To get the kids links out of the way really quickly here:
Dinosaurs for Kids
And now, on to what I wanted to look at today- putting Herrerasaurus into familial perspective. Herrerasaurus is a difficult character, not because of its age, not entirely anyway, but because of what has gone into making up this creature. Any lay person, and professional degree laden paleontologists could include amateur self in this group I suppose, would almost immediately associate Herrerasaurus with dinosaurs. Why then, do the career paleontologists not always necessarily associate the two?
The basal characteristics of Herrerasaurus along with the difficulty in dating Triassic land animal bone beds accurately has something to do with this difficulty. For today we will ignore the bone bed question because that topic alone could take up months and years of study. However, the traits we can look at. Some research has placed Herrerasaurus as a basal theropod, sauropodomorph, Eusaurischia (meaning closer to the most basal of origins of the saurischian tree than true theropods and sauropodomorphs without belonging to either group), and other groupings. The reasons, regardless of which clade, family, or group Herrerasaurus is placed into is because of their very primitive skeletal traits.
The most obvious of these are the ilium and other hip area traits. The ilia of Herrerasauridae are an amazing primitive hodgepodge of traits that can be singled out extensively in singular species down the evolutionary line such as the hour glass shaped vertebral centra seen in Allosaurus, the backward facing pubis seen in dromaeosaurs and birds, and a boot like shape on the pubis end seen in avetheropods. The femoral head sat in a less open area of the bony acetabulum than it would in later dinosaurs' pelvises as well. The ilium was also very basal in that it was held to the backbone by only two sacral vertebrae where more advanced dinosaurs could possess between 5 and 10 sacral vertebrae on average. Additionally, another rather curious fact about Herrerasaurus which raises eyebrows is that fact that not may reptiles at the time at which Herrerasaurus was roaming the Earth were bipedal even part time whereas Herrerasaurus was a fully bipedal running animal thanks, in part, to that partially open femoral-ilium attachment.
Tomorrow, along with Movie Monday, a discussion of the hands and the head of Herrerasaurus!
Oh, also, regardless of what the first 30 or 40 posts were about in this blog,
Happy 300th Post to Me!