The hind limb morphometry of terror birds (Aves, Cariamiformes, Phorusrhacidae): their functional implications for substrate preferences and locomotor lifestyle

DEGRANGE, F.J.

EARTH AND ENVIRONMENTAL SCIENCE TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH

ROYAL SOC EDINBURGH

Lugar: Edinburgo; Año: 2017 vol. 106 p. 257 - 276

1755-6910

The hind limbs of birds have long been considered a key feature in the conquest of different environments. However, the high level of morphological diversity encountered complicates the foundation of a good theoretical correlation between morphology, locomotor habits and substrate preference, and this in turn complicates paleobiological interpretations. Phorusrhacids (Aves, Cariamiformes) are a good example, since they have been unequivocally categorized as terrestrial birds due to their reduced forelimbs, and as apex predators with the ability to pursue prey based only on their hind limb morphology. Multivariate techniques (PCA and discriminant analysis) based on traditional metrics and geomorphometrics of the hind limb and pelvis were applied in order to explore terrestriality and cursoriality in phorusrhacids. Although several groups of birds could be identified, some phorusrhacids appear to be associated with walking birds while others with cursorial birds, when looking solely at hind limb metrics. However, the pelvis separates cursorial birds and phorusrhacids from walking and wading birds. This scenario is complicated further by a lack of clear definitions of the different locomotor modes and substrate preferences in extant birds, and this makes it difficult to confirm phorusrhacid cursoriality based solely on morphometrics. However, some qualitative features of the pelvis and foot make the panorama a little clearer. To study limb adaptations in fossil birds, a more holistic study of the whole posterior locomotor module is necessary, with emphasis on qualitative features, since morphometrics leaves some issues unresolved. A comparison with the wings is also needed in order to make a more complete analysis of locomotor behavior.