Geocapromys thoracatus

MAMMALIAN SPECIES No. 341, pp. 1-5, 3 figs. Geocapromys thoracatus. By Gary S. Morgan Published 26 October 1989 by The American Society of Mammalogists Geocapromys Chapman, 1901 CONTEXT AND CONTENT. Order Rodentia, Suborder Hystricognathi, Superfamily Octodontoidea, Family Capromyidae. Geocapromys includes six described species: G. brownii from Jamaica (see Anderson et aI., 1983); G. ingrahami from East Plana Cay, Bahamas; G. thoracatus from Little Swan Island; and three extinct species known from fossil deposits in Cuba, G. columbianus, G. megas, and G. pleistocenicus. An undescribed extinct species of Geocapromys has been reported from fossil deposits in the Cayman Islands (Morgan and Woods, 1986). Geocapromys is distinguished from the closely related genus Capromys by a number of external and cranial characters, including: considerably shorter tail « 25 % of total length); reduced first digit on front foot; shorter finer fur; origin of upper incisor root capsule high on maxilla above P4; broad vertically or posteriorly oriented superior zygomatic root of maxilla; anteriorly convergent upper tooth rows; 30° inclination of occlusal surface on all cheek teeth; and presence of third anterolingual reentrant (anteroflexid) on p4 (Morgan, 1985; Woods and Howland, 1979). The following is a key to the three Recent species of Geocapromys: 1. Size large (length of head and body greater than 370 mm; alveolar length of maxillary tooth row greater than 18.D mm); tail considerably shorter than hind foot; dorsal coloration dark, ranging from dark reddish-brown to blackishbrown; dorsal margin of frontals noticeably inflated anteriorly G. brownii Size small (length of head and body less than 350 mm; alveolar length of maxillary tooth row less than 16.5 mm); tail equal in length to or longer than hind foot; dorsal coloration lighter, generally grayish-brown; frontals not inflated 2 2. Tail approximately equal to length of hind foot; ears essentially naked; transverse band of cream-colored fur on venter between front limbs; braincase and auditory bullae not inflated; jugal spine present; small spinous process present on posterior margin of palate along midline . ............................................................................................................................. G. thoracatus Tail considerably longer than hind foot; ears densely furred, with two long tufts on dorsal margin; cream-colored spots generally absent on venter, but when present extend lengthwise between front and hind limbs; braincase and auditory bullae noticeably inflated; jugal spine absent; palatal spine absent G. ingrahami GENERAL CHARACTERS. Geocapromys thoracatus (Fig. 1) has grayish-brown upperparts and a light brown to tan venter. The majority of the hairs on the dorsum are light brown at the base with tan tips, but interspersed with these, especially in the middle of the back, are long unbanded dark-brown hairs. These darker hairs, together with the paler-banded hairs, produce the overall grayish-brown color. The guard hairs on the back average 20 to 25 mm in length, being slightly longer on the rump. The sides are lighter than the dorsum and darker than the venter, with the dark brown hairs on the back giving way to unbanded medium brown hairs. The uniform light brown underparts are interrupted by a band of lighter, cream-colored hair 1 to 3 em in width that extends transversely across the chest between the front limbs. The rhinarium has a dense covering of short hairs above the external nares, with somewhat longer hairs extending slightly distal to the nares. Eight to 10 fine mystacial vibrissae averaging 50 mm in length are present on either side of the snout. The ears are comparatively large and appear to be almost naked, although both external and internal surfaces have a sparse covering of extremely short fine hairs. Ears tufts are absent. The tail is short, aproximately equal to length of the hind foot, and has a scanty covering of long dark-brown hairs. The mammae, two on each side, are located about midway up on the thorax. Males possess a well-developed spatulate-shaped baculum. Sexual dimorphism is not marked, but males are slightly larger than females in most cranial and external measurements, although there is broad overlap between them (Morgan, 1985). The cranium of G. thoracatus (Fig. 2) is intermediate in size between the larger G. brownii and the smaller G. ingrahami. Cranial measurements of G. thoracatus average 15 to 20% smaller than G. broionii, depending on the measurement, with almost no overlap between the smallest G. brownii and the largest G. thoracatus. The Geocapromys thoracatus (True, 1888) Swan Island Hutia Capromys brachyurus thoracatus True, 1888:469. Type locality, "Little Swan Island, one of two small islands lying at the entrance of the Gulf of Honduras." Capromys (Geocapromys) thoracatus: Chapman, 1901:321. First recognition of thoracatus as a distinct species. Geocapromys thoracatus: G. M. Allen, 1917:8-9. First use of present name combination. CONTEXT AND CONTENT. Context in generic account above. No subspecies of Geocapromys thoracatus are recognized. FIG. 1. Photograph of Geocapromys thoracatus collected on Little Swan Island in 1937 (from Moyne, 1938). Capromys (Geocapromys) Chapman, 1901:314. Type species Capromys brownii Fischer, by original designation. First described as subgenus of Capromys. Geocapromys: G. M. Allen, 1917:8. First use of name as genus. Synodontomys G. M. Allen, 1917:5. Type species Capromys columbianus Chapman, by original designation. DIAGNOSIS. As noted in the key, G. thoracatus differs from the two other Recent species in the genus, G. brownii and G. ingrahami, in: size (length of head and body >330 mm and <350 mm); color; and length of tail. Ears comparatively large, almost naked, and lacking tufts; 17 caudal vertebrae present (G. brownii averages 14 caudals; G. ingrahami averages 19); frontals not inflated anteriorly or constricted posteriorly; temporal crests strong, but rarely meeting to form sagittal crest; braincase and auditory bullae not inflated; jugal spine present, but not large; internal nares constricted dorso-ventrally resulting from dorsal inclination of palate from anterior to posterior; small spinous process on posterior edge of palate along midline. Alveolar and occlusal lengths of upper and lower tooth rows comparatively shorter than in other two species as a result of reduced amount of cement on all cheek teeth (Morgan, 1985). MAMMALIAN SPECIES 341 2 FIG. 2. Dorsal, ventral, and left lateral views of the skull, and lateral and dorsal views of the left mandible, and outline drawings of the upper dentition (bottom left) and lower dentition (bottom right) of Geocapromys thoracatus (American Museum of Natural History 34547). Swan Island hutia averages 6 to 8% larger than G. ingrahami, but there is broad overlap between them in some measurements. The frontals show no evidence of the anterior infl (...truncated)