Mounted specimen on display at the American Museum of Natural History, NYC
Model on display at Dinosaur State Park, Connecticut
When: Late Triassic (~ 230 to 204 million years ago)
Where: North America
What: Rutiodon is a phytosaur. We have looked at another phytosaur before, Redondasaurus, which was one of the biggest and most derived of the phytosaurs. Rutiodon falls on the other end of the phytosaur family tree. Rutidon was about half (~25 feet/7.5 meters) as long as Redondasaurus, but as it was built so much more slenderly, it is more accurate to say it is only 1/3rd or even 1/4th the size of its gigantic relative. This different body construction naturally translated into a different mode of life in Rutidon. Notice how slender and long its snout is? Some modern crocodiles have this same style of snout and they are predominately fish eaters, thus it is likely that Rutidon was as well, and it did not prey on terrestrial vertebrates.
Phytosaurs strongly resemble modern crocodiles in other ways, and Rutiodon looks even more like a crocodile than many others of its kin. But this animal is most assuradly a phytosaur, /not/ a crocodile. One easy way to tell is if you look at the front end of its snout, look how the upper jaw is bent? That is a clear phytosaur feature. Another thing to look for is the position of the nose holes. Rutiodon has the phytosaur position of back near the top of its skull - whereas crocodiles have them in the more typically place at the end of the snout.
Minor side trivia about this particular specimen of Rutiodon. It is number FR:AMNH 1, this means it was the first specimen to be catalogue into the fossil reptile collection. This specimen comes from a coal mine in Chatham County, North Carolina, and was collected by the famous paleontologist William Diller Matthew in 1895.
Mounted specimen on display at Harvard Museum of Natural History
Reconstruction by Jaime Chirinos
When: Cretaceous (~ 125 - 99 million years ago)
What: Kronosaurus is an australian plesiosaur. Yes, it is a plesiosaur even though it lacks the long neck that many people associated with the group. Plesiosauria is roughly divided into two groups; Plesiosauroidea - the long necked forms and Pliosauroidea - the short necked forms. Kronosaurus is an example of the latter clade, and shows many of the defining features of this group - such as an enormous head with massive jaws, a short neck, and a relatively short tail- the opposite in many ways of their cousins the plesiosauroids. This australian sea monster was one of the largest of its clade, with estimates of up to 33 feet long (~10 meters). Its teeth reach almost 5 inches (~12 cm ) long in crown length - the part above the gumline. The total tooth would have been over double in size. The large size of its teeth, combined with distinct shape and the lack of clear cutting surfaces also for their easy identification if they are found as isolated material.
The Kronosaurus specimen seen above was found in on private property in central Queensland, Australia in the 1920s. A crew from Harvard was shown where the specimen was weathering out, and set about excavating the fossil. After years of work, the specimen was boxed up into over 80 crates, weighing in at over 6 tons and shipped to the states, where it was mounted at the Harvard museum. Decades later the original discoverer of the material finally got the see the results of the preparation and mounting of what he termed ‘his dinosaur’ at the age of 93. In life Kronosaurus was a top predator; there are fossils of Elasmosauridae plesiosaurs that show bite wounds that could have come from Kronosaurus! No fish for this animal, it was after much bigger prey, leading to amazing plesiosaur vs plesiosaur encounters. Or so I like to imagine!
Mounted specimen at the Museum of Paleontology at the University of Michigan.
Reconstruction by Dmitry Bogdanov
When: Triassic (~235 to 225 million years ago)
What: Hyperodapedon is a very basal saurian on the line leading to the archosaurs (dinos (including birds!) and crocs). As it is not either on the dinosaur linage or the crocodile lineage, it is insted refered to as a member of Archosauromorpha rather than Archosauria proper. Hyperodapedon lived during the latest Triassic and was one of the dominate herbivores. Its enlarged front teeth may look scary, but they were for shearing tough plant material. The enlarged upper teeth fit perfectly into a groove on the upper jaw, creating a natural pair of scissors. It is thought that Hyperodapedon did not only feed on exposed plant material, but that it dug up tubers and roots as well via the relatively enlarged claws on its hind feet.
Hyperodapedon was about 6.5 feet (~2 meters) long, making it one of the largest Rhyncosaurs. This group as a whole is one of the most common finds in all but the latest Triassic deposits, sometimes representing up to 60% of the recovered skeletons. Most of the rest of the fauna from these deposits was also basal archosauromorphs, with dinosaurs and crocodiles making up a very small percentage of the biota. By the end of the Triassic though, simular localities were instead dominated by true archosaurs. The reason for this quick replacment has been much debated, but it is now relatively well accepted that this was not a matter of ‘out compitition’, but that rather there was an extinction event roughly 225 million years ago that wiped out Hyperodapedon and its close relatives. Dinosaurs and Crocodiles, the archosaurs, then radiated to fill the now open ecospace.
Drawing of Skeleton by Sterling Nesbitt.
Reconstruction by Sean Murtha
When: Late Triassic (~205 - 200 million years ago)
Where: Found only in New Mexico
What: Effigia is an archosaur from the late Triassic of the Southwestern United States. Archosauria is the group that includes crocodiles and dinosaurs (including the birds), so looking at this it might seem like its fairly obvious it it a therapod dinosaur. Nope! Effigia is actually on the crocodile-line side of the archosaurs. The close resemblance to the therapods is another great example of convergent evolution, these things just keep happening!
Effigia was collected from the Ghost Ranch fossil site in New Mexico decades before it was recognized as a crocodile-line archosaur (Crurotarsi). The specimen was discovered by then graduate student Sterling Nesbitt as he was preparing out material from the Ghost Ranch fossil blocks. Nesbitt was working on studying the theropod Coelophysis at the time, and knew there were many unprepared specimens in the museum collections. These blocks were collected under the supervision of Edwin Colbert, but they were not prepared as he felt there was enough Coelophysis material prepared out already, and that there were no other large vertebrates to be found in the quarry. Nesbitt showed this was very wrong, as in one block he found a great surprise, an ankle that clearly did not match that of dinosaurs, but instead was a crocodile-type ankle. He followed the rest of the skeleton out though several separate jacket blocks, going back to the original field notes to find where all of these blocks were hiding in the massive collections. When he had fully prepared out the skeleton, he found something very amazing. A crocodile relative that was fully bipedal and had a toothless break. Later studies have confirmed that Effigia is indeed on the evolutionary line of crocodiles, not therapod dinosaurs, and has actually resultant in the recognition that at least one taxon previously placed as a theropod is infact a crocodile relative. The name ‘Effigia okeeffeae’ comes from the latin for ghost, and in honor of Georgia O’Keeffe, who payed many visits to the Ghost Range Quarry, including the day the blocks were originally removed.
Mounted skeletons from the Melbourne Museum of Natural History
Reconstruction on display at the Carnegie Museum of Natural History
When: Early Cretaceous (~130 to 100 million years ago)
What: Psittacosaurus is a ceratopsian. Yes, a ceratopsian like Tricerotops or Styracosaurus, even though it has no horns or even a neck frill. You have to start somewhere! Psittacosaurus is an extremely basal ceratopsian, with some studies finding this animal in the first group to branch off from the clade. Italso was most likely bipedal (quick remake all the reconstructions!), as its forelimbs were much shorter than its hind-limbs, and it possibly could not even rotate its hands enough to put its palms flat towards the ground. This isn’t really surprising, as despite the large number of quadrupedal dinosaurs, the last common ancestor of all dinosaurs has been reconstructed to be bipedal. Psittacosaurus was a plant eater, but it did not have the grinding cheek teeth of later ceratopsians, so it swallowed stones to help it grind its food. It is also possible that it fed on nuts, as its beak has been reconstructed to function very well as a nut-cracker.
There are hundreds upon hundreds of fossil specimens known for Psittacosaurus, making it one of the most well understood of all dinosaurs. There are over 10 species known, with the best known Psittacosaurus mongoliensis, reaching about 6.5 feet (~2 meters) long at its extreme maximum. This includes an amazing slab specimen that was preserved in soft mud that shows this little ceratopsian had bristles on the top of its tail. It is thought these were used for communication between individuals, and it is debated if these are homologous (same evolutionary origin)to the feathers of theropod dinosaurs or not. There is almost a full ontogenetic (growth) series of specimens, with oodles and oodles of hatchings to subadults. The close association of many hatchlings and adults shows that these ceratopsians, like many dinosaurs, had a good amount of parental care of the young dinosaurs.
One benefit of so many specimens is that destructive sampling can be used - this is where the original specimen is damaged, or even destroyed, to provide some information about the animal. Cutting long bones and examining the resulting cross-sections has lead to the determination that Psittacosaurus lived to about 10 to 11 years old.
Remember Repenomamus from a couple of days ago? The juvenile dinosaur found inside was a Psittacosaurus.
When: Early Permian (299-271 Million years ago)
Where: North America
What: Diadectes is a large reptiliomorph. That means that it is on the line towards amniotes (reptiles and mammals), but is not quite there yet. Diadectes is closer than most reptilomorphs, and is found in many studies to be the sister taxonto the amniotes. It is thought to have been amphibious, but spending most of its time on land. The dentition of Diadectes clearly marks it as an herbivore; its front teeth were procumbent(they tilted forward) and its cheek teeth were blunted and fairly wide compared to other stem reptilomorphs. Diadectes was one of the first large terrestrial herbivores, though it was not the only one of its time. Edaphosaurus was a synapsid (‘mammal-like reptile’) contemporary of Diadectes. The herbivorous diet of these two taxa was attained convergently, as there was by this time a large amount of plant material covering the land.
Diadectes looks very reptilian, and in fact some early studies placed it as a true reptile, but odds are the clade is belongs to is not directly ancestral to any of the amniotes. Though Diadectes with its large bulky form and size of up to 9 feet (~3 meters) is convergent on later reptiles such as Scutosaurus, the first true reptiles were small lizard like insect eating forms, such as Hylonomus.
Reconstruction by Matt Celeskey.
Mounted specimen on display at the American Museum of Natural History, NYC. I could find no reconstruction I liked so have a picture of Barnum Brown next to the specimen for scale.
When: Miocene and Pliocene ( ~11 to 3 million years ago)
Where: India, Pakistan, and Indonesia
What: Colossochelys is a very large land turtle. It mostly roamed in what is now India, but fossils have been found in Pakistan and parts of Indonesia as well. It reached almost 9 feet (~3 meters) long with an estimated weight of about 1 ton. For comparasen the living Galapagos tortoise is about 6 feet (~2 meters) long, and weighs 880 lb (~400kg). Colossochelys is the largest land turtle ever known, but larger turtles swam though the prehistoric seas, such as Archelon. It is thought that this extinct turtle lived much the same way as giant turtles today do, eating plants and drawing into its shell for protection from predators. They vanish from the fossil record at the dawning of the modern Ice House climate, about 2-3 or so million years ago.
This giant turtle has been known by other names in the scientific literature, and some museum displays have not been updated. So do not get confused! It has been labeled both Geochelone atlas and Testudo atlas in the past. Why the change? Turtle systematics have been in a state of confusion for a while, and both of these genera were found to be massively polyphyletic. This means that they were essentially random groupings of taxa that did not share a close relationship to one another to the exclusion of all other turtles. Colossochelys altas is not at risk for a name change again (due to this reason at least!) as it is the only member of this genus.
Also man, isn’t that just the happiest looking fossil you have ever seen?
When: Early Jurassic (~200 to 189 million years ago)
Where: North American and Europe
What: Ichtyosaurus is an Ichthyosaur (shock!). These fossils are common throughout western Europe, and thus the history of study extends back to the late 17th century. The first fragments known were found in Whales and published in 1699, but it was not until 1811 that a complete specimen was discovered on the southern coast of England by Mary Anning (who was an absolutely amazing paleontologist who you should all read up on). This was only a skeleton, however, and the first reconstructions of the marine reptile omitted a dorsal fin. The full morphology of the 6 and a half foot (~2 meter) long Ichtyosaurus (which is small for an Ichthyosaur!) was soon known due to the dozens upon dozens of complete skeletons found in the Holzmaden limestone quarry in Germany. These amazing skeletons commonly preserve soft tissue outlines, and so it could be seen that these reptiles were even more convergent upon dolphins than first assumed. They even gave birth like dolphins do, as seen in the amazing specimen above. Before specimens demonstrating that Ichthyosaurs had developed vivipary (live birth) were discovered, it was thought this beast had to drag itself on land to lay eggs, and you can find some really early reconstructions out there showing this behavior. It is thought that many, if not all, of the specimens demonstrating live birth did not actually die during childbirth; rather the mother-to-be died and sank to the bottom of the ocean and the unborn fetus was ejected during decomposition.
Ichthyosaurs compared to modern dolphins is a remarkable example of convergent evolution, though the reptilian roots of Ichtyosaurus and its kin are evident at a glance. it preserves hind flippers and has a vertical tail instead of a horizontal tail. Both of these trails relate to the different movement mechanisms in reptiles vs mammals; reptiles move side to side, whereas mammals have a more up-down movement. Thus, while the hind flippers of a marine reptile are useful for steering, they only increase water resistance for a dolphin. These two styles of movement are not just in aquatic animals. Think of how a lizard moves vs a dog. The lizard’s hindquarters shift side to side in relation to its front, whereas the dog pulls its rear legs forwards with no side to side motion.
When: Late Triassic (~210 million years ago)
What: Vallesaurus is the most complete drepanosaur (monkey lizard) ever found. This tiny lizard is only 6 inches (~16 cm) long, making it much smaller than most of its relatives. Like the rest of the clade it was an arboreal lizard, with not only long fingers and toes well adapted for gripping branches, but also a prehensile tail. Prehensile tails have developed several times in both reptiles and mammals, with chameleons an example of a living prehensile lizard. In many ways Vallesaurus and its close relatives can be thought of as triassic chameleons, occupying the same tree-dwelling and insect -eating reptile niche. More derived drepanosaurs also have opposed fingers, as in chameleons, and evidence of the same mechanism that allows chameleons to quickly dart their head forwards to capture prey. Little Vallesaurus itself does not have these adaptations, as it is a fairly primitive drepanasaur, and it is likely that it moved though the trees much faster than the rest of its clade and modern chameleons. Thus, it is shown that this group was already well adapted at climbing trees before converging upon a modern chameleon body plan. The vast majority (if not all) fossils of Vallesaurus and its kin are found in lake deposits, showing that these animals were at home high in the tree tops, with branches that reached out far over the waters. And that despite the large suite of climbing adaptations, they sometimes misstepped and took quite the plunge.
Vallesaurus is not closely related to any living lizard. Its clade is yet another group of ancient reptiles that do not have a very well understood position in the tree of life. However, it is universally agreed that they are diapsid reptiles, and more closely related to archosaurs than to lizards.
Reconstruction by Matt Celeskey at the New Mexico Museum of Natural History & Science
Mounted specimen on display at the American Museum of Natural History, NYC.
When: Late Permian (~252 million years ago)
What: Scutosaurus is an extinct reptile. It lived during the end of the Permian, and was one of the giants of its time. It reached lengths of over 8 feet (~2.5 meters) and was massively built. This bulky form was a plant eater, and in a way was the cow of its time. Scutosaurus lived in what is now Russia, and during the Permian this land was a semi-arid expanse. Thus, it is thought the herbivorous Scutosaurus would have had to have a large range in order to find enough food to support its huge body. Its flattened teeth imply it was able to grind up branches and other plant material that was not exactly the most nutritious of options. Scutosaurus was most likely a slow moving form, protected by its large size and the many osteoderms that covered its skin.
Scutosaurus is not closely related to any living reptile. It is an anapsid reptile, which is a grade of stem taxa that fall outside of the modern clade of reptiles (turtles, crocodiles, lizards, and birds). At one point it was thought turtles fell into this variety of stem reptiles, but more and more evidence is placing them closer to other living reptiles. Scutosaurus, like most of its kin, went extinct in the massive end Permian extinction event. As the fauna rebounded in the Triassic, the niche of large plant eaters was filled with basal synapsids at first, but by the end of the Triassic massive plant eating dinosaurs started to appear and quickly dominated.