Tag Archives: finger

‘Cursed’ yet adorable aye-aye has a sixth ‘pseudothumb’

Exclusively found in the north-eastern parts of Madagascar, the aye-aye (Daubentonia madagascariensis) is a dark-brown or black primate, distinguished by a bushy squirrel-like tail that is larger than its body, bat-like ears, and an over-sized, slender middle finger. But although the species has been known to science since the mid-1800s, scientists have just now discovered that the aye-aye has a sixth digit — a tiny pseudothumb that likely helps the creature grip branches.

The aye-aye uses its exaggeratedly long middle finger to forage for food, typically insects lying within hollow branches. The primate first uses its keen ears to listen for the activity of unsuspecting grub, after which it uses its rodent-like incisors to gnaw through the bark of the branch to make an opening for its middle finger, which is slender enough to nudge right through the hollow tree branch. The finger has a ball-and-socket joint, similar to a human shoulder, which allows a fantastic degree of motion. At the tip of the finger, the aye-aye has a hooked nail that can snag and drag out prey.

Unfortunately for our adorable-looking aye-aye, humans on the island don’t think of it too fondly. Its bizarre appearance is frightening to the locals, and its eery call doesn’t help too much in this regard. According to ancient Malagasy legends, the aye-aye is considered a symbol of death. The natives believe if an aye-aye ever points its middle finger at you, then death will surely soon befall. For this reason, the poor aye-ayes are often killed on sight by superstitious locals. Due to this persecution, as well as habitat loss, the aye-aye is listed as critically endangered, with experts estimating fewer than 1,000 individuals left in the wild. Perhaps that middle finger is rightfully called for.

The aye-aye’s newly found pseudothumb. Credit: Adam Hartstone-Rose.

New anatomical insights, however, are making things more complicated. According to a new study led by Adam Hartstone-Rose, a biologist at North Carolina State University, the aye-aye actually has six digits, which means there’s no actual middle finger. Take that!

“The aye-aye has the craziest hand of any primate,” says Adam Hartstone-Rose, associate professor of biological sciences at NC State. “Their fingers have evolved to be extremely specialized – so specialized, in fact, that they aren’t much help when it comes to moving through trees. When you watch them move, it looks like a strange lemur walking on spiders.”

The reason why it hasn’t been found thus far has to do with the pseudothumb’s anatomy. The bone itself is very small, whereas the rest of the finger is mainly made of cartilage and muscle, which doesn’t show up on X-rays.

The researchers found the tiny thumb by accident while they were employing dissection digital imaging techniques on six aye-ayes. They noticed that one of the hand tendons split from the base of the thumb, heading towards a wrist bone called the radial sesamoid (humans don’t have it).

“Using these digital techniques allows us to visualize these structures in three dimensions, and to understand the organization of the muscles which provide movement to the digit,” says Dickinson, who built the digital model of the anatomy and is co-first author of the paper.

“The pseudothumb is definitely more than just a nub,” Hartstone-Rose says. “It has both a bone and cartilaginous extension and three distinct muscles that move it. The pseudothumb can wriggle in space and exert an amount of force equivalent to almost half the aye-aye’s body weight. So it would be quite useful for gripping.”

According to the researchers, the aye-aye’s elongated middle finger gymnastics doesn’t allow for a very good grip on branches. Like the panda, which also has a pseudothumb, the aye-aye likely uses this extra digit to grasp branches. Besides the aye-aye and pandas, moles also have six digits, which they employ to move more dirt.

“Other species, like the panda bear, have developed the same extra digit to aid in gripping because the standard bear paw is too generalized to allow the dexterity necessary for grasping,” Hartstone-Rose says. “And moles and some extinct swimming reptiles have added extra digits to widen the hand for more efficient digging or swimming. In this case, the aye-aye’s hand is so specialized for foraging an extra digit for mobility became necessary.

“Some other primate species have reduced digits to aid in locomotion. The aye-aye is the first primate to dial digits up in the hand rather than dial them down. And it’s amazing that it’s been there the whole time, in this strangest of all primates, but no one has noticed it until now.”

The findings were described in the American Journal of Physical Anthropology.

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 1.85 million year old human-like bone

Anthropologists have discovered the oldest known fossil of a bone resembling that of humans; the 1.85 million year old bone is the oldest evidence of a ‘modern’ hand and suggests that ancient humans may have been much larger than previously thought.

The hand is one of the critical features distinguishing humans, and even a 3.6 cm(1.5-inch), two-million-year-old fragment provides valuable clues. Image credits: M. Domínguez-Rodrigo.

A key feature that distinguishes humans from other species is the ability to create and use tools. But in order to be able to create and use the tools, you need not only a big brain, but also very able hands. It’s not just the opposable thumbs – the entire structure of the hand is remarkable.

“The hand is one of the most important anatomical features that defines humans,” said study lead author Manuel Domínguez-Rodrigo, a paleoanthropologist at Complutense University of Madrid. “Our hand evolved to allow us a variety of grips and enough gripping power to allow us the widest range of manipulation observed in any primate. It is this manipulation capability that interacted with our brains to develop our intelligence.”

Many mammals and other animals have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The only true grasping appears in primates, and apes are sometimes considered to have 4 hands, because they can also grasp with their ‘feet’.

If the bone is proportional in size to human bones, then the possessor of this bone would have been 5 feet 9 inches (1.75 meters) – a remarkable size when you compare it to Homo habilis, a hominin that measured only 3 feet high. The fact that human ancestors were so large comes as a surprise, but then again, there’s also a chance that the finger/body ratio wasn’t the same for them as it is for us.

Tiny but significant. Credit: Jason Heaton

Some scientists have often proposed that our hands evolved in conjunction with our use of tools, but recent discoveries suggest that the history of human hands is much more complicated. Modern humans are the only living higher primates to have straight finger bones, while hominin fingers were more curved, because they spent a great portion of time in the trees.

In a study published Tuesday in Nature Communications, researchers report the finding of an old fossil which also indicates straight fingers, and this just makes things more complicated. The straightness and other features of this new bone suggest adaptations for life on the ground rather than in the trees. This fills an important gap, but also raises more questions.

“Our discovery fills a gap — we found out that such a modern-looking hand is at least 1.85 million years old,” Domínguez-Rodrigo said.

Unfortunately, before we find more fossils, those questions will likely remained unanswered.


Finger ratios predict how rude or kind men are towards women

Can you judge a person by his fingers? If that person’s a men, yes you can, some scientists would agree. Researchers at McGill University found that men with short index fingers and long ring fingers are on average nicer to women. Not entirely a correlative study, the findings seem to have weight as previously a link was found between high levels of testosterone in the womb and shorter index finger relative to the ring finger. You can stop watching your fingers now.


Credit: harshimg


Generally, index fingers are shorter than ring fingers  in men. This difference is less pronounced in women. The ratio between the second digit length and the fourth digit length   is an indication of the amount of male hormones, chiefly testosterone, someone has been exposed to as a fetus: the smaller the ratio, the more male hormones.

“It is fascinating to see that moderate variations of hormones before birth can actually influence adult behaviour in a selective way,” says Simon Young, a McGill Emeritus Professor in Psychiatry and coauthor of the study.

During 20-day-long study, 155 participants were asked to log in any social interaction that lasted more than 5 minutes and check a list of behaviours. These could be agreeable or quarrelsome. Men with small digit ratios reported approximately a third more agreeable behaviours and approximately a third fewer quarrelsome behaviours than men with large digit ratios.

“When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise or compliment the other person,” says Debbie Moskowitz, lead author and Professor of Psychology at McGill.

These men were also less quarrelsome with women than with men, whereas the men with larger ratios were equally quarrelsome with both. For women though, digit ratio variation did not seem to predict how they behaved, the researchers report.

This might serve to explain why men with shorter index figures have more children, the researchers write in the journal Personality and Individual Differences.

“Our research suggests they have more harmonious relationships with women; these behaviors support the formation and maintenance of relationships with women,” Moskowitz says.