Parasuchus is an extinct genus of basal phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. At its most restricted definition, Parasuchus contains a single species, Parasuchus hislopi.[1][2] Parasuchus hislopi is one of several species belonging to a basal grade of phytosaurs, typified by the genus Paleorhinus. Historically, Paleorhinus has been known from better-described fossils, and many species have been lumped into that genus. Parasuchus hislopi, despite being described earlier than Paleorhinus, was considered an undiagnostic chimera until new neotype fossils were described in the late 1970s. Parasuchus hislopi and the two unambiguously valid species of Paleorhinus (P. bransoni and P. angustifrons) are all closely related; some authors have historically described them all under the species Paleorhinus, while others place the two Paleorhinus species into Parasuchus according to the principle of priority.[3]
The name Parasuchus was first used by Thomas Henry Huxley (1870) in a faunal list. Since a diagnosis wasn't provided, it would have been considered a nomen nudum at the time. Richard Lydekker (1885) formally described and named P. hislopi, and proposed the family name Parasuchidae. However, Lydekker's description was based on a chimeric syntype, combining fossils from multiple unrelated reptiles: a rhynchosaurian basicranium mixed with the partial snout of a phytosaur, scutes and some teeth. Friedrich von Huene (1940) identified the basicranium as belonging to Paradapedon huxleyi (now known as Hyperodapedon huxleyi) and 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 while Gregory (1962) considered the material undiagnostic.
Sankar Chatterjee (1978) described many complete remains of the Indian parasuchian and showed that it is not assignable either to Brachysuchus (which is closely related to or synonymous with Angistorhinus), or to Phytosaurus (a dubious name, probably the senior synonym of Nicrosaurus). He argued that the rhynchosaur basicranium qualifies as neither the holotype of P. hislopi, nor the lectotype of Paradapedon huxleyi. He re-introduced P. hislopi, based on Lydekker's snout fossil and new well-preserved material.[1] 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).[4]
The partial premaxillary rostrum (snout) originally described by Lydekker, GSI H 20/11, was chosen as the lectotype of Parasuchus hislopi by Sankar Chatterjee. GSI H 20/11 was collected from the Lower Maleri Formation (Pranhita–Godavari Basin), near the Maleri village of Adilabad district, Andhra Pradesh. The lectotype was rendered obsolete when neotype fossils were approved for the genus in 2003.[4]
Sankar Chatterjee later described more comprehensive remains from the Lower Maleri Formation, as well as one nearly complete skull form the Tiki Formation that he also assigned to Parasuchus hislopi. Two complete and articulated skeletons that include complete skulls were collected from the Lower Maleri Formation 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.[4] The right individual, ISI R 43, is nearly complete and only missing part of the snout.[1][3]