucoelophysis'' (which lived in further south in

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

Gallery

File:Kwanasaurus maxillae 2.png, Additional maxillae File:Kwanasaurus dentaries 2.png, Additional dentaries File:Kwanasaurus teeth.png, Teeth File:Kwanasaurus ilium 2.png, Additional ilia File:Kwanasaurus complete femur.png, A complete femur File:Kwanasaurus proximal femur (large 1).png, Large proximal femora File:Kwanasaurus proximal femur (small).png, Small proximal femora

References

{{Taxonbar, from=Q67103336 Fossil taxa described in 2019 Late Triassic reptiles of North America Norian life Silesauridae Triassic Colorado