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THE LONGEST PUBLISHED MORTICHNIAL TRACKWAY: MESOLIMULUS WALCHI, HORSESHOE CRAB
Dean R. Lomax and Christopher A. Racay
A mortichnial trackway is one which ends in the track marker. This means that for one reason or another, the track maker died in its tracks. In the case of M. walchi, the crab likely died of asphyxiation in the low oxygen, hyper-saline enviroment of the lagoon it fell into. At the beginning of this 9.7m (32ft) trackway, there are impressions of what appears to be the crab's back. The authors think it was tossed into the lagoon by a storm, righted itself, and tried to escape the harsh environment until it succumbed. While it is sad for the crab, this trackway helps paleontologists illuminate the behavior of the trackmaker and others that leave similar tracks
Salt Gland Structures Identified in a Late Jurassic Ichthyosaur
William R. Wahl
Salt glands allow marine reptiles to drink seawater and have been noted on plesiosaurs and marine crocodiles. UW24816 is a large and almost complete opthalmosaur skull preserved in three dimensions, but fractured into a series of cross-sectional views. A section anterio-dorsal to the orbits revealed paired structures preserved within the sediment of the skull which extend to the external nares. The described pockets are sub-triangular, bordered by the prefrontal/lachrymal contact anteriorly and by the nasal bones dorsally and suggest preserved paired salt glands.
AN ICHTHYOSAURUS (REPTILIA, ICHTHYOSAURIA) WITH GASTRIC CONTENTS FROM CHARMOUTH, ENGLAND: FIRST REPORT OF THE GENUS FROM THE PLIENSBACHIAN
Dean R. Lomax
A well preserved ichthyosaur specimen from the paleontology collection of Doncaster Museum and Art Gallery, England is described with a focus on the gastric material scattered around the ribs and throughout the matrix. The
gastric material comprises coleoid cephalopod hooklets. The ichthyosaur has been dated from the Pliensbachian Stage
of the Lower Lias rocks of the Charmouth coastline, Dorset, England. The specimen is identified as Ichthyosaurus sp.
and thus extends the geologic range of the genus into the Pliensbachian. The specimen comprises a complete skull,
articulated vertebrae, ribs and a fully articulated forefin. The specimen may also contain coprolites preserved within
the posterior end of the matrix.
TAPHONOMY OF A NOSE DIVE: BONE AND TOOTH DISPLACEMENT AND MINERAL ACCRETION IN AN ICHTHYOSAUR SKULL
William R. Wahl
In July 1998, a partially articulated anterior skeleton of Opthalmosaurus was collected from the Redwater Shale Member of the Sundance Formation, Natrona County, WY. The skull was disconnected from the vertebral column at the atlas-axis and
rested upside down at a nearly 90◦ angle to the bedding. The skull and associated vertebrae are partially encased in at least two
generations of concretion. Borings on the partially articulated pectoral girdle, ribs and vertebrae suggest that the specimen was
exposed on the sea floor. No such evidence, however, was found on the middle and distal portions of the skull, further
suggesting that it was partially driven into the sediment by the impact of the carcass.
A HYBODONT SHARK FROM THE REDWATER SHALE MEMBER, SUNDANCE FORMATION (JURASSIC), NATRONA COUNTY, WYOMING
William R. Wahl
Remains of a shark specimen were found in the gastric contents of a small-bodied plesiosaur. The fossil material was identified as a member of the Hybodontiformes based on the teeth and dorsal spine denticles. The specimen is the first hybodont shark to be identified from the Upper Sundance Formation of Wyoming. Hybodont shark material previously described was limited to the Lower Sundance and not associated with marine reptile remains. The hybodont specimen described here may indicate a different type of predation on the marine vertebrate and invertebrate environment of the Sundance Formation biota.
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