Newly Discovered Fossil Shows Evolutionary Changes in Extinct Human Species

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The discovery of a very well-preserved fossil of extinct human species Paranthropus robustus shows that local climate change caused rapid evolution over a mixed period, resulting in anatomical changes related to sex. Credit: Picture courtesy Jesse Martin and David Strait

The fossil skull shows that environmental conditions are causing rapid changes.

Men of the extinct human species Paranthropus robustus was thought to be much larger than females – as were the differences in size seen in modern primates such as gorillas, orangutans and baboons. But instead, a new fossil discovery in South Africa shows this P. robustus About 2 million years ago, during a period of mixed local climate change, it developed rapidly and resulted in previously sex-related anatomical changes.

An international research team, including anthropologists at the University of Washington in St. Louis, said they had discovered the fossil-rich Drimolen cave system northwest of Johannesburg. Natural Ecology and Evolution today (November 9, 2020).

David's Throat

David’s Throat. Credit: WUSTL

“This is a type of phenomenon that is difficult to record in fossil records, especially in relation to early human evolution,” said David Strait, a professor of biological anthropology at the University of Washington in the arts and sciences.

The very well-preserved fossil described in the article was found by Samantha Good, a student at the Drimolen Cave Field School run by the Bosphorus.

Researchers already knew he had an appearance P. robustus It almost coincided with the disappearance of South Africa Australopithecus, a slightly more primitive early man and the emergence of early representatives in the region Homo, the breed to which modern humans belong. This transition took place very rapidly, perhaps in just a few tens of thousands of years.

“The hypothesis was that climate change was stressing the population,” he said Australopithecus eventually led to their destruction, but the environmental conditions were more favorable Homo and Parantrop, who can be scattered in the region from other places, “he said. “We have already seen that the environmental conditions are very difficult Parantrop but also that they need adaptations to survive. ”

Drimolen Site and Swartkrans

Drimolen territory and Swartkrans in South Africa. Credit: Map courtesy Andy Herries

The new sample, identified as DNH 155 in Drimolen, is clearly male, but differs from the others in its important features. P. robustus previously found near Swartkrans, where most fossils of this species are found.

It may be difficult to see the evolution within a species in fossil records. The changes may be subtle and the fossil record is unknown.

In general, fossil records provide larger-scale patterns, such as when species or groups of species appear or disappear in a fossil record. Thus, the discovery of Drimolen provides a rare window for early human evolution.

The new specimen is larger than a well-studied member of a species previously known in Drimolen, known as DNH 7, and is believed to be female, but smaller in size than the likely male of Swartkrans.

Jesse Martin

Jesse Martin. Credit: WUSTL

Jesse Martin, a doctoral student at La Trobe University, said: “Now the difference between the two areas cannot be explained simply as a difference between men and women, but rather differences in population levels between the sites.” is the first author of the work. “Our latest work shows that Drimole was about 200,000 years before Swartkrans, so we believed P. robustus developed over time, Drimolen represented an early population and a later, more anatomically extracted population of Swartkrans. ”

Martin said he could use the fossil record to “help reconstruct the evolutionary relationships between species, and that this example could provide all sorts of insights into the processes that shaped the evolution of certain groups.” “It simply came to our notice then P. robustuswe can see separate examples of species drawn from the same geographical region, but showing subtle anatomical differences at slightly different times, and this corresponds to a change within a species. ”

Drimolen Field School Students

Drimolen field school students filter the sediment and look for the remains of small mammals. Credit: David’s Strait

“It’s very important to be able to document evolutionary change within a lineage,” said Angeline Leece of La Trobe University, another early author of the study. “This allows us to ask very focused questions about evolutionary processes. For example, we now know that tooth sizes change over time in species, and this raises the question of why. There is reason to believe that environmental change is putting these populations under dietary stress and pointing to future research that will allow us to test this possibility. ”

Andy Herries of La Trobe University, co-author of the Drimolen project, said, “Like all living things on earth, our ancestors adapted and evolved in accordance with the surrounding landscape and environment. For the first time in South Africa, we have a meeting decision and morphological evidence that allows us to see such changes in the descendants of an ancient hominid through a short time window. ”

Evidence of rapid but significant climate change in South Africa during this period comes from a variety of sources. Critically, the fossils show that some mammals associated with forest or bushland environments have become extinct or less common – other species associated with drier, more open environments have first appeared locally.

P. robustus Skull

P. robustus skull. Credit: WUSTL

P. robustus It is noteworthy that the skull, jaw and teeth have a number of characteristics that indicate that a diet consisting of very hard or very hard foods is adapted to eating, ”said Strait. “We think that these adaptations have allowed us to live with foods that are mechanically difficult to change due to the colder and drier environment, which has led to changes in the local vegetation.”

“However, samples from Drimolen show skeletal features that show that the masticatory muscles are positioned so that they do not bite or chew as hard as they used to. P. robustus People from Swartkrans, ”he said. “For 200,000 years, a dry climate has probably led to natural selection, which favored the evolution of a more efficient and powerful feeding apparatus in species.”

Leece said it was noteworthy P. robustus appeared approximately at the same time as our ancestor Permanent man, as documented by a baby H. erectus cranium discovered by the group in 2015 at the same Drimolen site.

“These two are completely different species, H. erectus with relatively large brains and small teeth and P. robustus with relatively large teeth and small brains, they represent different evolutionary experiences. ” “Even though we are the winning family in the end, the fossil record shows that P. robustus more common compared to H. erectus about a landscape two million years ago. ”

Drimolen Area Site

The sun rises in the Drimolen region of South Africa. Credit: David’s Strait

More broadly, researchers believe that this discovery served as a warning for the identification of species in fossil records.

Numerous fossil human species have been discovered in the last quarter of a century, and many of these new species are based on a small number of fossils in only one or a few areas over a small geographical area and over a narrow period of time.

“We think paleoanthropology needs to be a little more critical to interpret changes in anatomy as evidence of the existence of many species,” Strait said. “Depending on the age of the fossil specimens, differences in bone anatomy may represent changes in lineage rather than evidence for multiple species.”

Drimolen Field Research Group

Members of a research team in the Drimolen area of ​​South Africa. Credit: David’s Strait

Project co-director Stephanie Baker University of Johannesburg He added, “Drimolen is rapidly becoming a hotspot for early hominin discoveries, and this is proof that the existing team as a whole remains committed to excavation and post-field analysis. DNH 155 cranium is one of the best protected P. robustus examples known to science. This is an example of what careful, large-scale research can tell us about our distant ancestors. ”

Reference: “Drimolen cranium DNH 155 documents microevolution in early hominid species” Jesse M. Martin, AB Leece, Simon Neubauer, Stephanie E. Baker, Carrie S. Mongle, Giovanni Boschian, Gary T. Schwartz, Amanda L. Smith, Justin A. Ledogar, David S. Strait and Andy IR Herries, November 9, 2020, Natural Ecology and Evolution.
DOI: 10.1038 / s41559-020-01319-6

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