Paleorhinus

''Paleorhinus'' (Greek: ''"Old Nose"'') is an extinct genus of widespread basal phytosaur known from the Late Triassic (late Carnian stage). The genus was named in 1904 based on the type species ''Paleorhinus bransoni'', which is known from Wyoming and Texas in the United States. Another valid species, ''Paleorhinus angustifrons'' from Bavaria, Germany, is also commonly referred to the genus. ''Paleorhinus'' had a length of about .

''Paleorhinus'' has had a complicated taxonomic history involving frequent synonymy between diagnostic and undiagnostic material. This is mainly due to the fact that it is a quintessential basal phytosaur, mostly distinguished by a lack of specializations rather than unique traits. Historically, it was common practice to lump all basal phytosaurs into only one or two genera, rendering those genera paraphyletic evolutionary grades ancestral to later phytosaurs. More recently, these grades have been broken up into multiple genera. ''Arganarhinus magnoculus'' (from Morocco) and ''Wannia scurriensis'' (from Texas) were two phytosaur genera originally considered species of ''Paleorhinus''. ''"Paleorhinus" sawini'' (from Texas) and ''"Paleorhinus" parvus'' (from Wyoming) are two more phytosaur species informally referred to ''Paleorhinus'', though likely closer to more advanced phytosaurs.

''P. angustifrons'' was originally considered a species of ''Francosuchus'' (a dubious phytosaur genus from the same area), and has also been compared to ''Ebrachosuchus neukami'', another ''Paleorhinus''-like Bavarian phytosaur. "''Paleorhinus"'' cf. ''arenaceus'' (formerly "''Zanclodon''" ''arenaceus''), fragmentary phytosaur remains from Poland, may represent ''Paleorhinus'' fossils.

''Parasuchus hislopi'', a basal phytosaur species named in 1885 from fossils discovered in India, was often lumped into ''Paleorhinus'' or considered a dubious chimera of phytosaur and rhynchosaur fossils. More complete neotype fossils for ''Parasuchus hislopi'' have helped to re-establish it as a valid genus and species. Some phylogenetic analyses suggest that ''Parasuchus hislopi'' forms a clade with ''Paleorhinus bransoni'' and ''angustifrons''. If this is the case, the valid species of ''Paleorhinus'' may instead be considered species of ''Parasuchus'', since that genus name has priority over ''Paleorhinus''.

Species

''P. bransoni''

''P. bransoni'' is the type species of ''Paleorhinus''. It was first described and named by Samuel Wendell Williston in 1904 on the basis of the holotype FMNH UC 632, a complete but fragmentary skull that has been extensively reconstructed with plaster. It was collected at Squaw Creek of Fremont County, Wyoming, from the Carnian-aged Popo Agie Formation of the Chugwater Group. The holotype was thoroughly described by Lees (1907). Hunt and Lucas (1991) referred PPM P217 to ''P. bransoni''. It is an incomplete skull that was collected at Palo Duro Canyon, Randall County, west Texas, from the Carnian-aged Camp Springs Member of the Tecovas Formation. Later, Long and Murry (1995) referred additional material, including isolated postcranial remains, to ''P. bransoni'' from the Carnian-aged Cooper Canyon Formation of the Dockum Group, Howard County, Texas. TMM 31025-172, a complete skull, was collected at Otis Chalk Quarry 1 (also known as SMU 122), TMM 31100-8, 101, 175, 418, 419, 453 were collected at Otis Chalk Quarry 3, and TMM 31185-11, 38 were collected at Otis Chalk Quarry 3A.

''P. angustifrons''

''P. angustifrons'' was first described and named by Oskar Kuhn in 1936 as a species of ''Francosuchus''. ''P. angustifrons'' is known exclusively from the holotype BSPG 1931 X 502 a partial skull lacking the rostrum and mandibles. It was collected at Ebrach Quarry, bed number 9 of Bavaria, southern Germany, from the late Carnian-aged Blasensandstein Member of the Hassberge Formation.

Hunt and Lucas (1991) mistakenly referred to ''F. angustifrons'' as ''Ebrachosuchus angustifrons'', and considered it and the other two ''Francosuchus'' species, '' F. broilii'' and '' F. latus'', to be synonyms of '' Paleorhinus neukami''. More recently, ''P. neukami'' was found to be more closely related to Mystriosuchinae than to ''Paleorhinus'' and thus the genus ''Ebrachosuchus'' was re-validated, while ''F. angustifrons'' was reassigned as ''P. angustifrons'' as it shares unique synapomorphies with ''P. bransoni'' and was found to be its sister taxon. The other two ''Francosuchus'' species, were not referred to ''P. angustifrons'' because they were found to be nomina dubia as their holotypes were destroyed during World War II.

''P. cf. arenaceus''

Dzik & Sulej (2007) assigned several skulls, partial articulated postcranial skeletons, and numerous isolated phytosaur bones in various ontogenetic stages from Krasiejów, Poland to ''Paleorhinus cf. arenaceus''. They found some similarities between the material and ''P. bransoni'' and also ''Ebrachosuchus neukami'' or ''F. angustifrons'' (mistakenly referred to as ''E. broili''), as well as some apparent differences with ''Parasuchus''. The shape of the external mandibular fenestra of the material resembled that of ''"Zanclodon" arenaceus'' but it is also shared with the proterochampsid '' Chanaresuchus bonapartei''. ''"Z." arenaceus'' was suggested to represent the oldest reliably dated phytosaur, and was reassigned to various phytosaur species over the years, including ''Belodon'', ''Mystriosuchus'' and ''Phytosaurus''. Although Hungerbühler (2001) redescribed ''"Z." arenaceus'' as not belonging to Phytosauria and referred it to Archosauria ''incertae sedis'', Dzik & Sulej (2007) noted that its holotype "does not differ significantly from corresponding parts of the juvenile Krasiejów ''Paleorhinus'', which is clearly a phytosaur". Furthermore, as the Feuerbacher Heide Schilfsandstein, from which ''"Z." arenaceus'' was collected, and Krasiejów share species of ''Metoposaurus'', it might be possible that they also share the same species of phytosaur. Even though they agreed that due to the very fragmentary nature of ''"Z." arenaceus'' holotype the Krasiejów ''Paleorhinus'' can't be referred to it, they tentatively used the name ''Paleorhinus cf. arenaceus'' for the Krasiejów ''Paleorhinus''.

Other species

Through the years, various species have been referred to as ''Paleorhinus''. The species that are no longer considered to belong to ''Paleorhinus'', are summarised in the list below:

*''Ebrachosuchus neukami'' Kuhn, 1936 - Hunt and Lucas (1991) reassigned the species as ''Paleorhinus neukami''. Subsequent researches accepted this referral. More recently, phylogenetic analysis found ''E. neukami'' to be more closely related to Phytosauridae than to ''Paleorhinus'' and thus the genus ''Ebrachosuchus'' was re-validated.
*'' Francosuchus broilii'' and '' F. latus'' Kuhn, 1933 - Gregory (1962) and Wastphal (1976) referred these species, as well as, ''E. neukami'' and ''P. angustifrons'' to ''Paleorhinus'' subgenus ''Francosuchus'', while Chatterjee (1978) placed the four species in ''Francosuchus'' in a different subfamily. Hunt and Lucas (1991) considered these species to be synonymous with ''Paleorhinus neukami''. More recently, ''F. broilii'' and ''F. latus'' were considered to be nomina dubia.
*'' "Francosuchus" trauthi'' Huene, 1939 - ''"F." trauthi'' was synonymized with ''Paleorhinus'', but a re-description of the species by Butler (2013) found no evidence to support the synonymy, or even a phytosaurian identification. Although it is based solely on a rostrum fragment, ''"F." trauthi'' was found to possess a unique combination of characters that distinguish it from all other Triassic tetrapods. Thus it was reassigned to a new genus, ''Dolerosaurus'', now referable to Tetrapoda ''incertae sedis''.
*'' Paleorhinus magnoculus'' Dutuit, 1977b - Long and Murry (1995) reassigned this species to a new genus '' Arganarhinus''. Although several studies reassigned it back to ''Paleorhinus'', more recent studies disagree with this referral. Kammerer et al. (2016) considered ''P. magnoculus'' to be a species of ''Parasuchus,'' alongside ''P. hislopi, P. bransoni,'' and ''P. angustifrons''.
*'' "Paleorhinus" parvus'' Mehl, 1928 - Hunt and Lucas (1991) considered this species to be synonymous with ''P. bransoni'', while Stocker and Butler (2013) suggested that ''"P." parvus'' may not be referable to ''Paleorhinus''.
*'' "Paleorhinus" sawini'' Long and Murry, 1995 - some studies considered this species to be synonymous with ''P. bransoni'', although recent species-level phylogenetic analyses of phytosaurs suggest that this species is more closely related to Phytosauridae than to ''P. bransoni'' and thus can't be referred to ''Paleorhinus''.
*'' "Paleorhinus" scurriensis'' Langston, 1949 - Hunt and Lucas (1991) considered this species to be synonymous with ''P. bransoni'', although recent species-level phylogenetic analyses of phytosaurs suggest that this species is basal to the clade formed by ''P. bransoni'' and the Phytosauridae, and thus can't be referred to ''Paleorhinus''. This species was reassigned to its own genus, '' Wannia'' by Stocker (2013), and represents the most basal known phytosaur.
*''Parasuchus hislopi'' Lydekker, 1885 - ''P. hislopi'' was based on a chimeric syntype material - a rhynchosaurian basicranium mixed with phytosaurian partial snout, scutes and some teeth. Friedrich von Huene (1940) identified the basicranium as belonging to ''Paradapedon huxleyi'' (now known as ''Hyperodapedon huxleyi''), thus he assigned the phytosaurian material to a newly named species "aff." ''Brachysuchus maleriensis''. Later, Edwin Harris Colbert (1958) designated all the Indian parasuchian material as ''Phytosaurus maleriensis''. Gregory (1962) accepted this proposal. Sankar Chatterjee (1978), who described many complete remains of the Indian parasuchian, showed that it is not assignable either to ''Brachysuchus'' (which is closely related to or synonymous with ''Angistorhinus''), or to ''Phytosaurus'' (a doubtful name, probably the senior synonym of ''Nicrosaurus''). He noted that since the rhynchosaur basicranium is neither the holotype of ''P. hislopi'', nor the lectotype of ''Paradapedon huxleyi'', the suppression of ''P. hislopi'' should be avoided. Nevertheless, Hunt and Lucas (1991) considered the species to be a nomen dubium, and provisionally created the combination ''Paleorhinus hislopi'' for the diagnosable phytosaur specimens from the Lower Maleri Formation, stating that the Indian species can be distinguished from other ''Paleorhinus'' species. To avoid additional confusion, the nondiagnostic holotype of ''P. hislopi'' was replaced by a neotype with approval from the ICZN (Opinion 2045) following the application of Chatterjee (2001). As a result, most subsequent studies referred all ''Paleorhinus'' species to ''Parasuchus'' in accordance with the rules of the ICZN, while others kept referring ''P. hislopi'' to ''Paleorhinus''. In light of the complex taxonomic history of ''Paleorhinus'', studies as of 2013 considered the synonymy between the genera to be premature. However, later studies argued that ''Paleorhinus bransoni'' and ''Paleorhinus angustifrons'' formed a strong clade with ''Parasuchus hislopi''. This clade would receive the name ''Parasuchus'' under ICZN rules, formally synonymizing the two genera in this more restricted sense.
*'' Promystriosuchus ehlersi'' Case, 1922 - Gregory (1962) and Hunt and Lucas (1991) referred this taxon to ''Paleorhinus'' on the genus level, and considered it to be a nomen dubium on the species level, due to the poor preservation of it holotype and only known specimen. Stocker and Butler (2013) suggested that ''P. ehlersi'' may not be referable to ''Paleorhinus'' and referred it to Phytosauria ''incertae sedis''.

Phylogeny

The following cladogram, from Kammerer et al., 2016, shows the relationships of ''P. bransoni'', ''P. angustifrons'', and ''"P." sawini'' to other phytosaurs. The authors placed ''P. bransoni'' and ''P. angustifrons'' into the genus ''Parasuchus'', owing to their close relationship with ''Parasuchus hislopi''.

References

{{Taxonbar, from=Q21711013

Phytosaurs
Prehistoric reptile genera
Carnian genera
Late Triassic reptiles of Europe
Late Triassic reptiles of North America
Chinle fauna
Fossil taxa described in 1904
Taxa named by Samuel Wendell Williston