Tag Archives: jaw

The trap-jaw is the fastest in the world — and it independently evolved several times in ants

Trap-jaw ants are infamous for having one of the strongest bites among all animals, but we didn’t really understand how they evolved from more traditional jaws. A new study looking at their evolutionary history found that the distinctive mechanism behind trap-jaws has evolved independently several times across the globe.

Unlike normal gripping jaws, which open and close through the contraction of muscles, trap-jaws use a complex mechanism to latch themselves open and clamp down when needed. This mechanism allows the jaws to store energy much like a spring, and this can be released to produce a lot of force quickly.

Bit bite

“One of the central questions in biology is: how does something complex arise from something simple?” said Professor Economo, who leads the Biodiversity and Biocomplexity Unit at the Okinawa Institute of Science and Technology Graduate University (OIST).

“Structures like the trap-jaw depend on multiple interacting parts to function correctly. At first it can be hard to see how such complexity can arise through the gradual stepwise changes of evolution. Nevertheless, when we look closely biologists can uncover evolutionary pathways to complexity.”

A new study led by Professor Economo and Dr. Douglas Booher from Yale University tracked the evolutionary history of trap-jaws, finding that they evolved independently, on several occasions, around the globe. Many of the species that sport such jaws come from the Strumigenys genus, which includes over 900 species found in tropical and subtropical regions.

For the study, the team sequenced the genetic information of 470 species in this genus recovered from all around the globe, including two types of gripping jaws (ancestral and with modified trap-jaws). From this, they reconstructed their family tree, which shows how different species are related.

Finally, they analyzed the jaws and ants themselves using micro-CT scanners, allowing them to create 3D models.

One of the first observations the team made was that only minor changes in structure were required to turn a gripping jaw into a trap-jaw. They further report that after this transition took place, the heads of (now trap-jawed) ants also started to morph quite dramatically. Muscle restructuring and changes in the length and open-width of the jaws were among the key changes.

“Previously, we had thought that all trap-jaws had both divergent form and divergent function, so it was much less obvious as to whether the change in function could occur at the start or whether a lot of changes to the form were first needed as a precondition,” said Professor Economo.

“But it turned out there are many intermediate forms out there of the trap-jaw mechanism that people just hadn’t identified before, some which differ only slightly from the ancestral form.”

In a collaboration with the lab of Andrew Suarez at the University of Illinois, the team also used high-speed video cameras to capture the jaws of Strumigenys ants in motion. They were thus able to determine that the trap-jaws have the fastest yet “acceleration of any animal body part that can return to its original position”. Such jaws were seen to accelerate a hundred times faster than standard mandibles, closing a thousand times faster than a human eye can blink. Which sounds impressively fast.

But they need all the speed they can get. Strumigenys ants use their jaws to capture springtails, their preferred prey, which employ a spring-loaded escape mechanism (hence the name). There’s still a lot we don’t understand about their hunting habits, but we do know that ants with shorter trap-jaws tend to be passive hunters, hiding in leaf litter with open jaws, waiting to bite down on any prey passing by. Longer-jawed ants, meanwhile, actively look for prey to bite into.

Both types of ants can be found in every region across the globe, the authors add. They believe that differences in behavior can explain why there are so many different shapes of trap-jaws out there. However, what is yet unclear is whether the genetic background that supported the change from normal- to trap-jaws is the same for all species, or whether they all reached the same solution through different genetic changes.

“It was really striking how we saw the same variations evolve again and again on different continents. It illustrates how repeatable evolution can be, finding similar solutions to life’s challenges,” said Professor Economo.

Going forward, the team plans to sequence the genomes of representative Strumigenys species across the world in order to determine this.

The paper “Functional innovation promotes diversification of form in the evolution of an ultrafast trap-jaw mechanism in ants” has been published in the journal PLOS Biology.

Dracula ants have the fastest body parts known to man: their jaws

A new study has found that their jaws can move at 90 meters per second (more than 200 mph), making it the fastest animal movement on record.

The mandibles of this Dracula ant species, Mystrium camillae, are the fastest known moving animal appendages, snapping shut at speeds of up to 90 meters per second. Image credits: Adrian Smith.

As you might infer from their name, Dracula ants (a generic name for species in the Adetomyrma genus) are pretty nasty creatures. Their name comes not from their jaws, but rather from their extremely unusual feeding habits. They practice a sort of “non-destructive cannibalism”, chewing holes into and feeding on the haemolymph (insect “blood”) of the colony’s own pupae and larvae.

Some species have also been known to drink the haemolymph of prey, and have also been observed to feed off of egg yolk. But these ants are also known for the incredible strength of their mandibles, which they can use both offensively or defensively.

“These ants are fascinating as their mandibles are very unusual,” said University of Illinois animal biology and entomology professor Andrew Suarez, who was one of the co-authors. “Even among ants that power-amplify their jaws, the Dracula ants are unique: Instead of using three different parts for the spring, latch and lever arm, all three are combined in the mandible.”

Not all that much is known about the lifestyle of these ants. They were only discovered a decade ago on a rotting log in Madagascar, and they quite confused researchers at first — because unlike many other ant species, their looks don’t necessarily betray their role in the colony. For instance, some workers sometimes become queen ants, which may or may not have wings, and these wings can be large or small. In addition, the genus has three different modes of reproduction, which makes understanding them even more challenging. However, in the new study, researchers didn’t focus on their ecology, but rather on their jaws.

Unlike trap-jaw ants, which have a pair of mandibles capable of shutting their jaws from an open position, Dracula ants power up their mandibles by pressing the tips together. This creates an internal stress that is released when one mandible slides across the other — somewhat similar to how we can snap our fingers, researchers say.

This way, they don’t necessarily bite off their opponents, but rather smack them around violently.

“The ants use this motion to smack other arthropods, likely stunning them, smashing them against a tunnel wall or pushing them away. The prey is then transported back to the nest, where it is fed to the ants’ larvae,” Suarez said. The workers use venom to stun their prey and then bring them back to the colonly to feed it to the larvae.

“Scientists have described many different spring-loading mechanisms in ants, but no one knew the relative speed of each of these mechanisms,” says Fredrick J. Larabee, a postdoctoral researcher at the Smithsonian National Museum of Natural History. “We had to use incredibly fast cameras to see the whole movement. We also used X-ray imaging technology to be able to see their anatomy in three dimensions, to better understand how the movement works.”

After they carried out computer simulations of mandible snaps from different species, researchers better understood just how the ants are capable of generating so much power and speed in their jaws. According to their results, these are the fastest moving appendages in the animal world.

“Our main findings are that snap-jaws are the fastest of the spring-loaded ant mouthparts, and the fastest currently known animal movement,” Larabee said. “By comparing the jaw shape of snapping ants with biting ants, we also learned that it only took small changes in shape for the jaws to evolve a new function: acting as a spring.”

However, it’s still not clear how all these mandibles are used in practical situations. Researchers want to better examine how Adetomyrma employ this power in offensive and defensive situations.

The paper “Snap-jaw morphology is specialized for high-speed power amplification in the Dracula ant, Mystrium camillae” has been published in Royal Society Open Science.

Mammaliaform Morgauncodon

Mammals’ evolutionary success relied on our ancestors growing very tiny

Mammals cashed in big on growing smaller, new research reveals.

Mammaliaform Morgauncodon

Morganucodon, a mamaliaformes and one of the best-preserved species from which all mammals originate, grew up to only 4-6 cm length.
Image credits Bob Nicholls.

The bubbly evolution of mammal species over the last 200 million years is owed in no small part to their propensity for growing smaller, a new paper reports. This trend is most evident when compared to that of the dinosaurs — the former de-facto winners of the evolutionary lottery — which spawned some of the largest beasts to ever walk the Earth.

Smaller, better, harder, stronger

When mammals first started popping up around 200 million years ago, our planet was still dominated by dinosaurs. So for the following 150-ish million years, mammals literally and figuratively kept a low profile. While dinosaurs were growing bigger, mammals shrank in size.

An international team of researchers set out to understand why and how this shift took place. Using modern computer modeling and analysis, they analyzed the skeletons of our tiny ancestors to better document their evolutionary path.

Mammals stand out among all other vertebrates on the planet in that they have a single bone bearing teeth for their lower jaw. Everyone else has more complex lower jaws, formed from no fewer than five bones linked together, the team explains.

As mammals evolved, most of these bones shrank in size and became more simplified. The new jaw retained a single bone, and the others moved higher in the skull, into the inner ear. They now help us hear.

The team focused their research efforts on understanding how this lower jaw restructuring process took place — as they were occurring, these changes had to allow the animal to keep feeding itself and hear, else they wouldn’t be viable organisms. Starting from X-ray computed tomography (CT) scans of several fossil skulls and lower jaws, the team created digital models of the bones. Later, they ran these models through extensive computer simulations to see how they would function.

For smaller animals, the team reports, jaw bones experience reduced stress when feeding. The jaws themselves could thus become simpler and tinier while still retaining enough structural strength to bite through prey.

“Our results provide a new explanation of how the mammalian jaw evolved over 200 million years ago,” says Dr Stephan Lautenschlager, lead author of the paper and lecturer at the University of Birmingham.

“Getting very small appears to have been crucial for our mammalian ancestors. This allowed them to reduce the stresses in the jaw during feeding and made the restructuring of the jaw bones possible.”

University of Bristol Professor Emily Rayfield, who co-authored the study, says that the research addresses a 50-year-old open debate in paleontology.

“Using computational methods we can offer explanations to how our mammalian ancestors were able to maintain a working jaw while co-opting bones into a complex sound detection system,” she explains. “Our research is about testing ideas of what makes mammals unique among the animal kingdom, and how this may have come about.”

The paper “The role of miniaturisation in the evolution of the mammalian jaw and middle ear” has been published in the journal Nature.

Pterosaur.

Largest pterosaur jaw ever found, recognized three decades after discovery in Transylvania

Three decades after being discovered, the largest pterosaur jawbone ever found has now been officially recognized.

Pterosaur.

Reconstruction of an (unrelated) pterosaur.
Image credits Sebastian Ganso.

Although the partial mandible itself is a mere 7.4 inches (18.8 centimeters) long, it suggests that the whole jawbone likely measured between 37 and 43 inches (94 and 110 cm) during the animal’s life, the researchers write.

Why the long face?

The jaw would be “more than three times the size of the complete, 290-millimeter-long  holotype mandible of Bakonydraco,” a closely-related pterosaur, the team explains.

The jawbone fossil was first unearthed by study co-author Dan Grigorescu, a geologist at the University of Bucharest, Romania, back in 1948. He made the discovery in the Hațeg Basin, near the village of Vặlioara in Transylvania, central Romania. However, his find wasn’t immediately recognized. In fact, the fossil wasn’t recognized as belonging to a pterosaur until 2011 when two of the paper’s co-authors, Mátyás Vremir, a geologist at the Transylvanian Museum Society and Gareth Dyke, a paleontologist at the University of Debrecen in Hungary, realized its importance, writes National Geographic.

During the pterosaur’s lifetime, a period known as the Cretaceous, the Hațeg Basin wasn’t actually a basin — it was an island. And, as oft happens with island-dwellers, the dinosaurs here evolved to be smaller than their counterparts on the mainland (a process known as ‘island dwarfism‘). The area, however, is also known for large pterosaurs (the other side of the coin, known as ‘island gigantism‘) such as Hatzegopteryx. This ancient flier is believed to have rivaled a modern giraffe in height, boasting a wingspan of up to 36 feet (10.9 meters) — and it’s not even the largest one.

Having a large jaw, however, does not make one the biggest pterosaur on the island. The animal — which has yet to be scientifically named — probably had a wingspan of over 26 feet (8 m) and likely belonged to a family of pterosaurs known as the Azhdarchids, the authors explain. This family of flying dinosaurs is generally thought to have had either long necks and thin skulls, or short necks and robust, hardy skulls.

The jawbone in this study likely belonged to “a robust, short-skulled azhdarchid,” the researchers conclude.

The paper “Partial mandible of a giant pterosaur from the uppermost Cretaceous (Maastrichtian) of the Hațeg Basin, Romania” has been published in the journal Lethaia.

We owe the shape of our jaws, at least in part, to our ancestors’ love of cheese

The advent of farming, with its ‘softer’ foods compared to previous hunter-gatherer menus, had a subtle but noticeable effect on the shape of human skulls, anthropologists from the University of California, Davis report.

Skull jaw.

Image credits Eliane Meyer.

Wild foods generally tend to be rougher than the stuff we’re used to nowadays. In other words, our hunter-forager ancestors had to put a lot more effort into chewing dinner than we do — they had to chew more and more often before dinner got in their bellies. Previous research has shown that there is a connection between skull shape and the advent of agriculture, but they haven’t gone as far as quantifying exactly how these changes developed over time.

So a team from UC Davis, made up of postdoc David Katz, statistician Mark Grote and associate anthropology professor Tim Weaver looked at 559 skulls and 534 lower jaws from over two dozen pre-industrial populations to see exactly how diet altered the shape and size of human skull bones as we transitioned to agriculture.

“The main differences between forager and farmer skulls are where we would expect to find them, and change in ways we might expect them to, if chewing demands decreased in farming groups,” said Katz, who is now a postdoctoral researcher at the University of Calgary, Alberta.

Overall, the team found subtle but noticeable changes in the skulls of communities that grew and consumed dairy, cereals, or both. The greatest effects were associated with groups whose diets included a large percentage of dairy and dairy products, which suggests a direct link between the softness of the food and morphological changes.

However, diet wasn’t the most important factor dictating skull characteristics. For example, the team reports that morphological differences between males and females, or those between individuals eating the same diet but came from different populations had a more pronounced effect.

It’s interesting to see how our lifestyles play a direct role in our evolutionary path. The effects are less pronounced than “neutral evolutionary processes” such as genetic drift, mutation, and gene flow structured by population history and migrations. But even diet’s more muted contribution to the Homo sapiens we all know and love today shows that we’ve been meddling with our evolution for a long time now — whether we want to or not.

With the advent of genetic engineering, we’re bound to have an even more pronounced influence in the future. Time will only tell what that influence will be.

The paper “Changes in human skull morphology across the agricultural transition are consistent with softer diets in preindustrial farming groups” has been published in the journal Proceedings of the National Academy of Sciences.

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.

Invasive ant has bear trap-like jaw which can propel it through the air

An invasive ant has been sweeping through southeastern United States; it has a jaw like a bear trap, which close faster than almost anything in nature. Naturally, it packs quite a sting, and if that wasn’t enough, it can propel itself through the air like a rocket.

Photograph by Alex Wild, Visuals Unlimited/Corbis.

“They look like little hammerhead sharks walking around,” said D. Magdalena Sorger.

That amazing jaw is so powerful that you can use it as a surgical staple (when adequate medical equipment is lacking). Especially in military situations, these ants can be quite useful in suturing wounds. But more often than not, their interactions with humans are not pleasant.

There are four species of trap-jaw ants native to the United States, and one of them was the focus of this research.  Odontomachus haematodus is especially aggressive. The species is  found in the tropics and subtropics throughout the world, but in the past 50 years it has grown its populations more and more in the US Gulf Coast. So what changes in the past half century ?

Sorger says population growth and climate change paved the way for this invasion, but the magnificent jaws also helped.

“Trap-jaw ants have little sensory hairs on the inside of their jaws,” said Sheila Patek, a biologist who studies the evolutionary mechanics of movements at Duke University. Patek explained that these hairs are linked directly to the muscles that hold the jaw open. “So they can fire those latch muscles even faster than their brain can process.”

Hey, and as if having one of the strongest bites (per size) in the animal kingdom wasn’t enough, the trap-jaw ants can actually bite the ground with so much strength that it propels them into the air – like popcorn from a frying pan. When a whole army of invasive ants does this at once, it can get a little scary.

“The next thing you know you have this ant flying through the air that you can’t even see, it’s moving so fast, with a big stinger on the end of its abdomen,” she said. “It is really nerve-racking working with them.”

The good thing is that unlike other invasive ants, these ones don’t have colonies, and therefore there’s a much reduced chance of them overwhelming the local flora and fauna – but that doesn’t mean that they won’t have a huge impact. They’re here, and we should be prepared for it.