Científicos han descubierto en un lago de China, el esqueleto de primate más antiguo hasta la fecha, de una criatura que se asemeja a la línea evolutiva humana, los homínidos y una línea de simios diferente llamada tarsios.
Han bautizado el espécimen como Archicebus achilles, en alusión a hueso de su talón, que se parece al de los monos modernos.
Los homínidos incluyen a los humanos, los simios y los monos. Los tarsios son primates nocturnos que solamente viven hoy día en el sudeste asiático. El estudio se publicó en la revista Nature.
'Arroja luz sobre una fase importante de la evolución de los primates y los humanos de la que teníamos poca información hasta ahora', dijo K. Christopher Beard, paleontólogo del museo de historia natural Carnegie y uno de los autores del estudio.
Lo completo del especimen, así como su edad y posición en el árbol familiar de los primates lo hacen muy especial, dijo Erik Seiffert, profesor asociado de Stony Brook University, que no participó en la investigación.
'En mi opinión es uno de los descubrimientos más importantes en la historia de la paleoprimatología', agregó en un correo electrónico.
Aunque ya se han encontrado fragmentos de otros primates primitivos, este esqueleto, de unos 55 millones de años de antigüedad, es con diferencia el más completo de un primate de este periodo, según Beard.
El archicebus achilles representa un vínculo nunca visto entre los homínidos y los tarsos, de acuerdo con Beard, pero anticipa una controversia en torno a la posición de esta criatura en el árbol evolutivo.
Para su grupo de investigación, los rasgos del espécimen insinúan que es más cercano a los tarsios que a los homínidos, pero otros podrían llegar a conclusiones diferentes. De todas formas, agregó, parece claro que tiene relación con ambos grupos.
Esta criatura era diminuta, de tan solo 7 centímetros de largo y menos de 30 grams de peso.
Los científicos lo descubrieron en un antiguo lago en la provincia de Hubei, en China, en la zona de Jingzhou.
http://www.nature.com/news/oldest-primate-skeleton-unveiled-1.13142
Oldest primate skeleton unveiled
Near-complete remains of tiny creature support early origin for lineage that led to humans.
Sid Perkins
The near-complete fossil of a tiny creature unearthed in China in 2002 has bolstered the idea that the anthropoid group of primates — whose modern-day members include monkeys, apes and humans — had appeared by at least 55 million years ago. The fossil primate does not belong to that lineage, however: it is thought to be the earliest-discovered ancestor of small tree-dwelling primates called tarsiers, showing that even at this early time, the tarsier and anthropoid groups had split apart.
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XIJUN NI
The slender-limbed, long-tailed primate, described today in Nature1, was about the size of today’s pygmy mouse lemur and would have weighed between 20 and 30 grams, the researchers estimate. The mammal sports an odd blend of features, with its skull, teeth and limb bones having proportions resembling those of tarsiers, but its heel and foot bones more like anthropoids.
'This mosaic of features hasn’t been seen before in any living or fossil primate',' says study author Christopher Beard, a palaeontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.
By analysing almost 1,200 morphological aspects of the fossil and comparing them to those of 156 other extant and extinct mammals, the team put the ancient primate near the base of the tarsier family tree. Dubbed Archicebus achilles, the creature’s genus name roughly translates as 'original long-tailed monkey', whereas the species name is a wry nod to the creature’s anthropoid-like heel bone.
The number of anatomical characteristics scrutinized by Beard and his colleagues is much higher than is typically covered by a single study, largely thanks to high-resolution scans of the well-preserved fossil and the team’s detailed, decade-long analysis.
'This is really fantastic, impressive work', says Zhe-Xi Luo, a vertebrate palaeontologist at the University of Chicago in Illinois. 'Every detail that can be extracted from these fossils has been extracted'.
The primate's remains were recovered from a layer of shale formed from sediments deposited in a lake in what is now eastern China between 54.8 million and 55.8 million years ago, says paper co-author Xijun Ni, a palaeontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. Fragmentary fossils of primates had already been unearthed from around this era, says Beard, but those usually consisted of just teeth and bits of jawbones; the oldest well-preserved primate skeletons until the new find came from around 48 million years ago.
Because the fossil indicates that the tarsier and anthropoid primate groups split before that era, the anthropoid lineage is also at least that old, says Beard. He says that he and others had suggested a tarsier/anthropoid split of about this time previously, but based on thinner evidence.
Its long hindlimbs and grasping feet suggest that A. achilles lived in trees, with a tail thought to be at least twice its body length helping it to maintain balance as it leapt from branch to branch. The moderate size of the primate’s eye sockets hint that it was active in the day.
The size and shape of the primate's teeth — particularly the sharply pointed premolars, which were well adapted for shearing prey — strongly suggest that the tiny mammal fed mostly on insects. Such prey would have been abundant, because A. achilles evolved during an era when global temperatures were exceptionally high and jungles stretched as far north as the Arctic. 'It was a great time to be a primate', says Beard.
Because A. achilles sits near the base of the tarsier family tree, scientists say it probably resembles the yet-to-be-discovered creatures that lie at the base of most primate groups — including the anthropoid lineage that ultimately gave rise to humans. 'If you retrace primate evolution to its beginning, [A. achilles] is what our ancestors most likely looked like', says Luo.
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