Answers are grounded in this paper and cite their sources.
Beds of the Rio Chico Formation containing the earliest known land mammals in Patagonia, southern Argentina, were calibrated by potassium-argon age determinations and paleomagnetic polarity data. The Riochican land mammal age encompasses the middle and late Paleocene and corresponds in time with Torrejonian and Tiffanian land mammal faunas in North America.
No takes yet. Share an insight, caveat, or question.
Marshall et al. (1981) studied this question.
Synapse has enriched 5 related papers. Consider them for comparative context: