Habrosaurus dilatus

A fragmentary, edentulous, right dentary of Habrosaurus, AMNH 8477, has been recovered from the Clambank Hollow locality. The dentary does not seem to be so curved in the medial direction as some of the later Lance specimens. Anteriorly the jaw is broken, but as in the Lance specimens the teeth reach close to the ventral border. The pleurodont teeth are in a tooth border which is wide anteriorly and narrows considerably posteriorly. Externally, there is a long, narrow groove leading into a foramen at the position of the third or fourth tooth from the posterior. DISCUSSION: Fossil sirens are reported in the Cretaceous of North America from the Albian of Texas, from the Maestrichtian of Montana and Wyoming, and now from the Campanian of Montana. Originally described by Gilmore (1928, p. 161), Habrosaurus dilatus was placed, " Amphibia incertae sedis. " Recent members of the family Sirenidae are restricted to the southern coast of North America. The family contains two genera, Pseudobranchus and Siren, the latter having two species, S. lacertina and S. intermedia. Phylogeny of the sirenids has been reviewed by Goin and Auffenberg (1955, 1957) and Estes (1964). The oldest known form is Prosiren elinorae from the Albian Trinity Sandstone of Texas (Goin and Auffenberg, 1958). It probably gave rise to the Upper Cretaceous Habrosaurus dilatus. Both Recent forms share a number of common features with the Cretaceous Habrosaurus.