Squirrels: phylogenetically miniaturized plesiadapiformes
A smaller size, larger orbit
and shorter snout mark squirrels as phylogenetically miniaturized ( = neotonous = retaining juvenile traits into adulthood) plesiadapiformes. Paramys (Fig 1) is a large transitional taxon in the large reptile tree (LRT, 2324 taxa). These taxa are both close to multituberculates in the LRT. These extend back to the Jurassic.
Figure 1. Plesiadapis, Paramys and two squirrels: Sciurus and Glaucomys, to scale.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/paramys588.jpg?w=111″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/paramys588.jpg?w=380″ tabindex=”0″ role=”button” class=”size-full wp-image-88785″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/paramys588.jpg” alt=”Figure 1. Plesiadapis, Paramys and two squirrels: Sciurus and Glaucomys, to scale.” width=”584″ height=”1573″ />
Figure 1. Plesiadapis, Paramys and two squirrels: Sciurus and Glaucomys, to scale. A smaller size, larger orbit and shorter snout mark squirrels as phylogenetically miniaturized = neotonous = retaining juvenile traits into adulthood.
That means the Plesiadapiformes are not extinct.
Just miniaturized. This runs contra to Maas, Krause and Strait 1988, who declared Plesiadapiformes extinct, perhaps due to “competition from rodents”.
Figure 1. Microsyops, Plesiadapis, Daubentonia, Carpolestes and kin in the LRT to scale.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/microsyops-plesiadapis-ignacius588-1.jpg?w=101″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/microsyops-plesiadapis-ignacius588-1.jpg?w=343″ tabindex=”0″ role=”button” class=”size-full wp-image-87487″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/microsyops-plesiadapis-ignacius588-1.jpg” alt=”Figure 1. Microsyops, Plesiadapis, Daubentonia, Carpolestes and kin in the LRT to scale.” width=”584″ height=”1742″ />
Figure 2. Microsyops, Plesiadapis, Daubentonia, Carpolestes and kin in the LRT to scale.
McKenna 1961 looked at the teeth of Paramys
(the only material then available) with regard to the origin of rodents. He wrote, “It could have given rise to many Eocene and later rodent tooth patterns.”
According to Wikipedia, “About 40 percent of all mammal species are rodents.”
Wu et al 2012 tested the origin of rodents with genes and fossils.
They wrote, “Our results indicate that rodents originated around 61.7–62.4 Ma, shortly after the Cretaceous/Paleogene (K/Pg) boundary.”
Neither Paramys nor Plesiadapis were mentioned in the text.
In the LRT
the extant aye-aye, Daubentonia (Fig 2), phylogenetically precedes Plesiadapis and Paramys. Restricted to the island of Madagascar, plus a close relationship with the basal multituberculate, Megaconus, puts the origin of rodent-like Daubentonia back to the Middle Jurassic.
Look for Cretaceous rodents and lagomorphs
– unless they waited for that asteroid to mark their appearance in the fossil record.
Figure 3. The extant marsupial, Dacylopsia compared to Paleocene Ignacius and Ignacius. Note the broad phylogenetic difference between taxa in figure 1, 2 vs 3, 4).
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/dactylopsila-588-3.jpg?w=170″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/dactylopsila-588-3.jpg?w=580″ tabindex=”0″ role=”button” class=”size-full wp-image-88216″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/dactylopsila-588-3.jpg” alt=”Figure 3. The extant marsupial, Dacylopsia compared to Paleocene Ignacius and Ignacius. Note the broad phylogenetic difference between taxa in figure 1, 2 vs 3, 4).” width=”584″ height=”1032″ />
Figure 3. The extant marsupial, Dacylopsia compared to Paleocene Ignacius and Ignacius. Note the broad phylogenetic difference between taxa in figure 1, 2 vs 3, 4).
PS
None of the above taxa are in any way related to primates in the LRT. Rodents and their placental relatives arose from marsupial sugar gliders like Dactylopsila trivirgata (Fig 3), apart from all other placentals (including primates) in the LRT, as discussed earlier here.
References
Maas MC, Krause DW and Strait SG 1988. The decline and extinction of Plesiadapiformes (Mammalia: ?Primates) in North America: displacement or replacement? Paleobiology 14(4):410–431.
McKenna MC 1961. A note on the origin of rodents. American Museum Novitates 2037:1–5.
Wu S et al (8 co-authors) 2012. Molecular and paleontological evidence for a post-Cretaceous origin of rodents. PLoSOne 2012;7(10):e46445.
Source: https://pterosaurheresies.wordpress.com/2024/09/15/squirrels-phylogenetically-miniaturized-plesiadapiformes/
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