Mixodectidae, Microsyopidae, and the insectivore-primate transition. Bulletin of the AMNH ; v. 140, article 4

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New York : [American Museum of Natural History]
"Contrary to the practice of many earlier workers, the author of the present paper clearly separates the Paleocene Mixodectidae and the Eocene Microsyopidae. The following species and genera of the insectivore mixodectids are considered valid: Mixodectes pungens, Mixodectes malaris, Elpidophorus elegans, Elpidophorus minor, Eudaemonema cuspidata, Dracontolestes aphantus, and Remiculus deutschi. Various Puercan fossils other than Dracontolestes probably have been incorrectly allocated to the family. The cranial and postcranial anatomy of mixodectids is virtually unknown. An undoubted derivation of mixodectids from any of the known Cretaceous or Paleocene families is not possible. Mixodectids may have originated from some unknown Cretaceous palaeoryctids, erinaceoids, or near-erinaceoid group. Leptictid ancestry for the family is not likely, because even the earliest leptictids are shown to be more advanced than mixodectids in certain important features of the molar teeth. Close ties of mixodectids with Adapisoriculus and Recent tupaiids are not improbable. The possibility of a close plagiomenid-mixodectid affinity is re-examined, and some new evidence is described and illustrated. There is no direct or meaningful indirect evidence to confirm a derivation of plagiomenids from the Mixodectidae. Allocation of the Mixodectoidea to the Dermoptera is considered to be unjustified. Thylacaelurus is not a plagiomenid. Its affinities may lie with insectivores close to the dimylid stem. The Eocene Microsyopidae are known from the following species and genera: Microsyops wilsoni, new species, M. alfi, M. angustidens, M. latidens, M. scottianus, M. lundeliusi, M. elegans, M. annectens, M. kratos, and Craseops sylvestris. Microsyopid cranial anatomy is described in detail; the postcranial anatomy is virtually unknown. From the evidence of the dental morphology, the microsyopids may be derivable from the earliest primates. Because it is not known whether Cretaceous and early and middle Paleocene primates had the relatively advanced basicrania of late Paleocene Plesiadapis and Eocene prosimians, the primitive basicranium of Microsyops is not necessarily decisive against the inclusion of microsyopids in the Primates. As opposed to the usual practice of overburdening the Insectivora and using it as a 'wastebasket,' the microsyopids are placed, although with a query, in the Primates. The late Paleocene Navajovius is allocated, with a query, to the Microsyopidae. Navajovius? mckennai, new species, from the Wasatchian Almagre facies of the San José Formation is poorly known. The insectivore-primate transition was probably initiated at the end of the Cretaceous or earlier by behavioral and physiological adaptations. As behavioral modifications (particularly preference for fruits, leaves, and similar foods as opposed to a predominantly insectivorous diet) affected the feeding habits and behavior, selection gradually altered the morphology and function of the feeding mechanism. The primitive therian and eutherian molar shear was gradually de-emphasized by a reduction of the long paracrista and metacrista, a straightening out of the centrocrista, and the acquisition of more bulbous and less acute cusps and conules. As prevallid-postvallum and postvallid-prevallum shear lost relative importance, the trigonid became narrower and less tall, and the talonid gained functional importance. The teeth, with other parts of the feeding mechanism, became more suitable for mastication and other aspects of oral digestion of a predominantly frugivorous-herbaceous diet. The apatemyids and tupaiids are considered to be independently derived families from the Insectivora, not the Primates. The Paleocene picrodontids, extremely specialized frugivores derived from early primates, epitomize (with other prosimians) the nature and direction of selection pressures responsible for the origin of the Primates"--P. 323.
p. 195-330, [41] leaves of plates : ill. ; 27 cm.
Thesis (Ph. D.)--Columbia University, 1969.
Includes bibliographical references (p. 324-330).