Xaymaca fulvopulvis, R D E Macphee & Clare Flemming, 2003

MacPhee, R. D. E. & Flemming, Clare, 2003, A Possible Heptaxodontine and Other Caviidan Rodents from the Quaternary of Jamaica, American Museum Novitates 3422, pp. 1-43 : 16-17

Xaymaca fulvopulvis , new species

HOLOTYPE AND ONLY REFERRED SPECIMEN: AMNHM 268011 , a left hemimandible retaining the incisor (presumptive i1) and excessively worn p4 (figs. 7–11). Recovered (but not then identified) in January 1995 by the senior author with the assistance of Lisa DeNault, Don McFarlane, and Alan and Adam Fincham.

TYPE LOCALITY: Brown Dust Passage of Drum Cave , near Entrance #3 (fig. 1). Drum Cave , part of the ‘‘upper’’ sequence of the ~ 10 km Jackson’s Bay cave system ( Fincham, 1997), is located on the south slope of Portland Ridge near Jackson’s Bay, in the southernmost part of Clarendon Parish, Jamaica. Entrance #3 is located at approximately 17°44'05̎N, 77°13'15̎W .

ASSOCIATED FAUNA AND DISTRIBUTION: A provisional vertebrate faunal list for late Quaternary levels in the Portland Ridge (Jackson’s Bay) caves has been assembled by McFarlane et al. (2002). The birds, which include some extinct forms, were identified and are now under study by Storrs Olson (Smithsonian Institution). Mammalian taxa recovered in Brown Dust Passage are either extant or survived until very recently (MacPhee and Horovitz, in press).

The most significant agent of small­mammal bone concentration in Jamaican cave deposits is the extant barn owl, Tyto alba . Since Xaymaca is evidently rare in such deposits, perhaps its size or behavior made it unlikely to be tracked by owls. Quemisia gravis , a relatively large species, is likewise known from very few specimens ( McFarlane et al., 2000), although in Hispaniolan localities remains of other endemic rodents are encountered in great abundance ( Woods, 1989b).

ETYMOLOGY: Species name (‘‘of the brown dust’’) is a manufactured Latin adjective in the nominative singular in agreement with the genus name. Reference is to type locality, Brown Dust Passage of Drum Cave .

DIAGNOSIS: Hystricognathous, lower premolar cylindriform and apparently hypselodont, showing marked apical hypertrophy. Other cheekteeth probably also cylindriform and hypselodont. Inferred features of cheektooth root development closest (among Antillean caviidans) to heptaxodontines Amblyrhiza and Elasmodontomys . Attributes of cheektooth ontogeny, alveolar construction, incisor procumbency, and other minor features are consistent with tentative allocation to Heptaxodontinae (family incertae sedis).

The jaw is hystricognathous because its angular process is morphologically lateral to a parasagittal plane drawn through the incisor alveolar sheath ( Landry, 1957). Cheektooth crown morphology not yet known. As may be seen plainly in figure 9 (bottom), the shape of the deeply striated p4 and the structure of the alveoli for m1–m 3 in Geocapromys brownii immediately rule out referral to this taxon, the only extant hystricognath on the island and the only endemic of any age in the new species’ body size range. Not an echimyid, because cheekteeth of all known species of Antillean spiny rats exhibit furcated roots, prominent cervix, and deep enamel infolds. Not a clidomyine, because all known clidomyines are far too large to be confused with the new taxon and in any case exhibit a substantially different tooth pattern.

EXCAVATION RECORD AND DATING: Detailed discussion of the stratigraphy, dating protocols, and chronology of the secondary deposits in Drum and associated caves is presented by McFarlane et al. (2002). The following remarks pertain to discovery of the Xaymaca holotype .

Pit 2, which yielded the holotype, was first opened in January 1995 and subsequently extended in July and September 1996. This relatively large amount of attention given to one site in one cave was warranted because the pit also yielded a well­preserved humerus of the extinct endemic monkey Xenothrix mcgregori and a number of jaws of the equally extinct endemic rice rat Oryzomys antillarum . The pit is located near Entrance #3, a major collapse feature (fig. 1). Excavations exposed ~ 1 m of deposits that have entered the cave through the collapse. A loose surface layer of limestone fragments, cave earth, and modern owl pellet debris 20 cm thick is underlain by a discontinuous calcite layer (<2 cm). This calcite caps a distinctive and sharply delineated dark­brown layer of subfossil bat guano 34 cm thick, designated ‘‘Guano I’’, beneath which 6 cm of limestone fragments, clay, and huge concentrations of bone extend down to a second guano layer (3 cm thick) designated ‘‘Guano II’’. Beneath this, material extends to a solid calcite floor at 125 cm below surface, beyond which excavation did not continue.

The enormous quantity of lightly cement­ ed small bones present in parts of Pit 2 formed a ‘‘bone cake’’ that had to be broken out and divided by hand. In this situation, dry screening was the only feasible method of recovering specimens. On the screen, representative samples of lizards, snakes, bats, and Geocapromys were collected by handpicking, but much material was also simply bagged for later identification. The jaw which became the holotype specimen of Xaymaca was missed on the screen and was not recognized as distinctive until we sorted the material at the AMNH in New York.

Bone is present throughout the Brown Dust Passage section, but bone recovered from the Guano I and II horizons (including the Xaymaca holotype) is invariably and characteristically stained a deep brown color not seen in other layers. Thus, although it is known that AMNHM 268011 came from a ~12­cm interval between the bottom of Guano I and the bottom of the thin Guano II horizon, its stratigraphic position cannot be fixed more firmly. Fortunately, however, its temporal position can be fixed with considerable accuracy. Radiocarbon dating of the acid­insoluble organic component (crude chitin) of Guano I provided isotopically corrected dates of 10,250 ± 80, 11,050 ± 70, and 11,260 ± 80 BP in correct stratigraphic sequence; similarly, Guano II dated to 11,980 ± 80 BP (see McFarlane et al., 2002). Thus although there is some uncertainty about the exact position of the holotype within Pit 2, its age can be fixed as lying between 10,090 – 11,420 BP (2 sigma error), or the terminal part of the late Pleistocene. Improved constraints on the ‘‘last occurrence’’ date for Fig. 7 .

Figures

Fig. 7. Left hemimandible of Xaymaca fulvopulvis AMNHM 268011 (holotype), in (A) medial, (B) ventral, (C) lateral, and (D) occlusal aspects. In C, the groove winding across the fossa for the superficial masseter is an artifact of some sort, perhaps created by a feeding invertebrate. Notice in D that empty cheektooth alveoli are smooth­walled and sharply inclined; m2 alveolus is normal to axis of camera lens, and thus appears larger than the other molar alveoli (which it is not).