Post by Infinity Blade on Aug 28, 2023 19:15:05 GMT 5
There is a paper which proposes that borophagine canids were gradually driven to extinction by competition from canine canids and felids (Silvestro et al., 2015). But I am very skeptical of this hypothesis and think it needs more testing.
This is a figure from the supplementary information of the aforementioned paper. The figure is meant to show a decline in borophagine occurrences through different slices of time, particularly from 15-5 Ma to 5-0 Ma. On the surface, this would seem to suggest that as time went on, borophagines declined as felids and canines became more common in North America.
But if we take a closer look, it doesn't appear as simple as a steady decline over time. This is a table listing occurrences of Borophagus in North America from the beginning of the Clarendonian (not shown in the part I screenshotted, but is considered, to the best of my knowledge, to have started ~12.5 Ma->) to the Early Irvingtonian (which immediately follows the Blancan ~1.8 Ma) (Bōgner & Samuels, 2022). I boxed the Late Blancan and Early Irvingtonian occurrences a while ago to illustrate a point on Twitter (I will get to this soon).
If you look at this, we see that during the Early Blancan (the Blancan is considered to have started ~4.75 Ma->) Borophagus had a fairly wide range across North America. It's in the western United States (California, Washington, Idaho) and the southwest (Arizona and New Mexico) to as far east as Tennessee and Indiana, and everywhere in between (Nebraska and Kansas). Now, if borophagines were gradually shrinking in distribution and going extinct from competition, we would probably expect to see Borophagus here reduced in distribution during the Late Blancan. Was it?
Judging from this table, no. Now look at the boxed and arrow-marked Late Blancan occurrences in the table above. Turns out nearly 3 million years later, Borophagus was still everywhere in America. It's still found in the western United States (California, Washington, Idaho, Nevada) to as far east as Florida (even further out east than the Early Blancan distributions from this table), with its one latest occurrence (during Irvingtonian-1) being here. In fact, if you look at the whole table instead of just this partial screenshot, you'll see that Borophagus was everywhere from California to Florida (even to freaking Mexico) during the period right before the Blancan, Hemphillian-4 (~5.7-4.75 Ma->), as well. This likely suggests that Borophagus was still in Florida during the Early Blancan too (but just hasn't been discovered there yet).
It appears, therefore, during the last three or so million years of Borophagus' existence, it lived quite literally from coast to coast in what is now the United States. It then just suddenly disappears during the Late Blancan/Early Irvingtonian. If borophagines like Borophagus were being gradually outcompeted by canines and felids over time, why was it literally everywhere in the country – living with said canines and felids – for millions of years, only to abruptly disappear around 1.8 Ma?
TL;DR: Borophagines (particularly Borophagus) lived more or less all throughout the North American continent for millions of years, even in the presence of their supposedly superior competitors (canines and felids), right up until their extinction. This does not appear consistent with the idea that they were gradually outcompeted and reduced in occurrences by these other carnivoran clades.
This is a figure from the supplementary information of the aforementioned paper. The figure is meant to show a decline in borophagine occurrences through different slices of time, particularly from 15-5 Ma to 5-0 Ma. On the surface, this would seem to suggest that as time went on, borophagines declined as felids and canines became more common in North America.
But if we take a closer look, it doesn't appear as simple as a steady decline over time. This is a table listing occurrences of Borophagus in North America from the beginning of the Clarendonian (not shown in the part I screenshotted, but is considered, to the best of my knowledge, to have started ~12.5 Ma->) to the Early Irvingtonian (which immediately follows the Blancan ~1.8 Ma) (Bōgner & Samuels, 2022). I boxed the Late Blancan and Early Irvingtonian occurrences a while ago to illustrate a point on Twitter (I will get to this soon).
If you look at this, we see that during the Early Blancan (the Blancan is considered to have started ~4.75 Ma->) Borophagus had a fairly wide range across North America. It's in the western United States (California, Washington, Idaho) and the southwest (Arizona and New Mexico) to as far east as Tennessee and Indiana, and everywhere in between (Nebraska and Kansas). Now, if borophagines were gradually shrinking in distribution and going extinct from competition, we would probably expect to see Borophagus here reduced in distribution during the Late Blancan. Was it?
Judging from this table, no. Now look at the boxed and arrow-marked Late Blancan occurrences in the table above. Turns out nearly 3 million years later, Borophagus was still everywhere in America. It's still found in the western United States (California, Washington, Idaho, Nevada) to as far east as Florida (even further out east than the Early Blancan distributions from this table), with its one latest occurrence (during Irvingtonian-1) being here. In fact, if you look at the whole table instead of just this partial screenshot, you'll see that Borophagus was everywhere from California to Florida (even to freaking Mexico) during the period right before the Blancan, Hemphillian-4 (~5.7-4.75 Ma->), as well. This likely suggests that Borophagus was still in Florida during the Early Blancan too (but just hasn't been discovered there yet).
It appears, therefore, during the last three or so million years of Borophagus' existence, it lived quite literally from coast to coast in what is now the United States. It then just suddenly disappears during the Late Blancan/Early Irvingtonian. If borophagines like Borophagus were being gradually outcompeted by canines and felids over time, why was it literally everywhere in the country – living with said canines and felids – for millions of years, only to abruptly disappear around 1.8 Ma?
TL;DR: Borophagines (particularly Borophagus) lived more or less all throughout the North American continent for millions of years, even in the presence of their supposedly superior competitors (canines and felids), right up until their extinction. This does not appear consistent with the idea that they were gradually outcompeted and reduced in occurrences by these other carnivoran clades.
