First record of seriemas (Aves: Gruiformes: Cariamidae) from Santacrucian (Early Middle Miocene) beds of Patagonia

NORIEGA, JORGE IGNACIO; VIZCAÍNO, SERGIO F.; BARGO, SUSANA

Puerto Madryn, Argentina

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2005

The extant seriemas are long-legged cursorial birds which represent surviving relicts in South America of an early gruiform radiation within the suborder Cariamae. Phorusrhacids, idiornithids, and bathornithids are also extinct components of this large terrestrial stock of predator or scavenger birds which were abundant during the Tertiary of South and North America, and Europe. The phylogenetic relationships and paleobiogeographic history of these clades are today far from being resolved. However, Tertiary fossils of cariamids Cariaminae are scarce and restricted to the questionable record of Riacama caliginea Ameghino 1899 from the Late Oligocene (Deseadan age) of Santa Cruz Province, and the Early-Middle Pliocene (Montehermosan age) record of Chunga incerta Tonni 1974 from Buenos Aires Province, both in Argentina. Living seriemas comprise only two very closely related, and perhaps congeneric species, Cariama cristata (Linnaeus 1766) and Chunga burmeisteri (Hartlaub 1860), which are endemic of South America. The fossils herein described come from the locality Puesto Estancia La Costa (= Corriguen Aike), situated at the coast of Santa Cruz Province, between Coyle and Gallegos rivers, and were recovered from the middle levels of Estancia La Costa Member, Santa Cruz Formation. The remains include three unassociated specimens: a fragmentary basicranium and two distal fragments of tibiotarsi, one of them slightly larger and more robust than the other. The leg bones are nearly indistinguishable from the homologous elements in living seriemas. We refer them tentatively to Cariama and Chunga respectively, based on their size differences. Morphology of condyles as well as size and robustness rule out allocation to psilopterines, the group of phorusrhacids more closely related to seriemas. The cranium resembles that of living cariamids in overall morphology, but more detailed and broad comparisons are needed to arrive to a more accurate systematic hypothesis.