“N” is for Nannodectes

“N” is for Nannodectes

Nannodectes is a member of the Plesiadapiformes, this group of mammals that are considered closely related to modern primates, if not truly primates themselves. I said a bit about them in my discussion of Chiromyoides.

This is the Chiromyoides lower third molar. Notice where I actually compare it with Nannodectes

This is the Chiromyoides lower third molar. Notice where I actually compare it with Nannodectes

Nannodectes and Plesiadapis (as well as Pronothodectes) are among the most important taxa used for defining the divisions of the Torrejonian and Tiffanian North American Land Mammal Ages. Different species of Plesiadapis in particular is used to define the divisions of the Tiffanian.

Torrejonian and Tiffanian biostratigraphy in The Breaks. From the published version of my work in Rocky Mountain Geology

Torrejonian and Tiffanian biostratigraphy in The Breaks. The species characteristic of each division are in the far left column. Notice that all are Plesiadapis for the Tiffanian. From the published version of my work in Rocky Mountain Geology

Plesiadapis gets all the emphasis in Torrejonian-Tiffanian biostratigraphy, of course, but Nannodectes and Pronothodectes are equally important. Nannodectes is considered restricted to the Tiffanian, and Pronothodectes is restricted to the Torrejonian. Pronothodectes is considered the ancestor of both Nannodectes and Plesiadapis.

A little sketch of a lower molar of Plesiadapis praecursor noting one of its important features.

A little sketch of a lower molar of Plesiadapis praecursor noting one of its important features.

Both Plesiadapis and Nannodectes are certainly known from The Breaks. Pronothodectes might also be present. Three teeth from the overlap zone might belong to Pronothodectes, which would refute the idea that Pronothodectes is strictly Torrejonian.

A sketch of the LP4 of Nannodectes simpsoni collected from The Breaks. UW 28391 from locality V-90063 (Ti3 in age).

A sketch of the LP4 of Nannodectes simpsoni collected from The Breaks. UW 28391 from locality V-90063 (Ti3 in age).

Things used to identify the species of Nannodectes includes the overall size of the specimen (annotated L and W in the drawing above) and the relative placement of all the main tooth cusps and some minor cusps as well. The relative size of the cusps (labeled A and B above) were really important in the identification.

Part of the A to Z Blogging Challenge.

For 4-16-13

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