Parasuchus

Parasuchus Temporal range: Late Triassic,
The skull of ISI R42, the neotype of Parasuchus hislopi
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	†Phytosauria
Genus:	†Parasuchus Lydekker, 1885
Type species
†Parasuchus hislopi Lydekker, 1885

Parasuchus is an extinct genus of phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. It contains a single species, Parasuchus hislopi (though see below).

Discovery

Parasuchus was first described on the basis of a chimeric material - a rhynchosaurian basicranium mixed with phytosaurian partial snout, scutes and some teeth. The partial premaxillary rostrum (snout), GSI H 20/11, was chosen as the lectotype of Parasuchus hislopi. GSI H 20/11 was collected from the Lower Maleri Formation (Pranhita–Godavari Basin), near the Maleri village of Adilabad district, Andhra Pradesh.

Later, Sankar Chatterjee (1978) described many complete remains from the Lower Maleri Formation, as well as one nearly complete skull form the Tiki Formation, that he assignated to Parasuchus hislopi. Two complete and articulated skeletons that include complete skulls were collected in the vicinity of the Mutapyram village of Adilabad district. Both individuals were roughly 8 ft (2.4 m) in length, lying side by side. The left individual, ISI R 42, is perfectly preserved, and was designated as the neotype of the species following the suggestion of Chatterjee (2001). The rostrum of the right individual, ISI R 43, is the only missing part of its skeleton.

In the presumable gastric contents of these two skeletons, two articulated and almost complete skeletons of Malerisaurus robinsonae (both designated as ISIR 150), a basal archosauromorph, were found. From the same locality as the neotype, three isolated conjoined basioccipital/basisphenoids (ISI R 45-47) were also recovered. A couple of miles north of that locality, near the Venkatapur village, two more excellently preserved skulls were found. ISI R 160 represents an isolated but nearly complete skull, while ISI R 161 represents partial skull and articulated postcranial remains. Finally, the skull recovered from the Tikisuchus holotype site of the Tiki Formation (Gondwana Group), about 4 miles west of Tiki village of Shadol District, Madhya Pradesh, is missing only the end of the snout and the squamosal. As the lectotype of the genus, it was found nearby Paradapedon remains. Both formations date to the late Carnian to early Norian stage of the Late Triassic period, about 222.5-212 million years ago.

Description

Palaeorhinus, a relative of Parasuchus which is sometimes considered a synonym of the genus.

The name Parasuchus was first used by Thomas Henry Huxley (1870) in a faunal list. Since a diagnosis wasn't provided, it was considered to be a nomen nudum. Richard Lydekker (1885) described and named P. hislopi formally, and proposed the family name Parasuchidae. However, the species 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. To avoid additional confusion, the nondiagnostic holotype of P. hislopi was replaced by a neotype (ISI R 42) with approval from the ICZN (Opinion 2045) following the application of Chatterjee (2001).

The two articulated skeletons, ISI R 42-43, alone represent the most complete phytosaurs known to date. Additionally, Parasuchus has been found as one of the most primitive phytosaurs in phylogenetic analyses of Phytosauria, making it very significant for understanding the origin of the Phytosauria. Some studies, like Chatterjee (1978) and Lucas et al. (2007), synonymized Parasuchus with another basal phytosaur, Paleorhinus. If this is the case, the name Parasuchus would have precedence over Paleorhinus because Paleorhinus was named in 1904, nineteen years after Parasuchus was named. A phylogenetic analysis conducted by Kammerer et al. (2016) confirmed that Parasuchus hislopi is nested within the least inclusive clade containing the species Paleorhinus bransoni and Paleorhinus angustifrons. The authors thus considered the genus Parasuchus to be a senior synonym of the genus Paleorhinus (as well as Arganarhinus), and referred the species Paleorhinus bransoni, Paleorhinus angustifrons and Arganarhinus magnoculus to the genus Parasuchus. The cladogram below follows Nesbitt (2011).

Archosauriformes	Proterosuchidae  Archosaurus rossicus Proterosuchus fergusi Erythrosuchus africanus Vancleavea campi  Proterochampsia  Chanaresuchus bonapartei Tropidosuchus romeri Euparkeria capensis  Phytosauria  Parasuchus hislopi Smilosuchus gregorii Pseudopalatus pristinus  Archosauria  Pseudosuchia Avemetatarsalia

Etymology

Parasuchus was first described and named by Richard Lydekker in 1885 and the type species is Parasuchus hislopi. The generic name is derived from the Greek para/παρα meaning "beside" or "near" and suchus from the Greek souchos, which refers to the Egyptian crocodile-headed god Sobek. The specific name, hislopi, honors Hislop who drawn attention in 1854 to the red clays near Maleri village in which the holotype (and later the neotype and other specimens) of P. hislopi was recovered.