Tuesday, November 6, 2007

A Case of Mistaken Identity

In science, it's important to keep an open mind, so you can evaluate all the facts equally and come to the most accurate result. This statement has the virtue of being true - but it's also convenient code for "oops!"

Yesterday, we reported the discovery of two separate Edaphosaurus found in two distinct layers at the K2 site. Early this morning, Dr. Bakker was examining several of the Daffy fossils from the lower layer, when two of them fit together, perfectly - in a way that couldn't possibly come from an Edaphosaurus. What we actually had was a single, giant Diadectes vertebra.

The first bones discovered at the lower level of the K2 site yesterday; the large bone on the right is one of the two we believed to be Edaphosaurus - until today.

At the K2 site yesterday, Dr. Bakker holds what was believed to be an Edaphosaurus vertebra.


The two pieces, together - a Diadectes! The seam can be seen running diagonally through the middle.

Here's how we know:

The fossils show evidence of four interlocking surfaces. Edaphosaurus - and humans, for that matter - have only two. However, Diadectes has four. Due to these extra connections, Diadectes could not twist its spine from side to side as we do, for example, when we turn to look over our shoulder.

However, these extra interlocking surfaces made Diadectes incredibly strong. As Dr. Bakker put it, "We could all stand on its back and ride it into town. Pound for pound, this species might have the strongest backbone that has ever evolved."

So, you certainly won't catch Diadectes dancing to Chubby Checker, but it had strength in spades. The question is - why? Why would an herbivore need such impressive might?

Another identifying feature is the actual structure of the individual vertebra - which can be seen more clearly when the two parts found are put together in the right way, as they were this morning. Diadectes vertebrae have an enormous superstructure - the part running along the top - that made each bone very top-heavy. This also made the top of the spine stronger, which was required for Diadectes - the stress of walking went through the top of it's spine, rather than the center.

So, one of our Daffys is really a single Diadectes - they are commonly found as individuals at Red Beds sites, so this is normal. But why? Were they loners by nature? Or were there great, unpreserved herds roaming the Permian plains somewhere else?

Reagrdless, this one was found near a shed Dimetrodon tooth, which is the first CSI evidence the team has uncovered of Dimetrodon eating Diadectes.

So what about the other supposed Edaphosaurus? We have 7 Edaphosaurus vertebrae from the upper level of the K2 site that do not have the additional interlocking surfaces; in addition, they do have distinctive bumps on the vertebrae that are only present in Edaphosaurus.

Now we just have to find the rest. In the meantime, here are some pictures from today's efforts, at the Amy site, a slope leading in to the main dig area:

The HMNS team begins to dig on the Amy site this morning. So far, they've found a site with several Dimetrodon fin spines in place (left); a site with tiny fossils of fish scales (top) and coprolite; and a site with many examples of Xenacanthus cartilage (right).

A tiny Xenacanthus tooth. In the background, a team member excavates a site yielding fossilized cartilage from this species.

The jawbone of a Permian amphibian, found by Kathleen Zoehfeld this morning.


An unidentified (so far) vertebra found at the Amy site this morning.
We'll post more information on today's finds this evening. What are you curious about? Let us know!

4 comments:

ryan mcmorris said...

which one will win a fight out of the dimetrodon and a raptor if thay lived at the same time??

Anonymous said...

How do you know if you have found a fossil or just a VERY odd looking rock?

Houston Museum of Natural Science said...

Hi Ryan,

I think you got your answer from Dave today in class - but it would definitely be the raptor. They're warm-blooded which gives them much better reflexes and speed.

Thanks for your question! Check back soon for more from the team.

Erin

Houston Museum of Natural Science said...

Hi there,

When you're looking for fossils in a pile of rocks, you look for organization - rocks that are in the shape of bones; rocks that have bilateral symmetry; and color - the fossils here tend to have a gunmetal color to them, a purplish blue. And, it takes practice - you get better at finding them the more you go out looking.

Once you get them back to a lab, you can put them under a microscope to determine whether they have holes for blood vessels or bone crystals.

Thanks for your question!

Erin