Charles teaches college courses in geology and environmental science, and holds a Ph.D. in Interdisciplinary Studies (geology and physics).
Mesosaurus and Its Fossils
You may reasonably wonder why a 270 million-year-old lizard is such a big deal. Turns out, it just happened to live in the right place at the right time. And that made it possible to use its fossils as evidence of the biggest idea in geology: plate tectonics.
Mesosaurus, meaning middle lizard, is the name of a genus of extinct aquatic animals that lived in the southern hemisphere during early Permian time. Genus names are very often descriptive. In this case, the reason for the 'lizard' part of the name (-saurus) is obvious; its body shape resembles that of modern lizards. The middle part of the name might refer to its size, or to its physical characteristics (midway between primitive and more advanced species), or to its place in the evolutionary path of reptiles (about halfway between their first appearance and dominance); or all three, or something else.
On top of all of that, there is today some doubt about whether mesosaurus were reptiles at all. If that is true, it means they weren't lizards, either. Because of the type of rocks in which the original fossils were found, they were presumed to be marine (ocean-living) reptiles, or at the least land-dwelling reptiles that returned to living (at least part of the time) in an aquatic environment.
Many paleontologists still think they were a type of reptile, but recent research has called that conclusion into question. Some researchers classify them as having a common ancestor with reptiles (making them first cousins, in effect), and others have even suggested (based on skull features) they might have belonged to the same group of animals from which mammals evolved (known as the synapsids).
Interesting, huh? This lack of agreement is just the kind of debate that makes paleontological conferences so enthralling!
Most Mesosaurus fossils have been found in rocks that were deposited in shallow coastal waters, but a few fossils have come from rocks deposited in very salty water and even fresh-water lakes. It seems that the animal was suited for a wide range of aquatic environments.
Mesosaurus had a long tail, and its elongated skull, which seems a tad undersized for its body, had the nostrils on top. It might even have been able to float near the surface, like modern crocodiles. It had a mouth full of sharp, outwardly angled teeth, nicely adapted for snagging small, swimming prey.
Adults averaged around one meter long, tip to tail. Its webbed feet were probably used for propulsion, and the narrow body was just perfect for slicing through the water. But could it walk on land? Sort of, maybe. The bones in Mesosaurus elbows and ankles weren't designed for traipsing along the beach, but it might have been able to push itself forward with its back feet, rather like sea turtles do today.
Mesosaurus were amniotes (egg-bearers) but fossilized embryos do not appear to be contained in eggshells, so the inference is that they gave live births like other marine reptiles do.
How This Relates to Plate Tectonics
Mesosaurus lived during the early Permian Period, from 299 to around 260 million years ago. They died out before the massive, end-Permian extinction that killed off a large percentage of marine and terrestrial animals.
During the Permian, all of the earth's land mass was combined into the supercontinent called Pangaea. Mesosaurus fossils are found today in rocks in southern Africa and eastern South America. Back in the Permian those two locations were jammed against each other as part of the southern half of Pangaea called Gondwana, so the living range of Mesosaurus did not span an entire ocean.
In fact, the distribution of fossils was one of the pieces of evidence that Alfred Wegener, a German geologist and meteorologist in the early 20th century who came up with the concept of continental drift, used in putting together his hypothesis about the existence of Pangaea.
Mesosaurus were a group of aquatic animals that lived in the southern hemisphere during early Permian time. The Permian Period was the geological time period spanning from around 299 to around 250 million years ago.
They were aquatic predators, and may have been one of the first land animals to return to an aquatic lifestyle. They share many physical features with reptiles, but debate continues over whether or not they were. Some scientists believe that Mesosaurus were synapsids, the group of animals from which mammals evolved.
Mesosaurus fossils were found near what would be considered the southern half of Pangaea, also known as Gondwana. They were used by Alfred Wegener, an early 20th century German geologist and meteorologist who came up with the concept of continental drift, as evidence for the existence of Pangaea, which was all of the Earth's land mass combined into a supercontinent.
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