Mechanical Analysis of Feeding Behavior in the Extinct “Terror Bird” Andalgalornis steulleti (Gruiformes: Phorusrhacidae)

CONICET-División Paleontología Vertebrados, Facultad de Ciencias Naturales y Museo, Museo de La Plata, Universidad Nacional de La Plata, La Plata, Argentina.
PLoS ONE (Impact Factor: 3.23). 08/2010; 5(8):e11856. DOI: 10.1371/journal.pone.0011856
Source: PubMed


The South American phorusrhacid bird radiation comprised at least 18 species of small to gigantic terrestrial predators for which there are no close modern analogs. Here we perform functional analyses of the skull of the medium-sized (approximately 40 kg) patagornithine phorusrhacid Andalgalornis steulleti (upper Miocene-lower Pliocene, Andalgalá Formation, Catamarca, Argentina) to assess its mechanical performance in a comparative context. Based on computed tomographic (CT) scanning and morphological analysis, the skull of Andalgalornis steulleti is interpreted as showing features reflecting loss of intracranial immobility. Discrete anatomical attributes permitting such cranial kinesis are widespread phorusrhacids outgroups, but this is the first clear evidence of loss of cranial kinesis in a gruiform bird and may be among the best documented cases among all birds. This apomorphic loss is interpreted as an adaptation for enhanced craniofacial rigidity, particularly with regard to sagittal loading. We apply a Finite Element approach to a three-dimensional (3D) model of the skull. Based on regression analysis we estimate the bite force of Andalgalornis at the bill tip to be 133 N. Relative to results obtained from Finite Element Analysis of one of its closest living relatives (seriema) and a large predatory bird (eagle), the phorusrhacid's skull shows relatively high stress under lateral loadings, but low stress where force is applied dorsoventrally (sagittally) and in "pullback" simulations. Given the relative weakness of the skull mediolaterally, it seems unlikely that Andalgalornis engaged in potentially risky behaviors that involved subduing large, struggling prey with its beak. We suggest that it either consumed smaller prey that could be killed and consumed more safely (e.g., swallowed whole) or that it used multiple well-targeted sagittal strikes with the beak in a repetitive attack-and-retreat strategy.

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    • "Andalgalornis steulleti (Kraglievich 1931), from the upper Miocene–lower Pliocene (≈6 million years ago) of Argentina, was a medium-sized patagornithine phorusrhacid of about 40 kg body mass, 1.4 m height, and 370 mm total skull length [11], [12]. Together with the long legs, the atypical large skull with high and narrow beak is a characteristic feature of all phorusrhacids [13]. "
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    ABSTRACT: Andalgalornis steulleti from the upper Miocene-lower Pliocene (≈6 million years ago) of Argentina is a medium-sized patagornithine phorusrhacid. It was a member of the predominantly South American radiation of 'terror birds' (Phorusrhacidae) that were apex predators throughout much of the Cenozoic. A previous biomechanical study suggests that the skull would be prepared to make sudden movements in the sagittal plane to subdue prey. We analyze the flexion patterns of the neck of Andalgalornis based on the neck vertebrae morphology and biometrics. The transitional cervical vertebrae 5th and 9th clearly separate regions 1-2 and 2-3 respectively. Bifurcate neural spines are developed in the cervical vertebrae 7th to 12th suggesting the presence of a very intricate ligamentary system and of a very well developed epaxial musculature. The presence of the lig. elasticum interespinale is inferred. High neural spines of R3 suggest that this region concentrates the major stresses during downstrokes. The musculoskeletal system of Andalgalornis seems to be prepared (1) to support a particularly big head during normal stance, and (2) to help the neck (and the head) rising after the maximum ventroflexion during a strike. The study herein is the first interpretation of the potential performance of the neck of Andalgalornis in its entirety and we considered this an important starting point to understand and reconstruct the flexion pattern of other phorusrhacids from which the neck is unknown.
    PLoS ONE 05/2012; 7(5):e37701. DOI:10.1371/journal.pone.0037701 · 3.23 Impact Factor
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    • "Psilopterus lemoinei (and all the phorusrhacids), as we stated previously , lack both hinges. This suggests that cranial kinesis was lost secondarily in the history of the Phorushracidae (Degrange et al., 2010). "
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    ABSTRACT: Psilopterus lemoinei, the largest species in this genus, was a small terror bird weighing 8–9 kg, and was a ground bird with functionally tridactyl feet. New remains of this phorusrhacid, including an exceptionally preserved anterior part of a skull recovered from the Patagonian Killik Aike Norte locality (Santa Cruz Formation, late early Miocene), is now available for study. The main purpose of this paper is to provide a detailed morphological description of Psilopterus lemoinei. The new fossils show for the first time that the internal structure of the beak is hollow and reinforced with thin-walled trabeculae. The absence of zona flexoria palatina and zona flexoria arcus jugalis are key features related to the evolution of cranial akinesis. Homologies of the narial and fenestra antorbitalis boundaries have been clarified. Our re-examination allows the establishment of primary osteological homologies useful in comparative anatomy, functional morphology, and phylogenetic studies.
    Journal of Vertebrate Paleontology 09/2011; 31(5-5):1080-1092. DOI:10.1080/02724634.2011.595466 · 1.98 Impact Factor
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    • "In a broad sense, we may assume that the skulls of other large phorusrhacids, characterized by high and compressed beaks, would respond similarly to that of Andalgalornis (body mass, 40 kg). Phorusrhacids chased and killed their prey using their huge beaks as a hatchet (Degrange et al., 2010). "
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    ABSTRACT: Analysing the effect of climatic/environmental changes on bird communities during the South American Cenozoic is quite complicated. Taking into consideration the extremely complex evolution of such environmental conditions and the incomplete and episodic fossil bird record in this part of the continent, any generalization should be considered with caution. However, some aspects may be noted: (1) certain typically South American bird groups evolved in total isolation, i.e. terrestrial or poorly flying birds, incapable of crossing important water barriers (Rheiformes, Tinamiformes, Phorusrhacidae, Brontornithidae, Anhimidae); (2) other good flyers did not cross until immediately before the definitive connection between both Americas (Teratornithidae, Passeriformes Suboscines); (3) most of the families established important intercontinental relationships (Anhingidae, Pelecanidae, Ciconiidae, Anatidae, Presbyornithidae, Rallidae, Falconidae and Accipitridae); (4) several taxa that are presently important members of the rich South American bird fauna are unknown for certain geological time periods (Throchilidae); and (5) there is a high prevalence of carnivorous birds over all other trophic habits, regardless of the association or age analysed. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 458–474. Analizar el efecto que los cambios climáticos y ambientales tuvieron en las comunidades de aves durante el Cenozoico sudamericano es complicado y cualquier generalización debe tomarse con cautela. Sin embargo pueden señalarse algunos aspectos: (1) algunos grupos de aves típicamente sudamericanas evolucionaron en total aislamiento (Rheiformes, Tinamiformes, Phorusrhacidae, Brontornithidae, Anhimidae); (2) otros grupos buenos voladores no cruzaron a América del Norte hasta establecido el puente Panameño entre las dos Américas (Teratornithidae, Passeriformes Suboscines); (3) la mayoría de las familias establecieron importantes relaciones intercontinentales (Anhingidae, Pelecanidae, Ciconiidae, Anatidae, Presbyornithidae, Rallidae, Falconidae, Accipitridae); (4) importantes miembros de la avifauna sudamericana actual son desconocidos en el registro fósil (Throchilidae); (5) hay una prevalencia de aves carnívoras en todas las asociaciones cualquiera fuere su antigüedad.
    Biological Journal of the Linnean Society 05/2011; 103(2):458 - 474. DOI:10.1111/j.1095-8312.2011.01658.x · 2.26 Impact Factor
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