Rugarhynchos
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''Rugarhynchos'' 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
doswelliid Doswelliidae is an extinct family of carnivorous archosauriform reptiles that lived in North America and Europe during the Middle to Late Triassic period. Long represented solely by the heavily-armored reptile ''Doswellia'', the family's composit ...
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
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
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, Ker ...
. The only known species is ''Rugarhynchos sixmilensis''. It was originally described as a species of ''
Doswellia ''Doswellia'' is an extinct genus of archosauriform from the Late Triassic of North America. It is the most notable member of the family Doswelliidae, related to the proterochampsids. ''Doswellia'' was a low and heavily built carnivore which liv ...
'' in 2012, before receiving its own genus in 2020. ''Rugarhynchos'' was a close relative of ''Doswellia'' and shared several features with it, such as the absence of an
infratemporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets, ...
and heavily textured skull bones. However, it could also be distinguished by many unique characteristics, such as a thick diagonal ridge on the side of the snout, blunt spikes on its
osteoderms 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 ...
, and a complex suture between the
quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
,
squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal The quadratojugal is a skull bone present in many vertebrates, including ...
, and
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 ...
. Non-metric multidimensional scaling and tooth morphology suggest that ''Rugarhynchos'' had a general skull anatomy convergent with some
crocodyliforms Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...
,
spinosaurids The Spinosauridae (or spinosaurids) are a clade or Family (taxonomy), family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous Geological period, period. Spinosaurid fossils h ...
, and
phytosaurs 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 g ...
(particularly ''
Smilosuchus ''Smilosuchus'' (meaning "chisel crocodile") is an extinct genus of leptosuchomorph parasuchid from the Late Triassic of North America. History The type species was first described in 1995 as a replacement generic name for ''Leptosuchus g ...
''). However, its snout was somewhat less elongated than those other reptiles.


Discovery

The only known specimen of ''Rugarhynchos'' is NMMNH P-16909, a partial skeleton consisting of several bones scattered over a small area. The largest component is a mostly complete right side of a skull. It was originally described as pertaining to part of the snout, until further preparation revealed that it included most of the skull. Other cranial fragments include a right quadrate, left
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 ...
, left maxillary fragments, and a partial right
quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
which was originally considered another maxillary fragment. A fragment originally described as an articulated parietal and
postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
was later considered part of 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 sepa ...
. The only preserved portion of the jaw is a left
surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular The articular bone i ...
, although a large right
pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medial ...
fragment was originally considered an
articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...
. Postcranial remains include 13
osteoderms 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 ...
, several
vertebral The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
fragments, a few isolated rib fragments, the lower end of a left
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 with ...
, and a possible
pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...
fragment which was originally described as a
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...
. These fossils were found at Six Mile Canyon in
McKinley County, New Mexico McKinley County is a List of counties in New Mexico, county in the northwestern section of the U.S. state of New Mexico. As of the 2020 United States Census, its population was 71,367. Its county seat is Gallup, New Mexico, Gallup. The county wa ...
. They were recovered from a massive purple
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
layer of the lower
Bluewater Creek Formation The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period. Description The formation consists of red sandstones and mudstones and has a total thickness in exce ...
, also known as the Bluewater Creek Member of the
Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...
. Other fossils from Six Mile Canyon include fragments of
aetosaurs Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs ...
,
phytosaurs 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 g ...
, and metoposaurids. The top of the Bluewater Creek Member was separated from overlying strata by a distinct
tuffaceous Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock c ...
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
layer (the "SMC bed") at Six Mile Canyon. The age of the SMC bed has been estimated by several studies involving various Uranium-Lead dating techniques. A 2009 conference abstract argued that it was 219.3 ± 3.1 or 220.9 ± 0.6 million years old based on Laser Ablation– Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS) and Isotope Dilution-
Thermal Ionization Mass Spectrometry Thermal ionization mass spectrometry (TIMS) is also known as surface ionization and is a highly sensitive isotope mass spectrometry characterization technique. The isotopic ratios of radionuclides are used to get an accurate measurement for the ele ...
(ID-TIMS) dating techniques, respectively. A 2011 study instead found a slightly younger date of 218.1 ± 0.7 Ma based on Chemical Abrasion–Thermal Ionization Mass Spectrometry (CA-TIMS) dating. These estimates suggest that the rocks which preserved ''Rugarhynchos'' were deposited in the vicinity of 220 Ma. The specimen was first described in 2012 as a new species of the armored archosauriform ''Doswellia''. It was given the
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
''Doswellia sixmilensis'', in reference to its site of discovery. Its original describers noted that there was relatively little overlap between ''Doswellia sixmilensis'' and ''Doswellia kaltenbachi'' (the original species of ''Doswellia''). They suggested that new material may lead to the two species being distinguished as two genera. Further preparation altered several interpretations of the specimen. The most notable of these was the discovery that the purported snout fragment was actually almost an entire skull. A 2020 study followed these new interpretations, describing how "''Doswellia sixmilensis''" had numerous unique features contrasting with ''Doswellia kaltenbachi''. "''D. sixmilensis''" was placed into its own genus. The genus name is derived from Latin words for "wrinkle" and "nose", in reference to the wide variety of rough ridges on its snout.


Description


Skull

The front of 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 ...
expands to the side, forming a bulbous structure similar to that of many
phytosaurs 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 g ...
. It possessed eight teeth, with the first four being much larger than the last four. Premaxillary teeth were conical and ornamented by longitudinal ridges, but lacked serrations or cutting edges. The tooth row was slightly downturned at an angle of 15-20 degrees. Unlike other
proterochampsians 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 ...
, the nares (nostril holes) did not seem to be oriented upwards. The rear branch of the premaxilla wedges into an extensive suture between the
nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...
and
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. The t ...
. There were 20 teeth in the maxillary tooth row, significantly more than in the maxillae of proterochampsids but in line with other doswelliids. Four enlarged teeth in the front half of the tooth row are covered by a convex extension, giving the maxilla a
sigmoid Sigmoid means resembling the lower-case Greek letter sigma (uppercase Σ, lowercase σ, lowercase in word-final position ς) or the Latin letter S. Specific uses include: * Sigmoid function, a mathematical function * Sigmoid colon, part of the l ...
lower edge akin to that of "robust-morph" phytosaurs. The maxillary teeth of ''Rugarhynchos'' had negligible curvature and were similar to the premaxillary teeth. The nasal is roughly textured, hosting a prominent ridge along the midline of the skull along with several other low ridges. The rear of the nasals are incised by the triangular front edge of the frontals, creating a wedge-shaped suture also seen in '' Proterochampsa''. The prefrontal and lacrimal form the front edge of the
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
(eye socket) and connect to the maxilla. Like other proterochampsians, there is no contact between the lacrimal and nasal. More unusually, there is also no trace of an
antorbital fenestra 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 ...
between the maxilla, nasal, and lacrimal. The only other early archosauriform known to lack an antorbital fenestra is ''
Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non- archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995. At that time, ...
''. One autapomorphy (unique distinguishing feature) of ''Rugarhynchos'' is the presence of a thick diagonal ridge on the side of the snout. This ridge extends from the upper part of the maxilla onto the lacrimal, prefrontal, and frontal. '' Chanaresuchus'' and ''Proterochampsa'' have a similar ridge in front of the orbit, though it is less pronounced and does not extend onto the maxilla. Various smaller ridges and rough spots are present near the large diagonal ridge of ''Rugarhynchos''. These include a raised, bulbous rim of the orbit, a thin horizontal ridge on the prefrontal, and a thicker ridge along the prefrontal-frontal suture. The upper edge of the orbit also has a prominent raised boss formed by the frontal. Behind and below the orbit lies the very large and blocky
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 ...
. It is textured by prominent bumps, ridges, and pits, though these features are less pronounced than those of ''Doswellia''. The overlying squamosal was also simple in shape and textured by long ridges and depressions. Its front edge formed the rear rim of a supratemporal fenestra, a hole in the upper part of the skull behind the orbits. The rear part of the squamosal connected to the quadrate and had a triangular horn-like structure similar to that of ''Doswellia''. The
postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
is missing in the fossil, but its position relative to other bones can be inferred by the space it left behind. It would have been tightly connected to the jugal, squamosal, and frontal, leaving no space for an
infratemporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets, ...
. This gives ''Rugarhynchos'' a
euryapsid __NOTOC__ Euryapsida is a polyphyletic (unnatural, as the various members are not closely related) group of Sauropsida, sauropsids that are distinguished by a single temporal fenestra, an opening behind the orbit (anatomy), orbit, under which the ...
skull akin to ''Doswellia''. The rear edge of the skull is formed by the
quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
, which connects to the rest of the skull in several unique ways. The upper part of the quadratojugal edges a shallow concave area formed by the rear edge of the squamosal and jugal. The lower part of the quadratojugal fits into a prominent notch on the jugal. Both of these traits are autapomorphies of ''Rugarhynchos.'' The quadrate is steeply angled to the rest of the skull (like ''Chanaresuchus'' and ''Doswellia'') and also has a large, hooked upper portion (like ''Vancleavea'' and allokotosaurians). The middle of the
pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medial ...
had a diagonal ridge with two rows of teeth stretching along its underside. This is intermediate between proterochampsids (which have one row of teeth on their pterygoid ridge) and ''Doswellia'' (which has at least three). A different ridge along the inner edge of the pterygoid also hosts a longitudinal row of teeth. A few teeth are randomly distributed between the two ridges, though there were likely many more originally present. A possible
palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ''pa ...
is also preserved. This bone has a crescent-shaped front half and a saddle-shaped rear half. This is similar to ''Proterochampsa'' and ''Chanaresuchus'', though insufficient data on basal archosauriform
palates 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 ...
prevents comparison to many other taxa. The only preserved jaw bone is a large
surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular The articular bone i ...
which is textured by rough longitudinal ridges. It is generally similar to that of ''Doswellia'', though its upper edge is not convex and its front tip is blunt and rounded. Unique to ''Rugarhynchos'', there is a cup-shaped depression on the rear edge of the surangular below where it connects to the
articular bone The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two othe ...
.


Postcrania

Postcranial material of ''Rugarhynchos'' is sparse. Several fragmentary or complete centra (main
vertebral The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
components) were among the fossils recovered. These centra were low and wide, similar to other doswelliids, ''Vancleavea'', and ''
Litorosuchus ''Litorosuchus'' is a genus of armored, semiaquatic archosauriform reptile from the Middle Triassic of China, closely related to the morphologically similar '' Vancleavea''. It contains one species, ''L. somnii''. Description For an archosau ...
'', but unlike proterochampsids. Low, elliptical rib facets were located on short stalks. Other doswelliids had similarly shaped rib facets though set on longer stalks. Like most other reptiles, ''Rugarhynchos'' would have had two rib facets on either side of a vertebra. The upper facets are termed diapophyses and connected to the upper rib head (tuberculum), while the lower facets are parapophyses and connected to the lower rib head (capitulum). No diapophyses are preserved, but large parapophyses were present close to the lower edge of the centrum. The capitulum and tuberculum of preserved ribs were closely set and cylindrical, as in ''Doswellia''. The vertebrae were likely cervicals (neck vertebrae) due to having low-set parapophyses and prominent midline keels along their lower edge. Prominent excavations on the side of the vertebrae gave them an X-shaped cross-section when seen from above. The centra were rectangular from the side and would have connected with each other on an even level, indicating that the neck was straight. A thick, curved bone fragment likely represents the upper part of a hip bone such as the pubis or
ischium The ischium () form ...
, though its identity cannot be determined precisely. A portion 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 with ...
near the knee is the only fragment of the leg preserved in ''Rugarhynchos''. Like other proterochampsians, this part of the femur was wide and had a subtle concavity on its front edge. The distal condyles were well-differentiated and both were slightly tapered. Although a pointed medial condyle is common to basal archosauriforms and
pseudosuchians 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 ...
, a pointed lateral condyle is only observed in '' Gualosuchus'' among eucrocopodans. Many
osteoderms 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 ...
(bony plates) have been preserved. They were roughly square-shaped and ornamented by large circular pits which radiated from the center of each plate, like other doswelliids. Also in line with doswelliids, the osteoderms articulate with each other via a smooth and flat front edge rather than spines or notches. However, several traits of ''Rugarhynchos'''s osteoderms differ from other doswelliids. The pits are shallower and the upper surface of the osteoderm has a central blunt spike-like eminence rather than a raised keel. None of the osteoderms fossilized in articulation, so it is uncertain how they were arranged on the body. Nevertheless, ''Rugarhynchos'' likely had multiple longitudinal rows (columns) of osteoderms, as with other doswelliids. More irregularly shaped osteoderms near the skull may have connected to form a "nuchal shield" similar to that of ''Doswellia''.


Classification

To test its relations to other early archosauriforms, ''Rugarhynchos'' was placed 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 ...
derived from an earlier study by Ezcurra ''et al''. (2017). This analysis was run under both
maximum parsimony In phylogenetics, maximum parsimony is an optimality criterion under which the phylogenetic tree that minimizes the total number of character-state changes (or miminizes the cost of differentially weighted character-state changes) is preferred. ...
and
bayesian Thomas Bayes (/beɪz/; c. 1701 – 1761) was an English statistician, philosopher, and Presbyterian minister. Bayesian () refers either to a range of concepts and approaches that relate to statistical methods based on Bayes' theorem, or a follower ...
search protocols. The parsimony analysis placed ''Rugarhynchos'' as a
doswelliid Doswelliidae is an extinct family of carnivorous archosauriform reptiles that lived in North America and Europe during the Middle to Late Triassic period. Long represented solely by the heavily-armored reptile ''Doswellia'', the family's composit ...
and 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 t ...
to ''Doswellia''. Doswelliids were the sister taxa to a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
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 ...
, and the Doswelliidae+Proterochampsidae
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, ...
was itself sister to a clade comprising ''
Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non- archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995. At that time, ...
'' and ''
Litorosuchus ''Litorosuchus'' is a genus of armored, semiaquatic archosauriform reptile from the Middle Triassic of China, closely related to the morphologically similar '' Vancleavea''. It contains one species, ''L. somnii''. Description For an archosau ...
''. All of these taxa cumulatively make up the 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 ...
. The bayesian analysis had a very similar result, but differed in one major way. Instead of having a clean break between proterochampsids and doswelliids, the bayesian analysis suggested that Proterochampsidae in its traditional form was
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 ...
rather than monophyletic. '' Proterochampsa'' was found as the sister taxon to doswelliids and separate from other proterochampsids. Though this novel result was unusual, it was considered more likely than the parsimony alternative because it accounted for variable rates of evolution. The results of the bayesian analysis are shown below:


References

{{Taxonbar, from=Q96084399 Proterochampsians Prehistoric reptile genera Chinle Formation Late Triassic reptiles of North America Fossil taxa described in 2020