Your Daily Fossil

Cotylorhynchus

Fossil specimen on display at the American Museum of Natural History

Reconstruction by Hirokazu Tokugawa

When: Permian (~299 to 265 million years ago)

Where: North America 

What: Cotylorhynchus is a member of one of the most basal groups of synapsids, the  Caseidae.  Cotylorhynchus was a herbivore, and reached lengths of up to 20 feet (~6 meters) long, with a massive barrel chest, putting weight estimates at around 2 tons. This animal is very large for its time… well at least its body is. Cotylorhynchus has one of the most extreme cases of ‘tiny head’ I have ever seen. Even more so than the sail-backed Edaphaosaurus! Which is closer to modern mammals than Cotylorhynchus is. It is one of the most primitive animals known that unambiguously falls on the synapsid lineage. It is so basal that it does not even have any differentiation seen in its dentition, though there are less teeth than found in the non synapsid contemporaries of this wee-headed creature. 

Ophiacodon

Mounted specimen on display at the American Museum of Natural History, NYC.

Reconstruction by Dmitry Bogdanov

When: Late Carboniferous to Early Permian (~305 - 280 million years ago)

Where: North America

What: Ophiacodon is a basal synapsid, meaning it is more closely related to mammals than modern reptiles. It was a fearsome predator of its day, with a long snout (over half of its skull length) full of pointy teeth. These teeth are so sharp that they are reminicent of the fangs of snakes - the name Ophiacodon means ‘Snake Tooth’. Ophiacodon reached up to 10 feet (~ 3 meters) in length and is thought to have preyed upon its fellow tetrapods rather than insects, as many previous predators focused on. 

Ophiacodon occurs very early in synapsid evolutionary history, it is even more basal than the ‘sailbacks’; almost at the base of the spilt between the major living aminote clades. Ophiacodon is part of the group Ophiacodontidae, which ranged from Mid Carboniferous to the Early Permian. About a half dozen genera are known for this group, and they all were good sized predators. Ophiacodontids and other basal synapsid clades were once grouped together under the name pelycosaurs, however, this group is not monophyletic/a natural group. That means that some synapsids that were held as pelycosaurs are more closely related to mammals than they are to other ‘pelycosaurs’. ‘Pelycosaurs’ can be though of as an evolutionary grade in the synapsid lineage; these are the members of our group that more closely resemble reptiles - they had sprawling gaits and their their teeth were not differentiated - there is not even a distinct canine. Ophiacodon and its kin are assuredly synapsids, however, as shown by the single opening behind their eye sockets - their single temporal fenestra. 

Rhynchonkos

Reconstruction by Smokeybjb. 

When: Late Permian (~275 - 270 million years ago)

Where: Oklahoma, USA 

What: Rhynchonkos is a very rare amphibian that lived in the swamp land covering what is now Oklahoma in the Permian. It was about 4.5 inches (~11 cm) long, not counting the tail, with an extremely elongated body and tiny tiny limbs. The elongation of its body compared to other amphibians was accomplished via replication of vertebrae, not elongation of each individual bone.  Rhynchonkos had at least 36 pre-sacral (before the hips) vertebrae. Its mouth was full of rows of tiny teeth, and it is likely that it ate insects and small fish in its swampy home. Older literature about this animal refers to it as Goniorhynchus rather than its current name. This change is due to the fact that the fossil taxon was named in 1970, however, a moth was given the name Goniorhynchus in 1896. Stupid insects. At least it wasn’t a beetle this time! The name  Rhynchonkos was applied in 1981. 

The phylogentic relationships of Rhynchonkos are fairly uncertain. For some time it was held as a close relative of modern caecilians (a group of limbless amphibians), but later fossil finds have cast doubt upon this affiliation. Within other fossil ‘amphbians’ Rhynchonkos has been placed in Lepospondyli (along with our friend Diplocaulus). This group as a whole has a much debated relationship with living amphibians. Some studies have them having nothing to do with living amphibians (lissamphibians), where as others link specific taxa with certain groups of living amphibians. Such as the now disputed Rhynchonkos - caecilian link. It may seem obvious to link this almost limbless fossil with the limbless amphibians, but amphibians (and lizards too!) seem to like to lose their limbs at the drop of a hat. It is very common in swimming and burrowing forms. 

Lycaenops 

Reconstruction by  Dmitry Bogdanov

When: Permian (~270 to 251 million years ago)

Where: South Africa

What: Lycaenops was one of the predatory synapsids (‘mammal like reptiles’) of the late Permian. It lived in what is now South Africa and was about the size of a living coyote, at 3 feet (~ 1 meter long). Lycaenops is a member of the Gorgonopsia, which were the dominate predators of the late Permian. Multiple species of gorgonopsians lived at the same time in South Africa, much like how multiple species of canids or felids will have over lapping ranges today. Lycaenops, like most of its kin, had an enlarged pair of canines to help capture its prey. It is unknown if the gorgonopsids had any hair or were covered with scales. 

Gorgonopsids are synapsids on the evolutionary line of mammalia. Of the synapsids I have covered before, they fall in the range between Edaphosaurus and Cynognathus. This is not to say they were closely related to either, ‘pre mammal’ synapsids were a long lived and very diverse array of taxa. 

Diadectes

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.

Mesosaurus

Reconstruction by Zdeněk Burian

When: Early Permian (~300 to 280 million years ago)

Where: Southern Africa and South America 

What: Mesosaurus is one of the first secondarly aquatic tetrapods.  It seems like almost as soon as tetrapods adapted to land, they were already moving back to the waters. Most Mesosaurus fossils have been found in costal depositions and are relatively small at only about ~1 foot (40 cm) long. The largest specimens, however, reach about 3 feet (~1 meter) long. It is possible that Mesosaurus had indeterminate growth, like most reptiles, and that the largest individuals were able to swim farther from the coast line, thus, they are not as well represented in the fossil record. Mesosaurus had what would become the fairly standard suite of adaptations for aquatic life in reptiles: its feet were webbed and becoming more like paddles, they had lost the ability to rotate at their wrists and ankles and thus were always held to the side, the tail was elongated and semi-flattened laterally, and the mouth was elongated and full of dozens of sharp teeth. It is possible that Mesosaurus was somewhat of a filter feeder, with its mouth closed these teeth would function like a sieve to allow it to filter water out and feed on the small fish and other animals trapped inside. As Mesosaurus has been predominately found in fresh water deposits in both South America and Africa, this is another fossil which heavily supported the concept of plate tectonics when the theory was just getting off the ground. 

The phylogenetic position of Mesosaurus is uncertain. It could be the basal most ‘parareptile’, falling in a clade with Scutosaurus, or this group could be non monophyletic and it is outside of most of the rest of reptiles, OR it could be a basal sauropsid (modern reptiles). There has even been the suggestion that it is a synapsid, but this has not received much attention.   

Scutosaurus 

Mounted specimen on display at the American Museum of Natural History, NYC. 

When: Late Permian (~252 million years ago)

Where: Russia

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. 

Solitary Rugose Corals - Horn corals 

When: Mid-Ordovician to End Permian (488 - 250 million years ago)

Where: Paleo-oceans worldwide

What: All modern corals are colonial; meaning each structure is actually made up of the shells of masses of tiny animals. Some members of the group Rugosa were instead solitary, growing orders of magnitude larger than any single living coral. Corals are cnidarians, a group that also includes jellyfish. The soft body of a single coral looks a lot like a jellyfish with only its tentacles visible outside of the shell. These tentacles have stinging cells which paralyze any prey animal that gets too close; and then it is guided towards the centrally located mouth.  

These large corals did not cement themselves to the substrate, but instead the tip of the ‘horn’ was shallowly buried in ocean floor sediments. This would lead to corals falling over on occasion due to strong currents; the animal would then build its shell towards the ‘new up’, which is why some rugose coral fossils are bent rather than straight shelled. These corals could grow to roughly 3 feet long (~1 meter), but most had shells only about 3-4 inches (8-10cm) long. These solitary corals were one of the groups lost in the end Permian mass extinction, the largest extinction event in Earth’s history. 

Diplocaulus

When: Permian (300-250 million years ago)

Where: North America

What: Diplocaulus is an amphibian. It reached lengths of roughly 3 feet (~1 meter long), making it the largest of its clade. We have an exceptional fossil record of these animals, including wonderful ontogenetic series of juveniles, which show that the two-phase metamorphosis of modern amphibians was not present in these taxa. Instead juvenile Diplocaulus looked mostly like small adults. The biggest difference is that the head shield became more and more elaborate as the animal grew, juveniles barely had any ‘boomerang’ shape to their heads.  Most Nectridea had head shields, but they were among their most developed in Diplocaulus. These animals were carnivorous and lived in the many rivers, lakes, and swamps covering North America during the Permian. 

How Diplocaulus is related to extant amphibians is a topic of much debate. It, along with a number of other extinct amphibian clades, have in the past been grouped as the Lepospondyli. However, modern interpretations are divided as to if this is a real group, with all of its members descended from a common ancestor, or if it is an artificial collection of taxa. It is not likely that they are found within the Lissamphibia (the modern amphibians), but they have been proposed to be stem taxa to this clade. Some members have also been proposed to be more closely related to amniotes (reptiles - including birds, and mammals)  than to these living amphibians. Detailed cladistic studies incorporating all relevant taxa are needed for a firm understanding of this part of the evolutionary tree. 

Helicoprion - the Sprial Saw shark

When: Late Permian (~290-270 million years ago)

Where: Fairly globally distributed 

What: Helicoprion is a fossil shark. Though it has been known to science for over 100 years, it is still poorly understood. Teeth are the part of it that has ever been found. This not that strange for a fossil shark, as sharks do not ossify their skeletons - they are cartilaginous all of their lives. Thus it is extremely rare to find a fossilized shark skull or skeleton. What makes Helicoprion such a scientific puzzle is the arrangement of these teeth.  They are in a spiral, with the smallest teeth in the center. Modern sharks go though dozens upon dozens of teeth in their lifetimes, and fossil sharks were no different. What was very different however, is these extinct sharks retained their older teeth, instead of shedding them as we see in all modern forms. There are well preserved fossil sharks from the Devonian which incorporated their older teeth into bumps and ridges on their heads, but they did not develop an elaborate spiral as seen in Helicoprion.  

The biggest problem with reconstructing Helicoprion is determining the location of the spiral. Some of the first studies of this shark located the spiral on the upper jaw (the first small image above), but closely related fossil finds have shown unarguably this structure was located on the lower jaw. However, even with the position on the lower jaw certain, there are other debates and various reconstructions, two more of which are shown above. A recent study conducted by researchers at the Smithsonian concluded that these placements outside of the body were not realistic, as this would create too much drag when the shark swam, not only slowing it down but alerting it’s prey as it approached. They have interpreted the spiral to be located in the throat region of Helicoprion - their reconstruction is the large one shown above.