Tag Archives: nails

Grooming claws.

Fossils reveal that primates initially had nails and claws, we just lost the latter ones

If you like having nails instead of claws, give a shout-out to society.

Nails.

Image credits Daniel Nebreda.

Unlike other mammals, us humans and our primate cousins sport nails instead of claws. However, this wasn’t always the case — new fossil evidence shows that ancient primates had specialized grooming claws as well as nails. The findings showcase how primate social structure helped shift claw and nail evolution, the team writes, and overturns our assumption that the earliest primates had nails on all their fingers.

Nailed it

“We had just assumed nails all evolved once from a common ancestor, and in fact, it’s much more complicated than that,” said Jonathan Bloch, study co-author and curator of vertebrate paleontology at the Florida Museum of Natural History.

Grooming goes beyond just looking good. The thick body hair of primates is an ideal habitat for ticks, lice, and a whole host of other creepy crawlies which are both annoying and potential health hazards. As such, the ability to remove these pests formed an evolutionary advantage — and they evolved specialized grooming claws for the purpose. Many primates today retain such claws. Lemurs (subfamily Lemuroidea), lorises (subfamily Lorinae), and galagoes (family Galagidae) have grooming claws on their second toe, while tarsiers (family Tarsiidae) boast them on their second and third toe.

Up to now, we’ve believed that grooming claws developed independently across several primate lineages up to those alive today. However, new fossil evidence suggests that such claws are, rather, a key feature — they date back at least 56 million years, to the oldest-known primates.

Back in 2013, the study’s lead author Doug Boyer found several curious primate fossils at the University of California Museum of Paleontology. These fossils — distal phalanges, the bones that make the tips of fingers or toes — were hidden in sediment samples collected in Wyoming several decades earlier; as often happens, however, they were left waiting in a drawer in the archives. Based on the shape of these fossils, Boyer suspected that their owners sported grooming claws — in general, distal phalanges topped with a claw will be more narrow and tapered, while those supporting a nail will be flat and wide.

Grooming claws.

Lemurs, lorises, and galagoes have nails on most digits and grooming claws on their second toes, as seen on the feet of two greater slow lorises, Nycticebus coucang, in the Florida Museum mammals collection.
Image credits Kristen Grace / Florida Museum.

Bloch’s work involved material recovered from Bighorn Basin, Wyoming. He discovered what initially looked like a “strange, narrow nail” bone, but on later comparison with modern specimens “it looked just like a tarsier grooming claw,” he recounts. Although smaller than a grain of rice, the bone matched the proportions of grooming claws of Teilhardina brandti, a mouse-sized, tree-dwelling primate.

Claw me, claw thee

These were the first hints that the fingers of early primates had grooming claws. To get to the bottom of things, the duo went out to Omomys Quarry, Wyoming, a site once inhabited by an early primate family, Omomys. Here, they found omomyoid grooming claws at three sites spanning 10 million years in the fossil record. The fossils proved beyond a doubt that early primates sported grooming claws.

Why, then, don’t we have some as well?

“The loss of grooming claws is probably a reflection of more complex social networks and increased social grooming,” said Boyer, an associate professor in the department of evolutionary anthropology at Duke University.

“You’re less reliant on yourself.”

This hypothesis could also explain why some species of (more) solitary primates, such as the titi (subfamily Callicebinae) or owl monkeys (family Aotidae) have re-evolved a grooming claw.

But why develop nails in the first place? The team believes it came down to shifts in how primates got around. As climbing, leaping, and grasping took center stage, claws simply became impractical — whereas nails wouldn’t snag or get in the way of anything.

Furthermore, the claws provide new insight into the lives of ancient primates, the team notes, many of which are only known from fossil teeth. Even these tiny claws can offer insight into how our ancestors moved about, their daily behavior, and their social structures.

“We see a bit of ourselves in the hands and feet of living primates,” Bloch said. “How they got this way is a profoundly important part of our evolutionary story.”

The paper “Oldest evidence for grooming claws in euprimates” has been published in the Journal of Human Evolution.

ingrown_toenail

How you get Ingrown Toenails, explained by Science

Having a ingrown toenail could ruin your day and a lot after if you don’t have it fixed. Yet, even though ingrown nails and other nail-related conditions are common and pesky, very little is known about them. Now, a team at University of Nottingham have published a mathematical model that explains what forces are tugged beneath your finger nails and what exactly happens when this delicate interplay is upset. Of course, there’s a piece of practical advice: always trim your nails with the curve bits following a parabola.

A gruesome pain at your fingertips

ingrown_toenail

The Greek physician Paul of Aegina was among the first to discuss surgical treatments for nail conditions in the 7th century, but humans have been forced to live with annoying pain long before. To understand how ingrown nails come to be, we first need to discuss, however, how nails are formed and what causes them to grow and pop from under your skin.

Basically, nails are nothing but dead skin cells coated with a hardening protein called keratin that stick out from the half-moon-shaped “lunula” at the base of the nail toward the fingertip. On average, fingernails grow by 0.1 to 0.2 millimeters per day, but it’s no smooth sailing. Keeping the nail in place are adhesive molecules behave like ratchets: They grab onto the nail above them, and as the nail slides forward during growth, they tilt and stretch, trying to hang on, until eventually the bond breaks. Once this happens, the molecules just attach themselves to another piece of nails.

Sometimes, though, the balance between nail growth and adhesion is interrupted. When this happens, the nail might change shape to compensate and end up in all the wrong places – like under your skin and into live flesh!

“We have discovered that three well-known conditions– ingrown nails, pincer nails, and spoon-shaped nails — are essentially three faces of the same coin,” says Cyril Rauch, lead author on the new paper. “They are related by the physics.”

“Ingrown nails, pincer nails, and spoon-shaped nails are essentially three faces of the same coin.”

Ingrown toenails happen when the nail extends into the flesh alongside the nail. Kids, teenagers, and pregnant women are among the most vulnerable because raging hormones are causing the nail’s growth to outpace adhesion, according to the University of Nottingham model. Pincers result from the opposite problem. In this condition, the sides of the nail curve down and towards each other, forming a “C” shape. Rauch’s model suggests that in this condition, adhesion overpowers growth, which may explain why pincers are more commonly found in the elderly, whose growth is slower.

How to stop ingrown nails

Overall, nail problems are predominantly caused by biological factors that are outside our control, yet with proper hygiene, it’s possible to minimize the risk of ingrown or pincer nails. Here’s the best way to trim your nails:

“Imagine you can flatten your nail out on your desk,” says Rauch. “The curved bits should follow a parabola shape.”

If you’re having an ingrown toenail (the most common sort), here’s what you can do:

  • Soak your foot in a mixture of hot (or as hot as you can stand it) water and Epsom salt. Do this for 15-30 minutes at least twice daily. The goal here is twofold: to soften the toenail and prevent the ingrown nail from becoming infected.
  • Trim your toenail, taking extra care around the ingrown section. Make sure your toenail is cut perfectly straight without any pointed parts near the edges. Toenails that are rounded off have an increased likelihood of growing into the skin, causing ingrown nails.
  • Keep your toenail slightly raised. Putting a small piece of cotton between your toenail and the skin should keep the ingrown toenail from coming back. Remove the cotton daily to prevent infections.
  • In fact, you should apply infection-preventing ointment to the site and keep it bandaged. Neosporin works fine for these purposes.
  • Don’t wear socks or shoes, at least when you’re at home.

Rauch is actually a veterinarian and is currently adapting the model for animals, where nail health is a big problem and can cause serious financial deficits.

“When animals develop hoof problems, it costs a lot of money,” says Rauch. It turns out the horse hoof is actually pretty similar to the human nail. “The main difference, of course, is that the horse walks on its nail and the human doesn’t, so we need to add that new stress to the model.”

The findings were reported in the journal Physical Biology. [via PopSci]