If you couldn’t tell I’m just cuckoo for Dimetrodons and Edaphosaurs and Eryops’es and Diadectes’es and Lysorophus’es and Seymourias and Captorhinus’es and Secodontosaurus’es and Varanosaurus’es…
Our newest dig site has a really great Dimetrodon, and that has us very excited because of the odd preservation and deposition. We are typically used to floodplain sediments, but this guy, nicknamed George, was preserved in conglomerates, which is essentially cemented gravel. Highly unusual for our area. Plus, the conglomerates seem to be Pennsylvanian limestone as well which dates back thirty or more million years, so double-weirdness.
So this is what we have…
Part One… The Setting
A Dimetrodon carcass that was swept downstream intact and articulated during a major flooding event in which older gravel has been stripped up and re-transported. The skeleton was still covered in flesh and muscle and tendons and so on as it flowed in the mix of gravel before settling to its present location. The finer sands then swept in as the flood concluded, so the majority of the bones are in the gravel, with portions of them in the overlying sands. The sand and conglomerates over time contributed to the excellent preservation of the bones, leaving them free of hard, penetrating and destructive caliche rinds. Over the past few thousands of years or so, the bluff that exposes the channel has been eroding, along with the conglomerate tombs.
Part Two… Who the heck is giganhomogenes?!
So our main bone bed a few miles to the west of the George site has a prettttty specific cast of characters. Abundant boomerhead Diplocaulus’es and Dimetrodon’s of the species grandis and loomisi. That’s pretty important. Our ecosystem at the main quarry represents two specific species of D-Don. The classic Dimetrodon giganhomogenes is really nowhere to be seen. Neither is any evidence of the boomerheads. The bones tell the story of who they are. Grandis is, well, grand. Very large, robust vertebrae. Truly a big boy in the Permian. Loomisi, the most common D-Don at the quarry is a pretty girl, so to speak. Very long, skinny vertebrae. Many of our D-Don skeletons have nicknames that refer to actresses with long necks. Don’t ask. Uma, for instance, referring to Uma Thurman, is a beautiful D-Don with a long, pretty neck. Keira Knightly, another loomisi with a long neck. Grandis has its own celebrity necks represented too. Alec Baldwin, for example is a D-Don with, er, a very wide, short neck. I suppose if grandis was human, he would be represented by William “The Refrigerator” Perry, the old great Defensive Lineman for the Chicago Bears. Basically, sporting a cervical vertebrae that is enormously robust and short, covered by thick muscles, gives the beast the impression of no neck at all. And then we have giganhomogenes. Described early in the history of Permian fossil studies back in the late 1800’s early 1900’s. The vertebrae are weird… short and stocky like grandis, but narrow in the middle of the centrum. Right in-between loomisi and grandis. George is the first of his species we’ve seen in articulation or partial articulation. The neck is hauntingly similar to a loomisi. However, when you look at his sacral and lumbar, and thoracic vertebrae, you are astounded by the difference.
George is pretty weird. Even his neural spines are odd. Loomisi has a pretty square, dainty neural spine. Grandis, very square, light grooves running up the side, but fat. Very very fat. Giganhomogenes seems to have some fluctuating thickness on his spines. They begin flat-ish in the articulation to the vertebrae, then widen grotesquely and then narrow again quickly, retaining a very strong figure-8 cross section. They also seem to lean posteriorly, which is much different than what we’ve seen in loomisi and grandis, whose neural spines are for the most part erect. So imagine if you will, the typical Dimetrodon with a fin whose spines rise straight up from the vertebrae. George’s fin seems to sway gently back. Pretty nifty.
Part Three… Now what?
The slope that has been weathering out for a few million years is loaded with fragments of neural spines. Most likely, George was laying on his side, his fin facing towards the eroding bluff. As the conglomerates weathered away, the fin fragmented along with it. The first project was collecting all the loose fragments, which number in the hundreds. Next, we have been digging into the soils at the base of the bluff that have accumulated from the weathering. These “float” sediments contain hundreds of fragments as well. Then we focus on the “in-place” sediments at the top of the bluff where we suspect the origin of the body is. There, we discovered and plaster-jacketed a portion of his skeleton represented by a few articulated neck bones, a few ribs, and a few sacral vertebrae. As we dig in to the hard sandstone overlying the gravel conglomerates, we have been finding more evidence of George, including ribs, spines, and possibly parts of a pelvis. A beautifully preserved adult D-don femur, or thigh bone, was found a few meters away, which may or may not be a part of George. We’ll be studying that more and making our conclusions. Right now its fifty-fifty as to who it belongs too.
George is coming along. He has many many more secrets to give us before we have a good idea of why he is where he is, and more importantly why his is, what he is. Stay tuned for more updates from the field!