No abstract

A new, articulated skeleton of an ichthyosaur from the Lower Cretaceous (lower Albian) Wabiskaw Member of the Clearwater Formation near Fort McMurray, Alberta, is the most complete and stratigraphically oldest known ichthyosaur from the Cretaceous of North America and represents a new genus and species of ophthalmosaurian, Athabascasaurus bitumineus . The specimen consists of a nearly complete, dorsoventrally compressed skull, a complete and articulated presacral and partial caudal vertebral series, portions of the right pectoral girdle, and the right pelvic girdle and femur. The new taxon is characterized by the lack of a robust supranarial process of the premaxilla, an elongate maxilla that has its tallest point (in lateral view) posterior to the external naris, a wide postorbital region, the presence of a rectangular squamosal, an angular with greater lateral exposure on the posterior jaw ramus than the surangular, a dentition with extremely light enameled ridges, and a reduced presacral count of 42 vertebrae. The first species-level phylogenetic analysis of Ophthalmosauria reveals that Athabascasaurus is neither the sister taxon of, nor nests within Platypterygius , a geographically widespread, geologically long-lived, and taxonomically problematic genus. Athabascasaurus adds important new data on the morphology of Cretaceous ichthyosaurs and expands our knowledge of the palaeoecology and marine tetrapod diversity of the early Albian Boreal Sea.

No abstract

Palaeognaths constitute one of the most basal lineages of extant birds, and are also one of the most morphologically diverse avian orders. Their skeletal development is relatively unknown, in spite of their important phylogenetic position. Here, we compare the development of the postcranial skeleton in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana) and elegant crested-tinamou (Eudromia elegans), focusing on ossification. All of these taxa are characterized by element loss in the appendicular skeleton, but there are several developmental mechanisms through which this loss occurs, including failure to chondrify, failure to ossify and fusion of cartilages prior to ossification. Further evidence is presented here to support a reduction in size of skeletal elements resulting in a delay in the timing of ossification. This study provides an important first look at the timing and sequence of postcranial ossification in palaeognathous birds, and discusses the influence of changes in the pattern of skeletal development on morphological evolution.