The synonymy of the Late Cretaceous mosasaur (Reptilia) genus Lakumasaurus from Antarctica with Taniwhasaurus from New Zealand and its bearing upon faunal similarity

MARTIN, J.E. AND M. FERNÁNDEZ

Mendoza

Simposio; Gondwana 12: Geological and Biological Heritage of Gondwana; 2005

In 2002, Novas et al. described and named a new mosasaur as Lakumasaurus antarcticus from the Late Cretaceous marine deposits of the Antractica peninsula. The specimen was recovered from the Late Campanian Santa Marta Formation on James Ross Island and consists of a partial cranium, jaws, and postcrania. A number of characters are noteworthy and indicate the affinities of Lakumasaurus with the tylosaurs, including slender, shallow dentaries with long anterior projections, long predental rostrum of the premaxilla, frontals excluded from the orbit, and position of the pineal opening. However, other characters of Lakumasaurus are unusual among tylosaurs, particularly the dentition bearing fine striae, teeth with non-serrated anterior carinae, anterior teeth without posterior carinae, relatively straight lateral margins on frontal, and relatively small size. Investigation of mosasaurs from New Zealand confirms these characters in the type specimen of Taniwasaurus oweni Hector, collected from the late Campanian Conway Formation of Haumuri Bluff. The type consists of the skull table and anterior portions of the dentaries. Although poorly preserved and with broken tooth crowns, remands and an erupting tooth are finely striated and do not exhibit posterior carinae. The lateral margins of the frontal of Taniwasaurus measuring 16.0 cm across the orbits whereas Lakumasaurus  measures 16.7 cm. Size and similar morphological characters indicate the synonymy of Lakumasaurus with Taniwhasaurus.             Fine striae have long been considered indicative of plioplatecarpine mosasaurs. The occurrence of a tylosaurinae with this feature casts doubt upon other isolated, straiated teeth assigned to plioplatecarpines in Gondwana (e.g. Martin et al. 2002; Martin in press). More complete material from Antarctica and Patagonia will confirm these generic assignments. Of note, among the relatively numerous specimens collected from well over a century in New Zealand, no evidence of a plioplatecrapine has been recovered.             The synonymy of Lakumasaurus with Taniwhasaurus  adds significantly to the evidence of some endemism among faunal elements in Antarctica, New Zealand, and Patagonia (Weddellian Province) during the Late Cretaceous. Taniwhasaurus along with the possible co-occurrence of Moanasaurus (Martin et al. 2002) are the first mosasaurs at  a generic level to indicate Gondwanan endemism. The mosasaur evidence is complemented by the plesiosaur Aristonectes, which occurs in the Maastrichtian of Argentina and Antarctica (Gasparini et al. 2003) and appears quite similar to Kaiwhekea from the Maastrichtian on New Zealand.