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Check the fingers and toes of your favorite vertebrates and you’re likely to find hardened little end-caps on them! This episode, we discuss the many forms and functions of Claws.
In the news
This ancient amphibian swam around like a croc
Linking major moments in the evolution of ants and angiosperms
Fossil eggshells reveal egg-laying habits of Troodon
These giant snails appear to have been cooked by ancient humans
The term “claw” is used to describe a wide variety of body parts, usually pointy bits at the ends of limbs or digits. In technical terms, “true claws” – also called ungues – are specifically found in tetrapods; they consist of the last bony element of a digit and the hardened sheath that covers it. These come in many forms, including sharp, pointy claws; flattened fingernails and toenails; and even hooves.
This doesn’t include other claw-like structures, such as the “claws” on the feet of insects or the pincers of crabs and scorpions, although these are often used very similarly to the claws of tetrapod animals.
Animals use claws for many purposes: climbing, digging, grabbing prey, keeping traction while running, and plenty more. Claw form and function are tightly tied, so the shape of a claw is usually a very good indicator of how the claw is used, even in cases where the differences are slight; in birds of prey, for example, subtle variations in talon shape are correlated with the varying ways that different species use their talons to handle prey.
Claws Through Time
Claw-like structures have evolved many times in vertebrates, invertebrates, and even plants. True claws seem to have first evolved around the origins of amniotes. Claws are rare in amphibians, but extremely common in reptiles, birds, and mammals, which suggests that early tetrapod claws might have been a key feature among the first amniotes as they explored habitats farther from the water’s edge.
Claws are abundant in the fossil record, including some truly famous examples like the giant claws of ground sloths or the sickle-shaped “killing claws” of dromaeosaurs. The hardened sheath of a claw – usually made of keratin – rarely fossilizes, but the underlying bone does, and the close relationship between claw form and function allows us to make reasoned interpretations about how ancient animals were using their claws.
Some recent claw-related studies:
Comparing modern seriemas with sickle-clawed dinosaurs. Popular article; technical paper.
Analysis of the strange claws of therizinosaurs and alvarezsaurs. Popular article; technical paper.
Oldest fossil grooming claws in primates. Press release; technical paper.
Using claw curvature to identify lifestyle in lizards, birds, and ancient dinosaurs (technical, open access)
Development and evolution of reptile claws (technical, paywall)
Development and evolution of mammal claws (technical, paywall)
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ok, since you mentioned the cat’s claw plant, now you need to do an episode on vines and their climbing adaptations, since about half of the many plants called “cat’s claw” seem to be vines … at least as far as my very limited knowledge of plants goes. : )
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