La mano di Lucy La mano dell’Australopithecus afarensis, la specie a cui appartiene la nota Lucy, avrebbe presentato caratteristiche sia del gorilla, sia dell’uomo moderno. pikaia.eu/EasyNe2/Notizie/La_mano_di_Lucy.aspx La mano dell’Australopithecus afarensis, la specie a cui appartiene la nota Lucy, avrebbe presentato caratteristiche sia del gorilla, sia dell’uomo moderno. Questo è il risultato di una ricerca pubblicata su American Journal of Physical Anthropology (*) che si è posta di esaminare i resti fossili della mano appartenenti al ritrovamento A.L. 333 (Hadar, Etiopia, 1990-2007 **). Lo studio ha prima fornito la ricostruzione il più possibile plausibile dell’anatomia ossea della mano a partire dai reperti raccolti, di per sé incompleti o insufficienti. Conseguentemente, la conclusione della ricerca è relativa a una ipotesi pur sempre probabilistica ma affidabile. I risultati indicano che le proporzioni della mano di A. afarensis sarebbero differenti da quelle di scimpanzé (immagine) ed oranghi (immagine), ma si ricondurrebbero nella parte superiore a quelle dei gorilla (mano del gorilla) mentre nella parte inferiore a quelle umane. Infatti, rispetto allo scimpanzé e all’orango le dita si presentano più corte, come nel gorilla. Il pollice invece risulta in proporzione più lungo rispetto a tutti i primati citati, ricordando quello umano. Per quanto riguarda il metacarpo, le sue proporzioni presentano invece caratteristiche intermedie tra quelle umane e quelle del gorilla, formando un palmo più largo e più basso rispetto a quello di scimpanzé e orango. A livello funzionale questi risultati suggeriscono che nonostante la struttura anatomica complessiva avrebbe permesso una miglior precisione nella presa rispetto a scimpanzé ed oranghi, non sarebbe stata comunque sufficiente per consentire ad A. afarensis un’attività manifatturiera litica come nei suoi successori. Ernesto Pozzoni da Storie di Scienza Riferiementi (*) Reassessing manual proportions in Australopithecus afarensis American Journal of Physical Anthropology 17 sep 2013, DOI: 10.1002/ajpa.22365 onlinelibrary.wiley/doi/10.1002/ajpa.22365/abstract Abstract Previous analyses of hand morphology in Australopithecus afarensis have concluded that this taxon had modern human-like manual proportions, with relatively long thumbs and short fingers. These conclusions are based on the A.L.333 composite fossil assemblage from Hadar, Ethiopia, and are premised on the ability to assign phalanges to a single individual, and to the correct side and digit. Neither assignment is secure, however, given the taphonomy and sample composition at A.L.333. We use a resampling approach that includes the entire assemblage of complete hand elements at Hadar, and takes into account uncertainties in identifying phalanges by individual, side and digit number. This approach provides the most conservative estimates of manual proportions in Au. afarensis. We resampled hand long bone lengths in Au. afarensis and extant hominoids, and obtained confidence limits for distributions of manual proportions in the latter. Results confirm that intrinsic manual proportions in Au. afarensis are dissimilar to Pan and Pongo. However, manual proportions in Au. afarensis often fall at the upper end of the distribution in Gorilla, and very lower end in Homo, corresponding to disproportionately short thumbs and long medial digits in Homo. This suggests that manual proportions in Au. afarensis, particularly metacarpal proportions, were not as derived towards Homo as previously described, but rather are intermediate between gorillas and humans. Functionally, these results suggest Au. afarensis could not produce precision grips with the same efficiency as modern humans, which may in part account for the absence of lithic technology in this fossil taxon. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc. (**) New postcranial fossils of Australopithecus afarensis from Hadar, Ethiopia (1990–2007) Journal of Human Evolution Volume 63, Issue 1, July 2012, Pages 1–51 sciencedirect/science/article/pii/S0047248411002302 Abstract Renewed fieldwork at Hadar, Ethiopia, from 1990 to 2007, by a team based at the Institute of Human Origins, Arizona State University, resulted in the recovery of 49 new postcranial fossils attributed to Australopithecus afarensis. These fossils include elements from both the upper and lower limbs as well as the axial skeleton, and increase the sample size of previously known elements for A. afarensis. The expanded Hadar sample provides evidence of multiple new individuals that are intermediate in size between the smallest and largest individuals previously documented, and so support the hypothesis that a single dimorphic species is represented. Consideration of the functional anatomy of the new fossils supports the hypothesis that no functional or behavioral differences need to be invoked to explain the morphological variation between large and small A. afarensis individuals. Several specimens provide important new data about this species, including new vertebrae supporting the hypothesis that A. afarensis may have had a more human-like thoracic form than previously appreciated, with an invaginated thoracic vertebral column. A distal pollical phalanx confirms the presence of a human-like flexor pollicis longus muscle in A. afarensis. The new fossils include the first complete fourth metatarsal known for A. afarensis. This specimen exhibits the dorsoplantarly expanded base, axial torsion and domed head typical of humans, revealing the presence of human-like permanent longitudinal and transverse arches and extension of the metatarsophalangeal joints as in human-like heel-off during gait. The new Hadar postcranial fossils provide a more complete picture of postcranial functional anatomy, and individual and temporal variation within this sample. They provide the basis for further in-depth analyses of the behavioral and evolutionary significance of A. afarensis anatomy, and greater insight into the biology and evolution of these early hominins.
Posted on: Sun, 29 Sep 2013 13:13:35 +0000
Trending Topics
Recently Viewed Topics
© 2015