A new Hyperodapedon (Archosauromorpha, Rhynchosauria) from the Upper Triassic of India: implications for rhynchosaur phylogeny

Abstract

A new species of the rhynchosaur genus Hyperodapedon, namely H. tikiensis, is described from well-preserved skeletal elements that were collected from the Upper Triassic Tiki Formation of India. Hyperodapedon tikiensis is diagnosed on the basis of several cranial and postcranial features including longer than wide basipterygoid process, crest-shaped maxillary cross section lateral to the main longitudinal groove, deeply excavated neural arches of mid-dorsal vertebrae, long scapular blade, a pronounced deltopectoral crest, proximal humeral end much broader than distal end, iliac length greater than iliac height, equal pre-and postacetabular iliac lengths and circular femoral cross section. Two distinct morphotypes of the maxillary tooth plates can be discerned, which are attributed to ontogenetic variations. A maximum-parsimony analysis was carried out to show that the order Rhynchosauria is characterized by nine cranial and one postcranial character states. The analysis reveals that Otischalkia elderae is invalid and the basal forms, Howesia and Mesosuchus, are closely related. The Mid-Triassic genus Ammorhynchus is more derived and forms a sister group to the Late Triassic subfamily Hyperodapedontinae. Isalorhynchus and Teyumbaita are basal to the pandemic genus Hyperodapedon. Twenty-four characters that are not homoplasious document major patterns of skeletal evolution in rhynchosaurs. From laterally oriented scapula and slender propodials, the postcranial skeleton evolved into a more robust form as is evident from nearly vertical scapula and increase in the robustness of the propodials. Shortening of the femur is noted in the derived Late Triassic forms as exemplified in Hyperodapedon gordoni, Hyperodapedon huxleyi and H. tikiensis. for internal carotid artery; inf, intertrochanteric fossa; int, internal trochanter; lg, longitudinal groove on the posterodorsal surface of the maxillary tooth plate; na, neural arch; nc, neural canal; ns, neural spine; oc, occipital condyle; OcL, length of occipital condyle; OcW, width of occipital condyle; pbs, parabasisphenoid complex; pcf, femoral posterior condyle; pf, posterior flange of the femur;

The Early Evolution of Rhynchosaurs

“…By contrast, four additional steps are necessary to force a sister-taxon relationship between R. articeps + L. brodiei (Templeton test using Wilcoxon signed-ranks, p = 0.0455). Therefore, the results recovered here are generally congruent with the most recent phylogenetic hypotheses [i.e., Langer et al, 2010;Montefeltro et al, 2013;Butler et al, 2015; but see Mukherjee and Ray (2014) for a different result] and support the erection of a new genus for "Rhynchosaurus" brodiei.…”

“…This is the typical rhynchosaurid morphology (Langer et al, 2000b;Nesbitt and Whatley, 2004), but differs from the more gentle curvature of H. browni and E. wolvaardti and the completely straight margin of M. browni (Benton, 1983b(Benton, , 1990Dilkes, 1995Dilkes, , 1998Langer and Schultz, 2000;Montefeltro et al, 2010;Mukherjee and Ray, 2014;Butler et al, 2015). The posterior end of the maxilla is dorsoventrally shallower ventrally to the jugal than in E. wolvaardti (SAM-PK-K10159) and R. articeps (SHYMS 1, NHMUK PV R1236; Figure 6).…”

“…gordoni, Hy. huxleyi, and Hyperodapedon tikiensis the lateral tooth bearing area is equal to or more developed than the medial area (Langer and Schultz, 2000;Langer et al, 2000bLanger et al, , 2010Nesbitt and Whatley, 2004;Montefeltro et al, 2010;Mukherjee and Ray, 2014). The lateral tooth bearing area is crest-shaped, as in R. articeps, S. stockleyi, B. sidensis, T. sulcognathus, and Hyperodapedon huenei .…”

“…More recently, Dilkes (1998) suggested that N. colletti might be potentially a junior synonym of the stratigraphically younger rhynchosaur Mesosuchus browni because the two are consistent in morphology and share two possibly diagnostic characters (a median ventral groove on the centra of the first two caudal vertebrae, a flattened first distal tarsal). N. colletti was ignored in most other recent discussions of rhynchosaur evolution (e.g., Benton, 1983bBenton, , 1990Wilkinson and Benton, 1995;Hone and Benton, 2008;Montefeltro et al, 2013;Mukherjee and Ray, 2014). ; and second sacral vertebra and ribs in dorsal view (SAM-PK-6046) (F) and left ilium in lateral view (SAM-PK-7416) (H) of M. browni.…”

Supradapedon revisited: geological explorations in the Triassic of southern Tanzania

“…More recently, Langer et al (2000) revised the inclusivity of the genus Hyperodapedon , proposing that it encompassed most Late Triassic rhynchosaurs, including Su. stockleyi (see also Mukherjee & Ray, 2014), but did not address the validity of that species. Such attribution was then used to stratigraphically correlate the strata bearing Su.…”