A rhynchosaur from the Upper Triassic Maleri Formation of India

Abstract

Six associated rhynchosaur skeletons, recently discovered by the Geological Studies Unit of the Indian Statistical Institute in the Upper Triassic Maleri Formation, allow an almost complete osteological description and restoration of the species Paradapedon huxleyi . The dentition is highly specialized, ankylothecodont, each tooth firmly fixed with a long root, new teeth added posteriorly in diagonal rows, without tooth replacement. The creatures probably lived in flood-plains or marshy environments, as shell eaters feeding mainly on mussels. Possible evolutionary trends within the family Rhynchosauridae are outlined. The seven genera of rhynchosaurs are grouped on their morphological characters into three well-defined subfamilies which represent three stages in rhynchosaur evolution, occurring in Lower, Middle and Upper Triassic respectively.

The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades

“…Sereno (1991a;character 20) hypothesized that the strongly mediolaterally compressed unguals in Ornithosuchus and Riojasuchus represented a synapomorphy uniting the two taxa. However, a similar morphology is present in phytosaurs (Smilosuchus, USNM 18313; Pseudopalatus, UCMP 27235; apparently in Parasuchus, Chatterjee, 1978), Saurosuchus (PVL 2557), Ticinosuchus (PIZ T2817), and the aetosaurs Aetosaurus (SMNS 5770 S-22) and Typothorax (MCZ 1488). Although this character is vaguely worded, it attempts to qualify the large differences among the unguals of basal archosaurs.…”

“…As with proterochampsians, Euparkeria (SAM 5867) has a similar arrangement of the antorbital fossa. Within phytosaurs, the antorbital fossa is present on the dorsal process of the maxilla and the lacrimal in the primitive phytosaurs Parasuchus (Chatterjee, 1978) and 'Paleorhinus' scurriensis (TTU-P 00539; Langston, 1949;Stocker, 2010) but absent on the maxilla and lacrimal in Smilosuchus (UCMP 27200) and Pseudopalatus pristinus (NMMNH 31292). In aetosaurs (Aetosaurus, SMNS 5770), Riojasuchus (PVL 3827), Gracilisuchus (MCZ 4117), Turfanosuchus (IVPP V 3237), Ticinosuchus (PIZ T2817), ''rauisuchians,'' crocodylomorphs, and dinosauriforms (e.g., Silesaurus ZPAL Ab III/361/26; Herrerasaurus PVSJ 407), the antorbital fossa is located on the lacrimal, the dorsal process of the maxilla, and nearly the entire dorsal margin of the posterior process of the maxilla.…”

“…Within Proterochampsia, Chanaresuchus (PVL 4647), and Gualosuchus (PVL 4576) have short anterior cervicals, whereas Tropidosuchus (PVL 4601) has anteroposteriorly elongated cervicals relative to the middorsal vertebrae. Phytosaurs (e.g., Parasuchus; Chatterjee, 1978), Riojasuchus (PVL 3827), Revueltosaurus (PEFO 34561), aetosaurs (e.g., Longosuchus; Sawin, 1947), Postosuchus kirkpatricki (TTU-P 9000), Saurosuchus (PVSJ 32), Ticinosuchus (PIZ T2817), and Prestosuchus (UFRGS 0156-T) have cervicals that are shorter or the same length as the middorsals. In Gracilisuchus (UNLR 08), Arizonasaurus (MSM P4590), Effigia (AMNH FR 30587), and basal crocodylomorphs (e.g., Hesperosuchus agilis, AMNH FR 6758; Dromicosuchus, UNC 15574), the anterior cervicals are elongated relative to the middorsals.…”

Supplemental Material for 'Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. (Bulletin of the American Museum of Natural History, no. 398)'

“…There is no clear medial ridge with which the ancestral sacral two articulated, in contrast to most archosauriforms (e.g., Erythrosuchus africanus; Gower, 2003). The sacral scars from ancestral sacral ribs one and two are similar in relative size to those of other early diverging archosauromorphs, such as Trilophosaurus buettneri (Gregory, 1945), Prolacerta broomi (BP/1/ 2676), and rhynchosaurs (e.g., MCZ 1529; Chatterjee, 1974).…”

“…The possible extension of these South American units into the early Late Triassic and the shared presence of the Massetognathus-Santacruzodon clade with the Makay Formation provide further evidence for a late Middle Triassic-early Late Triassic age for the Makay Formation. Additionally, we note that dinosaurs and other archosauriform taxa (e.g., phytosaurs, aetosaurs) typically found in Upper Triassic deposits of neighboring areas (e.g., Maleri Formation of India; Chatterjee, 1978) are absent thus far in the Makay Formation. The Makay Formation thus is almost certainly older (by an unknown span) than units producing the earliest dinosaurs, including the Ischigualasto Formation of Argentina and Santa Maria Series of Brazil (see .…”