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Re: Shark eating dino fossil found in Utah
This is the relevant abstract.
Kirkland, James I.; Milner, Andrew R.C.; and Nesbitt, Sterling, J.
2005. THE CASE FOR THEROPOD DINOSAURS EXPLOITING FISH AS A MAJOR FOOD
RESOURCE DURING THE EARLY JURASSIC. Tracking dinosaur origins - The
Triassic-Jurassic Terrestrial Transition, Abstracts Volume: 9-10.
Following the extinction of phytosaurs and metoposaurs (semi-aquatic
predators) at the end of the Triassic, there is gap in the record of
large semi-aquatic fish-eating tetrapods. The earliest Jurassic record
of a large semiaquatic predator is the crocodilian Calsoyasuchus from
the Kayenta Formation. With few taxa taking advantage of fish as a
food source, we suggest that large theropods may have fed on fish in
the Early Jurassic in the western United States.
The Whitmore Point Member of the Moenave Formation and the basal
Kayenta Formation preserve evidence of extensive lake systems across
southwestern Utah and northern Arizona. Although herbivore tracks are
relatively common in more upland eolian facies, theropod tracks
dominate almost to the exclusion of other ichnotaxa in the marginal
environments of these lakes. The most common large theropod ichnotaxon
is Eubrontes, which is usually referred to as the track of a large
coelophysoid theropod such as Dilophosaurus. The near-complete absence
of herbivorous dinosaurian ichnotaxa from this facies begs the
question, what did these large theropods eat in this habitat? The fish
from the Whitmore Point Member include abundant, heavy,
ganoid-scale-covered semionotids of relatively large size (30-60 cm)
as well as large coelacanths (~2 m), hybodont sharks (~1 m), and
lungfish (~1 m).
These fish could have served as a food source for large predators, as
comparably sized salmon do for bears today.
Bones and teeth of theropods large enough to produce Eubrontes tracks
have been found within the same beds as these Whitmore Point fish. The
theropod remains cannot be attributed to a specific theropod taxon at
present. Most of the long, slender, awl-shaped teeth display a
distinctive wear pattern, having the serrations along the anterior and
posterior carina that are worn off from the tip of the tooth to the
base of the crown. The only teeth the authors have observed with
similar wear are those of Spinosaurus, a theropod dinosaur that many
paleontologists agree was probably a piscivore to some degree. We
hypothesize that this kind of wear was produced by the teeth
penetrating the "chain mail" of heavy ganoid scales covering the
semionotid fish. In the case of the St. George theropods, the fish
would be Semionotus; for the mid-Cretaceous Spinosaurus, the fish
would be Lepidotes. The hard enamel covering on the scales would
rapidly wear the enamel on the teeth.
Additionally, Dilophosaurus and Spinosaurus share the following
characters that may be adaptive for piscivory: moderately long arms
with raptorial claws, posterior nasal openings, slim jaws, and
anteriorly expanded jaws with long, slender teeth (a rosette). Similar
jaws are present in a number of extinct and extant aquatic and
semiaquatic fish-eating predators (e.g., crocodilians, phytosaurs,
champsosaurs, and pliosaurs). A slender jaw displaces a minimum volume
of water when shut rapidly, and the rosette of teeth at the front
maximizes the area for catching fish. Posteriorly placed nasal
openings might permit the end of jaws to rest in water with head in a
vertical "striking" position. Furthermore, the recently documented
myriad of theropod swim tracks in both the Whitmore Point Member and
lower Kayenta Formation indicates that theropods were regularly
entering the lakes to water depths that would at least partially buoy
up their bodies.
2007/4/23, Gautam Majumdar <email@example.com>:
On Monday 23 April 2007 07:37, Jura wrote:
> Anyone else know anything about this? The article says
> it's a coelophysid, and that the fossil was found
> along with impressions (claw marks, and such). No
> mention of what paper this is getting published in.
Appears that it has been published in a book. From the same article
"The New Mexico Museum of Natural History and Science has just published a
book, "The Triassic-Jurassic Terrestrial Transition," which provides brief
mentions of many of the recent finds."