Mosaic nature in the skeleton of East Asian crocodylians fills the morphological gap between "Tomistominae" and Gavialinae.

Abstract

Crocodylian systematics has long been confounded by conflicting hypotheses of higher level relationships-although molecular data sets strongly supported the sister-taxon relationship of Tomistoma and Gavialis, morphological data sets placed Gavialis as sister to all other living taxa. One of the perceived difficulties in interpreting morphological character evolution on the molecular tree is the extensive character reversal occurring in Gavialinae, the mechanism of which has yet to be explained. Here, we provide evidence of gavialine-specific atavistic characters from East Asian "tomistomines" Penghusuchus pani and Toyotamaphimeia machikanensis. These taxa exhibit a mosaic assembly of "tomistomine" and gavialine features, which fill the gap between the two longirostrine groups. Although the parsimony analysis of morphological data (69 taxa, 254 characters) still supports the previous morphological hypothesis, the alternative tree that was forced to fit the molecular hypothesis was insignificantly (5/954 steps; 0.52%) longer than the unconstrained tree, suggesting that morphological evolution can also be interpreted on the molecular tree. Although the problem of stratigraphic gaps remains, future studies may be directed to resolving the interrelationships within Gavialoidea, a large longirostrine group of crocodylians, in the molecular tree context.