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Platecarpus tympaniticus A mosasaur from the upper Smoky Hill Chalk of western Kansas
Copyright © 2000-2009 by Mike Everhart last update 09/16/2009 LEFT: View of skull and lower jaws of FHSM VP-17017 as found. Skul was upside down and lower jaws were separated and lying off to the side. |
| IMPORTANT NOTE: The recent
publication of an article in the JVP by Takuya Konishi and Michael Caldwell clarifying the
identification and relationships of the various species of Platecarpus will
necessitate some major changes in some of my web pages. Please note that Platecarpus
planifrons Cope (1874) is now identified as the most common species of Platecarpus
in the lower chalk (late Coniacian to middle Santonian), and P. ictericus (Cope,
1871) is the most common species of this genera in upper chalk (middle Santonian through
early Campanian). P. coryphaeus (Cope, 1872) is a junior synonym of P.
ictericus. The name Platecarpus tympaniticus (Cope, 1869) is now
limited to a single specimen (holotype) from Mississippi. The species that I had
previously identified as Platecarpus planifrons (above) is now
"unidentified" and possibly a new genus / species which we are working to
identify / describe. I consider this paper to be a major improvement in mosasaur
phylogeny. The citation is: Konishi, T. and Caldwell, M. W. 2007. New specimens of Platecarpus planifrons (Cope, 1874) (Squamata: Mosasauridae) and a revised taxonomy of the genus: Journal of Vertebrate Paleontology 27(1): 59-72. And another revision.. Platecarpus tympaniticus is now the senior synonym over P. ictericus and P. coryphaeus. Konishi,
T., |
This Platecarpus tympaniticus mosasaur skull was found and mostly prepared in 1996, but was not photographed in any detail until January, 2000.
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A dorsal view of the back of the mosasaur skull. Scale is 15 cm (about 6 inches). |
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A slightly closer view of the frontal bone which covers most the top of the skull. The parietal, parietal foremen and parietal-frontal suture are also visible. |
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A close up the suture between the frontal and the post orbital frontal (POF). The POF provides the upper and rear portion of the orbit of the eye. The jugal and prefrontal complete the rest of the orbit. The large round object at the top of the picture is the left quadrate bone. For some unknown reason, both quadrates had been displaced forward into the orbits before the skull was buried. |
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A ventral view of the back of the skull, showing the left pterygoid bone and the displaced left quadrate. The rounded surface at the far right is the occipital condyle (where the vertebral column is attached to the skull). |
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The back of the skull from slightly above. The occipital condyle is in the center of this picture. |
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A dorsal view of the snout or muzzle of the mosasaur. The premaxilla is centered between the right and left maxillaries. The nasal openings (nares) of the skull are located near the center of the picture. |
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A ventral view of the muzzle. There were four teeth in the premaxilla and twelve teeth in each of the maxillaries.. |
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A close-up, ventral view of the premaxilla and anterior portions of both maxillaries. |
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A lateral view of the right quadrate. The right eardrum of the mosasaur was located on this surface. |
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A medial view of the right quadrate. The cracks were probably the result of extreme pressures during fossilization. |
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A medial view of the left quadrate. The broken bones at the upper left and lower right are probably the ends of the jugal which forms the back and lower portions of the orbit of the left eye. |
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A wider view of the left quadrate and the left pterygoid. |
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Lateral views of the right (top) and left (bottom) lower jaws. The jaws were found laying together and detached from the rest of the skull. |
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Medial views of the right (top) and left (bottom) dentarys. There are twelve teeth on each of the dentarys. |
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Loose teeth that were found associated with the specimen. These were probably new (forming) teeth that were not yet set firmly in the jaws. |
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An overhead view of the complete skull, lower jaws and cervical vertebrae. |
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Four cervical vertebrae in articulation as found. |
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The re-assembled atlas-axis vertebrae complex. In mosasaurs, the atlas vertebra is made up of four pieces of bone that articulate between the occipital condyle of the braincase and the axis vertebra. |
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Serrated bite marks on the lower edge of the left jaw are evidence of scavenging by Squalicorax sharks. Many of the mosasaur's ribs had similar bite marks. There was no limb material found with this specimen, suggesting that the carcass had been stripped fairly completely before it sank to the bottom of the seaway. In 1999, a large Squalicorax kaupi tooth was found at the same locality. |
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More shark bite marks on the angular of the left jaw. |
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LEFT: The skull of FHSM VP-17017 in dorsal view. The teeth would normally point downward, not off to the side. |
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LEFT: Close up of the back of the skull of FHSM VP-17017 in dorsal view |
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LEFT: Right (top) and left dentarys of FHSM VP-17017 in medial and lateral views |
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LEFT: The right quadrate of FHSM VP-17017 in lateral and medial views. |
