''Saxonella'' is a genus of extinct primate from the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

Epoch, 66-56 Ma. The genus is present in the fossil record from around ~62-57 Ma (Torrejonian-Clarkforkian North American Land Mammal Age). ''Saxonella'' has been found in fissure fillings in Walbeck, Germany as well as in the

Paskapoo Formation The Paskapoo Formation is a stratigraphic unit of Middle to Late Paleocene age in the Western Canada Sedimentary Basin. The Paskapoo underlies much of southwestern Alberta, and takes the name from the Blindman River (''paskapoo'' means "blind ...

in Alberta, Canada. ''Saxonella'' is one of five families within the superfamily Plesiadapoidae, which appears in the fossil record from the mid Paleocene to the early Eocene. Analyses of molars by paleontologists suggest that ''Saxonella'' most likely had a folivorous diet.Fox, R. (1991). Saxonella (Plesiadapiformes: ?Primates) in North America: S. Naylori, sp. nov., from the Late Paleocene of Alberta, Canada. ''Journal of Vertebrate Paleontology,'' ''11''(3), 334-349. Retrieved March 30, 2021, from http://www.jstor.org/stable/4523388

Taxonomy

There are currently two valid species within the genus ''Saxonella'': ''S. crepaturae'' and ''S. naylori''. The type species for the genus ''Saxonella'' is ''S. crepaturae'', which was discovered in fissure fillings in Walbeck, Germany in 1964; the holotype consisting of a lower jaw preserving the first incisor, third premolar, and first molar. ''S. naylori'' was first discovered in the Paskapoo Formation in Alberta, Canada in 1984; the holotype specimen consisting of a lower jaw preserving the first incisor, third and fourth premolars, and the first molar. Both fossils were determined to date to the late Paleocene. Saxonellidae falls within the superfamily

Plesiadapoidea Plesiadapoidea was an extinct superfamily of primates that existed during the Paleocene and Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene ...

, which also contains

Carpolestidae Carpolestidae is a family of primate-like Plesiadapiformes that were prevalent in North America and Asia from the mid Paleocene through the early Eocene. Typically, they are characterized by two large upper posterior premolars and one large lowe ...

and

Plesiadapidae Plesiadapidae is a family of plesiadapiform mammals related to primates known from the Paleocene and Eocene of North America, Europe, and Asia. Plesiadapids were abundant in the late Paleocene, and their fossils are often used to establish th ...

. There is still debate within the paleontological field as to whether or not Paromomyidae and Picrodontidae are also included in this group. ''Saxonella'' has dentition that is easily distinguishable from Carpolestids and Plesiadapids, warranting the formation of a new family. Specifically, the upper third premolar has a high degree of specialization. One of the most notable features in this genus is the presence of a plagiaulacoid blade on its lower third premolar. This morphology is not homologous with the lower fourth premolar found in members of the family Carpolestidae and is indicative of evolutionary convergence. This evidence suggests a significant gap in the fossil record, as there must have been ancestors of ''Saxonella'' that did not have specialized central incisors or premolars for shearing, as well as lacking a post-incisor lower diastema.

Description

''Saxonella''’s only lower incisor is procumbent, like that of other plesiadapiforms. It exhibits wear patterns similar to those found in tooth combs used for grooming in members of other taxa. Wear facets on the lower third and fourth premolars, as well as the lower first molar, are indicative of an adaptation for shearing. The lower third premolar has a plagiaulacoid blade and a shearing surface with a 45–60-degree angle. The lower fourth premolar is smaller than the third premolar, a feature that distinguishes this genus from other plesiadapiforms. The upper second premolar is double-rooted. ''Saxonella'' has a very specialized upper third premolar which is T-shaped and has the longest anteroposterior length relative to the rest of the upper dentition. ''Saxonella'' has one lower incisor and one upper incisor, though it is possible that there were additional upper incisors as there is a lack of incisor preservation in ''Saxonella'' specimens. There are no fossils of ''Saxonella'' that preserve canines; while it is clear that ''Saxonella'' has lost the lower canine, it is possible that an upper canine was present and has not been preserved in the known specimens. The upper second, third, and fourth premolars are present, but it is unclear if there was a first premolar. The lower third and fourth premolars are present, while ''Saxonella'' lacked the first and second premolars. The first, second, and third molars are present in both the upper and lower jaws.

Species

''Saxonella crepaturae'' was the first species of ''Saxonella'' discovered. The lower first molar and third and fourth premolars of ''S. crepaturae'' are more derived than that of ''S. naylori''. The roots of the fourth premolar in ''S. naylori'' are unconnected and divergent, while they are not in ''S. crepaturae''. ''S. crepaturae'' is not an ancestor of ''S. naylori.'' An ancestor of ''S. naylori'' would need to possess at least a partially plagiaulacoid third premolar.

Paleoenvironment and geographic range

The known geographic distribution of ''Saxonella'' ranges from North America to Europe during the Paleocene. Due to similarities in the faunas of Europe and North America during this time, it is clear that there were land bridges between the two continents.Fleagle, J. G. (2013). ''Primate adaptation & Evolution'' (Third ed.). Elsevier/Academic Press. Retrieved March 30, 2021. Fossils of ''Saxonella'' discovered in Europe and North America are additional evidence of a land bridge between the two continents.Acorn, J. (2007). ''Deep Alberta: Fossil Facts and Dinosaur Digs''. Edmonton, Alta.: University of Alberta Press. Saxonellids likely originated in North America before the middle Tiffanian; their main direction of travel across land bridges was likely west to east.Webb, M. W. (1996). ''Late paleocene mammals from near drayton valley, alberta'' (Order No. MM18332). Available from ProQuest Dissertations & Theses Global. (304296867). The climate of the Paleocene was cooler than either of the epochs that bordered it. Rather than the tropical trees of the bordering epochs, western North America flora had deciduous trees and conifers.

Functional morphology

Analysis of the lower incisor of ''Saxonella'' reveals wear patterns similar to those found in primate fossils that utilized tooth combs for grooming. This may be an indication of similar behavior in ''Saxonella.'' Additionally, the wear patterns on upper and lower molars suggest a diet that required shearing, crushing, and grinding, pointing to a folivorous diet. Though post-cranial bones of ''Saxonella'' have not been found, their relationship to Plesiadapids and Carpolestids denotes an arboreal and quadrupedal lifestyle.Sargis, E. J., Boyer, D. M., Bloch, J. I., & Silcox, M. T. (2007). Evolution of pedal grasping in Primates. ''Journal of Human Evolution,'' ''53'', 103-107. Retrieved March 29, 2021, from http://pages.nycep.org/boyer/data/publications/Sargis%20Boyer%20Bloch%20Silcox%202007.pdf

References

Prehistoric primate genera Extinct mammals of North America {{paleo-primate-stub