236 



GREGORY: XOTHAKCrVS, AN AMERICAN EOCENE PRIMATE 



palseotelic characters in their remote descendants, and the habitus of the ancestral stock has become the 

 underlying and more or less concealed heritage of the diversified branches. 



Therefore it is not surprising that, as regards the construction of the limbs, the Middle Eocene 

 Nothardus is a kind of synthetic lemuroid, foreshadowing many recent types in different characters, but 

 probably on the whole more primitive than any now living. But, some may say, the palseontological 

 record is obviously very imperfect, and doubtless there were many genera in each larger group of which 

 we have no direct knowledge; it is therefore very unlikely that the only Eocene lemuroid which is at 

 present known from adequate skeletal material should chance to be a primitive representative of its own 

 times. Against such an argument one may cite the fact that with respect to a long list of characters in 

 the skull and dentition, Nothardus is demonstrably more like other Eocene placental mammals of differ- 

 ent orders than are any of its modern relatives, the existing lemuroids and platyrrhine monkeys. 



It may be held by some that the long phalanges and more or less flattened nails of Nothardus are 

 less primitive than the shorter phalanges and compressed nails of the marmosets ; in other words that the 

 marmosets represent a primitive division of the primates, which have retained true claws, and that Noth- 

 ardus and the Lemuroidea have specialized away from the more primitive type. Against this view may 

 be advanced the following facts: 



(1) In the entire construction of the dentition and skull the marmosets are very closely allied to 

 the typical Cebida^, especially Callithrix. The compression of the nails in the marmosets is only an 

 accentuation of the tendency toward compression seen in Cebus, Ateles, Callithrix and Nydipithecus. 



(2) If the marmosets are primitive unguiculates, we should expect them to have very powerful 

 flexor and j^ronator muscles and stout short phalanges. On the contrary their phalanges are delicate 

 and narrow and are not dissimilar in type to those of the smaller Cebidse, such as Callithrix. 



(3) If the claws of the marmosets are primitive, how is it that the pollex and hallux still retain 

 obvious traces of a nail-like condition? 



Coming now to the structural relationships of Nothardus to the Lemuroidea, the writer has con- 

 stantly been impressed with the fact that only moderate changes would be required to convert the limbs 

 and the pectoral and pelvic girdles of Nothardus into any one of the modern lemuroid types. The indri- 

 sine type of skeleton would be derived immediately by lengthening all the limb bones, especially the 

 metacarpals and metatarsals. Otherwise there is surprisingly little change, except in proportions. 



In Ckiromys the chief specialization is the elongation of the hand, and the extreme attenuation of 

 the third digit. 



Even less modification would be required to convert the limbs of Nothardus into those of Adapis, 

 of Lepilemur, or of Lemur. Megaladapis is a specialized type with secondarily shortened, widened limb 

 bones, but its affinity with both Adapis and Nothardus is apparent in every bone of the limbs. The limbs 

 of Galago could be derived directly from the Nothardus type simply by lengthening the neck of the as- 

 tragalus and the cuboid, characters which are already foreshadowed in ordinary lemurs and which are 

 carried to an extreme in Tarsius. In the opposite direction, the limbs of Perodidicus have shortened 

 tarsals and a vestigial second digit in the manus, but everywhere the derivation from a less specialized 

 A^o^/iorc^MS-like type is patent. 



In general the modern lemuroids have merely accentuated different characters which were already 

 foreshadowed in Nothardus. 



On the other hand, the Cebidse show many radical differences from the Nothardus type, pointing to 

 a marked change in the direction of evolution. We find that in the Cebidse the simple technic of leaping 



