As I strolled along internet looking for something to blog about, the only thing that I could find was a report that was mentioned a few days ago.
As is typical, it features the world’s most popular reptiles: Dinosaurs.
From left to right: “Fierce eyed Dawn Shark” Eocarcharia dinops and “Old hidden face Kryptops palaios
In terms of diversity, the previous categories are essentially in reverse order. Easily the most diverse dinosaur group was the Ornithischia. They included “duck billed” hadrosaurs, crested lambeosaur…hadrosaurs, horned ceratopians like Triceratops horridus, armoured stegosaurs and super-armoured ankylosaurs. Two legged hypsilophodonts, and helmeted pachycephalosaurs. Ornithischians were all over the map in terms of diversity.
Next up we have the sauropoda (or to be more inclusive: the sauropodomorpha). On the outset one might think that these guys weren’t really that diverse. I mean if you’ve seen one long necked, long tailed behemoth, then you’ve seen them all right?
Sauropods ranged in size from the super tiny Mussaurus patagonicus*, which topped out at 37cm (15 inches), to titans like Argentinosaurus huinculensis, Sauroposeidon proteles, and Amphicoelias fragillimus; all of which grew to excesses of 39.6m (130ft), and had masses 1,000 times greater, with some estimates as high as 122 metric tonnes!
Besides this humongous size range, we also had sauropods that had sail-backs (Amargasaurus cazaui), sauropods that had tail clubs and armour like ankylosaurs (Shunosaurus lii, Saltasaurus loricatus). We even had sauropods with strange beaks and short necks (Bonitasaura salgadoi, Brachytrachelopan mesai).
Finally we come to the theropoda. All are bipedal carnivores (one possible exception in segnosaurs). They came in two size classes: Frickin huge, and medium sized. Some had long necks (Coelophysis bauri), some had display crests (Dilophosaurus wetherilli, Cryolophosaurus ellioti). Many show reduction in arm size, with Tyrannosaurus rex and Carnotaurus sastrei taking the cake for tiniest arms. There was also one weird group that had sail-backs and crocodile like heads (the spinosaurs). Still, in terms of overall diversity, a theropod was a theropod.
Oh, and one group spawned birds, if you’re into that angle.
It never ceases to amaze me at how often the Dinosaur Mailing list, or dinosaur related websites, devote so much time to theropods. Even news stories seem to put more focus on the big meat eaters rather than the numerous plant eaters. Heck just look at how often we watched theropods fight in the Jurassic Park movies (do you know there was never a scene in the JP movies where a theropod attacked a plant eater?).
One is forced to ask why that is. I believe the answer lies in the ecology alluded to above. Though sauropods and ornithischians were a highly diverse bunch, they were all herbivores. The only carnivorous dinosaurs were theropods.
To elucidate this hypothesis even further, check out this story on Digg.com:
Psychologists at Yale University found that the human brain is biased towards images of animals. We are more likely to notice a change in an image, if that change involves animals. I’m going to take this one step further and say that not only are we biased towards pictures of animals, but that bias is even stronger for predatory animals. Especially predators that are large enough to pose a threat to ourselves (e.g. lions, tigers, crocodiles, large sharks, and of course: big theropods).
So there you have it. Theropods might be the plane Jane group of the Dinosauria, but they will always hog the spotlight. Evolution would have it no other way.
*Technically M.patagonicus wasn’t actually that small. The type specimen was a hatchling. Adults were closer to 5m (16ft) in total length. Still small for a sauropod though.