Paleogeographic Distribution Of Desmostylians

[DD1991]

Regarding the geographic distribution of desmostylians, it's quite ironic that no desmostylians have ever been found in the West Indies or eastern North America or even Africa because DNA studies point to an African origin for all afrotheres and desmostylians themselves are afrotheres (as a matter of fact, a sirenian fossil from the Early Eocene of Tunisia described by Benoit et. al. 2013 is about the same age as the Caribbean forms Prorastomus and Pezosiren, confirming that sirenians did indeed originate in Africa along with other afrothere groups). What would be a possible explanation for the absence of desmostylians from Africa if an African origin of afrotheres implies that Desmostylia originated in Africa?

Benoit J, Adnet S, El Mabrouk E, Khayati H, Ben Haj Ali M, et al. (2013) Cranial Remain from Tunisia Provides New Clues for the Origin and Evolution of Sirenia (Mammalia, Afrotheria) in Africa. PLoS ONE 8(1): e54307. doi:10.1371/journal.pone.0054307

[Auspex]

...What would be a possible explanation for the absence of desmostylians from Africa if an African origin of afrotheres implies that Desmostylia originated in Africa?...

Their ancestors got across the ocean, at low latitudes (when they were more competent swimmers, and probably in stages) before evolving here?

[Boesse]

Desmostylians have been linked to the anthracobunids, which were a group of afrotheres that also inhabited southeast Asia during the Paleogene. One of the hypotheses for the origin of desmostylians is that they evolved from east Asian anthracobunids, adapted towards aquatic life in temperate western Pacific waters, and dispersed across to the eastern North Pacific following the coastline. Most desmostylian genera are known from Japan and the western US, indicating they were fairly mobile, just like sirenians; it's not very surprising that they apparently never crossed the equator given that they were likely to be kelp adapted.