Episode 3: Snakes!

I’m sure there’s some kind of joke to be made here about “third time’s the charm” and “snake charmers,” but I don’t know what it would be.

Anyway…

Play and download Episode 3 on PodBean! You can also now find us on iTunes!

The topic this time around… the diversity and evolution of Snakes!

Paleo News
Here’s this episode’s news:
Live Birth in an Archosaur
A fossilized pregnant reptile from China appears to be the first proof of live birth in any member of the Archosauria (that is, crocs, pterosaurs, dinosaurs and all their close relatives). [News Report]
Very Early Venom
A new approach to an old hypothesis: high-tech examination finds support for a venom system in Euchambersia, an ancient cousin of mammals. [News Report by David]
Strange Horse Evolution
An analysis of horse evolution shows that newly-evolved traits are not always associated with rapid species diversification – a surprising contrast to classic evolutionary models. [News Report]
Carnivorous Plants
Here’s a news story without any bones at all! Genetic studies find numerous groups of plants co-opted anti-disease proteins to help digest insects. [News Report]

What’s a Snake?

Snakes are lizards. They aren’t the only lizards with long bodies and reduced legs, but they are the group that has pulled it off most successfully. Even more unique than their body shape are their heads: their skulls are highly kinetic (many-jointed), and unlike any other animals.

ophiophagus_hannah_skull
King cobra skull. You can see that the jaw connects way at the back of the cranium, and the lower jaws don’t fuse at the “chin”. It’s a very mobile mouth. Photo by Mokele on Wikimedia Commons.
pythonleg
Not all snakes have totally lost their ancestral lizard-legs. This is one leg remnant in a Burmese Python skeleton, at the base of the tail. Photo by David

Snakes are incredibly diverse. There are around 3500 species today, belonging to around two dozen families, and they include fast snakes, burrowing snakes, swimming snakes, climbing snakes, sand-hopping snakes, and even gliding snakes. They range from several centimeters to 6 meters (20 feet) long. They eat just about any kind of prey you can imagine, ants to alligators. And all that without legs!

snakesbigsmall
Left: A reticulated python, photo by Gunawan Kartapranata. Right: Barbados thread snake, photo by Blair Hedges. Both from Wikimedia Commons.

Snake Evolution

Snake origins are shrouded in mystery. Exactly how the earliest snakes looked and behaved is unclear, and it’s a classic evolutionary debate as to whether or not snakes’ shared ancestors were burrowers or swimmers. There’s compelling evidence for both, and the debate goes on today.

The earliest snake fossils are from the Jurassic Period, around 160 million years ago. Little is known about them at this time except that they were already pretty diverse, so they probably first evolved some time earlier.

During the Late Cretaceous (100-66 million years ago), snakes had already diversified into marine forms, terrestrial forms, and even at least one large, dinosaur-eating species. Many of these early snakes still had well-developed hind legs!

sanajeh
Sanajeh indicus, a Cretaceous fossil snake discovered in a dinosaur nest in India. Fossils on the left, fossil map on the right. White bar = 5cm. From Wilson et al. 2010

During the Paleogene Period (66-23 million years ago), snakes continued to diversify following the end-Cretaceous mass extinction. This period included some of the largest snakes of all time, including the 10-metre (33-foot)-long Gigantophis from Africa, and the crazy-big 14-meter (46-foot)-long Titanoboa from Colombia.

6890466278_4a8f3643d4_k
Reconstruction of Titanoboa at the Smithsonian Natural History Museum, eating a crocodilian!  Image by Ryan Somma on Flickr

During the Neogene Period (23 million years ago to today), the ancient snake communities gave way to more modern snake faunas as grasslands took over the planet. This saw the rise of some of the most common living snake groups like the colubrids and vipers.

Snake Fossils

One of the biggest challenges paleontologists face while studying snakes is a limited skeleton. Snakes (mostly) have no limbs, hip bones, or shoulder bones. Ribs are abundant, but don’t really reveal much information, and skulls are super-useful but fragile and rare. Most snake fossils are identified from vertebrae – a single snake can have a couple hundred, and for a knowledgeable paleontologist, they can provide very useful information.

fossilsnakes
Most snake fossils look like this: isolated vertebrae. These are some snake vertebrae that David studied from China (left) and South Dakota (right).
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