Part 7

Although Osteocephalus and Argenteohyla have similar vocal sac structure, they are obviously distinct. The monotypic Argenteohyla is a rather specialized, semifossorial frog (Trueb, 1970b), characterized by smooth skin, moderate-sized digital discs, and a large inner metatarsal tubercle. The general architecture of the skull is not unlike that of Osteocephalus; the skulls of both are well roofed, broader than long, and characterized by posterolaterally oriented parasphenoid alae. Argenteohyla bears small, slightly curved prevomerine dentigerous processes in contrast to the large, angular processes of Osteocephalus. The skull of Argenteohyla shows specializations, apparently adaptations to its semifossorial mode of existence, which further distinguish the genus from Osteocephalus. In comparison with Osteocephalus, the cranium of Argenteohyla is slightly depressed anteriorly, the roofing bones extensively casqued, and the palatines robust.

Osteologically, Osteocephalus more closely resembles Phrynohyas than either of the other two genera, but Osteocephalus and Phrynohyas are clearly distinct on the basis of their respective vocal sac structure. Like Osteocephalus, skulls of the members of the genus Phrynohyas are broader than long, have extensive dermal roofing bones, and have posterolaterally oriented parasphenoid alae. In contrast to Osteocephalus, the dentigerous processes of the prevomers are curved, rather than angular in Phrynohyas. Furthermore, the latter genus is singularly distinguished from Osteocephalus, Argenteohyla, and Trachycephalus by having extensively developed parotoid glands that produce a viscous, milky volatile secretion.

Trachycephalus is the most readily identifiable of the four genera under discussion. Members of this genus are large frogs with heavily casqued and co-ossified skulls (Trueb, 1970a). The dermal roofing bones bear ornate and characteristic patterns of sculpturing. The medial ramus of the pterygoid does not articulate with the otic capsule, and the parasphenoid alae are laterally, rather than posterolaterally, oriented. A dermal sphenethmoid is present, and the parasphenoid bears odontoids. The basic structure of the skull has many characters in common with both Osteocephalus and Phrynohyas. The obvious modifications of dermal roofing bones and of palatal and suspensory elements seem to be specializations adapting members of the genus Trachycephalus to their peculiar phragmotic habits. The vocal sac structure of Trachycephalus is like that of Phrynohyas and therefore further distinguishes it from Osteocephalus.

Morphologically, Osteocephalus seems to be sufficiently diverse and generalized so as to represent a modern derivative of an ancestral type which might have given rise to Phrynohyas, Trachycephalus, and Argenteohyla. The specialized vocal sac structure in Phrynohyas and Trachycephalus suggests that these two genera may be rather closely allied and represent a single phyletic line from an ancestral stock similar to Osteocephalus. Argenteohyla is quite distinct from Phrynohyas and Trachycephalus and apparently represents a distinct phyletic line from the ancestral stock.

OCCURRENCE OF OSTEOCEPHALUS IN AMAZONIAN ECUADOR

All of our observations on members of this genus have been made at four localities: 1) Santa Cecilia at an elevation of 340 meters on the Rio Aguarico, a tributary of the Rio Napo, 2) Lago Agrio, 330 meters, about 14 kilometers east of Santa Cecilia, 3) Puerto Libre, 570 meters, on the Rio Aguarico just east of its formation by the confluence of the Rio Cofanes and Rio Chingua, and 4) south slope of the Cordillera del Due, above the Rio Coca, 1150 meters. Osteocephalus leprieurii was found at all four localities, and buckleyi was found at all but the last; taurinus was found at Santa Cecilia and Lago Agrio, and verrucigerus was found only in the Cordillera del Due. Our data are based on collections of 113 frogs and three lots of tadpoles, as well as observations on calling sites and young. The observations are summarized by species, as follows:

Osteocephalus buckleyi.--No breeding activity was observed. Males were found only at night in March, June, and July. One was perched on a Heliconia leaf in a swamp at Puerto Libre, and two were on bushes in the forest at Santa Cecilia. A gravid female was found on a recently felled tree at Lago Agrio on the night of 12 May 1969.

Osteocephalus leprieurii.--Males were heard calling sporadically at Puerto Libre in July 1968, and at Santa Cecilia in May 1969. A small chorus was found on the night of 12 May 1969 at Lago Agrio, where the frogs were perched on branches of fallen trees over a temporary pool. The call is a soft rattling chuckle. In late April and May many gravid females and males with well-developed nuptial excrescences were obtained from trees as they were felled at Lago Agrio. The reproductive condition of the frogs indicates that they probably breed in May. One individual called nearly every night from a large tree at Puerto Libre between 4-17 July 1968. The tree was felled on the latter date, but no frog was found. Two nights later apparently the same individual called from a bromeliad at a height of about 10 m on a large bamboo adjacent to the felled tree; the frog was collected when the bamboo was cut down.

Throughout the rainy months that we have worked in Ecuador (April-August) we have found occasional individuals perched on bushes or low trees at night. Large numbers of adults were observed only during a clearing operation which resulted in the felling of many large trees. Thus, it seems likely that leprieurii is a tree-top inhabitant. A partially digested adult male was removed from the stomach of a Hemiphractus proboscideus.

At Santa Cecilia many recently metamorphosed young and juveniles were found in June and July 1968. Most of these were on low bushes or herbs in swamp forest at night; some were found in unfolded Heliconia leaves by day, and one was observed on the forest floor by day. Snout-vent lengths of 18 specimens are 12.3-17.0 (mean 15.1) mm. The smaller frogs were recently metamorphosed as evidenced by the melanophore deposits above the vent. The coloration of the young is strikingly different from that of the adults (see account of O. leprieurii), so the association of the young and adults was not made until individuals with intermediate patterns were obtained at Lago Agrio in May 1969. Probably juveniles obtained in June and July are the offspring of an April or May breeding. We have been unable to associate tadpoles with this species.

Osteocephalus taurinus.--A small chorus occurred at Lago Agrio on 12 May 1969. Males were calling from the ground adjacent to a small pool amidst recently felled trees. The males were very wary and, when approached, jumped onto limbs and ran up branches; this behavior was noted by Bokermann (1964). The call consists of a series of low-pitched, short notes--like a slow trill--four to six notes per call group. Call groups are repeated two, three, or four times followed by a lapse of several minutes. Although no amplectant pairs were found, several gravid females were collected at Lago Agrio in May, so it can be safely assumed that the species breeds in May. From April through July occasional individuals were observed on bushes and trees at night. During clearing operations at Lago Agrio several individuals were obtained from the tops of trees as they were felled.

Osteocephalus verrucigerus.--Observations were made in a broad, shallow ravine, in which there was a small stream. On 2-4 August 1968, males were observed calling from low bushes and rocks at the edge of a quiet pool in the stream. The call consists of a series of well-pulsed, low-pitched, guttural notes produced at the rate of 5-10 per minute. One amplectant pair was found at the base of a bush adjacent to the pool on 3 August. Another female was found on a branch of a tree 2 m above the ground and 10 m from the stream. Tadpoles of this species were found in the quiet silt-bottomed pool.

SPECIMENS EXAMINED

The localities for each of the specimens examined are given in the following paragraphs. The arrangement of the data is as follows: alphabetically by country, state (department or province), and locality; alphabetically by the first letter in the abbreviations for the museums, and numerically after each museum abbreviation. Specimens lacking precise locality data are listed first in the most restricted political unit possible; localities which have not been found on maps or the positions of which are not known to us are given in quotation marks. Where more than one specimen is included under one museum number, the number of specimens is given in parentheses after the museum number. Unless noted otherwise, all specimens are alcoholics.

Osteocephalus buckleyi

BOLIVIA: El Beni: Ivon, BMNH 1967.2070-1. Santa Cruz: Buenavista, CM 4333, 4339, UMMZ 66563-5.

BRASIL: Amapa: No specific locality, WCAB 13284.

COLOMBIA: Amazonas: Rio Guacaya, USNM 152759. Huila: Acevedo, Rio Suaza, FMNH 69702. Narino: Rumiyacu, FMNH 54756. Meta: Rio Guejar, Campamento La Macarena, USNM 152199.

ECUADOR: No specific locality, NHMW 6209, WCAB 35499. Chimborazo: Pallatanga, BMNH 1947.2.13.46; Santiago, FMNH 42529. Morona-Santiago: "Rio Santiago" (= Rio Zamora), MIZS 2950. Napo: Lago Agrio, KU 126646; Puerto Libre, Rio Aguarico, KU 123172; Santa Cecilia, AUM 8138, KU 105208-9, 109506, 123171. Pastaza: Alpayacu, BMNH 1912.11.1.64; Canelos, BMNH 1947.2.13.40-1, 1947.2.13.43-5; Colonia Mena, Rio Conambo, ZSM 33/1962; Don Tomas, USNM 166014; Guache, Rio Pastaza, AMNH 79986; Rio Bobonaza, USNM 166005; Rio Capahuari, USNM 166554; Rio Conambo at Rio Shiona-yacu, USNM 166018; Rio Copataza, upper Rio Pastaza, USNM 166007-13; Rio Pastaza, NHRM 1946; Rio Pucyacu, USNM 165997 (skeleton), 165998-6001; Rio Rutuno, USNM 166006; Rio Villano, USNM 166002-4; Sarayacu, BMNH 1947.2.13.36-9, MCZ 26090, ZMB 10166.

GUYANA: Mazaruni-Potaro: Kartabo, AMNH 70971; Membaru River, upper Mazaruni River, UMMZ 85168; Oko Mountains, FMNH 26722-3. North West: Amakura River, Haulover, UMMZ 83558-9. Rupununi: Marudi River, AMNH 46233; Shudi-kar-wau, AMNH 49252. West Demerara: Dunoon, UMMZ 52449, 52508.

PERU: Junin: Chanchamayo, BMNH 1911.12.13.79-80. Loreto: Andoas, AMNH 79984-5; Cashiboya, AMNH 43454; San Antonio, Rio Itaya, AMNH 43218. Puno: Yahuaramayo, BMNH 1913.2.25.7.

SURINAM: Suriname: Powakka, CM 44217.

SOUTH AMERICA: No specific locality, NHMW 6208.

Osteocephalus leprieurii

BRASIL: Acre: Tarauaca, FMNH 83247. Amazonas: Rio Javari, Benjamin Constant, CAS-SU 12620; Rio Uaupes, north of Rio Japu, NHMG 489.

COLOMBIA: Amazonas: Gino-goje, lower Rio Apoporis, MCZ 28038, 28040-2, 28044, USNM 152136-8.

ECUADOR: No specific locality, WCAB 35452-3; "Napo-Pastaza," USNM 166571. Napo: Avila, UMMZ 92093; south slope Cordillera del Due, KU 123170; Lago Agrio, KU 125961-2 (skeletons), 126611-44, UMMZ 129326 (2); Limon Cocha, Rio Napo, KU 99210-6, UIMNH 63087-9, 63098, 63106-9, 63118-9, 64802-4, 64858, 87998-9, 88001-30, 88437-8, 88580, 88604-5, 89852-97, 89999-90000; Loreto, CAS-SU 11439, WCAB 36526; Puerto Libre, Rio Aguarico, KU 123190-1; Puerto Napo, UIMNH 55818-20; Rio Cotapino, UMMZ 92094; Rio Napo, UMMZ 92078; Santa Cecilia, AUM 8099, 8102, 8113-5, 8127-9, 8131, 8137, 8139-46, 8148, KU 105210-20, 109509-11, 111971, 122964-87, 123169, 126645. Pastaza: Canelos, BMNH 1947.2.13.42, KU 120915; Rio Alpayacu, UMMZ 92079; Rio Arajuno, USNM 166560-2, WCAB 40176; Rio Oglan, USNM 16655203, 166558; Rio Rutuno, USNM 166559; Rio Shilcayacu, below Puyo, USNM 166557; Rio Villano, USNM 166551.

FRENCH GUIANA: No specific locality, MNHN 4629. Inini: Lunier River, MNHN 98/217.