Sauropodomorpha and correcting myself

Original Source for the image http://www.gavinrymill.com/dinosaurs/Cladogram/SaurischiaSauropodmorpha.jpg

I said, I would source a rant about phylogeny later and this is my attempt to do so. Already, I have blogged about Crocodilians and Ceratopsians. In the original rant, I wrote:

May I ask, what is your view point? You point to this chart as evidence that “one thing, stayed one thing and never changed into anything else! What we see in the world today and what we read in the Bible is consistent and true.” As already mentioned “W” is Ceratopsians. Do you hold that transitioning from a biped to a quadruped is not changing? “O” is Prosauropods and “P” is Sauropods. Do you hold that quasi-quadruped prosauropods transitioning into sauropods is changing? If “W” is OK, then why is “O” to “P” not OK?

As I already mentioned there are at least three bipedal families in the generally quadruped ceratopsians. By Kerby [1] and Answers in Genesis [2], this is considered variation within a kind. However in this particular phylogeny, prosauropods and sauropods are separate branches. Kerby seems to suggest that each separate branch are their own separate “one thing” that “stayed one thing”.

Prosauropods, like ceratopsians, are both bipedal and quadrupeds[3]. They are named “prosauropods”, because they were thought to have evolved into sauropods. They seemed to be transitioning into obligatory quadrupeality. They grew bigger and their necks grew longer.[4] 

It is difficult to know what Answers in Genesis thinks about prosauropods. The word, “prosauropod”, does not occur on the Creation Museum website. It appears only once on the Answers in Genesis website. [5] Searching for “sauropod” on Answers in Genesis, yields over 300 hits. One contains the following quote:

Sauropods just appear and disappear in the fossil record, without connection and without explanation. According to The Complete Dinosaur, “The ancestry of the sauropods, before they burst onto the world scene on almost every continent in the Middle Jurassic, is obscure.”

No known process of change could derive them from any other known organism, and no evidence of such change is found in the fossil record. [6]

The rest of the paragraph in The Complete Dinosaur, reads:

Seems obvious
when you read
the chart :)

The frequent assumption that they arose from prosauropods, probably melanorosaurids, has yet to be verified. Furthermore, some characters, including the reduction of the fifth digit of the hind foot in all prosauropods (but not in sauropods), suggest that these animals were already too specialized to have served as sauropod ancestors, and that the sauropods may have arisen as a sister group in the Late Triassic. Indeed, the traditional assumption that the quadrupedal sauropods developed from bipedal prosauropods was questioned as early as 1965 by A.J. Charig, J. Attridge, and A.W. Crompton. [7]

So now we come to the portion of this blog where I need to
correct something in my rant. The current prevailing hypothesis is not that prosauropods evolved into sauropods, but that both prosauropods and sauropods share a common ancestor. I stated the following:

Do you hold that quasi-quadruped prosauropods transitioning into sauropods is changing?

As mentioned in The Complete Dinosaur this has long been known not to be the likely case. However, the question can be redeemed...I hope. Why is it not likely that both prosauropods and sauropods are the same kind or in Kerby’s language, “one thing”?

Grazing through Answers in Genesis, it is difficult to know what they think. Again, they only mention prosauropods by name once. They also seem reluctant to assign a non-sauropod ancestor.[8] [9] [10]