Land Before the Dinosaurs...
What would make a good state fossil for Oklahoma? Scientists, laypeople, and children all have their prehistoric favorites.
Dimetrodon might be a good compromise critter. Children would like it because it’s spectacular and sort of looked like a dinosaur. But scientists might appreciate it because it wasn’t a dinosaur. What was it?
Dimetrodon can be thought of as a cousin of the reptiles that evolved into dinosaurs. To understand its place in the animal kingdom, we must step back in time further than the Permian Period, when this odd creature lived.
More than 350 million years ago, certain fishes evolved into creatures that could crawl or walk on land. Gradually, these early landlubbers traded in their gills for lungs, but still couldn’t survive far from water. They had evolved into amphibians. Even today, most frogs and salamanders lay eggs in water that hatch into young with gills, such as tadpoles. Just as modern amphibians thrive in tropical rainforests, the first amphibians found moist, swampy coal forests to their liking.
Eventually, some amphibians evolved the ability to make eggs with hard shells that could be laid on dry land. We call these liberated amphibians reptiles.
There was lots of land — and water — to occupy, and these pioneer reptiles had little competition. They evolved into turtles, snakes, lizards, and crocodiles, dinosaurs, flying pterosaurs, and such marine animals as mosaurs, ichthyosaurs, and plesiosaurs. Most of these animals became extinct by the end of the Cretaceous Period some 65 million years ago.
Still another group of pioneer reptiles were the synapsids or mammal-like reptiles. It’s strange they aren’t more widely known, for their descendants survived the Cretaceous along with turtles, snakes, lizards, and crocodiles. In fact, they included our ancestors.
Pelycosaurs
The most spectacular mammal-like reptiles were the pelycosaurs, or sail-finned reptiles. Pelycosaurs had short legs that sprawled out to the sides, similar to crocodiles. Over time, they evolved into species whose legs held their bodies off the ground, akin to dinosaurs and mammals.
Dimetrodon was the best known of the carnivorous pelycosaurs. Growing to a length of 11½ feet, it wasn’t big by dinosaur standards. But pelycosaurs ruled the late Pennsylvanian and early Permian periods.
Some people might say pelycosaurs were more primitive than the dinosaurs that evolved later. But Dimetrodon was in some respects ahead of its time.
All the teeth in a Tyrannosaurus ’ mouth were shaped like daggers, while all of a Brontosaurus ’ teeth were blunt pegs designed for eating plants. Dimetrodon was similar to modern mammals in that its teeth were varied. The dagger-like teeth in the front of its mouth were followed by teeth designed for slicing, similar to a cat.
Today, many mammals have even more varied teeth. People, for example, use their front teeth (incisors) to take a bite out of an apple, using the molars in back to chew the apple and the teeth in between to bite chunks out of meat. We even have pointed canines, though they’re nowhere as long or sharp as the canines found in baboons, cats or dogs.
One thing mammals didn’t inherit from pelycosaurs was the magnificent sail some species sported. Long spines stretched upward from the vertebrae that made up Dimetrodon ’s backbone. Skin stretched between these spines was well supplied with blood vessels.
Scientists think sun shining on these sails warmed the animals. If this was the case, then they probably turned at an angle to the sun or sought shade when they became too hot. Or did they pant like dogs or go swimming?
The Permian Period was the last period of the Paleozoic Era. During the Permian, North America slammed into Africa and Europe, raising the Appalachians. All the continents joined to form the super-continent Pangaea, which was covered with vast deserts.
By the early Permian Period, when Dimetrodon lived, the magnificent coal forests of the early Mississippian and Pennsylvanian periods had already vanished. It appears that these sail-fins lived along a “Gulf Coast” that shifted back and forth near today’s Oklahoma-Texas border. Rivers watered lush vegetation along the coast that was similar to the earlier coal forests. If there were already deserts inland, they probably didn’t appeal to large animals adapted to a cool, moist climate.
A pelycosaur that shared Dimetrodon ’s world was Edaphosaurus, which was about the same size. Its teeth were designed for eating plants, however.
It’s tempting to think that carnivorous mammals evolved from Dimetrodon, while herbivores evolved from Edaphosaurus. However, scientists think all mammals evolved from carnivorous pelycosaurs. Over millions of years, their fierce teeth evolved into tools useful for catching fish, chewing through hard-shelled nuts, grazing grass, or crushing clams. And some mammals, like anteaters, have no teeth at all.
Geology & Fossils
Where can you find a pan full of oil with a handle made of ice? Where can a buffalo rub shoulders with an alligator? The answer is Oklahoma, a geographic and cultural crossroads. Oklahoma is shaped like a pan, the “panhandle” is covered with Ice Age sediments, and oil is buried deep beneath Oklahoma.
Three great geological regions converge in Oklahoma — the Great Plains in the west, the Central Lowlands in the east and, in southeastern Oklahoma, the highlands that extend from Missouri and Arkansas.
Scattered across Oklahoma are smaller areas of rocks from various geological periods. A few dinosaurs have been discovered in some of these areas.
The Paleozoic
Fossils of marine invertebrates that lived long ago in the Paleozoic Era can be found in places in eastern Oklahoma, where most rocks date back more than 230 million years to the end of the Permian Period. Rocks in the Ozarks and Ouachitas (Oklahoma’s highlands) may be even older.
The Ice Age
Sediments left from Ice Age glaciers cover Oklahoma’s Panhandle. Fossils of animals that lived during the Ice Age, or Pleistocene Epoch, are found here and elsewhere across Oklahoma.
Fossils in Our Lives
Oklahoma’s most important fossil resource is its fossil fuels. Extensive coal beds occur in northeastern and central Oklahoma. But the state is best known for the petroleum, natural gas, and coal which account for about 95 percent of its mineral production.
Oil is found in almost all of Oklahoma’s 77 counties, often in conjunction with natural gas. Tourists flock to Capitol Site No. 1, an oil well on the grounds of the capitol in Oklahoma City. It and nearby wells tap a vast reservoir over a mile beneath the surface.
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