Tag Archives: tooth

Fossil Friday: this meat-eating dino could grow a fresh tooth in 60 days

One meat-eating dinosaur from today’s Madagascar replaced all its teeth once every few months, according to a new study.

CT scan-generated models of the jaws of Majungasaurus (left), Ceratosaurus (center), and Allosaurus (right), with microscopic views of the interior of their teeth below.
Image credits Michael D’Emic et al., 2019, PLOS One.

Majungasaurus, a species of dinosaur that went extinct around 70 million years ago, could replace a tooth in around 56 days, reports a new paper. This rate of growth is similar to that of herbivorous dinosaurs — whose teeth see a lot of heavy use — but very quick for a meat-eater.

A gnashing of teeth

“This meant [Majungasaurs] were wearing down on their teeth quickly, possibly because they were gnawing on bones,” says paper lead-author Michael D. D’Emic, an assistant professor of biology at Adelphi University.

“There is independent evidence for this in the form of scratches and gouges that match the spacing and size of their teeth on a variety of bones—bones from animals that would have been their prey.”

D’Emic worked with Patrick O’Connor, professor of anatomy at Ohio University, to examine a collection of isolated fossil teeth for microscopic structures known as growth lines. These are fairly similar to tree rings but form on a daily basis rather than once a year.

At the same time, they used computerized tomography (CT) on fossil Majungasaurus jaws to see how unerupted teeth grew inside of the bone. Taken together, the two sets of data allowed the team to estimate the rate of tooth replacement. Several jaws were used for this step and the results cross-checked between them to avoid errors.

The team further looked at two related theropods, Allosaurus and Ceratosaurus, and performed the same analysis.

Majungasaurus definitely took the cake, with a tooth growth rate of roughly 56, 104, and 107 days per tooth, respectively. Judging from other animals that have elevated rates of tooth replacement today, such as rodents, the team believes this is evidence of Majungasaurus gnawing on bones. Such behavior is meant to secure access to certain nutrients that may otherwise be scarce or hard to acquire, the team notes, but also requires exceptionally strong teeth — which Majungasaurus didn’t have. Its softer teeth would get worn out very fast if used in such a way, they write, which would explain why it needed to regrow them so often, and so fast.

“That’s our working hypothesis for why they had such elevated rates of replacement,” D’Emic said.

For comparison, the team explains that Tyrannosaurus rex likely evolved “exceedingly robust teeth and slow replacement rates”

The paper “Evolution of high tooth replacement rates in theropod dinosaurs” has been published in the journal PLOS ONE.

Tooth.

Fossil Friday: tiny tooth belonged to the smallest monkey ever found

An 18-million-year-old fossil tooth points towards a tiny primate no heavier than a hamster.

Tooth.

Scan of the fossil tooth.
Image credits Richard F. Kay et al., (2019), JoHE.

The lonesome tooth was found in Peru’s Amazon jungle by a team of Peruvian and American scientists from an exposed river bank along the Río Alto Madre de Dios. A single upper molar, the specimen was just “double the size of the head of a pin” and “could fall through a window screen,” said first author Richard Kay, a professor of evolutionary anthropology at Duke University.

Tiniest monkey

“Primate fossils are as rare as hen’s teeth,” said Kay, who has been doing paleontological research in South America for nearly four decades.

The team found the tooth after sorting through roughly 2,000 pounds of sandstone and gravel collected along the Río Alto Madre de Dios. They report finding hundreds of fossils of rodents, bats, and other animals — but a single monkey tooth. Luckily, it was a molar.

Paleontologists can tell a lot from primate teeth, but molars are particularly telling. Judging from its shape and size, the authors estimate that the animal likely had a diet heavy on fruits and insects, and weighed under half a pound. Some of the larger monkeys in South America today can grow to over 50 times that weight. The team dubbed the animal Parvimico materdei, or “tiny monkey from the Mother of God River.”

“It’s by far the smallest fossil monkey that’s ever been found worldwide,” Kay said.

 

But, its diminutive size isn’t the only thing that sets this tooth apart. It’s also one of the precious few clues scientists have from a missing chapter in monkey evolution. Primates are believed to have arrived in South America some 40 million years ago from Africa, and quickly diversifying into the 150-plus New World species we know today. The details of how that process unfolded is a bit of a mystery, however, in large part due to a gap in the fossil record (for primates in the area) between 13 and 31 million years ago. Parvimico lies comfortably in that gap.

The new fossil is aged between 17 to 19 million years, “smack dab in the time and place when we would have expected diversification to have occurred in the New World monkeys,” Kay said.

The tooth is now housed in the permanent collections of the Institute of Paleontology at Peru’s National University of Piura. The team is currently on another fossil collecting expedition in the Peruvian Amazon until August, concentrating their efforts in remote river sites with 30-million-year-old sediments. They hope to find more primate fossils.

The paper “Parvimico materdei gen. et sp. nov.: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru” has been published in the Journal of Human Evolution.

Scientists activate tooth regeneration in mice

Credit: Pixabay.

Humans have two sets of teeth, the second of which is meant to replace our temporary deciduous teeth or “baby teeth.” Other animals, such as reptiles or fish, can regenerate teeth indefinitely during their lifetime. Mice, however, are born with a single set of teeth.

Looking to understand the evolutionary drivers between different tooth replacement strategies, researchers at the King’s College London studied dental development in mice. They identified a molecular signaling pathway in the rodents’ dental lamina, the area that forms the teeth, and using genetic techniques managed to regenerate a new set of teeth.

The researchers, led by Professor Abigail Tucker, first compared gene expression in the dental lamina of the mouse and the minipig, which has two sets of teeth. 

The research team found that Wnt signaling, which is normally required for tooth replacement in other vertebrates, is missing in a rudimentary form of the dental lamina (RSDL) in mice.

Using genetic techniques, the researchers activated this signaling pathway in the mouse RSDL, revitalizing the structure and ultimately leading to the formation of new teeth.

The study shows that RSDL may be a source of replacement teeth in mice and provides an experimental framework for studying the mechanisms behind replacement.

“Why the potential for tooth replacement varies so much across vertebrates is an intriguing question”, explains PhD student Elena Popa. “Our results show that, although the mouse normally does not form a second replacement set of teeth, it still has the potential to do so given the right signals.”

The authors also reported that culturing RSDL in isolation resulted in tooth formation, suggesting that the previous set of teeth also influences the development of the next.

Professor Tucker explains: “This is relevant to human tooth replacement, as structures similar to the RSDL have been identified next to the permanent teeth during development. In normal development of our teeth, therefore, the second set or permanent tooth may inhibit the generation of a third set of teeth.”

The findings appeared in the journal Development

The first hominids might have evolved in Europe, fossil jaw suggests

A new paper examines whether Europe and not Africa was the cradle of hominids some 7 million years ago.

Greece Jaw.

This jaw and teeth were found in Greece and belonged to what might have been the oldest hominid.
Image credits W. Gerber / University or Tübingen.

The teeth of a chimp-sized primate known as Graecopithecus, which lived in southeastern Europe some 7 million years ago, suggests that the species is actually an early hominid and not an ape as we previously believed, a team led by geoscientist Jochen Fuss of the University of Tübingen, Germany, reports. They cite partial fusion of the second premolar root as a particular similarity between Graecopithecus and early hominids.

What makes a man

Graecopithecus could be the first hominid to pop up, the researchers write. One lower jaw, found in Athens with most teeth still in their sockets, was dated to about 7,175 million years ago, and a single upper second premolar found in Bulgaria, to approximately 7.24 million years ago. Still, with only these bits on hand, it’s hard to make an airtight case for Graecopithecus as a hominid. Although the dates match, it’s still a mystery if this creature walked upright — a hallmark of hominids.

So it’s still unclear whether Graecopithecus was an ape with hominid-like features or a hominid with some apelike characteristics. At the same time, however, the team notes that fossil evidence of humanoids in Africa around this time is also pretty sketchy, in some cases even controversial, and revolves around two hominid lines dating to between about 7 million and 6 million years ago, Sahelanthropus and Orrorin.

“Europe is as likely a place of [hominid] origins, and even of the last common ancestor of chimpanzees and humans, as Africa,” says University of Toronto paleoanthropologist and study co-author David Begun.

The team used a CT scanning device to view Graecopithecus’s teeth in full 3D, including the roots hidden by jawbone. Using this model to compare to other early hominids, they discovered the partial fusion of the second premolar root as a striking similarity. Previous research has found that the number of these roots is tightly controlled genetically and doesn’t change due to environmental factors — so the root fusion in Graecopithecus, similar to those seen in later hominids, would suggest a direct evolutionary link.

Model Teeth.

Image credits Jochen Fuss et al, PLOS ONE (2017).

The findings are not without their own criticisms. First of all, some say that the number of premolar roots varies enough even among early hominids to make the fused roots a less conclusive piece of evidence. But, when working with so few fossils from so long ago, it’s hard to prove anything conclusively — for example, the team which discovered one East African hominid, Ardipithecus kadabba, later argued that Sahelanthropus and Orrorin aren’t distinct lineages but can be folded into Ar. kadabba — and that’s not an isolated case.

A lack of hominid precursor (our chimp and gorilla ancestors) fossil, in particular, makes it difficult to establish if creatures such as Graecopithecus or Ar. kadabba are truly hominids since there’s nothing to compare them against. Finally, there was quite a bit of back-and-fro going on between Africa and Europe’s eastern Mediterranean region between 9 million and 7 million years ago, with apes, giraffes, antelopes, hippos, and a host of other critters living and transiting through the region or between the continents, Begun adds, making it hard to pinpoint where everyone came from. So Graecopithecus could have evolved in either Europe or Africa.

But if evidence mounts that Graecopithecus was a hominid and evolved in Europe, the out of Africa theory could find itself into even rougher waters.

The full paper “Potential hominin affinities of Graecopithecus from the Late Miocene of Europe” has been published in the journal PLOS One.

Amateur archaeologists find 560,000 year old human tooth

A half a million year old human tooth was discovered in France in a place called Tautavel, one of Europe’s most important prehistoric caves. Anthropologists hailed the discovery as an extremely important one, with chief researcher Tony Chevalier calling it a “major discovery”.

Volunteer archaeologists Camille and Valentin pose for the cameras in the Arago cave. Camille, 16, found the adult tooth, which dates back 565,000 years

Volunteer Camille, 16, was working with an archaeology student when they found the tooth. They are among the hundreds of archaeology trainees or volunteers come to dig out the Tautavel cave, searching for evidence of early human inhabitants.

Older human fossils are known in Europe (dating back to 1.2 million years ago), but this one bridges a gap in the fossil evidence in the Lower Paleolithic. Thousands of other finds were made in the same site, including tools and bones from animals, especially horses, reindeers and buffalos.

“We believe these men have lived for a long time in the cave or have regularly come back into it,” Chevalier said. “We also know that the area was quite cold at the time. It was a steppe, with no trees. There had to be some long periods with snow.”

The owner of the tooth – a very worn lower incisor – lived during a much colder climate than today’s; he and his people hunted horses, bisons and reindeer, and used tools. They took cover in caves.

“A large adult tooth – we can’t say if it was from a male or female – was found during excavations of soil we know to be between 550,000 and 580,000 years old, because we used different dating methods,” paleoanthropologist Amelie Viallet told the AFP news agency. “This is a major discovery because we have very few human fossils from this period in Europe,” she said.

Barium levels in fossil teeth show change in breast feeding behavior in Neanderthals and early humans

Just yesterday we were telling you about a change in diet 3.5 million years ago, modifying the way our hominid ancestors evolved and, in turn, how we evolved. Now, we’re moving a little closer to the present day – researchers calculating the barium levels in fossil teeth claim that they’ve found a difference in the way humans and Neanderthals were breastfeeding their babies.

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Image by Ian Harrowell, Christine Austin, and Manish Arora
Molar tooth model with the cut face showing color-coded barium patterns merging with a microscopic map of growth lines, which have been accentuated to reflect their ringlike nature.

Tanya Smith, an associate professor of human evolutionary biology, and Katie Hinde, an assistant professor of human evolutionary biology, worked with colleagues at the Icahn School of Medicine at Mount Sinai in New York and Westmead Hospital in Australia found a correlation between barium levels in teeth and an increase in breastfeeding, confirming what many anthropologists already suspected. As they explain, barium levels can survive unhampered for thousands of years, meaning the test can show breast-feeding changes among both early humans and Neanderthals.

“There’s an ongoing debate about whether Neanderthal and contemporary Homo sapiens would have practiced different behaviors in terms of their breast-feeding,” Smith said. “People have speculated that an early weaning process in modern humans may have been part of their evolutionary advantage. We don’t have the data to answer that question yet, but we now have the method to be able to start collecting that data. It’s clear that there are developmental differences between Neanderthals and modern humans — we’ve amassed good evidence for that in the fossil record,” she continued. “What we haven’t been able to do is make a direct comparison using a biomarker like first reproduction age, or life span, or weaning age. That’s why this is so exciting, because now we can get at one of these ‘life history’ variables directly.”

But that’s not all they did – they calculated weaning age, taking advantage of the unique way in which teeth grow. Pretty much like trees, teeth grow in concentric layers – various substances (such as calcium, oxygen and small amounts of metal) get deposited in the tooth enamel.

tooth 2

Using both chemical analysis and microscopic studies, they showed that initially, barium levels are very low, because very little of it passes through the placenta. Then, as the baby is born and is breastfed, the barium levels rise significantly, only to drop as he starts supplementing his meal with other foods. It then drops again, significantly, once breastfeeding is stopped.

tooth 3

“We can see when the barium shows up in the tooth after birth, and we see it increase over time, because an infant will take more milk as they get bigger and more active, and then you see it drop off in this beautiful, inverted U-shaped function,” Hinde said. “This is a game-changer in many ways, because this will allow us to go to museum collections and look at this as a proxy for how much milk different infants got from their mothers and what their weaning process was like. We can now look at that within species, but we can also look at that among species. That will tell us about the evolution of how mothers invest in their young.”

Some researchers believe that this also provided an evolutionary advantage over the Neanderthals – one of the many things which ensured our survival as a species.

“This can give us a window into one aspect of life that may have separated modern humans from Neanderthals,” she said. “This topic has been debated for a long time in the scientific community. What does it mean that human and Neanderthal cranial development was different? What does it mean that their dental development was different? We haven’t been able to get at these questions in the fossil record, but now we can actually get at a real developmental benchmark. That’s why this is so exciting.”

The entire research: here.