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Ceratodus: The Iconic Lungfish of the Mesozoic Era

Ceratodus was a genus of prehistoric lungfish which existed on Earth for a surprisingly long time, from the middle of the Triassic Period approximately 227 million years ago to the beginning of the Eocene Epoch of the Tertiary Period about 55 million years ago – a jaw-dropping span of 172 million years! That’s impressive by ANYBODY’S standards!

Lungfish as a whole are a primitive group of fish. They first appeared during the early Devonian Period about 416 million years ago (MYA), and it’s believed that they represent an evolutionary “missing link” between fish and amphibians. The closest relatives of the lungfish are the coelacanths, meaning “hollow spines”. That’s not surprising, considering that both lungfish and coelacanths have prehistoric origins as well as that both groups are classified as “lobe-finned fish”.

Lungfish do not have individual teeth like many fish today. Instead, they have four large bone plates (two in its upper jaw, and another two in its lower jaw) that were ridged in texture and crowned with thick triangular projections, and were used for crushing and cracking. Many species of modern lungfish feed on worms, freshwater snails, crustaceans, small fish, and amphibians.

Today, there are only six surviving species of lungfish, and all of them are found in hot tropical environments. With the exception of one species found in the Amazon Jungle and another species found in northern Australia, the remaining lungfish species are found in Africa.

  1. The South American Lungfish (Lepidosiren paradoxa), found in the Amazon River.
  2. The Marbled Lungfish (Protopterus aethiopicus), which is found throughout much of eastern and central Africa.
  3. The Gilled Lungfish (Protopterus amphibius), which is also found in eastern Africa.
  4. The West African Lungfish (Protopterus annectens), which is found, not surprisingly, in western Africa.
  5. The Spotted Lungfish (Protopterus dolloi), which inhabits the Congo Jungle of central Africa.
  6. The Australian Lungfish, also called the Queensland Lungfish (Neoceratodus forsteri), found in northeastern Australia. Of all of the extant lungfish species, this one is believed to be the most primitive.

Special attention must be given to the Australian Lungfish (Neoceratodus forsteri), for not only is this species regarded as the most archaic of all of the extant lungfish, but it was once believed to be the sole surviving member of the prehistoric lungfish genus Ceratodus alive in modern times.

Skeleton of Neoceratodus forsteri. From Günther, Albert. “Description of Ceratodus, a Genus of Ganoid Fishes, Recently Discovered in Rivers of Queensland, Australia”. Philosophical Transactions of the Royal Society of London, volume 161 (1871). Plate XXX. https://www.jstor.org/stable/pdf/109041.pdf.

The lower jaw of Neoceratodus forsteri, seen from above. From Krefft, Gerard. “Description of a gigantic amphibian allied to the genus Lepidosiren from the Wide-Bay district, Queensland”. Proceedings of the Zoological Society, volume 16 (April 28, 1870). Page 222. https://ia800405.us.archive.org/16/items/biostor-107043/biostor-107043.pdf.

The genus Ceratodus was established in 1837 by the famed Swiss ichthyologist Louis Agassiz based upon teeth which were found in European rock layers dated to the Triassic and Jurassic Periods. Most Ceratodus fossils that are found consist of isolated tooth plates, and different species have been named based largely upon difference in tooth morphology. Twenty-two species of Ceratodus have been named since the genus was first described in 1837. For a long time, Ceratodus was what is known as a “waste basket taxon” – all North American lungfish fossils were ascribed to this genus, regardless of how different they were from each other. Recently, a careful re-examination of lungfish fossils have revealed that these animals are remarkably different from each other and may constitute numerous genera, not just one. If that’s the case, then the overall lifespan of Ceratodus as a genus may be dramatically shorter than was previously supposed (Günther, Albert. “Description of Ceratodus, a Genus of Ganoid Fishes, Recently Discovered in Rivers of Queensland, Australia”. Philosophical Transactions of the Royal Society of London, volume 161 (1871). Page 512).

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Ceratodus, painted by Heinrich Harder. From Animals of the Prehistoric World (1916). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Ceratodus.jpg.

Ceratodus’ length varied depending on the species. Most sources which I have seen give an average length of 3 feet long. However, one species of Ceratodus may have reached truly gigantic proportions, possibly reaching 10 to 12 feet long. This estimate is based upon a single bone plate, which is the largest-known of any lungfish. The tooth plate was found in central Nebraska in rocks dated to the Miocene or Pliocene Epochs of the Tertiary Period. Shimada and Kirkland hypothesized that the tooth had been carried into central Nebraska by river from older rock layers that were located further to the west within Wyoming, in rocks dated to either the late Jurassic or early Cretaceous Periods. However, the tooth isn’t as banged up as you would expect from such a long journey. It’s possible that the tooth is endemic to central Nebraska, and if that is the case, 1) Ceratodus was alive in North America for a much longer geologic time span than previously supposed, or 2) This species is mis-identified and belongs to a new un-described genus of giant lungfish which lived in central North America about 5 million years ago, or 3) This was a species which happened to have unusually large teeth within its jaws, and the overall length of the animal was much smaller than the 4 meter estimate given by Shimada and Kirkland. Unfortunately, only one tooth plate has been discovered. Until more specimens are found, everything that we have to say about this specimen needs to be taken with a great degree of skepticism. (Kenshu Shimada and James I. Kirkland, “A Mysterious King-Sized Mesozoic Lungfish from North America”. Transactions of the Kansas Academy of Science, volume 114, issue 1 (2011). Pages 135-141. https://www.researchgate.net/publication/261964060_A_Mysterious_King-Sized_Mesozoic_Lungfish_from_North_America).

For the artwork accompanying this article, I decided to change up my style. For this drawing, I chose to evoke the whimsical style of the paleo-art of Patricia Bujard. If you don’t know who Patricia Bujard is, then I highly recommend that you check out her work. She is a children’s author and illustrator with a love for prehistoric life, and I find her artwork adorable. There aren’t too many people who can make an Allosaurus “cute”, but dag-nabbit, she somehow manages to pull it off. You can see her artwork on her WordPress page, Pete’s Paleo Petshop. My own drawing, which you can see below, was made with an ordinary Crayola black marker.

Ceratodus © Jason R. Abdale. February 9, 2021.

Keep your pencils sharp, and in this case, also keep your markers properly stored so they don’t dry out.

Champsosaurus: The Croc-Lizard of the Cretaceous

When most people hear the words “aquatic reptile”, they usually think of two things: turtles and crocodilians. Some clever people might mention sea snakes, and others might mention marine iguanas. Those who are keen on impressing you may bring up some obscure species like the water monitor, the basilisk lizard, and other species of snakes which venture into water.

In prehistoric times, the list of options that you could choose from was much more expansive. In fact, there were animals around then which aren’t around today which fit into this category. One such group of prehistoric water-going reptiles was known as the “choristoderans” (pronounced as Kore-RISS-toe-DEER-rans).

The choristoderans were a group of semi-aquatic reptiles which lived during the Mesozoic Era. Although not as well-known as other non-dinosaurian reptiles of the Mesozoic such as pterosaurs and ichthyosaurs, they nevertheless shared their environments with dinosaurs for a span of approximately 110 million years and even survived the dinosaur extinction. Choristoderans first appeared during the middle of the Jurassic Period about 175 MYA. The oldest-known genus which is recognizably a choristoderan was Cteniogenys, which measured just one and a half feet long and was very lizard-like in appearance. In life, it probably resembled a small monitor lizard and it likely filled a similar ecological niche. However, the heyday for the choristoderans occurred during the early Cretaceous Period from about 144 to 100 MYA, after which they went into decline. They were fortunate to survive the K-T Extinction, but they were always second fiddle to their crocodile neighbors. Most of the surviving species went extinct about 50 MYA, with the remainder just barely hanging on. The last of the choristoderans completely went extinct around 20 MYA.

The choristoderans belonged to a group of vertebrates called the “diapsids”, meaning that they had two holes in their skull behind each eye socket. Lizards, snakes, crocodilians, pterosaurs, dinosaurs, and birds are all classified as diapsids.

At first glance, choristoderans might be mistaken for crocodiles. However, despite their crocodile-like appearance, they are more closely related to lizards than to crocodiles, at least according to a study made by Mike Lee in 2013 (“Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds”). Their placement in the reptile tree is primarily based upon the structure and arrangement of their ear bones, which is more advanced than those seen in lizards but not as advanced as those seen in crocodilians and birds. Also, the skulls of choristoderans are structurally more lizard-like than crocodilian.

The order Choristodera is divided into four families: Champsosauridae, Hyphalosauridae, Monjurosuchidae, and Simoedosauridae. The more primitive the species, the more lizard-like it is in form. The more derived, then the more crocodilian it is in appearance. The most primitive choristoderans were the monjurosuchids, which looked similar to the modern-day Water Monitor Lizard (Varanus salvator). Even at this early stage in their development, there is fossil evidence that some species like Monjurosuchus possessed webbed fingers and toes. Already, they were adapted to living a semi-aquatic lifestyle.


Skeleton of Monjurosuchus splendens, a primitive choristoderan from China. Photograph by Jonathan Chen (June 13, 2019). Creative Commons Attribution-Share Alike 4.0 International license. https://commons.wikimedia.org/wiki/File:Monjurosuchus-Beijing_Museum_of_Natural_History.jpg

Even more advanced were the hyphalosaurids, which bear a remarkable resemblance to the earlier nothosaurs and thalattosaurs of the Triassic Period. Form tends to follow function in evolution, and these creatures almost certainly led a similar lifestyle. The act of species from completely different groups evolving into more-or-less the same shape is called “convergent evolution”.

The champsosaurids and the simoedosaurids are the most crocodile-like in appearance, and together they form the super-family Neochoristodera. Like crocodiles, these creatures were almost certainly living as shallow-water ambush predators, fitted with long slender jaws lined with small conical teeth. Like modern-day gharials, they may have been primarily or even exclusively fish-eaters.

Probably the most famous choristoderan genus was Champsosaurus (pronounced as CHAMP-so-SORE-us). It first appeared about 90 MYA during the Turonian Stage of the late Cretaceous Period, persisted through the K-T Extinction, and finally went extinct during the Paleocene Epoch of the Tertiary Period about 56 MYA. Impressive. Most genera don’t last that long.

Champsosaurus was named by the famed paleontologist Edward D. Cope in the year 1877. Despite not having an easily-recognizable name (most members of the general public have likely never heard of it), it has been rigorously studied by paleontologists ever since then. For example, three academic articles were published about it just in the year 2010, and another article was recently published in April 2020. So, from an academic standpoint, interest in this animal has been pretty consistent.

There are seven species which have been ascribed to the genus Champsosaurus. Most of them measured 5 feet long or thereabouts, but the largest, which was appropriately named Champsosaurus gigas, reached 10 feet long. Most Champsosaurus fossils have been found in south-central Canada and the north-central United States within rocks dated to the late Cretaceous Period from 90 to 66 MYA, but a few have also been found in Belgium and northern France in rocks dated to the Tertiary Period.

Champsosaurus skeleton from Montana, USA on display in the Royal Ontario Museum. Photograph by Daderot (November 21, 2011). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Champsosaurus_sp.,_Montana,_USA,_Late_Cretaceous_-_Royal_Ontario_Museum_-_DSC00088.JPG.

 

Upper jaw of Champsosaurus, above view (left) and underside view (right). The skull’s length measures about 13 inches. Illustration by Samuel W. Williston. From The Osteology of the Reptiles (1925). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:The_Osteology_of_the_Reptiles_p76.png.

Champsosaurus appears to have been able to tolerate both freshwater and saltwater environments. Fossils of a species called Champsosaurus laramiensis have been found in rocks from the Fox Hills Formation, a geological layer which represents a coastal or estuary environment on the edge of the Western Interior Sea. Fossils of mosasaurs and dinosaurs including Tyrannosaurus have also been found in these rocks.

Preserved skin impressions show that, unlike many lizards, choristoderans like Champsosaurus did NOT have overlapping scales. Instead, the skin consisted of tiny non-overlapping scales, with no crocodile-like dorsal scutes, giving it a very smooth-skinned appearance when seen from a distance.

Unlike crocodiles, which have their nostrils on the top of their upper jaw, Champsosaurus had its nostrils on the front tip of its upper jaw. Perhaps they would use their long nose like a snorkel, sticking just the tip out of the water’s surface in order to stay as concealed as possible.

Champsosaurus had a pair of long thin gharial-like jaws lined with tiny conical teeth. Because of its close affinity towards lizards than to crocodiles, it is highly likely that Champsosaurus had lips and a fully enclosed mouth. But that’s just speculation based upon phylogenic relationships to other reptiles. In terms of hard physical evidence, the teeth themselves are quite small, and are inset from the edge of the jawline rather than standing on the rim of the jaw like a crocodile. This suggests that Champsosaurus had lips covering its teeth like a lizard, unlike crocodiles which don’t have lips.

Compared with crocodilians, the eye sockets of choristoderans are positioned much further forwards on the skull, located halfway or two-thirds of the way back from the tip of the snout. This provides more space for jaw muscles, and the temporal fenestrae (the holes in the back of the skull that accommodate the jaw muscles) were very large in proportion with skull size. Champsosaurus, in particular, had very large temporal fenestrae, which indicates that it had strong jaw muscles and could quickly snap its mouth shut within a fraction of a second – an important adaptation if your diet consists primarily of small fish.

Unlike lizards, Champsosaurus might not have had external ears. Analysis of its skull structure shows that Champsosaurus had internal ears, similar to turtles. This is an important adaptation if you are spending much of your life in the water. Therefore, you would not have seen a pair of ear holes on a Champsosaurus head. Instead, there likely just would have been a slight depression (or maybe not even that) on the side of the head marking where the tympanum (the part of the ear that vibrates in order to make a sound) would have been.

If you spend much of your life in the water, walking really isn’t an issue. Therefore, the limbs of choristoderans are not well-developed. In fact, the more “advanced” the species, the weaker its limb bones appear to be. Champsosaurus is no exception to this – its legs are downright puny in comparison with its body. The bones that make up the arms and legs are short and stumpy, and the hands and feet are small, although the feet are noticeably bigger than the hands. The fingers and toes are thin and end with very tiny claws. This was an animal that would have had a hard time pushing itself onto land. However, there is some evidence that females had more robustly-built limbs than the males due to the need to haul themselves onto land in order to lay their eggs.

The tail of Champsosaurus was flattened, and looked more like that of a crocodile or even a mosasaur than to a lizard. Even so, this animal was definitely not a power-swimmer. If it was, then one would expect the tail to be both longer and broader. Instead, the tail seems to be peculiarly under-developed. Keep in mind, though, that this was likely not an animal that was actively chasing after its prey. If all it was doing was hunkering down on the bottom of a lake or river and waiting motionless for fish to carelessly swim by, then it doesn’t need a well-built tail that’s designed for plowing through the water.

Skeleton of Champsosaurus laramiensis. From “The Osteology of Champsosaurus”, by Barnum Brown (1905). Memoirs of the American Museum of Natural History, volume 9, part 1. Public domain image. http://commons.wikimedia.org/wiki/File:Large_williston_champsosaurus.jpg.

Below is a drawing made of Champsosaurus laramiensis drifting about in a murky pond or stream somewhere in Montana during the late Cretaceous Period. This five-foot-long piscivore would have shared this environment with alligators, crocodiles, turtles, large freshwater fish like gars, sturgeons, and bowfins, and of course dinosaurs like Triceratops and Tyrannosaurus. The drawing was made with No.2 pencil on printer paper.

Anyways, keep your pencils sharp.

Dinosaur Day 2015 at the Garvies Point Museum

GP Museum 1

Well, it was that time of year again! Every April or so, at around the time of Easter, the Garvies Point Museum and Preserve, located in Glen Cove, Nassau County, New York, holds it annual “Dinosaur Day”. This is one of the days that I really look foward to for a few reasons. First, I get to work at a place that I absolutely love and meet with some good friends. Secondly, I get to be out of NYC for a little while, which is something that I ALWAYS look foward to. Third, I get to talk about a subject that has fascinated me since my earliest days – paleontology.

Veronica, the museum’s de facto head of administration, did a wonderful job along with other members of the museum staff of setting up the classroom where the day’s major activities would be taking place. Recently, the museum’s library was substantially increased. The Sands Point Museum and Preserve had closed down its library a short while ago, and all of the books and papers were sent to the GPM. I should state, though, that almost all of these documents were originally part of the GPM collections anyway, and they just got them back, that’s all. However, Louis (one of the workers at the Garvies Point Museum, but works primarily at the Old Bethpage Village – another place that I really love) has been working hard to re-catalogue all of these books and papers back into the museum’s database.

The name of the event was somewhat misleading, as it concerned all prehistoric life, not just dinosaurs. We had exhibits on primitive mammal-like-reptiles, dinosaurs, and prehistoric mammals.

Here are some pictures of what the room looked like both during and after the hoards of kids showed up.

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Most of the really young children gravitated immediately towards the dino toy area and the fossil digsite. The older children and a lot of the adults were interested in the information that I and others were giving. They were especially interested in Dimetrodon, the famous sail-backed pelycosaur from the early Permian Period. I don’t think that I have ever had to say the name”Dimetrodon” so many times within the course of a single day! It seemed to be the only thing that many of them wanted to talk about!

Some of the major topics of interest on this day were: the Permian Mass Extinction, which occured about 251 million years ago, when an estimate 95% of all life was wiped out; of course, T. rex was a favorite; as too was Allosaurus, who competed with its larger relative for attention from the crowds. This was helped in no small part to the fact that we had a lot of Allosaurus “stuff” arrayed for them: a picture of the skull, a hand model, bone casts, a model, and my drawing which you might recognize from an earlier post on this blog.

Finally, here’s a picture of me, “the Dinosaur Man” as several members of the museum staff call me, dressed up as an amateur paleontologist. In addition to my olive drab Garvies Point Museum shirt, I also wore a khaki utility vest, because apparently ALL paleontologists wear khaki utility vests! I thought that wearing it would help to enhance my ethos with the audience, and by my reckoning, it worked.

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