Following the people and events that make up the research community at Duke

Author: Marie Claire Chelini

250,000-Year-Old Child Adds to the Mystery of Our Human Origins

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Based on the small size of Leti’s skull and on the combination of baby teeth and unerupted adult teeth, researchers estimate that the Homo naledi child would have been 4-6 years old.

Look at the palm of your hand and spread your fingers wide. Now imagine squeezing your body through a gap narrower than the distance between the tip of your thumb and the tip your pinkie finger. Let’s make this a bit worse: the gap is in complete darkness, its walls are rough stone, and all you have is a tiny headlamp. Ok, now that you are there, all you have to do is carefully find and recover dime-sized fragments of an invaluable treasure.

That’s how researchers recovered the first Homo naledi child’s skull ever to be found.

The finding was revealed this week in two papers published in the journal PaleoAnthropology by an international team of 21 researchers.

Homo naledi are possibly our most mysterious long-lost cousins. They are an ancient human relative that lived in what is now South Africa, approximately 350 to 250 thousand years ago. They were first discovered in the Rising Star Cave system in 2013, in a research expedition led by Lee Berger, Professor and chair of Palaeo-Anthropology and Director of the Centre for Exploration of the Deep Human Journey at the University of Witwatersand.

The research team, which includes Steven Churchill, professor of evolutionary anthropology at Duke, named the child Leti (pronounced Let-e), after the Setswana word “letimela” meaning “the lost one”.

Leti was found in one of the previously unexplored narrow fissures that radiate from Rising Star’s known chambers. His resting site was a 15 cm wide and 80 cm long gap where only the smallest (and bravest) of explorers could fit.

Explorer Becca Peixoto wedges herself between cave rock walls to get to Leti’s skull.

Marina Elliot, lead author of the first paper and one of the explorers to first discover Homo naledi, said in a press conference that excavating Leti’s remains required explorers to wedge themselves practically upside down between two rock walls.

Finding yet another fossil in a prolific site may not seem groundbreaking, but finding a child’s skull is a major achievement. First of all, children’s bones are thin and fragile, and rarely withstand the test of time.

Second, finding a child’s skull gives researchers a precious glimpse into the development of Homo naledi.

“A child’s skull allows us to study how Homo naledi grew and developed, and how their growth rate and schedule compares to other hominid species, and to our own,” Churchill said.

In addition to skull fragments, researchers also recovered two worn baby teeth and four unworn adult teeth that were yet to erupt. These findings show that Leti would have been between four and six years old at the time of her or his death.

Based on similarities between the soil of the fissure where Leti was found and the better-known areas of the cave, Tebogo Makhubela, senior lecturer of Geology at the University of Johannesburg and author of the papers, estimated that Leti has been hidden in Rising Star for over 250,000years.

The discovery of Leti’s skull also deepens the mystery of how Homo naledi’s remains ended up in such a deep, dark, and treacherous cave.

Berger’s team had previously hypothesized that the first 15 Homo naledi individuals found in Rising Star had been disposed there by their own species, as a burial. This hypothesis created an uproar: could a small-brained hominin from over 300,000years ago bury their dead, just like we do?

Leti’s skull was found on a small shelf at the back of the cave’s fissure. No other bones were found, suggesting that Leti’s head may have been deliberately placed there. Leti, as well as all other Homo naledi fossils ever found, showed no evidence of being dragged by predators, carried by water, or tumbled around in any other way.

“Those were social individuals. Seeing one of their own being picked apart by animals could have been very distressing,” Churchill said. “Purposeful disposal of their bodies still seems like the most likely explanation.”

Berger is undeterred by nay-sayers. “This is science,” Berger said at a press conference. “We will continue testing and challenging our hypotheses with every piece of data that we get.”

The researchers hope that other teams around the world will study Leti and other Homo naledi fossils. To that end, Leti’s skull was CT-scanned, and its scans can be downloaded from Morphosource, an open access repository of museum specimens’ 3D scans hosted at Duke University.

Leti will probably not be the last treasure to come out of Rising Star’s spider web of narrow passages.

“I can’t wait to go back to South Africa and see what else is waiting for us in that cave,” said Juliet Brophy, Professor of Geography and Anthropology at Louisiana State University and lead author of the paper describing Leti’s skull.

“This finding makes us remember that exploration is always worth doing,” said Elliot, who is a researcher at Simon Fraser University and Witwatersand University. “There is a lot still out there to be found”.

The Rising Star cave system is known for being extremely dangerous to explore.

Elliot et al. was funded by the National Geographic Society, the Lyda Hill Foundation, the South African National Research Foundation, and the Gauteng Provincial Government, for funding the discovery, recovery and ongoing analyses of the material. Additional support was provided by ARC (DP140104282).

Brophy et al. was funded by the National Geographic Society, the Lyda Hill Foundation, the South African National Research Foundation, the South African Centre for Excellence in Palaeosciences, The University of the Witwatersrand, the Vilas Trust, the Fulbright Scholar Program, Louisiana State University, North Carolina State University, the Texas A&M University College of Liberal Arts Seed Grant program and the Texas A&M College of Liberal Arts Cornerstone Faculty Fellowship.

Citations:

“Expanded Explorations of the Dinaledi Subsystem, Rising Star Cave System, South Africa.” Marina C. Elliot,Tebogo V. Makhubela, Juliet K. Brophy, Steven E. Churchill, Becca Peixoto, Elen M. Feuerriegel, Hannah Morris, Rick Hunter, Steven Tucker, Dirk Van Rooyen, Maropeng Ramalepa, Mathabela Tsikoane,Ashley Kruger, Carl Spander, Jan Kramers, Eric Roberts, Paul H.G.M. Dirks,John Hawks,Lee R. Berger. PaleoAnthropology, November 2021. DOI: https://doi.org/10.48738/2021.iss1.68.

“Immature Hominin Craniodental Remains From a New Localityin the Rising Star Cave System, South Africa.” Juliet K. Brophy, Marina C. Elliot, Darryl J. De Ruiter, Debra R. Bolter, Steven E. Churchill, Christopher S. Walker, John Hawks, Lee Berger. PaleoAnthropology, November 2021, DOI: https://doi.org/10.48738/2021.iss1.64.

By Marie-Claire Chelini
By Marie-Claire Chelini

Two Ways to Weird: How Whale Noses Moved to the Top of Their Head

A blue whale skeleton suspended in London’s Natural History Museum

Odd skulls are nothing new to V. Louise Roth, a professor in the Department of Biology. Much of her research centers on how animals’ shapes and sizes evolve and develop, so weirdly shaped bones are at the core of her work. But when Ph.D. student Rachel Roston drew her attention to the peculiarities of whale skulls, even Roth was astounded.

“There are some pretty weird mammal skulls out there,” Roth said. “I have studied morphological development in elephants, which are also kind of a crazy choice, but in terms of which bone goes where I think cetaceans are the weirdest ones.”

Cetaceans are the group that includes baleen whales – such as humpback whales – and toothed whales – such as dolphins and killer whales. Unlike almost all other vertebrate animals, cetaceans don’t breathe out of their mouths or from a nose placed in front of their face, but from a blowhole located on top of their head.

How did it get up there?

Rachel Roston, a graduate student in the Duke Biology department, recently published a paper with Professor Louise Roth, about some of the ways dolphin, whale and porpoise skulls break the rules of anatomy.

A new study published in the Journal of Anatomy by Roth and Roston, now a postdoctoral researcher at the University of Washington, reveals how whale and dolphin skulls undergo a complete transformation through their embryonic and fetal development, resulting in a re-orientation of their nasal passages.

What’s more, there’s not just one way to do it: baleen whales and toothed whales move their nostrils to the tops of their heads in two very different ways.

“It’s not just that they are developing the same thing in different ways,” said Roston, who led this work as part of her Ph.D. in Biology at Duke. “Looking from the outside of the body all you see is that both of them have their nose on the top of their head, but when you look inside their skulls, they are actually totally different blowholes.”

A toothed whale clears its blowhole. Photo by Friedrich Frühling

To figure out which bone went where and in which way, Roston looked at CT scans of baleen and toothed whales’ embryos in different stages of development and drew a dotted timeline of anatomical changes through the animals’ development.

Early-stage embryos look very much alike in most vertebrate animals: small, with a disproportionally large head, big eyes and oral and nasal cavities in the front of their face. As the embryos develop, they take different paths and become more and more similar to their own species.

Most of them keep their noses and their mouths in front of their face, but dolphins and whales transform their whole heads to change the direction of their nasal passage while keeping the snout facing forward.

“We think of the nostrils as something you find at the tip of the snout,” Roth said. “But whales go through some key changes in bone orientation that decouple one from the other.”

“It’s like looking at a cubist Picasso painting,” Roston said. “The eyes, nose and mouth are all there, but their relationships to each other are completely distorted.”

Whale embryos at different developmental stages. The white arrow shows how the nasal cavity shifts position through embryonic development.

This internal shuffling requires that the parts forming the roof of the embryo’s mouth move away from those that form its nasal passage. Initially parallel in small young embryos, they end up at an angle of about 45 degrees in baleen whales. In toothed whales this final angle is even wider, closer to 90 degrees.

In baleen whales, a key rotation happens at the back of the skull, where it meets the spine. Rather than being perpendicular to the ground, as in the head of a dog, the back of the skull is tilted forward towards the snout.

In toothed whales, the point of inflexion for this rotation is in the middle of the head. A bone in the center of the skull changes shape, curving upwards as the nasal passage ends facing up.

Roston and Roth both say that museum collections and non-destructive scanning techniques, such as CT scans, were key for this project because whale embryo specimens are difficult to come by. When a gravid female dies, small embryos often go unnoticed in their mother’s massive carcass. But older fetuses are larger than your typical sedan, making them difficult to preserve intact and store in museums. The few specimens found in museums must therefore be studied with the proverbial velvet gloves, or, in this case, CT scans.

“In science you always question ‘how come no one’s done this before?’” Roston said. “Here, it was because specimens are precious, so you don’t want to cut them up and destroy them.”

“Sometimes we’re looking at museum specimens that are 100 years old. This was an opportunity to describe them in a way that I hope will still be useful 100 years from now.”

Read more about weird whale skulls.

The research was funded by Duke University. Roston has also been supported by the National Institutes of Health.

CITATION: “Different Transformations Underlie Blowhole and Nasal Passage Development in a Toothed Whale (Odontoceti: Stenella attenuata) and a Baleen Whale (Mysticeti: Balaenoptera physalus),” Rachel A. RostonV. Louise Roth, Journal of Anatomy. DOI: 10.1111/joa.13492

Post by Marie Claire Chelini PhD, Duke Biology

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