Palaeos Vertebrates Archonta

The name Euprimateformes was coined fairly recently by Bloch et al. (2007) for a clade uniting crown-group Primates and the extinct plesiadapoids (the exact definition was "the clade stemming from the most recent common ancestor of Carpolestes simpsoni and Homo sapiens), excluding even more basal stem Primates such as paromomyids. The plesiadapoids include the taxa Plesiadapidae, Carpolestidae, Saxonella and Chronolestes and were found in North America and Eurasia from the late Early Palaeocene to the end of the Early Eocene (a possible plesiadapoid has also been described from Africa).

Plesiadapoids would have been not dissimilar to squirrels or modern tree shrews in size and appearance. They possessed large, forward-pointing lower incisors and originally fairly long skulls. Few plesiadapoids are known from extensive postcranial remains but what we do know indicates a fair amount of ecological divergence (Bloch et al., 2007). Carpolestes possessed a nail rather than a claw on its hallux (opposible big toe) and shorter claws overall, indicating that it was a grasping climber (wrapping its digits around branches) like modern primates rather than a clinging climber (hanging onto branches with its claws) like squirrels. Plesiadapis, on the other hand, had long narrow claws and was probably more of a clinging climber. Some authors have suggested a more terrestrial lifestyle for Plesiadapis; such interpretations are not currently popular (Kirk et al., 2008) but it would be interesting if postcrania were available for the largest and one of the latest of the plesiadapids, the European Platychoerops, which was comparable in size to a groundhog (Gingerich, 1976). Also notable among plesiadapids was Chiromyoides which appears to have been a specialised seed-eater with a short and deep jaw (and presumably skull) and massive incisors.

Carpolestids also showed a trend towards reduction in the length of the skull, but the really neat thing is what they did with their teeth, for which Carpolestes simpsoni can be taken as one of the best-known examples (Bloch & Gingerich, 1998). In the lower jaw, the anterior teeth were greatly reduced except the large first incisors which were followed by two teeth reduced to mere nubbins (identified as the second incisor and the canine). Only a single premolar remained (identified as the fourth) but to make up for it that tooth was huge, a massive blade-like multi-cusped structure that ground against the similar obscenely complex third and fourth premolars in the upper jaw (another derived carpolestid, Carpomegodon jepseni, retained a small third premolar in the lower jaw - Bloch et al., 2001). In comparison to all this, the three molars that followed were rather pedestrian. Biknevicius (1986) interpreted this tooth arrangement (comparable only to the multituberculates among other mammals) as indicative of a diet of foods with a tough exterior that would have been pierced by the premolars but a soft interior that did not require a huge amount of molar processing. Carpolestids were probably omnivorous, feeding on insects, seeds and fruit, with later forms becoming increasingly frugivorous. CKT100215

Descriptions

Note: there is little or no agreement on why this is a clade, although multiple lines of evidence suggest that there is something here. The greatest controversy seems to be whether the bats belong here.

Scandentia: = Tupaioidea): Ptilocercus, tree shrews (Tupaia), Urogale. Squirrel-like omnivores of S and SE Asian forests & esp. Borneo & Philippines.

Long, narrow skull; dental formula: 2/3, 1/1, 3/3, 3/3; I 1&2 are caniniform; C1 reduced; d1-2 form tooth comb; upper molars with cutting surfaces & dilambdodont; lower molars basic tribosphenic form; snout long & pointed; vibrissae absent; some arboreal species have forward-facing eyes & may have binocular vision; orbits completely surrounded with bone; well-developed postorbital process joins zygomatic arch; zygomatic arch complete, with prominent fenestra; relatively large brain (esp. arboreal forms); auditory bulla complete, formed from entotympanic; tail long & heavily furred; pubic bones united in a long symphysis; digits 5/5; 1st digits point somewhat inward with some grasping ability; all digits have claws; scrotal testes; opportunistic foragers, both arboreal & terrestrial; frequently frugivorous or insectivorous, with simple gut, small cecum; highly active and voracious; leaping runners (scansorial?); mostly diurnal; some have permanent social groups with dominance hierarchy; vocalizations; territoriality & scent-marking common; substantial time spent foraging at ground level; altricial young; tail used in communication.

Primatomorpha: monkeys > tree shrews? Originally defined as Dermoptera + Primates.

Notes: Molecular phylogenies usually include the dermopteran bats among the primatomorphs.

Characters: very small to large squirrel sized; snout long; orbits face laterally; postorbital bar absent (plesiomorphic); auditory bulla absent; floor of middle ear chamber derived from entotympanic; lower incisors large; diastema present; tail long; flexible hands/feet; opposable digits probably absent; digital nails absent; arboreal and terrestrial, with some gliders. ATW030706.

Comments: Paraphyletic assemblage of lemur-like proto-primate forms. MAK120708

Archonta

Beginning to Grasp Things (Euprimateformes)

Descriptions