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#CrawliesConverge

We are writing on convergent evolution in reptiles and amphibians.
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My favorite example of convergent evolution is that between old (e.g., lappet-faced vulture) and new (e.g., turkey vulture) world vultures. Both groups of scavenging birds fill the same niche in their habitat and look so much alike that scientists classified them together until we had genetic tools to tell us otherwise. Turns out that new world vultures are more closely related to storks than old world vultures, which are raptors (e.g., hawks, eagles). That characteristic bald head, easier to keep clean when regularly submerged in carcasses, has independently evolved in both lineages. Like all the classic examples of convergent evolution, the bald head is a physical trait shared between lineages… So what about behavior?

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Kin-based sociality has been well-known in Egernia skinks, an Australian lineage, for some time. White’s skinks, for example, live in small, stable family groups, usually consisting of an adult male, adult female, and their kids. But we actually have (at least one) lizard in North America doing the same thing.

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Desert night lizards also form small, stable groups and juveniles are often found in groups with one or both of their parents and siblings. Unlike the vulture’s bald head, convergent social systems are not so easily explained. Davis and colleagues (2011) speculated that viviparity (giving birth to live young) may have led to similar social systems, but there are many viviparous lizards and snakes that, as far as we know, are not social. White’s skinks and desert night lizards do share a common habitat theme: a home where they stay or return to each winter. White’s skink families tend to occupy a single rock crevice or burrow and desert night lizards overwinter together under fallen Joshua tree logs. Again, there are numerous lizards that occupy similar habitats but are not, as far as we know, social.

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Now you’re probably asking yourself, what about snakes? Well, you can read my thoughts on how rattlesnakes may be doing similar things here.