680 W. D. MATTHEW OElGIX OF THE ANTILLEAN MAMMALS 



judgment, be referred to the Upper Pliocene; the}^ are certainly much 

 later than the Santa Cruz. 



Although Megamys and Tetrastylus are without doubt more nearly 

 related than any modern type to the Antillean chinchillids and are con- 

 siderahly older, they can not be regarded as ancestral. The common 

 ancestral stock is to be found in the Santa Cruz chinchillids, all of which 

 are of small or medium size. These Santa Cruz species are much more 

 primitive, and the precise relationships will require more careful study .^ 



The remaining Antillean rodents are of South American t3^pe and 

 broadly derivable from Santa Cruz rodents, but their more exact affini- 

 ties are disputed and require more thorough and critical consideration 

 and, if possible, more complete material. A thorough revision of the 

 fossil rodent faunas of South America is an almost necessary groundwork 

 for a correct estimate of their affinities. It is clear, however, that with 

 the exception of Capromys they are not very closely related to the South 

 American rodents, the common ancestral stock dating back probably to 

 Pliocene or late Miocene, as Miller believes. Capromys (and Geoca- 

 promys) would seem to be an exception, being quite close to the Vene- 

 zuelan Procapromys. 



TEE EDENTATA 



The edentates include four quite distinct genera from Cuba and a fifth 

 from Porto Eico, all referred to the family Megalonychidse, but not closely 

 related to any of the mainland forms. The largest, Megalocnus/ is about 

 the size of a black bear ; the smallest, Microcnus, about the size of a cat, 

 and there are two of intermediate size, Mesocnus, with a rather long, 

 narrow muzzle, and Miocnus, with a broad, square muzzle. The Porto 

 Rican genus is related to Miocnus, both having heavy triangular tusks 

 like the modern Choloepus; the other three genera have large tusks, but 

 of a peculiar dished shape, with a tendency to approach toward each other 

 like the incisors of rodents. (They are not at all of the scalpriform 

 gnawing type, however.) While these ground-sloths are sufficiently re- 



^ Miner apparently associates the Santa Cruz fauna of southern Patagonia with the 

 very different and much later Entrerian fauna of northern Argentina, as he speaks of 

 the two as though they were essentially one fauna, and refers to the "enormous extinct 

 Pagatonian rodents" as the nearest relatives of the Antillean chinchillids. The largest 

 Santa Cruzian rodents are species of Perimys, which is not nearly related to the Antil- 

 lean genera. Most of the species are quite small. As between the Santa Cruz and the 

 Hermosan (Pliocene) group of faunas, the tendency to rapid increase in size and speciali- 

 zation of numerous phyla is very marked, and is further emphasized in the Pampean 

 (I'leistocene) group of faunas. 



^ Megalocnus, Leidy, 1868. Proc. Acad. Nat. Sci. Phila., 1868, p. 179. 

 MicrocnuSj etc., La Torre and Matthew, 1915. Bull. Geol. Soc. Am., vol. xxvi, p. 152 

 (names only ; descriptions have been reserved pending the securing of more complete and 

 better associated skeleton material). 



