Herrerasaurus

We move from the Late Cretaceous to the Middle Triassic and about 231.4 million years ago this week to explore one of the earliest and most primitive theropod carnivores that man has unearthed. Herrerasaurus comes to us from Argentina, and Argentina only, and is such a basic animal that debate has swirled it since before I used it in my Zoo Tycoon games where it was definitely a dinosaur. The reason I mention it definitely being a dinosaur in the game is because part of the debate about Herrerasaurus is centered around whether or not it even is a dinosaur! It has been called a basal theropod, a basal sauropodomorph, a basal saurischian, and a non-dinosaurian reptile. Lately, the trend has been to call it a basal theropod and a basal saurischian, according to recent literature concerning theropod evolution. It has even been given its own group, the Herrerasauridae, which includes other very early theropods or similar animals and which are also heavily debated in their pasts as to where they lay in dinosaur evolution.

Herrerasaurus, at first glance, certainly looks like an early dinosaur; it possesses large flexible claws on its hands, a long reptilian skull filled with conical teeth which clearly mark it as a predatory animal, a long flexible tail which was held horizontal from the body for balance, and even the basal ischian pubis found in later theropods (though much more primitive) which caused the femoral attachment to face directly, or nearly so, vertical and thus without having a bowed effect like we see in modern reptiles but a more mammal-like carriage of gait with the legs swinging in a nearly vertical arc of movement like we see with later theropods and other dinosaurs. Mammal-like isn't exactly the best description for the overall movement, but if you think of your own hip attachment (where I am taking mammal-like from in this instance) then you can imagine the movement of the femoral attachment site of Herrerasaurus. Compare this image if you disagree with my description or are still confused:

Herrerasaurus, as well as other dinosaurs and humans, use the femoral attachment schematic seen in the center image, reptiles use the left-most image.

There is a lot to discuss this week concerning this animal and, due to this fact, I may alter some of the days such as Sunday to discuss more of how this primitive dinosaur led to the dinosaurs we quickly recognize and love as children and adults.