Rev. Biol. Trop., 49(1): 347-357, 2001 www.ucr.ac.cr www.ots.ac.cr www.ots.duke.edu A new species of Osteocephalus (Anura: Hylidae) from Guyana Eric N. Smith1 and Brice P. Noonan1 1 Department of Biology, The University of Texas at Arlington, Arlington, Texas 76019, USA. Fax: (817) 272-2855. E-mail: [email protected]; [email protected] Received 6-X-1999. Corrected 6-VI-2000. Accepted 19-IX-2000. Abstract: A new member of the genus Osteocephalus is described from the Pakaraima mountains of western Guyana. This species is the smallest known member of the genus and is probably closely related to O. subtilis. Both share a small size (less than 40 mm snout-vent length), large and bulgy eyes directed somewhat rostrally, green bones, smooth and brownish dorsal skin, relatively short and truncate snout, small tympanum, subgular and laterally expanded vocal sac, poorly developed subarticular and supernumerary tubercles, a supra-anal glan- dular ridge, and cream-white venter and subocular region. The new species can be distinguished from O. sub- tilis by the Buff iris (vs black), smaller overall size (32.7 vs 35.8–38.8 mm snout-vent length), relatively larger toe disks, and less developed foot webbing. The cranium of the new species is well ossified, relatively reduced in width between the orbits, without an exposed frontoparietal fontanelle and with the anterior arm of the squa- mosal extending to about half the distance to the maxillary. The vocal sac is subgularly poorly developed and possess lateral extensions to the area behind the jaw angles. Well developed supraocular and suprasquamosal cartilages give support to the enlarged eyes of this species. Key words: Anura, Hylidae, Osteocephalus, New species, Guyana, Osteology, Myology. Recent herpetological exploration into the the first time O. cabrerai from Guyana. O. ca- interior mountains of Guyana by the junior brerai was placed in the synonymy of O. buc- author has lead to the collection of several spe- kleyi by Trueb and Duellman (1971), later O. cies of Osteocephalus, namely O. buckleyi, O. cabrerai was resurrected by Duellman and cabrerai, O. leprieurii, O. taurinus, and a very Mendelson (1995). Originally, O. cabrerai distinctive undescribed species. The descrip- was described based on two specimens from tion of the later species is the main purpose of Colombia and one from Amapá Territory, eas- this paper. These represent all species of Os- tern Brazil (Cochran and Goin 1970). Gorzu- teocephalus currently known to us to inhabit la and Señaris (1998) report this species from Guyana, and with O. oophagus all of those pre- the Amacuro Delta in Venezuela. Based on sently known from the Guiana Shield (O. ayar- these distributional data it is not surprising to zaguenai Gorsula and Señaris (1996) from the find this species in Guyana, where it was pro- Gran Sabana, Venezuela is considered a junior bably confused with O. buckleyi. synonym of O. leprieurii for reasons stated by Although the junior author only collected E. N. Smith et al. , unpublished). We report for a single specimen of the undescribed species, 348 REVISTA DE BIOLOGÍA TROPICAL the fact that other trips to the collecting locality using a stereo microscope with an ocular mi- have yielded no more specimens and the uni- crometer. queness of this species when compared to ot- The skin on the head of the holotype he- her Osteocephalus leds us to describe it herein. rein described was carefully peeled back in or- This species is presumably closely related to der to examine the underlying musculature. the large eyed and small bodied O. subtilis After jaw musculature examination the skull Martins and Cardoso (1987) from Acre, Brazil, was removed by cutting at the level between approximately 2 000 km to the southwest. We the occipital condyles and the atlas. The head also describe the cranium and vocal sac struc- skin was then returned to its original position. ture of the new species. The removed cranium was cleared and double stained according to the Kansas University Museum of Herpetology modification of the MATERIALS AND METHODS procedure of Dingerkus and Uhler [1977] revi- sed by Taylor and Van Dyke (1985). Jaw mus- Measurements of tympanum and eye dia- culature terminology is that of Tyler (1971). meter, head, foot, tibia, and snout-vent lengths Cranial descriptions follow the format of (SVL) follow Duellman (1970); measure- Trueb and Duellman (1970) and the termino- ments of head width and inter-orbital distance logy of Trueb (1970). follow Lynch and Duellman (1980), webbing Specimens examined are listed in Appen- notation follows Savage and Heyer (1967), as dix I. Museum abbreviations follow Leviton et modified by Myers and Duellman (1982), and al (1985) or are defined in the text, referred toe and finger terminology is that of Savage specimens are presented with their field catalo- (1987). The following measurements were al- gue number. so included: internarial distance—distance Color descriptions of live specimens were between medial borders of nares; snout length- made based on Kodachrome color transparen- —distance from tip of snout to anterior margin cies deposited at The University of Texas at of eye; orbit-jaw distance—shortest distance Arlington (UTA) and the Kansas University between deepest region below eye and margin (KU) herpetological slide collections (Appen- of upper jaw; naris-jaw distance—shortest dis- dix I). Colors are taken from the Naturalist’s tance between naris and margin of upper jaw; Color Guide (Smithe 1975). Colors taken from choana width—maximum width of choana; fe- this color guide, in the case of slide-descrip- mur length—distance from tip of urostyle to tions, are presented in capital letters, others are distal end of femur; arm length—distance from not. Color descriptions in the diagnosis refer proximal end of radio-ulna to proximal base of to live specimens. The number in parentheses pollex; hand length—length from proximal ba- after a color first appears in a paragraph refers se of pollex to tip of third finger; interfascicu- to that of the color swatch in the guide. lar distance—shortest distance between denti- All specimens examined were stored in 70% gerous fascicles; and tarsal length—distance ethanol. Most were probably fixed in the field from proximal border of inner metatarsal tu- with a 10% formalin solution and later transfe- bercle to proximal end of tibiale. The widths rred to ethanol, as was done for the holotype of of the pads of the third finger and the fourth toe the species described herein. The sex of preser- were also measured. Lengths were recorded ved specimens was determined by the presence from the right side of each specimen, unless of prepollical nuptial excrescences in adult males the specimen was damaged or abnormal on and their absence in adult females. Sex of young that side. Measurements greater than 10 mm individuals was determined by examining go- were taken to the nearest 0.1 mm with digital nads. Gonad development was observed to ve- calipers. Those less than 10 mm were taken rify maturity in seemingly small adults. INTERNATIONAL JOURNAL OF TROPICAL BIOLOGY AND CONSERVATION 349 Fig. 1. Holotype of Osteocephalus exophthalmus, adult male, 32.7 mm SVL. DESCRIPTION ted with the vocal sac is unmodified and the well developed vocal slits are located near the Osteocephalus exophthalmus sp. nov. angle of the jaw. Osteocephalus exophthalmus (Figs. 1, 2, 3) is probably closely related to O. subtilis, with whom it shares a small size (less than 40 mm Holotype: The University of Guyana SVL), large and bulgy eyes directed somewhat Center for the Study of Biological Diversity rostrally, green bones, smooth and brownish UG/CSBD HA-722, (cranium, The University dorsal skin, relatively short and truncate snout, of Texas at Arlington UTAA-51620) (Original small tympanum, subgular and laterally expan- number BPN 166), adult male collected at ca ded vocal sac, poorly developed subarticular 30 km SE Imbaimadai, Mazaruni-Potaro Dis- and supernumerary tubercles, a supra-anal trict, Guyana, ca. 585 m, on 10 June 1997 by glandular ridge, and cream-white venter and Brice P. Noonan and Daniel W. Carpenter, ap- subocular region. The new species can be dis- proximately 5°37’30’’ N, 60°14’42’’ W. tinguished from O. subtilis (comparison in pa- Diagnosis: The smallest known member rentheses, pad ratio and webbing formulae ta- of the genus Osteocephalus (32.7 mm, SVL of ken from illustration in Martins and Cardoso, only known specimen). Eyes large and bulgy, 1987) by its Buff iris with a black cross (vs. directed rostrally. Iris Buff (24) with black black), smaller overall size (32.7 vs. 35.8–38.8 markings, somewhat forming a cross with the mm SVL), relatively larger toe pads (0.9 vs. pupil as the center. Male with poorly develo- 0.6, pad width of Toe IV/pad width of Finger ped vocal sac that extends as a tube of thin III), and less developed hand and foot webbing muscle and fascia from the throat to the area (I 21/3–21/2 II 12/3–3 III 22/3–22/3 IV, I 11/2 –2 behind and slightly above the angle of the jaw, II 11/2 –2 III 11/2 –2 IV 2–11/2 V vs. I 2–21/3 where it is more muscular. The skin associa- II 11/2 –21/3 III 21/2 –2 IV, I 1–12/3 II 1–11/2 350 REVISTA DE BIOLOGÍA TROPICAL III 1–11/2 IV 11/3 –1 V). Male O. exophthal- 24 % head width; nostrils slightly protuberant mus can easily be distinguished from all other laterally; internarial area depressed; lips thin, adult members of the genus by its smaller size.