Pachycephalosaurus Timeline

Pachycephalosaurus   >   Timeline


Pachycephalosaurus Timeline

220 million years ago
First dinosaurs evolve during the Triassic period.
76 million years ago
First Pachycephalosaurus appears during the Cretaceous period.
65 million years ago
Cretaceous-Tertiary extinction event: All non-avian dinosaurs (including Pachycephalosaurus) go extinct.

The K/T Extinction Event may have been caused by an asteroid impact:
K/T Extinction Event may have been caused by an asteroid impact

Unknown fossil hunter finds Pachycephalosaurus in the Lance Formation in Southeastern Montana. The earliest name used to refer to the animal is "Tylosteus".

Map of Hell Creek and Lance Formations:
Map of Hell Creek and Lance Formations

Joseph Leidy identifies the fossil as belonging to the armor of a reptile or an armadillo-like animal (more than a century later it turned out to be a bone from the knobs on Pachycephalosaurus's skull).

Joseph Leidy:
Joseph Leidy

What is today known as Pachycephalosaurus wyomingensis is named by Charles W. Gilmore as Troodon wyomingensis.

Charles W. Gilmore:
Charles W. Gilmore

Barnum Brown and Erich Maren Schlaikjer, using newer and more complete specimens, establish the Genus Pachycephalosaurus. They identify two species: Pachycephalosaurus reinheimeri and Pachycephalosaurus grangeri (although neither are generally recognized as distinct species today).

Barnum Brown:
Barnum Brown

Donald Baird successfully campaigns to get the officially recognized name for the Genus to be "Pachycephalosaurus", even though the normal rules of zoological nomenclature would dictate "Tylosteus", since this was the first name used. As a result of this the only species generally recognized today is Pachycephalosaurus wyomingensis.

Pachycephalosaurus wyomingensis
at the Academy of Natural Sciences, in Philadelphia, Pennsylvania:
Pachycephalosaurus wyomingensis


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