June 20, 2014
“Mosaic Pattern” Of Cranial Evolution Supported By Study Of Neanderthal Skulls In Spain
redOrbit Staff & Wire Reports – Your Universe Online
Analysis of several skulls found in a Spanish cave reveal that the trademark facial features of the Neanderthals appeared prior to their braincases, lending new support to the “mosaic pattern” theory that the long extinct human predecessors did not evolve their defining characteristics all at the same time.
The study, which appears in the journal Science, uses new data obtained from 17 fossilized human skulls obtained from the Sima de los Huesos (Pit of the Bones) site in the Atapuerca hill region of northern Spain. The skulls date back to the Middle Pleistocene and include seven new specimens that will help paleontologists better understand hominin evolution during this era.
Scientists working at the site identified both Neanderthal features and those associated with more primitive human predecessors in the bones, and the findings should help clear up some of the controversy surrounding hominin evolution during the Middle Pleistocene era, according to the researchers.
The skulls demonstrate that early Neanderthals “sported their telltale ‘beetle brows’ and heavy jaws about 430,000 years ago, long before they evolved Neanderthal features in their crania, including larger brains,” explained National Geographic‘s Dan Vergano.
“The discovery provides clues about when the common ancestor of modern humans and Neanderthals lived, what happened after the two groups diverged, and how the two became so different over a relatively short period of time,” added Jennifer Viegas of Discovery News. “There is consensus about the ending of the story: Modern humans and Neanderthals interbred, and Neanderthal DNA is still present in people of European and Asian ancestry.”
The thousands of years separating the beginning and end of that tale, however, have long been a mystery. In their research, though, Juan Luis Arsuaga of the Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos in Madrid and his colleagues were able to characterize the cranial morphology of humans living in Europe during the Middle Pleistocene for the first time.
“Based on this morphology, we think the Sima people were part of the Neanderthal clade, although not necessarily direct ancestors to the classic Neanderthals,” Arsuaga explained in a statement. They were part of an early European lineage that comprised Neanderthals, but this population was said to be more primitive than those living in the Pleistocene.
“Other fossils of the same geological period are different. They don´t fit the Sima pattern. This means there was a lot of diversity among different populations in the Middle Pleistocene,” he added. Specifically, the researchers reported that many of the Neanderthal-related features found in the Sima skulls were related to chewing, as Arsuaga explained that the “modifications had to do with an intensive use of the frontal teeth.”
The results of their analysis suggest that this facial modification marked the first step in the evolution of the Neanderthal, which lends critical support to previously difficult to substantiate model claiming that the features of these human predecessors evolved in stages.
To evaluate this notion, scientists have required an accurate portrait of European populations from roughly 400,000 years ago, but an isolated fossil record that has been dispersed widely across the continent has made this extremely challenging. One of the keys to this study is that the fossils used all came from the Sima site, meaning they all represent the same biological population and allow scientists to study variation at the individual level.
“While considerable differences in size are apparent within the collection, with some larger skulls and some smaller ones, the anatomical features that anthropologists study to examine evolutionary relationships do not vary much within the Sima population,” the Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humano said in a statement.
“This combination of mosaic evolution and anatomical homogeneity led the authors to favor a branching pattern of evolution, known as cladogenesis in evolutionary studies, in the European Middle Pleistocene,” the institute noted, adding that the fossils studied by Arsuaga and his colleagues are not specifically early Neanderthals, nor are they members of Homo heidelbergensis, as the mandibles do not match fossils representing this species.