Megalocnus zile, R D E Macphee & Jennifer L White & Charles A Woods, 2000

R D E Macphee, Jennifer L White & Charles A Woods, 2000, New Megalonychid Sloths (Phyllophaga, Xenarthra) from the Quaternary of Hispaniola, American Museum Novitates 3303, pp. 1-32 : 7-11

Megalocnus zile , new species

HOLOTYPE: Scapula (left side, UF 169930; fig. 2), found 20 March 1979 by C. A. Woods and party. No unambiguous association at type locality with other bones referred to same species.

TYPE LOCALITY AND AGE: Trou Gallery, Île de la Tortue, Département du Nord­Ouest, Haiti; late Quaternary (see appendix 1).

SYNONYMS: None (but see below).

REFERRED SPECIMENS: Several molariforms ( UF 170490–170492 ; see fig. 3), acetabular fragment ( UF 169931), femoral head ( UF 169932), several patellae ( UF 169924– 169928 ), distal and proximal fibulae ( UF 169929 and 169933), and partial scapula ( UF 169934), all from Trou Gallery. Also includ­ ed in the hypodigm is a fragmentary scapula from an unnamed locality near the town of Bayaguana , Prov. San Cristobal, Dominican Republic, from the Marcano collection (#318/325) and currently housed at UF (see appendix 1) .

ETYMOLOGY: Haitian Creole noun (in apposition) meaning ‘‘island,’’ pronounced ap­ proximately [zee­leh]; reference is to species’ presence on Île de la Tortue as well as Hispaniolan mainland. Recommended common name: Hispaniolan megalocnus.

DISTRIBUTION: Haiti (including Île de la Tortue) and Dominican Republic.

DIAGNOSIS OF NEW SPECIES: With respect to known elements, agrees with features that define the genus as given above. The new species can be distinguished from M. rodens by reference to the fossa for teres major on the caudal border of the scapula, which is notably expanded beneath the secondary scapular spine (cf. fig. 2 and Matthew and Paula Couto, 1959: pl. 13). Parocnus contrasts with M. zile in the same regard, indi­ cating that an expanded teres major fossa is a derived feature within megalocnines. Also, the femoral head of M. zile is more spherical than that of M. rodens , nearly to the degree seen in the subfamily Choloepodinae .

DISCUSSION: The possibility that Megalocnus or a close relative lived in Hispaniola or one of its satellite islands has been raised repeatedly but inconclusively. Originally, Mill­ er (1922) tentatively proposed that certain fragmentary postcranial remains from a cave near St.­Michel­de­l’Atalaye (Département de L’Artibonite) belonged to ‘‘ Megalocuus?’’ [lapsus calami]), there being at this time no other place for their reception. Some years later he moved the St.­Michel material to a new genus, Parocnus (Miller, 1929) . Hoffstetter (1955) challenged this maneuver, contending that Miller’s sloth was indeed a member of Megalocnus and should therefore be designated M. serus . Most authors have recognized Parocnus and retained serus therein (e.g., Matthew and Paula Couto, 1959; Varona, 1974; White and MacPhee, in press; but see Hooijer and Ray, 1964, who retained M. serus without comment).

Although it has long been known that Cuban Megalocnus is distinctive in possessing incisiform maxillary front teeth, no similar teeth have as yet been found in Hispaniola. However, large molariforms, very like those of Cuban Megalocnus , have been recovered at Trou Gallery (fig. 3). It is possible that the highly specialized upper front teeth of M. rodens are autapomorphic, but this possibility cannot be evaluated in the absence of relevant remains of the Hispaniolan species. The postcranial material of M. zile , although limited, is distinctive of this genus and strongly corroborates the conclusion that Megalocnus was represented on both sides of the Windward Passage in the late Cenozoic. As far as we can ascertain, none of the material originally referred to Megalocnus sp. by Miller (1922, 1929) actually belongs to that taxon (i.e., all of it belongs to Parocnus serus as here delimited.)

Until sample sizes for this species are improved, we resist making any deeper inferences about the distribution of Megalocnus zile in Hispaniola. At least in comparison to M. rodens in Cuba, whose remains are frequently encountered in Quaternary localities (Matthew and Paula Couto, 1959), it seems that M. zile may have been relatively rare (or rarely preserved in the usual fossil locales). Whether it actually was or not can be determined only by additional discoveries and relevant analyses.

SUBFAMILY CHOLOEPODINAE GRAY, 1871 TRIBE ACRATOCNINI VARONA, 1974 Acratocnus Anthony, 1916 At one time or another, the name Acratocnus has been entered into the faunal lists of

each of the three northern Greater Antilles (cf. Miller, 1929; Matthew and Paula Couto, 1959; Arredondo, 1961). Unfortunately, concepts and content of this taxon have differed greatly from author to author, making it quite uncertain whether, in fact, Acratocnus in any phylogenetically meaningful sense enjoyed the wide distribution claimed. Cladistic evaluation of the available character evidence, however, makes it abundantly clear that this taxon had a multi­island distribution with representatives in Puerto Rico, Cuba, and Hispaniola (White and MacPhee, in press). Additionally, in all probability Paulocnus petrifactus from Curaçao (Hooijer, 1962) is closely related to Acratocnus from the Great­ er Antilles, as is the unnamed sloth from Grenada described by MacPhee et al. (2000). In short, it is now evident that acratocnin sloths enjoyed a wide distribution in the West Indies—indeed, larger than that of any other Antillean land­mammal group except Capromyidae .

DIAGNOSIS OF GENUS: Cranium relatively tall and domed, with prominent postorbital constriction, sagittal crest, pronounced rostral mediolateral flare; symphyseal spout pointed and short; first maxillary tooth spikeshaped, trigonal, anteriorly projecting, and curved (i.e., caniniform); last maxillary molariform convex and narrowest lingually; first mandibular tooth straight, trigonal, and lacking posterointernal groove; last mandibular molariform convex lingually; femoral shaft cylindrical; tibial surface of astragalus parallel­sided, not divided, and posteriorly squared; fibular facet on astragalus deeply concave and funnel­shaped; radius with long, well­developed, abrupt pronator quadratus flange.