Over the course of evolutionary history there have been a number of animals that have sported elongated neural spines, the structures sometimes aiding in the support of a hump (as in bison) and other times as the framework for a great sail (as in Spinosaurus). Of the group of "sail-backed" and "bison-backed" animals, the pelycosaur Edaphosaurus (the spines of which are pictured above) are unique, and the presence of transverse bars arranged on either side has long vexed paleontologists.
One of the facts that many people come away with after being acquainted with the history of the late 19th century "Bone Wars" is that E.D. Cope and O.C. Marsh named far more prehistoric creatures than were actually present, creating a morass of taxonomy that is still sometimes difficult for paleontology to extricate itself from. One creature that was named by Cope but later folded in to Edaphosaurus was "Naosaurus", an animal that was reconstructed with the body & sail of an Edaphosaurus and the head of a Dimetrodon. A mount a of this creature was created, but it was ultimately disassembled, locked away, or lost (although Dan Varner tells me that Charles R. Knight ultimately fixed a sculpture with the head of an Edaphosaurus, and the now resides at the Academy of Natural Sciences in Philadelphia). You can still find mention of Naosaurus in a few sources, though. In Charles Sternberg's autobiography The Life of a Fossil Hunter, the author briefly describes the excavation of a "Naosaurus" specimen;
Three days [after "I made my first camp on Bushy Creek, ten miles north of Seymour"] I found what I believed promised to be a fine specimen of the ladder-spined reptile, Naosaurus, called fin-backed by Cope. A number of perfect spines were exposed, presenting the possibility of securing a complete specimen. I worked very carefully over this skeleton, hoping to take it out whole and in good shape. It lay in red and white sandstone, which easily disintegrated on the surface into shale-like flakes. The spines and transverse projections, which terminate in rounded knobs, were all broken in situ, and were also flexed and tilted with the strata, so that great care was necessary in following them. They were about three inches apart. I numbered the spines 1, 2, 3, etc., not with reference to their natural position, but to the order in which I came to them. A good many of the rounded ends of the lateral spines were missing, having been washed down the slope. I hoped to find them later.
As I studied these remarkable spines, many of them, near the center of the body, three feet high, with the lateral spines alternating or opposite, I instinctively called the creature the ladder-spined reptile; and I cannot see how Professor Cope could have imagined that these spines had any resemblance to the mast and yard-arms of a vessel, and that there was a thin membrane stretched between them which caught the breeze and acted as a sail. Later discoveries show it to be a land animal.
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How beautiful. It looks like a wrought-iron fence from a Tim Burton movie.
Just a pedantic semantic note: "bison-backed" may be confusing to some readers, as bison <- bi-con <- 2-cone <- 2-horn,
so it might be confused for an animal with 2 horns sprouting from the back, which for all I know may indeed have been the case in some other dinosaur, but probably not this one.
The spine bars are interesting. The "sail": It does occur to me the possibility of a deceptive and/or sexual dimorphic trait, as in the peacock tail. Is this is found only in males? The external spines (if covered by a skin sail or had overlapping plates/"feathers") would give an illusion of great body size to a potential mate or conspecific competitor or predator when viewed from the side rather than the front or rear. It may have instinctually turned sideways when meeting any foe. One indication of this would be the position of the eyeballs, if the eyes only faced forward (tarsier-like) this idea is less likely, but if either eye could view well to the side/front/rear it would be more likely. Isn't that the case in some small reptiles with humps (chameleons)?
I wonder if it wasn't a mimicry device among either Edaphosaurus or Dimetrodon to either nullify the threat/blend in to a group of the other animal. But the cross spines are certainly intruiging.
just an odd coincidence, but i was at the met. museum of natural history today and i actually got into a discussion with someone about the very same specimen in todays photo.. just odd to come home and find it here
I actually saw (in "Die Wirbeltiere" by Otto Jaekel, published sometime in the early 20th century) an old restoration of "Naosaurus" without the sail, i. e. with just the spines sticking out of its back. It looked rather strange.
DDeden: As far as I know, no sailless Dimetrodon or Edaphosaurus have been found, so it doesn't look like only the males had it. Baron Nopcsa actually had the same idea, he thought Dimetrodon might have been the male of Sphenacodon. He was wrong: The two animals didn't even occur together.