''Kwanasaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

silesaurid Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compri ...

dinosauromorph Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lag ...

reptiles from the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

. 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 (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

. It was described along with new specimens of '' Dromomeron'' 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 The Town of Eagle is the Statutory Town that is the county seat of Eagle County, Colorado, United States. The town population was 7,511 at the 2020 United States Census, a +15.41% increase since the 2010 United States Census. Eagle is the part ...

. This area contains the most northern exposures of the Chinle Formation, which is famous for its Late Triassic fossils of dinosaurs and other reptiles. 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 B ...

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

Revueltian Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...

biozone of the mid to late Norian stage of the Triassic, 215-207 million years ago. 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 sever ...

of ''Kwanasaurus'' is a partial

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 The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...

, and a humerus.

Dinosauromorph Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lag ...

-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 '' Dromomeron'' material. The genus name incorporates ''kwana'', the Ute name for eagle. The specific name commemorates paleontologist Bill Parker.

Description

Skull

The

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates 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. T ...

is much deeper and more robust in ''Kwanasaurus'' than in any other

. 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 body ...

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 Ntawere Formation is a Middle Triassic (Anisian) geological formation in Zambia, preserving fossils of synapsids, archosaurs, and temnospondyls. Geology Several different facies are present in the Ntawere Formation, reconstructing a floodp ...

. 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 mammal has ...

ry facet and thick, sharp

vomer The vomer (; lat, vomer, lit=ploughshare) 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 max ...

ine flange. The ascending process of the maxilla is a thin, anteroposteriorly wide, and steeply-rising prong, and the

antorbital fossa An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...

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 separ ...

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 Eur ...

''. These complex traits include a posterolateral flange which likely shielded part of the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

, 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 (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since 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 The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.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 ( grc-gre, Διόδωρος ; 1st century BC), was an ancient Greek historian. He is known for writing the monumental universal history ''Bibliotheca historica'', in forty books, fifteen of which su ...

'' 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 archosaurs. 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 ''Asilisaurus'' ( ); from Swahili, ''asili'' ("ancestor" or "foundation"), and Greek, (, "lizard") is an extinct genus of silesaurid archosaur. The type species is ''Asilisaurus kongwe.'' ''Asilisaurus'' fossils were uncovered in the Manda Bed ...

''.

Forelimbs

A long and slender humerus 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 period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

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 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 Sacral may refer to: *Sacred Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property ...

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

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). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...

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 '' Dromomeron'' 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 knob-like feature on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'' ...

, 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 (; 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 ...

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 An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

along with ornithischians 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 lon ...

. 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 ''

'', and finally a clade containing all other silesaurids. This clade 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. 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 ''

'' 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 lon ...

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 during the Carboniferous approximately 335 million y ...

in the Norian 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 amniotes, explaining the diversity of non-dinosaur herbivores in the Chinle Formation. These include allokotosaurs (''

Trilophosaurus ''Trilophosaurus'' (Greek for "lizard with three ridges") is a lizard-like trilophosaurid allokotosaur known from the Late Triassic of North America. It was a herbivore up to 2.5 m long. It had a short, unusually heavily built skull, equipped wi ...

''),

pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

ns (''

Revueltosaurus ''Revueltosaurus'' ("Revuelto lizard") is an extinct genus of suchian pseudosuchian from Late Triassic (late Carnian to middle Norian stage) deposits of New Mexico, Arizona and North Carolina, United States. Many specimens, mostly teeth, have bee ...

'',

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, herbivoro ...

s, and shuvosaurids), and

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, typic ...

s (''

Placerias ''Placerias'' (meaning 'broad body') is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (230–220 million years ago). ''Placerias'' belongs to a group of dicynodonts called Kannemeyeriifor ...

''). ''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 ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ke ...

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 Silesaurids Triassic Colorado