Tikisuchus romeri, Chatterjee & Majumdar, 1987

Gower, David J., 2002, Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis, Zoological Journal of the Linnean Society 136 (1), pp. 49-76 : 66-67

TIKISUCHUS ROMERI

Tikisuchus romeri Chatterjee & Majumdar is a rauisuchian from the Upper Triassic Tiki Formation of India, known from a single incomplete specimen, ISI R 305. The osteology of this taxon has been described only briefly by Chatterjee & Majumdar (1987). These authors figured a restoration of the braincase in posterior view and presented the following description: ‘braincase very deep with elongated and well pronounced basipterygoid processes; supraoccipital tapers dorsally and makes a movable contact with parietal’ ( Chatterjee & Majumdar, 1987: 788). Furthermore, they (p. 787) included ‘ossified laterosphenoid’ in a list of archosaurian features possessed by the specimen.

I have re-examined this material as part of this study. The surface preservation of ISI R 305 is very crumbly, and sutures and other details are hard to make out. In addition, several regions of the braincase are not preserved or could not be located at the time of this study. This makes it impossible to comment on the laterosphenoids (which could not be located), exoccipitals, metotic region, fenestra ovalis. The paroccipital processes are fairly short with strong distal expansions. The basioccipital bears dorsal facets that indicate that the ventral ends of the exoccipitals met along the midline to form the ventral border of the foramen magnum. The basal tubera of the basioccipital are barely bilobed. There is no sign that the entrance foramina for the cerebral branches of the internal carotid arteries were located on the posterior or posteroventral wall of the parabasisphenoid. The anterolateral surfaces of the same element are even less perfectly preserved, but I tentatively interpret that this is where the foramina for the cerebral branch of the internal carotid artery are positioned.

The braincase of T. romeri resembles that of P. kirkpatricki , particularly in the elongated region of the parabasisphenoid between the basipterygoid processes and the basal tubera, and in the way this region harbours a dorsoventrally elongate median pharyngeal recess. This is a derived feature within Suchia, and it represents a potential synapomorphy shared by P. kirkpatricki and T. romeri to the exclusion of other known suchians, including B. kupferzellensis (although the braincase UMMP 7473 appears to possess a similar feature, see above). One clear difference between the parabasisphenoids of P. kirkpatricki and T. romeri lies in the presence of paired short hook-like (in the transverse plane) processes on the parabasisphenoid of the latter taxon. These are not apparent in Chatterjee & Majumdar’s (1987) figure 2, but they can be clearly detected on the posterior surface of the element between the bases of the basipterygoid processes.

In summary, rauisuchian braincases are slowly becoming better known. The braincases of B. kupferzellensis , S. galilei , P. kirkpatricki and T. romeri share many features. Most of these are apparently plesiomorphic for Archosauria (e.g. undivided metotic foramen, external foramina for hypoglossal nerve not posterior to subvertical ridge), some are probably derived for Archosauria (e.g. well ossified otic bullae, lateral foramen for the cerebral branch of the internal carotid artery), but few if any seem to be both derived for Suchia and restricted to rauisuchians. The elongate median pharyngeal recess of P. kirkpatricki and T. romeri is perhaps the only such character. B. kupferzellensis and P. kirkpatricki share a separate foramen possibly for the posterior cerebral/cephalic vein above the dorsal end of the metotic foramen, but a probable equivalent is also present in at least some crocodilians, and the condition in S. galilei and T. romeri is unknown.