Tag Archives: leg

Fossil Friday: lizard foot trapped in amber helps us better understand fossilization

A new paper describing the foot of a lizard preserved in amber broadens our understanding of the fossilization processes.

The fossil seen under natural light (A, B) and false coloring (C, D).
Image credits H. Jonas Barthel et al., (2020), PLOS One.

The tiny foot belonged to a lizard in the genus Anolis which became trapped in resin around 15 to 20 million years ago. It is very well preserved, with every detail of the limb visible under the microscope.

However, this dandy exterior hides a very different core: the bone inside this foot is heavily decomposed and chemically transformed, with very little of the original structures still present.

Foot for thought

“This is surprising, because we assumed that the surrounding amber largely protects the fossil from environmental influences” says Jonas Barthel, a doctoral student at the Institute for Geosciences at the University of Bonn and first author of the paper.

Every fossil begins with a rapid embedding in a protective material — in this case plant resin, which turned into amber over time. This layer of material protects the biological material from scavengers and microorganisms. After the animal is encased in a protective layer of material, its tissues start being gradually replaced by mineral compounds as pressure from sediments on top compresses everything — in essence, it starts becoming a rock.

“That’s the theory,” says Barthel. “How exactly fossilization proceeds is currently the subject of intensive scientific investigation.”

The fossil described in this study is pretty rare; it’s usually small organisms such as insects that get trapped in resin (which over time becomes amber), not vertebrates (which are larger). It was analyzed as part of a larger research project between the University of Bonn and the German Research Foundation centered on fossilization processes, which has been ongoing since 2018.

The whole piece of amber than encases the limb is about two cubic centimeters in size and was recovered from the Dominican Republic. It belongs to a genus that is still alive today and was housed at the Stuttgart State Museum of Natural History.

For the study, the team asked the Institute for Evolutionary Biology at the University of Bonn to cut the amber down into thin sections to allow for investigation of the fossil inside. The claws and toes inside the amber were very well preserved, the team reports, suggesting that resin had dripped onto the limb. Further investigations at the university’s Institute for Geosciences using micro-computer tomography revealed that the forefoot had been broken in two places. The area around one showed slight swelling, indicative of a fracture that happened prior to fossilization

“This is an indication that the lizard had perhaps been injured by a predator,” says Barthel.

The other fracture, however, seems to have formed after fossilization, and coincides with a tiny crack running through the amber.

Analysis of the bone inside showed that the mineral hydroxyapatite in its tissues had been transformed into fluoroapatite, implying that fluorine penetrated the tissues. Additionally, they found that the collagen in the bones has largely degraded now. In other words, although the fossil seems very well-preserved at first glance, very little of the original tissues remain intact. So far, the researchers were unable to detect complex molecules such as proteins in the fossil.

The team believes that the tiny crack in the amber allowed mineral-rich solutions to filter through into the leg and destroy the organic matter.

“We have to expect that at least in amber from the Dominican Republic, macromolecules are no longer detectable,” says the supervisor of the study, Prof. Dr. Jes Rust from the Institute for Geosciences.

It was not possible to detect more complex molecules such as proteins, but final analyses are still pending. The degradation processes in this amber deposit are therefore very advanced, and there is very little left of the original substance.

Amber is generally considered to be an ideal preservative, as a fully-encased fossil will be completely isolated from the environment. However, in the case of this fossil, the team was surprised to see that the amber might have actually promoted the degradation of soft tissues. Acids in the original tree resin have probably reacted with apatite in the bones in a process similar to tooth decay, the researchers conclude.

The paper “Fluoridation of a lizard bone embedded in Dominican amber suggests open-system behavior” has been published in the journal PLOS One.

Fossil Friday: bird encased in amber has an unique, “extreme” toe

The bird’s hyper-elongated third toe is longer than its whole lower leg, the authors report.

Bird in amber.

The fossilized bird, encased in amber. Image credits Linda Xing et al., (2019), Cell Biology.

Researchers in China have discovered a new species of ancient bird preserved in amber– and it’s packing one seriously impressive toe. The fossilized beast, which lived around 99 million years ago, likely used the appendage to draw food out of tree trunks. According to the team, it’s the first time such a food structure has been observed in either living or extinct birds.


“I was very surprised when I saw the amber,” says first author Lida Xing at China University of Geosciences (Beijing). “It shows that ancient birds were way more diverse than we thought. They had evolved many different features to adapt to their environments.”

The fossils include two isolated wings, an isolated foot with wing fragment, and two partial skeletons, most of them from juvenile individuals. The fossils date back to the Cretaceous period and were found encased in amber in 2014 in the Hukawng Valley of Myanmar. It was christened Elektorornis chenguangi. The new species’ most distinctive feature is its very, very long third toe measuring 9.8 millimeters. It is a full 41% longer than its second toe and 20% longer than its tarsometatarsus, the main bone in the lower legs of birds. Comparison to 20 other extinct bird species from the same time and 62 living birds showed that, showed that Elektorornis chenguangi is the only species so far discovered to evolve this foot structure.

Elektorornis chenguangi is part of a group of extinct birds called Enantiornithes, the most abundant type of bird known from the Mesozoic era. To the best of our knowledge, the Enantiornithines became extinct during the Cretaceous-Paleogene extinction event about 66 million years ago (the one where all the dinosaurs died) and left no living descendants behind. Elektorornis means “amber bird”.

Bird leg.

A 3D reconstruction of the birds’ leg.
Image credits Linda Xing et al., (2019), Cell Biology.

Based on the measurements they’ve taken of the fossils, the team reports that Elektorornis was smaller than a sparrow and that it was arboreal (i.e. it liked trees as opposed to the ground or water surfaces). The bird’s foot measures 3.5 centimeters in length, and weighs 5.5 grams.

“Elongated toes are something you commonly see in arboreal animals because they need to be able to grip these branches and wrap their toes around them,” says co-author Jingmai O’Connor at the Chinese Academy of Sciences. “But this extreme difference in toe lengths, as far as we know, has never been seen before.”

During the Mesozoic area, the Hukawng Valley of Myanmar was heavily forested with trees that produced resin as a defensive mechanism. The area is famed for its amber and fossil-bearing amber bits to this day, all thanks to those trees. The oldest known bee and a feathered dinosaur tail, among many others, have been discovered in amber from this valley. The team obtained the amber from a local trader, who didn’t know what animal this weird foot belonged to.

“Some traders thought it’s a lizard foot, because lizards tend to have long toes,” Xing says. “Although I’ve never seen a bird claw that looks like this before, I know it’s a bird. Like most birds, this foot has four toes, while lizards have five.”

As to why the bird needed such a long leg, the team still can’t say for sure. The only animal today to sport similar digitation is the aye-aye, a lemur that uses its long middle fingers to fish larvae and insects out of tree trunks for food. The team suspects Elektorornis chenguangi used its toe in a similar way.

“This is the best guess we have,” O’Connor says. “There is no bird with a similar morphology that could be considered a modern analog for this fossil bird. A lot of ancient birds were probably doing completely different things than living birds. This fossil exposes a different ecological niche that these early birds were experimenting as they evolved.”

The paper “A New Enantiornithine Bird with Unusual Pedal Proportions Found in Amber” has been published in the journal Current Biology.

Scientists find the earliest creature to stand tall on four legs

About 260 million years ago, this pre-reptile might not have looked like much. With its knobby face and about as big as a cow, Bunostegos akokanensis was actually pretty remarkable. According to a new analysis, it was actually the first creature to walk upright on all four legs, maintaining a fully erect gate.

Scientific Reconstruction of Bunostegos akokanensis. Image via Wikipedia.

“Imagine a cow-sized, plant-eating reptile with a knobby skull and bony armor down its back,” said co-author Linda Tsuji, of the Royal Ontario Museum. She and her co-authors discovered the fossils in Niger with a team of paleontologists in 2003 and 2006.

Dogs and reptiles both have 4 legs, but they walk differently. Reptiles generally have their legs on the exterior of their body, while dogs have their legs right under them. But ironically, this posture was first developed by a pre-reptile.

“We don’t see upright posture, with the legs underneath the body, in both the forelimb and the hindlimb in a single animal until much later, in mammals and in dinosaurs,” Morgan Turner, a Ph.D. student at Brown University in Rhode Island and lead author of the study, told The Huffington Post in an email. “Bunostegos is much further back on the evolutionary tree than anything else that exhibits this posture [and] hints at a larger story about posture and locomotion evolution… The anatomy of Bunostegos is unexpected, illuminating, and tells us we still have much to learn.”

Artist’s rendering of Bunostegos, a cow-sized, plant-eating reptile that roamed the ancient central desert of Pangea more than 250 million years ago. Image credits: Marc Boulay.

Walking upright may have provided the creature with some major advantages – first of all, it would have allowed it to walk longer distances, a very useful ability in the deserts of the supercontinent Pangaea where it lived.

“Here’s this big, cow-sized animal in this very arid region,” Dr. Nick Fraser, vertebrate paleontologist at the National Museums of Scotland, who was not involved in the study, told The Huffington Post in a telephone interview. “You don’t think of big herbivores in arid regions. What was going on there? Do we really understand what the climate was?… The more we learn about this creature, the more we will learn about what appears to be an isolated environment in the center of Pangea.”

The study, which was published in the Journal of Vertebrate Paleontology, detailed an analysis of fossilized Bunostegos, including those of the shoulder, the elbow, the forelimb bone known as humerus and another forelimb bone known as the ulna. Analysis on how the bones fit together show that the animal walked upright.

“Aspects of the anatomy of the shoulder and the forelimb indicate that the humerus could not have jutted out in a ‘sprawling’ posture,” Dr. Linda Tsuji, contract assistant curator at the Royal Ontario Museum in Canada and a co-author of the study, told The Huffington Post in an email, “and in Bunostegos we see limited motion at the elbow joint, which is an indication of upright posture in other animals.”




The first mind-controlled leg prosthesis is amazing!

A freak accident from his childhood in Iceland caused Gudmundur Olafsson’s right ankle to collapse. After 28 years of living in pain and more than 50 surgical operations he decided to amputate his lower leg entirely. For years, he wore the  Proprio Foot – a prosthetic motorized ankle developed by an Icelandic company called Ossur which can automatically adjust the angle of the foot using its built-in sensors. Now, Olafsson prosthesis got a major upgrade: his new Proprio is controlled subconsciously by electrical signals sent from his brain to special sensors directly embedded in his muscles, all via the nerves in the muscle itself. Then a decoded signal is sent to a control unit which directs all the fine moving parts that make up his new, robotic leg. All his intentions are translated seamlessly by the sensors and Olafsson, now 48, can walk almost entirely like a normal person. “The first time, to be honest, I started to cry,” said Olafsson.


The brain-controlled bionic Proprio Foot. Credit: Ossur


“Gummi” Olafsson is among two patients who received this experimental prosthesis. It’s been 14 months now since he’s wore it, and each day it’s getting better. What’s amazing is that there’s strain put on the muscles again, so they’ve started moving away from atrophy – always a big concern.

Image: Ossur

Image: Ossur

“You have to learn how to use those muscles again,” says Olafsson. “How to tighten them up, in front and back. And that’s the main thing. Those muscles start getting bigger, so you get better at walking. I have more stamina. My gait is better. I don’t limp as much,” he said to PopSci.

At the very core of this technology are the myoelectric sensors (IMES). Ossur claims these are “lifetime sensors” since they don’t require any batteries. The tiny sensors (3 millimeters-by-80 millimeters) are instead powered by magnetic coils embedded in the socket – a hollow component that fits over the residual limb and connects to the prosthesis. Compared to what Olafsson had to deal with in his youth, the implant surgery was a piece of cake. It only took 15 minutes and the sensors fit in a single-centimeter-long incision.

Image: Ossur

Credit: Ossur

I couldn’t find anything about cost, though. These sort of details will likely surface once the prosthesis is out of clinical trial. Right now, Ossur is still busy collecting data and improving their prosthesis. For what it’s worth, it all looks very promising already!