Diversity and paleobiology of the Santacrucian (late Early Miocene) birds

DEGRANGE, F.J.; NORIEGA, J.I.; ARETA, J.I.

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

The late Early Miocene vertebrate fauna of the Santa Cruz Formation (Patagonia) comprises one of the richest fossil assemblages known in the South American continent. This works presents the paleobiology and state of knowledge of the avian diversity recorded in Santacrucian beds, with an updated systematic summary of all taxa. Phorusrhacids outnumber seriemas, rheas, and basal falconiforms in diversity and abundance. More fragmentary occurrences are reported of pelecaniforms, anseriforms, gruiforms, and ciconiiforms. Body masses of fossil forms are inferred from the dimensions of their hindlimb bones, based on logarithmic equations previously modeled from living analogues. In some cases, body sizes of the extinct species are inferred from the relative sizes of other bones of similar extant species. Inferences about diet and foraging strategies are based on the size and shape of the limb elements and cranial elements, by analogy with extant birds. The predator niche is represented by falconids, four species of phorusrhacids and a seriemid. Phorusrhacids and seriemids probably lived in open areas because of their cursorial capabilities. However, birds such as the waterfowl, limpkins, spoonbills and darters indicate the presence of temporarily flooded savannas or permanent water bodies in forested areas. Habitat preferences of extant seriemas, rheas, tinamous, and the falconid Herpetotheres are consistent with Chacoan-like conditions, and they allow inferring by extrapolation similar Santacrucian paleoenvironments for their extinct analogues. Santacrucian scenarios were probably characterized by seasonality in temperature and rainfall and the presence of alternating areas of herbaceous vegetation with shrubby or wooded areas.