Athabascasaurus

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Athabascasaurus
Temporal range: Lower Cretaceous, 112.6–109 Ma
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Athabascasaurus bitumineus holotype.jpg
Holotype specimen in Royal Tyrrell Museum of Palaeontology
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Ichthyosauria
Family: †Ophthalmosauridae
Subfamily: †Platypterygiinae
Genus: †Athabascasaurus
Druckenmiller & Maxwell, 2010
Species:
†A. bitumineus
Binomial name
†Athabascasaurus bitumineus
Druckenmiller & Maxwell, 2010

Athabascasaurus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from Alberta, Canada.[1][2]

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.[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]

Description[]

Athabascasaurus is a medium-sized ichthyosaur, with a total estimated length of 3.5 meters.[1]

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.[4] 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.[1]

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.[1]

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.[1]

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.[1] 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).[4][1]

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.[5][6]

See also[]

References[]

  1. ^ a b c d e f g h i Patrick S. Druckenmiller & Erin E. Maxwell (2010). "A new Lower Cretaceous (lower Albian) ichthyosaur genus from the Clearwater Formation, Alberta, Canada". Canadian Journal of Earth Sciences. 47 (8): 1037–1053. Bibcode:2010CaJES..47.1037D. doi:10.1139/E10-028.
  2. ^ "†Athabascasaurus Druckenmiller and Maxwell 2010". Paleobiology Database. Fossilworks. Retrieved 17 December 2021.
  3. ^ Henderson, D. (2013). "A one-in-a-billion dinosaur find". The Guardian. Retrieved 2013-11-21.
  4. ^ a b Ji, C.; Jiang, D. Y.; Motani, R.; Rieppel, O.; Hao, W. C.; Sun, Z. Y. (2016). "Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China". Journal of Vertebrate Paleontology. 36 (1): e1025956. doi:10.1080/02724634.2015.1025956. S2CID 85621052.
  5. ^ Fischer, Valentin; Edwige Masure; Maxim S. Arkhangelsky; Pascal Godefroit (2011). "A new Barremian (Early Cretaceous) ichthyosaur from western Russia". Journal of Vertebrate Paleontology. 31 (5): 1010–1025. doi:10.1080/02724634.2011.595464. hdl:2268/92828. S2CID 86036325.
  6. ^ Valentin Fischer; Michael W. Maisch; Darren Naish; Ralf Kosma; Jeff Liston; Ulrich Joger; Fritz J. Krüger; Judith Pardo Pérez; Jessica Tainsh; Robert M. Appleby (2012). "New ophthalmosaurid ichthyosaurs from the European Lower Cretaceous demonstrate extensive ichthyosaur survival across the Jurassic–Cretaceous boundary". PLOS ONE. 7 (1): e29234. Bibcode:2012PLoSO...729234F. doi:10.1371/journal.pone.0029234. PMC 3250416. PMID 22235274.
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