Your Daily Fossil

Koskinonodon formerly known as Buettneria

Mounted specimen on display at the American Museum of Natural History

Reconstruction by Matt Celeskey

When: Triassic (~228 - 216 million years ago)

Where: North America

What: Koskinonodonis one of the later surviving of the giant amphibians. This beast could read up to 10 feet (~ 3 meters) long and was very common in the ancient American southwest. Koskinonodon  was known by the name Buettneria for over 80 years, until a long standing nomenclature problem was resovled. See, the name Buettneria was applied to this animal in honor of W. H. Buettner, a fossil collector in the first part of the 20th century.  This was in 1922, however, a living species of katydid was given the genus name of Buettneria decades earlier in 1889. Thus the name was not actually availble to be used for this giant amphibian. The name Koskinonodon was applied in 2007. This name was used because a specimen that was named Koskinonodon  in 1929 was later determined to belong to the same genus as the previously known specimens that were then called Buettneria. When a genus is renamed this is typically how it is done, you comb though the past literature and use the oldest available name that has ever been used for any species (or specimens!) now housed in that genus. Sadly sometimes you end up using names that are just not as cool as the original. Sorry W. H. Buettner. At least your namesake fossil lives on in outdated museum exhibits. ;)

Koskinonodon is closely related to another large amphibian I have posted, Metoposaurus. It is likely that these two animals occupied the same habitates in life. What differentiates them? At just the general morphology level Koskinonodon has a much longer skull, a longer tail, and less robust limbs. It is common that when a paleo environment is reconstructed just one example of each ‘type’ of animal is used, but this is not really realistic. Think about the average North American forest today. Multiple species of all sorts of ‘types’ of animals are found there, multiple squirrels, deers, and birds that resemble each other very closely but are distinct species. This is how it was in the Mesozoic world as well! 

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. 

Metoposaurus 

Mounted specimen from the Krasiejów Museum in Poland. 

When: Mid Triassic (~228 - 216 Million Years Ago)

Where: Europe and North America 

What: Metoposaurus is an amphibian that lived on the northern continents during the mid Triassic. It was very large compared to modern amphibians, at 10 feet (3 meters) long and weighing an estimated 1000 lbs (450 kg), but these large amphibians were typical of this time, and for tens of millions of years previously. Its limbs are fairy small and weak for its body size, leading researchers to conclude it spend much of its time in the water. Its head was very well adapted for catching fish, with its dozens upon dozens of needle like teeth. Its head was extremely flat, again typical for these amphibians. A flat head like this would have allowed it to breath and look over the surface of the water with out causing disturbances which would have scared away fish. The flat head of Metoposaurus would also allow it to wait at the surface with out easily being seen by  predators on the shore. Large groups of Metoposaurus have been found in some areas, in what appear to be pools that were drying out. These animals clustered together in the last remaining water there was during droughts, but alas, the rains didn’t return again in time. 

Metoposaurus fairy typical member of the Temnospondyli. This group is known from most of the continents from the Carboniferous to the Triassic, with some species making it all the way to the Cretaceous. Temnospondyls include the largest amphibians ever known, some of them easily dwarfing Metoposaurus. All of these large forms still spend a lot of time in the water, shown by a variety of skeletal features, such as the weak limbs seen in Metoposaurus. It is uncertain how the temnospondyls are related to the rest of Tetrapoda. They are farther down the tetrapod line than Pederpes,  but past this there is a lot of controversy. Some researchers place them as outside of crown tetrapods (modern amphibians + amniotes), while others place them on the line leading to the modern amphibians (frogs, salamanders, and caecilians). It is also very likely that Temnospondyli is not even a natural group, and that some species are closer to amphibians than others. 

Did I mention they have really really flat heads?

Recon by Dmitry Bogdanov (DiBgd)

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.

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.