Hairy Museum of Natural History

Spiny-Brush Shark Edition

At the dawn of the Carboniferous period, around 350,000,000 years ago, great changes were taking place in the waters of the world. Many once-diverse and successful groups of fish hadn’t made it past the end of the previous period (the Devonian), so a plethora of aquatic opportunities had just become available for the fish that were fortunate enough to survive.

One of these fortunate groups were the sharks and their relatives, collectively known as chondrichthyans or “cartilaginous fish” for their most distinctive feature, a skeleton made largely of cartilage. Chondricthyans exploded into a fantastic diversity of forms during the Carboniferous, many of them odd and bizarre. Some developed tooth-rows like buzzsaw blades or pinking-shears, some grew winglike fins from the sides of their necks, some evolved long, antler-like pincers on their snouts, and some developed large clusters of spines atop their heads and over their dorsal fins. This last group is known as the stethacanthids, or spiny-brush sharks.

Stethacanthus (shown here in purple) is the most-familar of the group, and the most commonly illustrated. Its strange, wedge-shaped dorsal fin topped with dozens of sharp denticles must have cut quite a profile in the Carboniferous seas. Several suggestions have been made about the purpose of this unusual feature. Some have suggested that, from above, the two patches of tooth-like denticles on its fin and head might have appeared to be the gaping maw of a much larger shark. Others have thought that it might have served as a sort of velcro attachment point, allowing Stethacanthus to hitch a ride on larger fish, as remora do with sharks today. Unfortunately for these hypotheses, the spiny-brush of Stethacanthus and the closely-related Akmonistion (at left) were not particularly flexible and probably wouldn’t be of much use in those suggested situations.

One clue comes from the fact that all known stethacanthid specimens that bear the spiny-brush are male (this is easy to tell in most sharks, because males have prominent claspers behind their pelvic fins). Clasper-less (female) stethacanthid specimens are known, but none have been found with the dorsal spiny-brush. Some researchers have classified them as different animals, but it seems just as likely that they are female Stethacanthus or Akmonistion. Fossils of close stethacanthid relatives named Falcatus and Damocles support this idea.

Falcatus (“hook/sickle”) and Damocles (named after the king with a sword hanging over his head) have even more extensively-modified dorsal fins that curve forward over their heads like prongs, with the spiny denticles forming barbs near the tip. A spectacular fossil of two Falcatus from the Bear Gulch Limestones of Montana preserves a prongless, clasperless female was preserved biting the prong of a claspered (and presumably excited) male in what appears to be Paleozoic foreplay. The drawing shown here depicts a Damocles couple in a similar romantic moment.

Because the prongs of Falcatus and Damocles are modified versions of the same spiny-brush that adorns Stethacanthus and Akmonistion, it seems probable that all these sharks used their fins for similar purposes—as distinctive structures that males could use to advertise their prowess, and where females could focus some toothy affection during courtship and mating.

This artwork was used in PowerSharks!, “the Fintastic game for card sharks everywhere” developed by Ray Troll and myself.

—Matt Celeskey.

File under: Carboniferous, Sharks.

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For the sake of completeness (and for those who, like me, can’t get enough of those drepanosaurs), I’ve assembled a list of additional resources to supplement the new Monkey-Lizards of the Triassic gallery.

Happy reading!

—Matt Celeskey.

File under: Reptiles, Triassic.

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Monkey-Lizard Edition

Megalancosaurus preonensis

The Age of Reptiles (Mesozoic Era) kicked off in grand fashion with the Triassic Period, which began about 250,000,000 years ago and ended about 45,000,000 years later. During the Triassic, reptiles evolved to fill almost every corner of the globe. Plant-eating reptiles munched fronds on vast fern praries, stalked by reptiles who very much wanted to much on them. Reptiles could be found ambushing prey in lakes and rivers, chasing fish in the open ocean, and crushing clams on the sea floor. Reptiles spread membranous wings and flew through the skies. And for a few million years near the end of the Triassic, one strange group of reptiles could be found climbing through the treetops. This group was so well-adapted for an arboreal lifestyle that they have been named the Simiosauria, or Monkey-Lizards.

Hypuronector limnaos

Dolabrosaurus aquatilis

More info and art is available in a new Hairy Museum gallery: Monkey Lizards of the Triassic.

—Matt Celeskey.

File under: Reptiles, Triassic.

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Invertebrate tidbits from around the web:

BBC reports on a Cambrian oddball from 500 million years back, Vetustodermis planus. Annelid, arthropod, mollusc, or none of the above?

Also from across the pond, the Natural History Museum’s insect collections are on the move.

And in a spectacular diplay of scientific eye candy, Pharyngula presents brightly-colored steroscopic digital reconstructions of a Silurian Brachiopod.

—Matt Celeskey.

File under: Recent Discoveries.

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The main part of my time in Cobre Cañon was spent at a Sphenacodon quarry. Interspersed between layers of red and grey mudstone lay beautiful, purple-bronze bones from the early Permian—ribs and vertebrae and elegant, sharp-toothed jaws. In life, these bones would have supported sleek, sprawling predators, running down their prey on stout, muscled limbs and dispatching them with bone-crushing bites from their powerful jaws—jaws which, 300 million years ago, were some of the strongest the earth had ever seen.

300 million years of burial, however, weakened them considerably.

I hate to say that much of my first day at the quarry was spent learning how not to collect fossils. Few things can match the frustration of digging through a layer of hardened mud with a dental pick, miscalculating the required amount of force, and uncovering a pile of beautiful, tiny, purplish tiles that are all that remains from a bone that had rested, if not exactly comfortably then at least intact, for more than 15,000,000 generations. Although I feel fairly safe in assuming that the bones’ original owners had long since moved beyond any lingering attachments, each tiny fragment seemed to bristle with unfulfilled promise, accusing me of not holding up my end of the bargain. After all, they had done their part by staying put for an unfathomable length of time, beating astronomical odds on preservation—only to be rendered worthless by a moment’s clumsiness. Each tiny, shattered chip seemed to scream at me with 300,000,000 years of pent-up rage.

How could I argue with that? I accepted the crushing condemnation of the shards with a heavy groan, apologized to the more experienced (and understanding) members of the team, brushed the bits aside, and made a deep and solemn vow to the bone I lost that I would not, under any circumstance, make the same mistake with the next one.

After my third or fourth pile of little purple fragments, I grimly joked, “Well, its not everyone who can say they’ve spent the day beating the crap out of sphenacodonts.”

In the end, though, I did learn enough to collect a few bits and pieces without dinging them up too badly, and hopefully someday the folks in the prep lab will be able to salvage something worthwhile from the jackets we pulled from the quarry. My last day there, I picked up some of the deep red mud that surrounded the fossils, mixed it into a wash, and painted a rough sphenacodont portrait. I brought a few handfuls of the grit home and used it to create the scene you see here, Sphenacodon making its way down to an ancient riverbed. Click on it to open a larger version in a new window.

This piece is dedicated to the bones that I let down.

—Matt Celeskey.

File under: Carboniferous, Permian, Synapsids.

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