Mariana B. J. Picasso

Flexibility along the Neck of the Neogene Terror Bird Andalgalornis steulleti (Aves Phorusrhacidae)

Background 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. Methodology/Principal Findings 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. Conclusions/Significance 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.

Neurocranial and Brain Anatomy of a Late Miocene Eagle (Aves, Accipitridae) from Patagonia

ABSTRACT The neurocranial fragment from the Late Miocene (Huayquerian SALMA, 9,0 to 6,8 Ma) of Estancia La Pastosa new locality, Puerto Madryn Formation, Patagonia, Argentina, is described. This is the first available fossil skull of Accipitridae in South America. Features as the elongated-triangular shape of the cranial roof, vast separation between the processus postorbitalis and between both fossae temporalis, and narrow and acuminate outline of the fossa temporalis allow to assign the fossil to Accipitridae Vieilloit, 1816. The well-preserved cavum cranii allowed construction of an endocast that partially reflects brain anatomy. The latter is very similar to those of extant and fossil species of Accipitridae. This fossil eagle is the only predator recorded at this new Miocene locality thus far.

Hindlimb myology of the monk parakeet (Aves, Psittaciformes)

We studied the hindlimb myology of the monk parakeet (Myiopsitta monachus). Like all parrots, it has zygodactyl feet enabling perching, climbing, hanging, moving easily among trees, and handling food. Muscles were described and weighed, and physiological cross‐sectional area (PCSA) of four flexors and one extensor was calculated. In comparison to other muscles, the M. tibialis cranialis and the M. fibularis brevis show increased development and high PCSA values, and therefore, large potential force production. Also, a large proportion of muscle mass was involved in flexing the digits. We hypothesize that these muscle traits are associated with the arboreal locomotion and food manipulation habits. In the monk parakeet, the M. extensor digitorum longus sends a branch to the hallux, and the connection between the M. flexor digitorum longus and the M. flexor hallucis longus is type I (Gadows classification). We reaffirm the presence of the M. ambiens as a plesiomorphic condition that disappears in most members of the order. Among Psittaciformes, the M. fibularis brevis is stronger and the M. fibularis weaker in arboreal species than in basal terrestrial ones (e.g., Strigops). J. Morphol. 275:732–744, 2014.

Comparative brain morphology of Neotropical parrots (Aves, Psittaciformes) inferred from virtual 3D endocasts

Psittaciformes are a very diverse group of non‐passerine birds, with advanced cognitive abilities and highly developed locomotor and feeding behaviours. Using computed tomography and three‐dimensional (3D) visualization software, the endocasts of 14 extant Neotropical parrots were reconstructed, with the aim of analysing, comparing and exploring the morphology of the brain within the clade. A 3D geomorphometric analysis was performed, and the encephalization quotient (EQ) was calculated. Brain morphology character states were traced onto a Psittaciformes tree in order to facilitate interpretation of morphological traits in a phylogenetic context. Our results indicate that: (i) there are two conspicuously distinct brain morphologies, one considered walnut type (quadrangular and wider than long) and the other rounded (narrower and rostrally tapered); (ii) Psittaciformes possess a noticeable notch between hemisphaeria that divides the bulbus olfactorius; (iii) the plesiomorphic and most frequently observed characteristics of Neotropical parrots are a rostrally tapered telencephalon in dorsal view, distinctly enlarged dorsal expansion of the eminentia sagittalis and conspicuous fissura mediana; (iv) there is a positive correlation between body mass and brain volume; (v) psittacids are characterized by high EQ values that suggest high brain volumes in relation to their body masses; and (vi) the endocranial morphology of the Psittaciformes as a whole is distinctive relative to other birds. This new knowledge of brain morphology offers much potential for further insight in paleoneurological, phylogenetic and evolutionary studies.

Virtual Reconstructions of the Endocranial Cavity of Rhea americana (Aves, Palaeognathae): Postnatal Anatomical Changes

We examined the external anatomy of the endocast of the Greater Rhea (Rhea americana, Palaeognathae), during 3 main stages of its postnatal life, and compared it with information available on other palaeognathous birds. Series of scans with spiral computed tomographies were obtained from 3 skulls of different ages (chick, juvenile and adult) of R. americana; digital 3-dimensional reconstruction was performed and brain volumes were calculated from the models obtained. Qualitative assessment of the brain anatomy of R. americana indicates a conical and ventrally located bulbus olfactorius, laterally expanded hemispherium telencephali, well-developed eminentia sagittalis, and conspicuous cerebellum and tectum mesencephali. Anatomy of the chick brain was markedly different: less lateral expansion of the hemispherium telencephali, and lesser development of the eminentia sagittalis and auricula cerebelli. Little change between chicks and adults was observed in some brain regions such as the tectum mesencephali, while the eminentia sagittalis showed great increase in size. The large size of the eminentia sagittalis coupled with its increasing development during ontogeny could reflect its importance for visual processing functions and the way these improve during growth. Finally, the brain of R. americana is similar to that of Struthio and Dromaius, but differs from that of the Tinamidae and of Apteryx, allowing recognition of 3 distinct brain morphologies among the Palaeognathae.

The hindlimb myology of Milvago chimango (Polyborinae, Falconidae).

We describe the hindlimb myology of Milvago chimango. This member of the Falconidae: Polyborinae is a generalist and opportunist that can jump and run down prey on the ground, unlike Falconinae that hunt birds in flight and kill them by striking with its talons. Due to differences in the locomotion habits between the subfamilies, we hypothesized differences in their hindlimb myology. Gross dissections showed that the myology of M. chimango is concordant with that described of other falconids, except for the following differences: the m. flexor cruris medialis has one belly with a longitudinal division; the m. iliotibialis lateralis does not have a connection with the m. iliofibularis; the m. fibularis longus is strongly aponeurotic; the m. tibialis cranialis lacks an accessory tendons and the m. flexor hallucis longus has one place of origin, instead of two. The presence of the m. flexor cruris lateralis can be distinguished as it has been described absent for the Falconidae. We associated its presence with the predominant terrestrial habit of the M. chimango. Each muscle dissected was weighed and the relationship between flexors and extensors at each joint was assessed. The extensor muscles predominated in all joints in M. chimango. Among the flexors, the m. flexor hallucis longus was the heaviest, which could be related to the importance of the use of its talons to obtain food. J. Morphol. 274:1191–1201, 2013.

Geometric morphometrics of the skull of Tinamidae (Aves, Palaeognathae)

The Tinamidae comprise exclusively Neotropical palaegnathous birds, with homogeneous body morphology and no sexual dimorphism. The goal of this work was to explore the variation in skull morphology between taxa and its possible correspondence with features such as diet or gender using geometric morphometric tools. Eleven landmarks were analyzed in 53 skulls of 4 genera that inhabit grasslands: Nothoprocta, Eudromia, Nothura and Rhynchotus. Intrageneric and intergeneric variability was analyzed. The genera studied here can be distinguished based on the geometric shape of their skull, with prenarial region length and neurocranium shape as the most outstanding features. In the genus Eudromia, males and females could be differentiated, while in the genus Nothoprocta, the species differentiated according to their trophic habits. This study allows establishing that genera and, in some cases, the gender of the Tinamidae can be differentiated based on cranial shape.

Diversity of extinct Rheidae (Aves, Palaeognathae): historical controversies and the new taxonomic status of Rhea pampeana Moreno and Mercerat 1891 from the Pleistocene of Argentina

Abstract Rhea pampeana Moreno and Mercerat 1891 is an extinct species of Rheidae (Aves, Palaeognathae) from the Pleistocene of Buenos Aires province, Argentina. This taxon has been the subject of different and confusing changes of its taxonomic status, and an adequate description is still lacking. This study re-examines the materials assigned to Rhea pampeana with the objective to evaluate their status as a distinct fossil species. The poor preservation of the materials plus certain osteological features of the tibiotarsus and tarsometatarsus allowed to reassign these materials to the living species Rhea americana.

Ontogenetic Scaling of the Hindlimb Muscles of the Greater Rhea (Rhea americana)

The greater rhea (Rhea americana) is the largest South American bird. It is a cursorial, flightless species with long powerful legs and reduced forelimbs. The goal of this study was to explore how hindlimb muscles scale with body mass during postnatal growth and to analyze whether the specialized locomotion of this species affects the growth of muscle masses. The mass of 19 muscles and body mass were weighed in 21 specimens ranging from 1‐month‐old individuals to adults. Seventeen muscles scaled with positive allometry with respect to body mass, whereas two muscles scaled isometrically. The predominance of positive allometric growth in hindlimb muscles results in a limb with massive and powerful muscles specialized to support a large body mass and to attain relatively high running speeds. Analysis of muscle mass scaling is a simple and useful way to compare possible differences between locomotor styles, and it is valuable in studies that reconstruct the paleobiology of extinct taxa.

New insights about Hinasuri nehuensis (Aves, Rheidae, Palaeognathae) from the early Pliocene of Argentina

Picasso, M.B.J. & Mosto, M.C., February 2016. New insights about Hinasuri nehuensis (Aves, Palaeognathae) from the early Pliocene of Argentina. Alcheringa 40, xxx–xxx. ISSN 0311-5518. Hinasuri nehuensis Tambussi was a robust, extinct rheid bird from the early Pliocene of Buenos Aires province, Argentina. This paper revisits the femoral morphology of H. nehuensis and provides an updated osteological description together with new insights into its palaeobiology. Size estimates and a comparison of standardized measurements relative to Rhea americana demonstrate that H. nehuensis had an above-average body mass. The femoral dimensions of H. nehuensis were also proportionately greater than those of R. americana, but its reconstructed musculature is otherwise very similar. This suggests that H. nehuensis had powerful proximal muscles consistent with its enlarged size. This could have been an advantage for avoiding predators and to tolerate the seasonally harsh environments of the Pampean region during the Pliocene–Pleistocene. Mariana B.J. Picasso [mpicasso@fcnym.unlp.edu.ar] and María Clelia Mosto [cleliamosto@conicet.gob.ar] División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo Universidad Nacional de la Plata, Paseo del Bosque s/n, La Plata (1900), Buenos Aires, Argentina. CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas).