When pre-primates split from pre-rodents

A quick look at two closely related taxa today.
Hapalodectes (IVPP V5235, Fig. 1; Paleocene. China) nests at the base of the clade of primates (lemurs through humans, Fig. 3). Notice the narrow, transverse premaxilla and large canine.

Figure 1. The IVPP V5235 specimen of Haplodectes. Note the large canine and small, transverse premaxilla, traits shared with higher primates.

Figure 1. The IVPP V5235 specimen of Hapalodectes. Note the large canine and small, transverse premaxilla, traits shared with higher primates.

On the other hand
Ptilocercus
(Fig. 2; extant, Thailand, the pen-tailed tree shrew) nests at the base of the clade of rodents and rabbits and kin. Notice the large premaxilla (yellow) and small canine (orange). This represents the genesis of gnawing teeth in this clade.

Figure 2. The skull of Ptilocercus, nesting at the base of the rodent/rabbit clade. Note the large premaxilla (yellow) and small canine (orange).

Figure 2. The skull of Ptilocercus, nesting at the base of the rodent/rabbit clade. Note the large premaxilla (yellow) and small canine (orange).

These mouse-sized arboreal taxa
are late survivors of an earlier Middle Jurassic radiation. Both have a complete circumorbital ring, atypical for most mammals.

Figure 3. Subset of the LRT focused on Primates and basal Glires.

Figure 3. Subset of the LRT focused on Primates and basal Glires.

 

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