Who Are My Closest Reptile Relatives?

Common grackle in Toronto, Ontario (photo from Wikimedia Commons)

3 November 2020

Since the 1980s scientists have known that birds are highly specialized dinosaurs that survived the K-T extinction 66 million years ago. Dinosaurs were reptiles. Therefore so are birds. Who among the reptiles is the bird’s closest relative?

The cladogram below shows how mammals and reptiles had a common “stem reptile” ancestor. However, during the Carboniferous period mammals diverged from the rest of reptiles and became very different (left branch).

(from a diagram at biologycorner.com, Creative Commons license)

During the Permian, Turtles diverged from the rest of the reptiles. Later the Archosaurs did, too (far right branch). Some of the Archosaurs resembled crocodiles.

Rutiodon validus (image from Wikimedia Commons)

Crocodiles didn’t change much in the past 80 million years.

Crocodile (image from Wikimedia Commons)

But dinosaurs changed a lot and the Theropod dinosaurs became birds!

Microraptor gui (artistic restoration from Wikimedia Commons)

These unlikely relatives reunite at the St. Augustine Alligator Farm Zoological Park where wild birds nest in the trees above the crocodiles.

Rookery at St. Augustine Alligator Farm (photo from Wikimedia Commons)
Saltwater crocodile at St. Augustine Alligator Farm (photo from Wikimedia Commons)

(photos from Wikimedia Commons, diagram derived from Creative Commons licensed cladogram; click on the captions to see the originals)

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