Athabascasaurus

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.[1] The specimen resides at the Royal Tyrrell Museum of Palaeontology.[3]

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.[1]

Athabascasaurus is a medium-sized ichthyosaur, measuring 3.5 m (11 ft) long and weighing 200 kg (440 lb).[1][4]

The long maxillae (rear upper tooth bearing bones) of Athabascasaurus extend the furthest upwards behind the external nares (nostril openings).[1] Each maxilla of Athabascasaurus bears a ridge towards its upper edge.[5] The lacrimals of Athabascasaurus are short from front to back, and do not go underneath the external nares. The frontals (paired skull roof bones) do form any of the border of the temporal fenestrae (openings on top of the skull).[1] 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), a distinctive characteristic of the genus. The elongate region of the skull behind the orbit (eye socket) differs from that of Ophthalmosaurus and Aegirosaurus. The squamosals (paired bones towards the skull's rear) of Athabascasaurus are rectangular in shape. 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.[1] More of the outer surface of the rear part of the mandible is occupied by the angulars than the surangulars in Athabascasaurus. Unusually for an ophthalmosaur, the enamel ridges on the teeth of Athabascasaurus are very poorly pronounced.[1]

There is no visible boundary between the first two vertebrae (atlas and axis), which are firmly fused together, similar to Platypterygius. A unique trait of Athabascasaurus is the neural spine of its first vertebra, which bears a spur-like projection pointing forwards. There are only 42 vertebrae present before the hips, a low number for an ophthalmosaur.[1] The lower hip bones (pubic bones and ischia) on each side are fused into a single unit that lacks an opening.[5][1]

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.[6][7]

• List of ichthyosaurs
• Timeline of ichthyosaur research