Evidence of a fossil stork (aves: Ciconiidae) from the late Miocene of the Pisco Formation, Peru (página 2)
REFERRED MATERIAL
MUSM 255 left tarsometatarsus broken into three fragments, from the Aguada de Lomas vertebrate locality, Pisco Formation, Department of Arequipa, South-central coast of Peru. Collected by M. Urbina.
Proximal width: 20 mm.; width at half shaft: near 9.1 mm. The three fragments together have a length of 210 mm, but the bone was longer.
The specimen (Fig. 2) consists on an incomplete left tarsometatarsus broken into three fragments, with the epiphyses partially eroded. In the proximal region, calcaneal ridges of the hypotarsus are damaged. In the distal region, the trochleas for metatarsi II and IV are missing; the trochlea for metatarsi III only possesses its dorsal side. The tarsometatarsus of Ciconiids is diagnosed by the presence of the following characters: (1) A furrow in the external side of the intercotylar prominence (Fig. 2A); (2) A high intercotylar prominence, with a rounded region facing to the external side; (3) A very marked tuberculum for the fibularis brevis muscle (Fig. 2C); (4) The foramen vasculare distale is at the same level or very near of the proximal end of the trochlea III; (5) Distal region flared with the trochlea III anterior to the II and IV. The specimen MUSM 255 possesses all the preceeding diagnostic characters of Ciconiidae with the exception of the fourth. MUSM 255 possesses a distal foramen that is far from the proximal end of the trochlea
III. The fibularis brevis muscle tuberculum is more developed than in the other members of the family. Due to the fragmentary nature of the specimen, it was impossible to place it in a lower taxonomic category than family or to give some hint about its relationships with the extant members of the family. It is possible through measurement of the epiphysis width to say that MUSM 255 appears to have medium to large sized stork. It is difficult to estimate the total length of this tarsometatarsus (and also the size of the bird), since there is no direct relationship between both dimensions.
Figura 2.- Tarsometatarsus of Ciconiidae indet. (MUSM 255) of the Pisco formation, Peru. Scale bar: 20 mm. A: dorsal aspect;
B: plantar aspect; C: lateral aspect. FIP: Furrow in the external side of the intercotylar prominence; FBMT: Fibularis brevis muscle tuberculum
This is the first report of a Ciconiidae for the Pisco Formation, where ten avian families had previously been registered: Sulidae, Spheniscidae, Phalacrocoracidae, Procellariidae, Pelagornithidae, Pelecanidae, Diomedeidae, Vulturidae, Laridae and Scolopacidae (Stucchi & Urbina, 2005). For the Aguada de Lomas locality, where the MUSM 255 was found, only the first four families were previously mentioned. Marocco & Muizon (1988) proposed that this locality represent a paleoenviroment of open sea and turbulent beach. This is supported by the presence of broken mollusks shells, dissociated skeletons and smooth and isolated bones, like MUSM 255. Little is known about the coastal environment of Peru during the Miocene. It is probable that due to the ancestral Humboldt Current (Alpers & Brimhall, 1988) and to the uplift of the Andes, the climate conditions may have been as arid and desert-like than at the present.
It is under such environmental conditions that Ciconiids could occur in Aguada de Lomas. However, these birds travel widely and occur today in a wide ability of habitats, including savannas, forests and deserts. They forage in shallow water for a wide variety of prey (usually small vertebrates such as fish, frogs, snakes, some birds and invertebrates like mollusks and arthropods in not very deep waters). The South American species will also occasionally scavenge around carcasses, like it is the case of the maribous of the genus Leptotilos of Africa and Asia, which can steal scraps from vultures or other carrion feeders, or snatches up morsels that plows dropped (Elliot, 1992).
Based on these arguments and to their scarce presence in the paleontological record, we suggest that this bird was a solitary occasional visitor (as its current relatives) and that discharge the high offer of fish and carcasses coming from the remains of birds, seals and cetaceans that lived in that area. Also, we can suggest that in the past the distribution of the Ciconiidae in the Peruvian territory was wider, like it is possible to appreciate in the fossil record of the Pisco Formation and Talara tar seeps.
We thank Paul Velazco, David Willard, John Bates and José Tello of the Field Museum Natural of History in Chicago, for their support, comments to the manuscript and help with the osteological collections. Rodolfo Salas and Manuel Laime of the Museo de Historia Natural de San Marcos in Lima, for their comments and help with some information about Pisco formation. Gonzalo Cárdenas, Michael McGowan, Paul Velazco and Judith Figueroa for their help in Chicago. Carolina Acosta-Hospitaleche did many important comments to the manuscript. Thomas Schulenberg provided access to his library. Finally, we thank Claudia Tambussi for her review and comments.
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Autor:
Mario Urbina
Marcelo Stucchi
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