Athabascasaurus
Athabascasaurus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from Alberta, Canada. Discovery. "Athabascasaurus" is known from the holotype TMP 2000.29.01, articulated nearly complete postcranial skeleton and nearly complete skull preserved in dorsal view, missing the premaxilla. It was collected in 2000 on the western side of the Syncrude Canada Ltd.'s Base Mine, an open-pit mine near Fort McMurray. The specimen was found in the Wabiskaw Member of the Clearwater Formation, which dates to the earliest Albian stage of the Early Cretaceous epoch, about 112 million years ago. The specimen resides at the Royal Tyrrell Museum  of Palaeontology. "Athabascasaurus" was first named by Patrick S. Druckenmiller and Erin E. Maxwell in 2010 and the type species is "Athabascasaurus bitumineus". The generic name is derived from the name of the Athabasca River, which runs through Athabasca oil sands area where the holotype was collected, and "sauros", Greek for "lizard". The specific name refers to the fact that it was recovered at an oilsand mine. Description. "Athabascasaurus" is a medium-sized ichthyosaur, with a total estimated length of 3.5 meters. Skull. Unlike "Ophthalmosaurus" and "Aegirosaurus", the maxillae (rear upper tooth bearing bones) of "Athabascasaurus" are elongate. Their highest  points are located behind the external nares (nostril openings), unlike "Platypterygius americanus". Each maxilla of "Athabascasaurus" bears a ridge towards its upper edge. The lacrimals of "Athabascasaurus" are short from front to back, unlike those of some other ophthalmosaurids, and don't extend beneath the external nares. The frontals (paired skull roof bones) do not reach the temporal fenestrae (openings on top of the skull), unlike the condition in "Platypterygius australis". The region of the skull behind the orbit (eye socket) is not narrow, as it is in "Ophthalmosaurus" and "Aegirosaurus". The postfrontals (paired skull roof bones) of "Athabascasaurus" bear  triangular projections that extend on top of the upper regions of the postorbitals (paired bones located behind the orbits). The squamosals (paired bones towards the skull's rear) of "Athabascasaurus" are rectangular, unlike the triangular squamosals of "Ophthalmosaurus" and "Aegirosaurus", and the entirely absent squamosals of "Platypterygius". There is very little surface on the rear face of the basioccipital (skull bone that connects to the vertebral column) that is not occupied by the occipital condyle (part that connects to the vertebrae) in "Athabascasaurus", less than in some other ophthalmosaurids. While the angulars and surangulars (two pairs of rear lower jaw  bones) occupy a similar amount of space on the mandible's outer surface in multiple ophthalmosaurids, the angular takes up much more area than the surangular in "Athabascasaurus". The teeth of "Athabascasaurus" bear very faint enamel ridges, like those of "Platypterygius americanus" and "Maiaspondylus", though unlike those of most other ophthalmosaurs. Postcranial skeleton. The first two vertebrae (atlas and axis) are firmly fused together without any evidence of a boundary visible, as in "Platypterygius" and some specimens of "Ophthalmosaurus". In "Athabascasaurus", the neural spine of the atlas bears a spur-like projection that points forwards. There are only 42 vertebrae  present before the hips, a low number for an ophthalmosaur. The lower hip bones (pubic bones and ischia) on each side are fused into a single unit. This bone lacks an ischiopubic foramen (a small opening). Classification. Two cladistic analyses by Fischer and colleagues, one in 2011 and the other in 2012, found it to be most closely related to ""Platypterygius" australis", and to nest within Platypterygiinae.