Further complication: How long of a temporal gap is there between the oldest known Tyrannosaurus and the youngest known non-Tyrannosaurus tyrannosaurid in North America? According to Eberth et al. (2013), the stratigraphically highest Albertosaurus reported in the Edmonton Group is a single phalanx (TMP 2011.007.0005) from the Carbon Member of the Horseshoe Canyon Formation (Eotriceratops faunal zone), while diagnostic Tyrannosaurus material does not occur until the Scollard Formation. As far as I can tell, not enough of a mid-Maastrichtian tyrannosaurid record is known to tell us for how long albertosaurins and tyrannosaurins overlapped in this area, or whether they even did.
From: firstname.lastname@example.org <email@example.com> on behalf of Thomas Richard Holtz <firstname.lastname@example.org>
Sent: August 11, 2020 8:10 AM
To: Poekilopleuron <email@example.com>
Cc: DML <firstname.lastname@example.org>
Subject: Re: [dinosaur] How long did Tyrannosaurus rex exist
Honest to goodness we do not know.
While the top of the Hell Creek is the single best studied and best dated horizon in Mesozoic stratigraphy (rivaled only by the base of the Triassic, for similar reasons...), the base of the Hell Creek isn't as well constrained. There aren't good datable markers at the base of the Hell Creek Formation, so we don't know how old the oldest Hell Creek dinosaurs were. All we can do is extrapolate (with large error bars) based on issues like the thickness of the sediment. Hence the different possible time estimates. It may even be shorter than those you listed: the small end of the models suggest less than a million years for the entire unit.
Additionally complicating factors:
Are all Tyrannosaurus specimens T. rex? (Carr 2020 certainly makes that case strongly, but others disagree. We definitely see successions of species within other lineages in the Hell Creek.)
There is no requirement that Tyrannosaurus rex popped into existence with the Hell Creek, so its origin might predate that lithostratigraphic unit.
The best answer we have is "on the order of 1-2 million years.
On Tue, Aug 11, 2020 at 3:44 AM Poekilopleuron <email@example.com> wrote:
Good day, I would like to ask, how long did T. rex probably exist as a species? What is the earliest record of its presence in the late Maastrichtian strata? It went extinct 66.0 mya, which is quite well known, but when did it first appear? Was it 68.5, 68.0 or rather 67.5 mya? Thank you very much, in advance!
Thomas R. Holtz, Jr.
Office: Geology 4106, 8000 Regents Dr., College Park MD 20742
Dept. of Geology, University of Maryland
Office: Centreville 1216, 4243 Valley Dr., College Park MD 20742
8000 Regents Drive