Newsflash: Shrews evolved from Apatemyidae! (or vice versa)

Wikipedia reports,
“A shrew (Figs. 2, 3) or shrew mouse (family Soricidae) is a small mole-like mammal classified in the order Eulipotyphla.”

“Apatemyidae is an extinct family of placental mammals that took part in the first placental evolutionary radiation together with other early mammals such as the leptictids.” 

Figure 1. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be a basal shrew. So this clade is not extinct.

Figure 1. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be an Eocene sister to the shrew. So this clade is not completely extinct.

As it turns out
shrews are less like moles in the large reptile tree (sorry, not yet updated) and more like members of the Apatemyidae, like Apatemys (Marsh 1872; Fig. 1),  thought to have originated in the Paleocene and disappeared in the Eocene. Both are derived. At present they nest as sisters. Neither can be shown, at present, to be more primitive than the other.

Apatemys chardini (Eocene, 50-33 mya; Fig. 2) was a squirrel-lke arboreal herbivore with a massive skull. It had long slender fingers, a long flexible lumbar region, and a long gracile tail. From head to tail, the matrix scores for apatemyids and shrews are quite similar. It’s not just the dentition, which remains amazingly conservative in living shrews.

By contrast
moles have a set of small procumbent anterior dentary teeth and the posterolateral premaxillary teeth are large and canine-like while the medial premaxillary teeth are small like typical incisors. Moles nest closer to Solenodon and rodents [and I need to update that webpage].

Figure 1. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable.

Figure 2. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable and unique to themselves. Note sure how this was overlooked. The resemblance is remarkable.

Wikipedia reports,
“Like most Paleocene mammals, the Apatemyids were small and presumably insectivorous. Size ranged from that of a dormouse to a large rat. The toes were slender and well clawed, and the family were probably mainly arboreal.The skull was fairly massive compared to the otherwise slender skeleton, and the front teeth were long and hooked, resembling those of the modern aye-aye and marsupial Dactylopsila, both whom make their living by gnawing off bark with their front teeth to get at grubs and maggots beneath.”

Evidently others have missed the shrew connection. Let me know of any literature that predates this blogpost. I’d like to promote it, if it’s out there.

Figure 2. Scutisorex (below) and Crocidura (above) are extant shrews.

Figure 3. Scutisorex (below) and Crocidura (above) are extant shrews.

The book ‘Evolution of Shrews’ reports,
“Shrews are among the most ancient of all living mammals. They are small and have rather unspecialized body plans, retained almost unchanged since they evolved about 45 million years ago. They appear to be extremely successful as a group in comparison to all other families of Insectivora: the living species of shrews represent approximately 80% of all insectivorans, which in turn make up some 10% of all mammmalian species extant today.”

The apatemyid connection described here
pushes the origin of shrews back another 5-10 million years. True shrews are not to be confused with elephant shrews. They are more closely related now, then what was recovered earlier, but more work needs to be done to figure this out precisely. Then I’ll update the cladogram.

Earlier I posted on Hyopsodus, the pre-dog, former condylarth. One the images appeared in editing, but did not appear in publication. I was not aware of this until today. The JPEG had a ‘bad marker’, whatever that is. Please let me know if you see a technical problem here. That Hyopsodus image has been repaired and is visible now.

Churchfield S 1990. The Natural History of Shrews online. Comstock Publishing; 1st edition (January 1990) Amazon link.
Multiple Authors 1998. Evolution of Shrews. Edited By: JM Wójcik and M Wolsan. Cornell Paperbacks. 458 pp.  online.
Gingerich PD and Rose KD 1982. 1. Dentition of Clarkforkian Labidolemur kayiGingerich PD 1982. 2. Labidolemur and Apatemys from the early Wasatchian of the Clark’s Fork Basin, Wyoming. Studies on Paleocene and Early Eocene Apatemyidae (Mammalia, Insectivora). Contributions from the Museum of Paleontology. The University of Michigan. 26(4):49-69.
v. Koenigswald W, Schierning H-P 1987. The ecological niche of an extinct group of mammals, the early Tertiary apatemyids. Nature. 326 (6113): 595–597. doi:10.1038/326595a0.
Marsh OC 1872. 
Preliminary description of new Tertiary mammals. Part II. American Journal of Science 4(21):202-224.



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