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Today Cordillera, tomorrow the world.
Ammonite evidence suggests the top of the Navesink correlates with the
bottom of the Hell Creek. Basal Hell Creek strata have yielded hadrosaurs
and small theropods similar to those from the Navesink. Apparently the last
1-2 million years of the terrestrial Cretaceous record is undocumented in the
east, and faunal exchange was well underway with the shrinking of the
Ceratopsids were always unknown in the east, but tyrannosaurs entered
eastern America in the Campanian, proving their ability to traverse marine
barriers (presumably via island chains) even when the seaway was at its
greatest extent. How far might they have gotten in the latest Maastrichtian,
when seaways were vanishing?
It is interesting that "Betasuchus" is similar to Dryptosaurus, which
argues for a continued connection of America and Europe via Greenland. Also,
the primitive nature of Thescelosaurus (unlike most Cordilleran
contemporaries) and its lack of clear American ancestry, suggests
immigration, hence contact with a formerly isolated region. Perhaps that was
a European island, given the tentative identification of Thescelosaurus from
In addition to a probable America-Europe link, Tarascosaurus, in
particular, supports a Europe-Africa connection, inasmuch as abelisaurs are
otherwise known only from Gondwana. Chattergee noted strong similarities
between the dinosaur faunas of India and Europe. Krause et al determined
that virtually all extant Malagasy vertebrates arrived post-Cretaceous,
undermining the notion of an isolated Madagascar by the latest Cretaceous.
Czerkas once mentioned probable South American tyrannosaurs, based on
"fragmentary fossils." This seems unverified, but together with Notoceratops
is intriguing. Perhaps Kritosaurus was not the only dinosaur able to
radiate southward in the Campanian, or subsequently.
Cousin et al wrote "...theropods were briefly the dominant group
before they died out together with the sauropods...c. mid-Maastrichtian."
That is intriguing as it suggests an alternative to climatic change as the
cause of the extinction of Ampelosaurus, Rhabdodon, and Struthiosaurus.
Composed mostly of weak defenders, the w. European menagerie seems highly
vulnerable, and its demise foreshadowed extinction elsewhere.