Everybody loves dinosaurs.
That’s just a fact. Dinosaurs are huge, awe-inspiring, amazing animals. They’ve been extinct for 66 million years. They inspire our imaginations and stimulate our curiosity. We always want to know more.
I had (who am I kidding, I still have) a box of plastic dinosaurs when I was a kid. It was all “dinosaurs” to me for a while, but then I started showing my true nerdling colors, and I started learning everything I could about my dinosaurs. That was when I learned that they weren’t all dinosaurs at all.
Dinosaurs belong to the group of reptiles called archosaurs. This includes still-living crocodiles and birds. But the Mesozoic—the period of time spanning from 252 to 66 million years ago—was known as the “Age of Reptiles”, not just the age of dinosaurs. Other kinds of reptiles, from the completely bizarre kinds that lack any living relatives, to gigantic relatives of modern monitor lizards and snakes, also dominated this time period. Pterosaurs (another group of now-extinct archosaurs) dominated the skies. Gigantic crocodiles swam in the rivers and oceans. Some crocodiles, early on in the Mesozoic, even grew very large and looked rather dinosaur-like.
We always think of the land-based reptiles. The dinosaurs, the pterosaurs, the crocodiles. And that means we miss one of the most spectacular group of reptiles ever—the marine reptiles. The ocean during the Mesozoic was a time of rapid evolutionary change, an arms-race between predatory animals and their prey. Prey species, like clams and mussels, were growing thicker shells—those that didn’t have thicker shells were crushed by large crabs or enormous marine reptiles. In response to those thicker shells, predators that could crush those shells were more successful. This led to a very different ocean than what had been seen before the Mesozoic.
Dominating these oceans were the marine reptiles. These included ichthyosaurs (“fish-lizards”), which are aptly named as they do strongly resemble large fish, mosasaurs (named after the Meuse river, where their fossils were first found), which are large marine lizards closely related to monitor lizards and snakes, and plesiosaurs (“near-lizards”), which are a unique group of reptiles more closely related to ichthyosaurs than anything else. There were also groups of fully marine crocodiles that lived exclusively in the ocean, and got quite big.
Plesiosaurs are, perhaps, the most famous Mesozoic marine reptile—the famed “Loch Ness Monster” is purported to be a plesiosaur. (This is impossible, as Loch Ness did not exist before the last Ice Age!) There are two major “groups” of plesiosaurs; long-necked and short-necked. Long-necked are categorized by having a long neck and a short head, and a mouth filled with long, sharp teeth that often jut out of the mouth. Short-necked plesiosaurs are categorized by a short neck and a long head with long, narrow, crocodile-like jaws. Both setups are perfect for catching slippery fish.
Ichyosaurs are also famous, large-eyed, fat-bodied reptiles that look almost identical to the untrained eye to tuna, or perhaps a dolphin. Like dolphins (but unlike tuna), they breathed air and lacked gills. They did have flippers, like dolphins, and a tail fin, but their fin was held vertical, not horizontal, like a dolphin’s. They also would have feasted on fish, squid, and crustaceans, as well as, perhaps, the occasional swimming ammonite (a hard-shelled mollusk related to the squids and nautilus). Just recently, an ichthyosaur with blubber was found—showing that these reptiles were even more similar to dolphins than we thought!
The one few people have heard of are the mosasaurs. Probably because, while ichythosaurs dominated the oceans of the early Mesozoic, and Plesiosaurs show up in the middle Mesozoic, mosasaurs don’t show up and truly dominate until the late Mesozoic, the Cretaceous. But mosasaurs are, in my opinion, the most impressive and dominant predators in the Mesozoic seas. Some species of mosasaurs, like Tylosaurus prongeri, could reach at least 40 feet long. Centre College has a specimen of Mosasaurus hanging in the front foyer of Young Hall, courtesy of Dr. Jack Hankla—come by and check it out!
80 million years ago, the center of North America was underwater. Parts of Arkansas, Texas, Oklahoma, Kansas, Nebraska, Montana, and central Canada were covered in the shallow, warm, Western Interior Seaway. This shallow epicontinental sea was home to millions of amazing marine animals, and Erth’s Prehistoric Aquarium will show us what it might have been like to dive beneath those waves and swim with the great Mesozoic marine reptiles. Though, thankfully, without the chance of getting eaten.
Dept. of Biology
Mark Lucas is an Assistant Professor of Biology at Centre College. Falk has expertise in paleobiology, evolutionary biology, functional morphology, and fossil behavior. Her current research interests are studies of fossil avian anatomy, avian ichnology (the study of preserved behavior known as trace fossils—footprints, burrows, etc.), comparative studies of modern avian anatomy, studies of modern avian footprint production and tracemaking behavior, laser-stimulated fluorescence of fossils, and paleobiodiversity and mass extinction.
For more information regarding Erth’s Prehistoric Aquarium Adventure.