‘Taeniodonta’ is polyphyletic, part 4: Ectoganus, Stylinodon and Psittacotherium

These three bear-sized aquatic wolverines,
Ectoganus (Fig. 5), Stylinodon (Fig. 1) and Psittacotherium (Fig. 2), are traditional members of the invalidated polyphyletic (Fig. 3) clade ‘Taeniodonta’. We looked at other nestings for former taeniodonts earlier here, here and here. The large reptile tree (LRT, 1365 taxa) recently nested fanged Machaeroides basal to these taxa, rather than with its traditional marsupial sister, Oxyaena. Taxon exclusion kept the real sisters apart until now.

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Stylinodon mirus (Marsh 1874; middle Eocene, 45 mya) was originally considered a taeniodont, perhaps derived from the basal phenacodont, Onychodectes. Here it nests within Carnivora in the clade of Mustela the living mink, Gulo the living wolverine and Ursus the living polar bear. The largest anterior teeth are canines. The peg-like molars also continued growing throughout life. There were twice as many molars (4), each with a single root, as in the two double rooted molars of the mink. The teeth continued growing throughout life, as in edentates like Glyptodon. Large claws indicate that digging remained part of its lifestyle.

Figure 7. Psittacotherium in various views.

Figure 7. Psittacotherium in various views.

Psittacotherium multifragum (Cope 1862; Paleocene, 60mya; 1.1m length) is a related taxon with canine teeth transformed into a parrot-like rostrum. Wortman 1896 considered it a type of ground sloth and a member of the Edentata (= Xenarthra).

Figure 3. Subset of the LRT labeling several traditional taeniodonts in red, indicating the traditional clade Taeniodonta is polyphyletic and should therefore be abandoned.

Figure 3. Subset of the LRT labeling several traditional taeniodonts in red, indicating the traditional clade Taeniodonta is polyphyletic and should therefore be abandoned.

Ectoganus copei (Schoch 1981; USNM 12714; early Eocene) is a sister to Stylinodon with a longer, lower skull, two upper incisors and a kinked maxilla.

Figure 5. Ectoganus nests with Stylinodon and Psittacotherium within the Carnivora, derived from Gulo, the wolverine.

Figure 5. Ectoganus nests with Stylinodon and Psittacotherium within the Carnivora, derived from Gulo, the wolverine.

Even as recently as 2013, Williamson and Brusatte
supported the traditional clade ‘Taeniodonta’, but only by the ‘authority’  of untested tradition (they employed the dataset and analysis of Rook and Hunter 2013).

Here we test from a wide gamut of taxa,
which minimizes the possibility of taxon exclusion. There’s no need to repeat a rumor, tradition or paradigm without a thorough testing in the LRT. The big picture is missing in traditional paleontology. That’s what the LRT is here for.

Again, this is low hanging fruit,
ignored by traditional paleontologists due to the easy sin of omission: taxon exclusion.

References
Cope ED 1882. A new genus of Tillodonta. The American Naturalist, 16: 156–157.
Rook DL and Hunter JP 2013. Rooting around the eutherian family tree: the origin and relations of the Taeniodonta. Journal of Mammal Evolution
DOI 10.1007/s10914-013-9230-9
Schoch RM 1983. Systematics, functional morphology and macroevolution of the extinct mammalian order Taeniodonta. Peabody Museum of Natural History Bulletin 42: 307pp. 60 figs. 65 pls.
Williamson TE and Brusatte SL 2013. New specimens of the rare Taeniodont Wortmania (Mammalia: Eutheria) from the San Juan Basin of New Mexico and Comments on the Phylogeny and Functional Morphology of “Archaic” Mammals. PLoS ONE 8(9): e75886. doi:10.1371/journal.pone.0075886
Wortman JL 1896. Psittacotherium, a member of a new and primitive suborder of the Edentata. Bulletin of the American Museum of Natural History 8(16):259–262.

wiki/Psittacotherium

 

 

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