Doctoral Day! – Mammals of the Torrejonian-Tiffanian (Paleocene) Transition – #365papers – 2017 – 45

#365papers for February 14, 2017

Higgins, 2003, A Wyoming succession of Paleocene mammal-bearing localities bracketing the boundary between the Torrejonian and Tiffanian North American Land Mammal “Ages”: Rocky Mountain Geology, v. 38.

What’s it about?

This paper discusses the nature of the boundary between two adjacent North American Land Mammal “Ages” (NALMAs). NALMAs are defined by the presence or absence of certain mammal species and are usually quite different in species composition. The 136 localities studied here bracket the Torrejonian-Tiffanian boundary, so we can examine the transition more closely.

Why does it matter?

This particular case is important because the 136 localities studied are spread over about 500 meters of rock thickness. This means that the boundary is ‘spread out,’ and we can observe whether the transition is instantaneous, rapid, or gradual. The definition of NALMAs kind of depend on very rapid transitions. Alas, what is seen here is that the transition is gradual and there is significant overlap between adjacent NALMAs for quite a while.

Why did I read this?

Heck, I wrote this. On February 14, 2000, I successfully defended my Ph.D. dissertation, the vast majority of which is contained in this paper. Thus, February 14 is Doctoral Day. I’ve had my Ph.D. 17 years now. Holy crap.

Now looking at this again, I’m reminded that I want to eventually use geochemical methods to examine what caused the transition to take place. Some authors claim global cooling, but evidence for this is severely lacking….