Posted by: Rob Viens | July 6, 2013

How the Lizard Lost His Legs (and Grew Really Big)

In early July, Darwin was back on board the Beagle and preparing for another trip to points south.  But at the moment, it was the many “treasures” he collected in Maldonado that still caught his attention:

“Have been employed in arranging & writing notes about all my treasures from Maldonado. — The Captain informs me that he hopes next summer to double the Horn. — My heart exults whenever I think of all the glorious prospects of the future.” (June 30-July 2)

Oh – if he only knew the treasures that awaited him, Darwin would have to agree that this was quite the understatement.  Furthermore, what would he think of the all the species – living and fossilized –  that would be discovered over the next 180 years?

One such species, discovered recently (in 2009), was a really, really big snake.  With that discovery in mind, I thought I’d follow up my last post with a few words about the origin of snakes and some of the larger representatives to grace the Earth over the past 100 million years. Part of this story actually comes from the South American fossil record, so it seemed relevant, as well as timely.

Snakes evolved from a lizard-like ancestor (though remember not to think of this as a modern lizard – but instead a lizard-like ancestor to both snakes and modern lizards). As with any other examples of evolution, these ancestors lost there limbs because having legs must have been a disadvantage in some way. In other words, those lizards with smaller legs had a better chance of surviving (and reproducing) than those with larger legs.   So generation after generation, the legs of these snake-ancestors got smaller and smaller until eventually they had no legs at all.  (The fossil record seems to suggest that they lost the front limbs first, as there are fossil snakes with hind limbs and some modern snakes (pythons and boas) that still have vestigial hind limbs.

This (to me anyway) raises two questions: when and why? The first is a little easier, to let me start there.

The earliest fossils that have been currently identified as part of the snake lineage are about 100 million years old. One of those early snakes was Najash (from about 90 million years ago) which still had hind legs.  Interestingly, although many of the earliest snake fossils where first found in the Middle East, this particular species was found in Patagonia.

Najash – notice the back legs (from Lost Beasts).  (Modern interpretations, however, suggest it was fully terrestrial.)

Najash from Lost Beasts

Najash, by the way, is named after the snake that tempted Adam and Eve in the story of Genesis.

As to the “why” – the leading hypothesis is that snakes adapted to hunting prey in underground burrows.  Underground, in a burrow, limbs can actually be a disadvantage.  They can slow you down or get “hung up” and injured.  Without them, a snake can be more agile, and hence, more likely to capture their prey.  Those that eat, survive. (Other characteristics of snakes –such as having transparent, fused eyelids and no external ears – are also consistent with moving through a burrow.)

Not all snakes go underground, however, so some have speculated that snakes evolved from marine reptiles, such as mosasaurs.  The large number of early snake fossils found in marine sedimentary rock lends some support to this idea.  Najash was a terrestrial snake, but proponents of this hypothesis would suggest that after evolving in the sea, snakes migrated back onto the land.

In any case, the story of snake evolutions is still, shall we say, evolving…

Fossil of Eupodophis descouensi, a fossil snake from about 90 to 100 million years ago (from Wikipedia Commons):

Eupodophis descouensi fossil

As snakes continued to evolve, they diversified into over 3000 species that can be found today. In addition, they grew larger. Paleontologists working in the Middle East last century, discovered the “dinosaur” of the snake world – a 33-foot long snake called Gigantophis.

The problem with giving a snake the name Gigantophis is that we are always finding new fossils, and inevitably someone will find a bigger species. (This happened with sauropod dinosaurs resulting in escalating names such as Titanosaurus, Supersaurus, Ultrasaurus, and Seismosaurus. To be fair, the last two “species” turned out to be existing sauropods and the names did not stick. But you get the idea.) Sure enough, someone did find a larger snake – and now we have Titanoboa. (What’s next Gargantua?) Titanoboa, which was discovered in Columbia, grew up to 50 feet long and may have weighed up to a ton!

Titanoboa (and friends) by Jason Bourque (via Smithsonian.com)

Titanoboa

So what exactly does a 1-ton python eat? The canned answer is “anything it wants, of course”, but the real answer is not necessarily simple. Titanoboa lived bout 60 million years ago – shortly after the extinction of the dinosaurs. So many of the large land animals that could have served as potential prey had recently gone extinct.  And living off a diet of mice would probably not have exactly been practical (you’d need an awful lot).  At least one source suggests that these monstrous snakes were mega-crocodile hunters (there is one in the picture above). What would Steve Irwin think of that!

I digress further, but paleontologists also found a 1-ton turtle that living in the region of Columbia at the same time as Titanoboa – named Carbonemys (ita also shown in the painting above with Titanoboa).  Did these two monsters fight it out – an epic precursor to the modern-day battles of Godzilla and Gamera?  Although possible, no evidence exists, but that didn’t stop Bob Strauss from speculating a bit about what it would be like (see Carbonemys vs. Titanoboa – Who Wins?)

The Smithsonian Channel did a show on Titanoboa which is available online in its entirety.  I’ve not had a chance to see it, but feel free to take a look below and, if you have a chance to view it, please leave a comment and let me know what you thought.

Back to the present, where the longest snake we have to worry about is the reticulated python – the largest of which reached a mere 32 feet long. (The heaviest snake – a green anaconda – has a maximum recorded weight of “only” about 550 pounds.) (RJV)

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