HARVARD UNIVERSITY Library of the Museum of Comparative Zoology OCCASIONAL PAPERS of the MUSEUM OF NATURAL HISTORY The University of Kansas Lawrence, Kansas ^ UMBER 20, PAC;ES 1-7 NO\ EMBER 13, 1973 LtlRARY nPr 1^ ^¥ GENUS AND SPECIES OF "^TvnCRDHYLID FROG FROM ECUADOR HARVARD By UNJVCRSlTy Charles F. Walker Two tiny frogs were collected in the Oriente of Ecuador in 1962, and were presumed, at the time, to be juveniles. Subsequent dis- section of these specimens revealed them to be adults of an un- described microhylid. Additional specimens of this frog have been secured more recently by William E. Duellman and his associates at The Universit}' of Kansas. He generously has made this material available and has encouraged me to describe the creature. Syncope new genus Type species. — Syncope antenori, new species. Diagnosis. — Seven presacral vertebrae, the first two partially or completely fused ( Fig. 1 ) ; coccyx articulating with sacrum by two narrowly separated condyles; a small tympanum distinctly differen- tiated; foot with only four toes evident externally. The first of these character states alone serv^es to distinguish the new genus from other American microhylids, the second from the African genus Breviceps which shares the vertebral count, and the third and fourth afford convenient external means of recognition. Among the American genera only Otophnjne possesses a tympanmii and in this genus the structure is relatively huge, about equal to the orbit in diameter; although the inner toe of Otophryne is small, it is quite distinct. Other osteological features of Syncope are: ^ Curator, Division of Herpetology, Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48104. OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Cyx ii Fig. 1. Vertebral column of Syncope in ventral aspect. vertebrae procoelous; sacral diapophyses expanded; coccyx with basal transverse processes, vestigial or well developed; procoracoid cartilage and clavicle present but reduced, the latter curved, meet- ing the coracoid in its distal third; omosternum absent; ethmoids paired {sensu Parker, 1934); quadratojugal absent, the maxillaiy arch incomplete; edentulous; premaxilla with notched palatal shelf; maxilla thin, bladelike, with no palatal shelf posteriorly; inner nares bordered anteromedially by a narrow crescentic anterior prevomer; posterior prevomer well developed, medially fused with ethmoid (Fig. 2); no discrete palatine; pteiygoid with long anterior ramus MICROHYLID FROG FROM ECUADOR Pmx 1mm Fig. 2. Anterior cranial elements of Syncope in palatal aspect. articulating with maxilla; anterior ramus of squamosal vestigial; nasals and frontoparietals closely approximated in midline; pha- langeal formula of hand 2, 2, 3, 3, of foot 1, 2, 3, 4, 3, the terminal phalanges of inner finger and of inner and outer toes reduced to minute but discrete nodules. Syncope antenori new species Holotype. — University of Kansas Museum of Natural History (KU) 124009, an adult female collected on 18 July 1968 by W. E. Duellman and Linda Trueb at Puerto Libre, Rio Aguarico, 570 m, Provincia Napo, Ecuador. Pomtypes.—KU 124001-08, 124010-11, all from the type locality, July 1968. Allotype. — University of Michigan Museum of Zoology (UMMZ) 131699, a male, 7 August 1962, C. F. Walker, 9 km E of Puyo, Provincia Pastaza, Ecuador. Description of Holotype. — Viewed from above, snout somewhat truncate, interorbital width twice that of eyelid; canthal area rounded; loreal region oblique; head skin smooth; no postorbital fold. In lateral aspect, snout strongly projecting over lower jaw, nostril much closer to snout than to eye; tympanum distinct, its diameter nearly half that of eye. Fingers bluntly rounded at tips, 3>2>4>1, 1 and 4 rudimentary, 3 much the longest, all margined 4 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY with fleshy web; pahiis smooth, subarticular tubercles absent. Foot with only four toes evident, small but distinct disks at tips, 4>3>5>2, the normal first toe not developed externally; soles smooth except for a feeble, rounded inner metatarsal tubercle. Tongue elongate, oval, extensively free posteriorly; two low, rounded, transverse palatal dermal ridges, the posterior the longer. Color dark brown above and below, flecked with small white spots, more numerous and larger ventrally than dorsally. Snout-vent length 12.3, tibia 6.0, foot 4.9, head width 4.2, tympanum 0.8 mm. Variation. — The largest specimen, an adult female paratopotype, is 13.2 mm in length; the male allotype is 11.2 mm in length with well developed testes, and shows no external sexual dimorphism in structure or color. No vocal sac is apparent nor are there any aper- tures present indicative of an internal sac. The membrane covering the testes is lightly pigmented. The vertebral number, as shown by X-ray photographs, is con- stant throughout the series of 13 specimens, as is also some degree of fusion of the first two vertebrae. In those individuals in which the fusion of vertebrae I and II is complete ( Fig. 1 ) , there are only six functionally independent presacral elements. Thus the reduc- tion of the column has been achieved in part by fusion, a frequent occurrence among anurans, and in part by elision, a much rarer event. The partial fusion of vertebrae V and VI of the figured specimen represents an individual variation. The coccygeal proc- esses vary from mere vestiges to the maximum shown in the figure, which is approached by only one other indi\'idual. The forward tilt of the processes supplies evidence that the shortening of the column has been achieved by the incorporation of a former verte- bral element into the coccyx, concurrent with the transfer of the sacral function from vertebra IX to vertebra VIII. A parallel situa- tion has been described by Tihen (1960) in the African bufonid genus Mertensophryne, and may be inferred in certain species of the American bufonid genus Rhamphophnjne (Trueb, 1971) which exhibit seven presacral vertebrae with no evidence of fusion. The coccygeal processes of Syncope are thus not strictly homologous with those of discoglossids and ascaphids. Their presence is to be interpreted as a derived rather than primitive condition. It has been remarked frequently that departures from the standard foot structure, four fingers and five toes, are rare among anurans. Most of the exceptions seem to occur among diminutive species. In the African bufonid genus Dichjnaniipus, with a maxi- mum recorded length of 18 mm, only three toes are apparent ex- MICROHYLID FROG FROM ECUADOR 5 ternally. Still smaller is the Neotropical brachycephalid Pstjllo- phrijne didactyla ( $ 10.2 mm, $ 8.6 mm) recently described by Izecksohn ( 1971 ) , in which only two fingers and three toes are obvi- ous. The phalangeal formula of these genera is not of record. In Syncope the phalangeal formula reveals that suppression of the inner toes has not been complete, nor has it in GeobatracJms, a genus of disputed familial relationship, which also lacks an ex- ternally evident inner toe and shares with Syncope the pedal for- mula: 1, 2, 3, 4, 3. Dwarfing seems to have been accompanied by paedomorphosis affecting the foot structure independently in these four unrelated lines. Although patently specialized in most respects. Syncope retains two primitive character states, distinct tympanum and posterior prevomer. Derived states include loss of a presacral vertebra, re- duction of clavicle, absence of palatine, quadratojugal, externally evident inner toe, and diminutive size. Examination of Table 1, in which the principal character states of the American microhyline genera are presented, shows clearly that Syncope could not have evolved from any existing genus. Presumably it has arisen from a Table 1. 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