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At the origin of rodents, multituberculates and plesiadapiformes

Thursday, August 8, 2024 14:12

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Mice, rats, squirrels, porcupines, cabybaras,
are all rodents that nest together in the large reptile tree (LRT, 2323 taxa). The giant squirrel from the Late Paleocene, Paramys (Fig 1), is the most primitive rodent in the LRT.

Figure 1. Ignacius, Plesiadapis and Paramys at the origin of Rodentia = rodents. The multituberculate, Kryptobaatar, is thrown in for comparison to Paramys.

Outgroup taxa in the LRT
include Plesiadapis and Ignacius (Fig 1). The former is basal to the Multituberculata. The latter is basal to rodents, too.The extant aye-aye, Daubentonia (Fig 2) , is closer to Plesiadapis and Megaconus, a Middle Jurassic multituberculate.

So placentals go back a little further. This is the evidence.

Figure 2. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it convergences with the lemuroid primates.

Members of the Multituberculata
underwent several reversals in the jaw joint and ankle that are responsible for the traditional misunderstanding that traditionally nested them closer to monotremes, which they do not resemble.

Figure 3. Ptilocercus is a basalmost member of Glires, the gnawing clade. At this node it also shares many primitive traits with bats, mouse lemurs and the transitional marsupials in the genus Monodelphis. Note the resemblance to Daubentonia in figure 3.

Traditionally
Plesiadapis and the plesidapiformes nest at the base of the Primates.

By contrast,
in the LRT no primates have enlarged incisors and a diastema like Plesiadapis and Daubentonia. Both taxa are members of the gnawing clade, Glires. The extant tree shrew, Ptilocercus (Fig 3), is the most basal member tested in the LRT.

Trait analyses, like the LRT, model actual microevolutionary events based on fossils and extant taxa. Genomic cladograms do not match those based on trait analysis.

Build your own LRT and let us all know your results on this issue.

References
Cope ED 1881. Eocene Plagiaulacidae. American Naturalist 15, 921–922.
Kielan-Jaworowska Z 1970. New Upper Cretaceous multituberculate genera from Bayn Dzak, Gobi Desert. In: Kielan-Jaworowska (ed.), Results of the Polish-Mongolian Palaeontological Expeditions, pt. II. Palaeontologica Polonica 21:35-49.
Kielan-Jaworowska Z and Gambaryan PP 1994. Postcranial anatomy and habits of Asian multituberbulate mammals. Fossils & Strata 36:1-92.
Rãdulescu R and Samson P 1986. Précisions sur les affinités des Multituberculés du Crétacé supérieur de Roumaine. C R Acad Sci II: Mec-Phys, Chim, Sci Terre, Sci Univ 303p, p. 1825-1830.
Wible JR Rougier GW 2000. Cranial anatomy of Kryptobaatar dashzevegi (Mammalia, Multituberculata), and its bearing on the evolution of mammalian characters. Bulletin of the American Museum of Natural History 247:1–120. doi:10.1206/0003-0090(2000)247<0001:caokdm>2.0.CO;2.

wiki/Kryptobaatar
reptileevolution.com/reptile-tree

Source: https://pterosaurheresies.wordpress.com/2024/08/09/at-the-origin-of-rodents-multituberculates-and-plesiadapiformes/

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