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Ceratodus: The Iconic Lungfish of the Mesozoic Era

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Ceratodus was a genus of prehistoric lungfish which existed on Earth for a surprisingly long time, from the late 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).

File:Ceratodus.jpg

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.


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