Bears, bears and more bears

This post had its genesis
in a recent YouTube video all about bears by Moth Light Media. After phylogenetic analysis in the large reptile tree (LRT, 1834+ taxa, subset Fig. 1) ‘bears’ are no longer monophyletic. Instead the various extant ‘bears’ are better considered giant kinkajous, weasels, wolverines and bush dogs, all converging on similar ‘bear’-like morphologies.

Figure 1. Subset of the LRT focused on Carnivora, a placental mammal clade. Note the polyphyletic nesting of various ‘bears’ indicating that they are all just large kinkajous, weasels, wolverines and bush dogs converging on similar bear-like morphologies. Note the separation of seals (dark yellow) from sea lions (peach).

Jiangzuo and Flynn 2020
discussed the earliest ursine bear and the origin of plant-dominated omnivory in Carnivora. Unfortunately they worked within an invalid phylogenetic context brought about by taxon exclusion. The wolf, Canis lupus, was their outgroup taxon. So their cladogram was upside-down compared to the LRT (Fig. 1). Basalmost members of Carnivora and their outgroups among basalmost Placentalia were all agile arboreal omnivores, not digitigrade cursors (runners), like Canis.

Jiangzuo and Flynn consider the spectacled bear,
Tremarctos, a member of the ursine bears. In the LRT Tremarctos arises from the bush dog, Speothos, far apart from ursines.

Jiangzuo and Flynn consider the wolverine,
Gulo, a member of the mustelids. In the LRT the short face bear, Arctodus, arises from the wolverine, Gulo, apart from ursines. 

Jiangzuo and Flynn consider the giant panda,
Airluropoda, a type of bear. In the LRT it arises from the herbivorous kinkajou (genus: Potos) before the appearance of the ancestor of the rest of the ‘bears’, Mustela, the weasel.

Jiangzuo and Flynn do not include
Speothos or Potos in their text. The authors separate Gulo in the clade Mustelida, apart from bears in their study. So taxon exclusion mars this otherwise detailed study of bear dentition and diet.

In like fashion,
McLellan and Reiner 1994 also excluded a long list of pertinent taxa in their review of bear evolution.

Sharp-eyed readers will note the addition of two taxa
to the Carnivora, the sea otter (Enhydra) and the basal walrus (Protodobenus).

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References
Jiangzuo Q and Flynn JJ 2020. The earliest ursine bear and the origin of plant-dominated omnivory in Carnivora. iScience 23, 101235, June 26, 2020.
McLellan B and Reiner DC 1994. A review of bear evolution. Int. Conf. Bear Res. and Manage. 9(1):85-96

 

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