The Obligate Scientist: A Dinosaur on the Christmas Dinner Table

If you recall my post from back around Thanksgiving, the Wild Turkey -- like all birds -- is a modern day dinosaur. What better opportunity to share this little fact with your friends and family than over the Christmas Turkey?

Below are some resources for turning the remains of your holiday feast into a biology lesson, but before we get into details I want to first answer a simple question: What exactly is a dinosaur anyway?

Dinosaur's are a group of (mostly extinct) reptiles that arose around the early Triassic period about 230 million years ago (mya). They persisted until the mass extinction event that occurred 65mya at the end of the Cretaceous period, (also the end of the Mesozoic era and start of the Cenozoic era), when all of the dinosaur lineages save modern birds died out.

To put this talk of dinosaurs and birds into perspective, lets take a crash course in vertebrate taxonomy. Starting with the ancestor of all land vertebrates, we can follow evolution forward to the present, noting major points of divergence along the way. We're of course skipping a lot, taking the fast track from the first vertebrate land animals to modern day birds.

The first amphibian-like terrestrial tetrapods appeared over 350mya (Late Devonian into the Carboniferous period), with the Synapsids (whose descendants became the modern mammals) splitting off 25+ million years later. Another 25 million years or so later, ancestral turtles and other Testudines appeared, then the sphenodonts (the tuatara) and the squamates (lizards and snakes), then crocodilians, then dinosaurs and birds.

These relationships can be summarized as follows (here I've included proper group names as well as extant representatives):

Amniotes - Descendants of the first egg-laying terrestrial vertebrates (~ 340mya) split around ~325mya

Synapsids - Mammalian ancestors

Mammals ~ 200 mya

Primates ~ 55+ mya

Human-Chimp Split ~ 5-10 mya

Saurapsids - Modern Reptilians

Anapsids - Turtles
Diapsids - Other modern reptiles (including birds), split ~ 300mya

Lepidosauria -Tuatara, Lizards and Snakes

Sphenodonts - Tuatara
Squamates - Lizards, Snakes

Archosauria - Crocodilians, Dinosaurs (including birds)

Crocodilia

Dinosauria - Two dinosaur groups diverged ~250 mya

Ornithischia - "bird-hipped", beaked - but not birds!
Saurischia - "lizard-hipped", toothed ancestors of birds.

Sauropodomorpha - big herbivores like Diplodicus.
Theropoda - bipedal carnivores like T. rex, Velociraptor and...

Aves - modern birds, originating ~ 150mya

Whew! So to sum up, birds have been around since their divergence from the other dinosaurs during the Cretaceous period (145-65mya), and are the only surviving Dinosaurs of the big Cretaceous extinction 65mya. Their closest living relatives are the Crocodilians (together with dinosaurs and other relatives, these are the Archosaurs), then the lizards and snakes (which all together form the Diapsid reptilians), then turtles (all together, the Saurapsids). After all the reptilians, the next closest relatives are the mammals (all together, these are all of the living Amniotes), then amphibians, fishes, etc.

So how do you bring all this information to the dinner table? Well the easiest way to see the relationship between dinosaurs and birds is from the differences and similarities in their skeletal structure.