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Crocodiles and birds have more in common than you might think

It may seem hard to find two animals more different than a hummingbird and an crocodile  But as strange as it may be, birds and crocodilians (the group containing alligators, crocodiles and gharials) are each other’s closest relatives.  In fact, crocodilians and birds are the sole survivors of a much larger and more diverse group called the archosaurs. Archosaurs translates into ‘ruling reptiles’ which explains why it contains all extinct dinosaurs and pterosaurs (flying reptiles).  Archosaurs actually were ruling reptiles for a while, at least in a certain sense.

One large division among vertebrates is synapsids vs. diapsids.  This division is named for holes in the skull. Diapsids have one more hole in their skulls (to lighten them) than do synapsids; ‘di’ meaning ‘two’.  Synapsids include all mammals and the ancestors of mammals, the ‘mammal-like reptiles’. During the Permian Period, the mammal-like reptiles were doing very well, occupying a large amount of niches available.  

The Permian-Triassic extinction changed the balance though.  Enough mammal-like reptiles died off that it left the door open to the archosaurs, which is why we see the beginnings of true dinosaurs appear in the Triassic.  200 million years ago toward the end of the Triassic is when the first crocodilian fossils show up. Of course, it was a while later before modern birds arrived.  

Computer illustration of an Archosaur, Image Credit: Michael Rosskothen/Shutterstock

Modern birds eventually evolved from dinosaurs.  The similarities between today’s birds and extinct dinosaurs are numerous – they have similar hip sockets (different from any other animals), they both have feathers, the feet of some dinosaurs were eerily similar to those of modern birds.  Looking at dinosaur trackways drives home the last point; the first scientifically described dinosaur tracks were hypothesized to be bird prints.  Given the thinking of the time, it was even suggested that the tracks were those of the ravens Noah released from the ark.  It’s easy to see the similarities between extinct dinosaurs and modern birds – they even nest in similar patterns. But you still have to dig a little harder to find the connections between crocodilians and birds.  

Of course, dinosaurs (birds) split from crocodiles at some point in the distant past, specifically sometime in the Triassic.  Interestingly, there is a fossil animal that showed up around when this split should’ve occurred. Carnufex was discovered in North Carolina in 2003, according to PLOS.  North Carolina State University reports that researchers led by Lindsay Zanno reconstructed Carnufex and found the creature to have a combination of crocodile and bird traits.  Carnufex seems to represent the beginning of a split between what would one day become modern birds and those that would become modern crocodilians.

Carnufex was about nine feet long, which shows that at that early time, land dwelling crocodile-like animals were competing directly with early dinosaurs for niches as top predators.  Eventually dinosaurs pushed those that would become crocodilians into their own niches but for a while, there were eerie similarities between the two.

For anyone who’s watched a sea turtle pulling itself laboriously across a night time beach to dig a hole with her back flippers and lay eggs, only to leave them, it’s obvious reptiles aren’t good parents.  As soon as the turtle has filled in her hole, she crawls back to the ocean, leaving only an odd trackway and her hidden eggs to mark her passage. I’ve even watched sea turtles dig holes too low in the tide where water fills their nests and lay their doomed eggs anyway.  Birds, on the other hand, are great parents.

For three months I helped collect data on nesting sea birds, especially black-legged kittiwakes.  The parent kittiwakes dutifully take turns sitting on eggs while the other is out hunting the sea for fish and other food.  There were variations in the parenting care for sure. When it was time to measure the eggs or chicks, most of the parents would simply fly from their nests, returning an hour later to resume parenting.  Some birds were relentless, like angry soccer moms out for blood. These birds would scream and circle, diving at the head of whoever was collecting data on their baby. Either way, the kittiwakes all put in a lot of time caring for chicks despite squabbles over prime nest platforms.  

Sometimes a pair would be pushed from their nest and replaced by a new ruthless pair of parents hungry for prime real estate.  Once I watched a new pair take over a nest with a chick. Instead of killing the chick or letting her die, the new pair simply adopted her, feeding her fish until she could fly away.  These are some of the more anthropocentric reasons that many people look more kindly on birds than other reptiles – they’re good parents, they perhaps even show something we could call empathy.  Interestingly, this is one trait shared between birds and crocodilians.

When I interviewed for a position as a kayak naturalist guide in the Everglades, the head guide told me he’s only been rushed by an alligator once – when someone on a trip knocked baby alligators off a log without him noticing.  Crocodilians are better parents than sea turtles, and mother crocodilians can be similar to mother bears; if you mess with their babies you better watch out! All crocodilians put a bit of effort into building nests, digging a hole or mounding vegetation depending.  Rotting vegetation can actually warm the nest, incubating it. Some species depend on specific temperatures to determine the gender of the young. When the infant crocodilians are hatched, they’re carried in their mother’s mouth when danger is around. According to the San Diego Zoo, the only species that doesn’t carry her young this way is the gharial with a mouth too narrow for its young.  Crocodilians stay with their mothers for about a year, riding on her back and learning to swim. But it isn’t just behavior, either.  

According to the Harvard Gazette, researcher, Arkhat Abzhanov has been looking at genes involved in bird and crocodile development.  Unsurprisingly there are some very similar genes expressed in very different ways between the two groups.  After all, birds and crocodilians are just two small pieces of the mystery and science of evolution that connects us to all life on Earth.       

By Zach Fitzner, Contributing Writer                                

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