Friday, October 26, 2007

Secodontosaurus: The "Fox-Faced Finback"

When first discovered in the 1880s, Secodontosaurus was a petrified enigma. The slender muzzle meant its bite would have been a quick snap – perfect for small, hard-to-get prey. But the body was huge, almost 250 pounds, and the low, massive forequarters could perform heavy work.

This new species could also easily be confused with the Dimetrodon - both have four stubby limbs and tall fins on their backs. However, it had an unusually narrow skull - hence the nickname "Fox-Faced Finback" - which was probably used for some kind of adapted feeding strategy, like burrowing.

(c) Robert T. Bakker

And, instead of the Dimetrodon's enlarged killing fangs, Secodontosaurus had a long row of small teeth, each sharp-edged like a little knife blade.

This species is also much more rare than Dimetrodon, fossils of which are all over the Texas Red Beds. The last fossil of Secodontosaurus found there was unearthed in 1936.

That is, until dig team member and teacher Nancy Lauletta Bowen discovered a piece of one in 2006. This is the first Secodontosaurus fossil found in 70 years, and it's the first excavated with modern, CSI methods - which means that much more diverse information has been preserved about this fossil than any other of its kind.

Lauletta Bowen and Dr. Bakker point to her Secodontosaurus find. Detailed image below.

Seymouria, our hometown favorite

In case you haven't guessed it already, Seymouria is our hometown favorite because this species was discovered near and named after Seymour, TX - the town situated closest to the fossil beds that made Texas Dimetrodon Central.

Seymouria was small, about two feet long, with many razor-sharp teeth in its triangular head as well as legs that were both longer and stronger than the first amphibians - meaning that it could live in water and on land. In fact, some scientists can't agree whether Seymouria was a land-loving reptile or a water-addict of the amphibian class. The consensus seems to be that this species marks the evolutionary transition between the two.

This scientific conundrum is found almost exclusively in the Red Beds of Texas - yet another reason to keep digging for more evidence.

Multiple Seymouria are often found curled up together, meaning that they might have been burrowers. The team has found Seymouria vertebrae and leg bone fossils at the main site, and an almost complete backbone from one individual at another site, that looks so strong "You could probably stand on it," according to Dr. Bakker.

Diplocaulus, aka "Boomerang Head"

The weirdest species the team has found in the Red Beds is the “Boomerang Head,” or, as it's officially known, the species Diplocaulus, meaning "two tailed," a reference to its double-spined tail bones.

It has an extrememly odd-looking body, with a flattened body and legs. The head, however, is pulled out to the sides in the shape of a boomerang - so extremely that by adulthood, the head could be 4 to 6 times wider than it was long. It was armor plated as well, with extremely strong jaws.

Some scientists contend that this shape may have helped Diplocaulus glide through the water - but the flattened lower body could not have contained the muscles of a strong swimmer. It's much more likely that this was an ambush predator, who waited unseen on the bottom of a murky river until unwary prey came along.

It's also possible that the skull served as a defensive mechanism - in which Diplocaulus may have used the points of its head as sideways horns to punch with - or as an aid for mating. Since Diplocaulus' eyes were on the top of its head, finding and impressing a mate by sight would be near impossible. So, a larger skull makes a love connection much more likely.

In any case, it's hard to imagine a predator - even the mighty Dimetrodon - swallowing this easily.

(c) Robert T. Bakker

After Dimetrodon, Diplocaulus fossils are the next most common find at the team's site. They've found pieces of skull - which has a unique shiny, pitted surface that feels very much like it came from a living thing - everywhere they look. They've also found leg fossils and pieces of backbone that show how incredibly strong this species was - perhaps the strongest example of sideways locomotion that's ever evolved.

A piece of Diplocaulus skull discovered at the HMNS site.

Texas Red-Beds: World's Largest Dimetrodon Cemetary

The Texas Red Beds are the finest, most gloriously complete fossil record of a critical threshold in evolution: The Dawn of the Land Ecosystem. The fossil record at this location shows us the rise of the first top predator the world had ever seen on land - as well as the many species it hunted.

Kimberly Beck looks closely for tiny fossils that might lead to a new excavation site.

But we didn't always know what we know now. The discovery of the Texas Red Beds came late in the history of paleontological science. Dinosaurs, Pterodactyls and Woolly Mammoths were all found far earlier. But there was the immense slice of time, labeled the Paleozoic Era - which begins with the Cambrian roughly 540 mya and ends with the Permian, about 250 mya - with almost no fossil record. Museum cases had only a few bones from Russia.

All that changed when Philadelphia paleontologist E.D. Cope discovered fossils in the Texas Red Beds in 1877. Not one or two or a dozen pieces - thousands of bones. Scores of species. Complete skulls, nearly every tooth in place. Entire feet, every toe perfect. Torsos and shoulders, hips and tails.

Chris Flis and Johnny Castillo prepare a Dimetrodon spine to be removed from the site.

About 80% of the big vertebrates (defined as having a body weight 100 pounds or more) found in the region were reptiles. The most formidable were carnivores growing up to 400 pounds, as heavy as a modern-day tiger - what would eventually be called Dimetrodon. It soon became the most well-known of all Red Beds' new species, and it ruled over a land ecosystem full of primitive reptiles.

Now, as in Cope's era, the Red Beds are a harsh environment- unfailingly hot and dry, with ground water in the summer that's a nasty brew of alkali and pink mud, heated to the temperature of afternoon tea. So much calcium is dissolved in the water that a few weeks camping out could give you kidney stones.

Since the Cope's discovery, dozens of scholars have braved the elements to dig into the Red Beds of Texas, and their efforts have given us 95% of all known fossils from the Paleozoic era - including many, like Seymouria, that are known almost exclusively from Texas Red Beds sites. Fossils found here continue to serve as the standard for the rest of the world.

A new discovery in the Texas Red Beds.

(Information excerpted from Texas Redbeds Revolution, by Dr. Robert T. Bakker.)

Xenacanthus: Permian Oddball

Xenacanthus was an oddball shark, even for a prehistoric species. It was shaped like an eel, with a nasty poisonous spine sticking straight out of the top of it's head. Since it lacked the well-known speed; large, fearsome teeth; and seemingly endless jaw capacity of modern sharks, it's comforting to know the poor guy had at least this one way to defend itself from the big, bad Dimetrodon, the Godzilla of the Permian world.

(c) Robert T. Bakker

Xenacanthus was found exclusively in freshwater environments - like the swampy shallows of North Texas 290 mya, but also all over the world, in places like Europe, Australia, South America and North America - such as the Museum's site near Seymour. It would have slithered through these ancient waters like an underwater snake, using a fin that ran along its back from head to tail.

This Permian oddball was part of an evolutionary line of sharks that first appeared in the Devonian, proliferated like mad through the Carboniferous and Lower Permian periods before taking a final bow towards the end of the Triassic. 220 million years in all - not bad.

Field sketch of Xenacanthus with Diplocaulus - possible prey? (c) Robert T. Bakker

By nature sharks don't make good fossils - most of their bodies are soft cartilage, which decays before the necessary processes can take place. However, Xenacanthus jaws and braincases were hard bone, meaning that we can recover more of this species that most other sharks. In Seymour, the team has found pieces of these, along with lots of Xenacanthus teeth and poison spines. Also in the area - shed teeth and coprolite from Dimetrodon, meaning this wasn't a site Xenacanthus came to relax.

Xenacanthus vs. Dimetrodon: a battle of epic proportions

"Imagine you’re the star of the Red Beds, a big, bull Dimetrodon. You’re just lounging around the edge of a wide lake, on a sultry hot day near the present-day town of Seymour, Texas. Time: 285 million years ago.

A stream of ripples is coming towards you, like a low-speed torpedo just below the surface. You’re reptilian brain is intrigued….you take a few steps closer…

Worried? Nope. You’re the biggest, baddest predator in the ecosystem. A quarter ton of taut muscle and bone. All your neighbors on land fear you. Your saw-edged fangs can bite through any reptile’s hide. You’re the fastest thing on four legs – you have limbs longer and quicker than anyone your size.

Suddenly, the lake erupts in an explosion of fins and fangs. Great gleaming shark teeth slash through the spray..."

Dr. Bakker holds a Dimetrodon humerus found at the site to illustrate its location in this species' body.

Like a scene from the Jaws: The Pre(history)quel, Dr. Bakker describes a scene we might have witnessed in Seymour, had we been there almost 300 million years ago. Dimetrodon fangs meet the sharp teeth of a Xenacanthus, a species of prehistoric shark that's completely unlike the species we know today.

To begin with, they don't have a dorsal fin - so the situation described above would have been missing the obligatory Spielberg-ian music.

"Complete Xena skeletons from Germany show a most un-sharkey profile. The body has no pointy dorsal fin at all. Instead, there’s a low, continuous fin extending from the back of the head all the way to the tip of the tail (with a slight notch over the bum). No shark alive today has that fin design."

No forked tail fin.

"The tail is long and muscular and strong but hasn’t a hint of a fork – the tail just gets thinner and thinner towards the rear and finally ends in a point. Xenas couldn’t generate the thrusts needed to accelerate into a great, long burst of speed, white-shark fashion."

No giant teeth.

"Xenacanth teeth weren’t great, huge saw-edged fangs. The xenacanth chompers were tiny. Each one had two thin, sharp cusps, sticking up at and angle, plus an even smaller cusp between the two main cusps. That dental design is not for chopping up big victims. It’s for snagging small fry."

Field drawing of Xenacanthus with Diplocaulus, a freshwater neighbor. (c) Robert T. Bakker.

Doesn't sound very threatening. So what makes Xenacanthus a shark?

"The skeleton around the brain says so. Braincase elements are the most complicated sector of the whole skeleton, because there are dozens of muscles, nerves, arteries, veins and joints. And each major division of fish has its own way of designing a braincase. Take apart the braincase and put it back together. It’s built like a shark."

So was Xenacanthus a Dimetrodon-slayer? Based on the evidence found by the team in Seymour, the answer is an emphatic no.

"We find giant, saw-edged shed teeth all around the Xenacanth corpses in Seymour, and elsewhere in the same general layers. The biggest shed teeth are mighty daggers, fifty millimeters tall, reinforced with a central pillar of enamel and dentine, and sharp-edged front and back. A tooth like that could kill any xenacanth shark. The ballistic evidence is overwhelming – these shed teeth are the “bullets” left at the crime scene by the shark-eater."

So, despite today's sharks' reputation as super-predators, Xenacanthus had a reason to be scared.

(c) Robert T. Bakker

"Shed Dimetrodon teeth are everywhere, including all the spots where shark skulls and spines are dug. The CSI evidence is undisputable – finbacks ate sharks, including big sharks."

But Xenacanths were by no means defenseless. They had a potent weapon to fight back.

"The Xenacanth head spine is the tip, the spine is smooth and ultra-sharp, so it would penetrate easily into the mouth of any predator foolish enough to grab the shark by the front end. It probably wasn’t a passive weapon. It has a strong, moveable joint with the head, so muscles and ligaments could have pivoted the spine around."

Plus, the spine was poisonous. Back to the battle:

"Our big bull Dimetrodon is watching a Xenacanth, as it zips out to grab its prey. The big finback isn’t shark-wise. His hunting instinct kicks in. He can’t resist the temptation – The quarter ton reptile leaps with jaws wide open. He bites down hard to inflict the killing bite. A searing pain penetrates the Dimetrodon’s mouth. It’s like being stabbed with a red-hot poker.

The finback staggers backward out of the water, rubbing his face into the soft red mud – the goop soothes the pain just a little bit. It will be a week before the swelling goes down.

Next time he will treat Xena with respect."

(Quotes excerpted from Xena - Warrior Shark Princess, a Red-Beds Surprise, by Dr. Robert. T. Bakker.)