Punctuated Equilibrium Example: Some Dinosaurs

The talk.origins "Transitional Vertebrate Fossils" FAQ recommends:

Horner, J.R., D.J. Varrichio, and M.B. Goodwin. 1992. Marine transgressions and the evolution of Cretaceous dinosaurs. Nature 358:59-61.

The paper describes some new fossils from Montana:

transitional ceratopsids between Styracosaurus and Pachyrhinosaurus
50 specimens of lambeosaurids, transitional between Lambeosaurus and Hypacrosaurus.
a transitional pachycephalosaurid between Stegoceras and Pachycephalosaurus.
a transitional tyrannosaurid between Tyrannosaurus and Daspletosaurus

Until these transitional fossils were found, these dinosaur groups were known only from the large Judith River Formation. There, the fossils showed 5 million years of evolutionary stasis, followed by the apparently abrupt appearance of the new forms.

It is now known that the sea level rose, drowning the Judith River Formation for 500,000 years. The dinosaurs were forced to move to smaller areas such the place in Montana. Being under pressure, all of these species evolved fairly rapidly, as shown by the transitional fossils in Montana. When the sea level fell again, the new forms spread back to the Judith River area.

Punctuated Equilibrium Example: Some Dinosaurs

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