Acratocnus, Anthony, 1916

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 : 11-13

Acratocnus ye, new species

HOLOTYPE: Skull and mandible ( UF 170533; fig. 4, 5) in unambiguous association (same individual), collected 26 January 1984 by C. A. Woods and party.

TYPE LOCALITY AND AGE: Trouing Vapè Deron, Plain Formon, Département du Sud, Haiti; late Quaternary (see appendix 1).

SYNONYMS: None.

REFERRED SPECIMENS: Hypodigm also includes several sets of associated postcranial

elements from other localities (a sample of which are illustrated in fig. 6): left tibia (UF 75434), left scapula (UF 169985), and associated right femur (UF 76283), right and left fibulae (UF 75486, 75487), right astragalus and right and left calcanei (all numbered UF 170270), and right and left pelves (UF 170276), from Trujin Bridge, Morne la Visite; associated left humerus, ulna, radius (UF 169822) from Trouing Jérémie #3, Plain Formon. Other material: from Trujin Bridge, mandible (UF 76796), right tibia (UF 170271), right astragalus and left calcaneus (UF 170269), right humerus (UF 75528), right radius (UF 75579/80); from Trouing Jeremie #3, right fibula (UF 170453); from Trouing Bois Formon #1, Plain Formon, left ulna (UF 170089).

ETYMOLOGY: Haitian Creole noun (in apposition) meaning ‘‘yesterday,’’ pronounced approximately [yeh]; reference is to this species being part of Hispaniola’s extinct fauna. Recommended common name: Yesterday’s acratocnus.

DISTRIBUTION: Currently known only from Haiti, but presumed to have had a wider distribution in Hispaniola.

DIAGNOSIS OF NEW SPECIES: Agrees with A. odontrigonus ( Puerto Rico) and A. antillensis ( Cuba) in features that define the genus (see Anthony, 1918). Differs from these species in the following features: Skull markedly domed along sagittal crest in many individuals, forming a significant angle with rostrum; postorbital constriction not extreme; palatine foramina consistently prominent and abundant; symphyseal spout relatively short and pointed, laterally pinched and not smoothly conical, extremely ventrally pinched on either side of ventral keel, and projecting anteriorly at an angle significantly different from that of anterior border of mandible; rectus tubercle of pelvis very prominent and laterally projecting, creating a right angle in posterior view; acetabular rim nearly closed and pit (fossa) partly or completely filled in; femoral neck and head projecting anteriorly at an extreme angle; femoral head extremely large, globular, and afoveate; femoral shaft with great torsion and reduced third trochanter; tibial shaft with prominent anteromedial muscle scar; tibia with posterolaterally projecting proximal fibular articu­ lation; distinct ridge separating cuboid and sustentacular facets of calcaneus; calcaneal tuberosity waisted and relatively symmetrical; humeral head extremely large; humeral trochlea mediolaterally flat with reduced distal flare; bridge over entepicondylar foramen bears distinct eminence; entepicondylar foramen slightly visible posteriorly; pectoral crest markedly projecting medially; forelimb greatly elongated (brachial indices of 0.97 and 0.96 on two associated skeletons, as compared to a mean of 0.90 for A. odontrigonus [White, 1993a]); ulnar shaft with prominent anterolateral ridge.

DISCUSSION: This species is very similar to Acratocnus odontrigonus in cranial, mandib­ ular, femoral, humeral, ulnar, calcaneal, and pelvic features, and virtually identical in scapular, radial, tibial, fibular, and astragalar features. However, thanks to large sample sizes, we have been able to assess, both qualitatively and quantitatively, this species’ normal range of individual variation for virtually all elements and thereby assess its differentiae from A. odontrigonus with some confidence.

As far as can be determined, published referrals to Acratocnus in the older literature seem in most cases to involve misallocations of specimens properly placed in a different taxon, Neocnus (see below), and are therefore not cladistically supportable. Although all choloepodines possess trenchant first maxillary teeth that are triangular in crosssection (see above), they can be distinguished by the diagnostic cranial and postcranial traits cited here.

TRIBE CUBANOCNINI VARONA , 19745