The Shark-Like Edestus: An Interview With Wayne Itano

We've heard from Wayne Itano before, when he told us about the Kremmling Cretaceous Ammonite Locality in Colorado. (To read the post, click HERE.) A physicist at NIST (National Institute of Standards and Technology) in Boulder, Colorado, Wayne also has a hobby interest in paleontology, and is a curator adjoint at the Natural History Museum of the University of Colorado. He has also been doing some very interesting work with a shark-like animal called Edestus, and he graciously agreed to answer a few questions for me regarding this creature! So please join me in welcoming Wayne Itano, as he tell us about this fascinating prehistoric creature!

Scissor-tooth model for Edestus.  Credit Ray Troll, www.trollart.com

The Natural World:  You've been doing some work with an ancient shark-like creature called Edestus. What can you tell us about it?

Wayne Itano:  Edestus is my candidate for the strangest shark of all time. In my opinion, it is even stranger than the better-known spiral-toothed Helicoprion, since it is harder to imagine how the teeth might have been used.  (Read more about Helicoprion HERE.)  Almost the only fossil remains of Edestus are its symphyseal (midline) tooth whorls, which consist of triangular, serrated teeth, joined together at the bases (roots).

Edestus had one tooth whorl in the upper jaw and one in the lower jaw. Since the whorls are bilaterally symmetric (same on the left side as on the right side), they must have been located in the middle of the jaws.

This is a photograph of a specimen of a species called Edestus mirus. It was found in Pennsylvanian-aged deposits (about 300 million years old) of Iowa.

Smithsonian Institution Specimen USNM V 7255. Scale in cm.  To see a better resolution of the picture, click HERE.  Photo Credit: http://collections.si.edu/search/results.htm?view=&dsort=&date.slider=&q=Edestus+mirus+holotype&tag.cstype=all

This is a rare specimen, since it shows both the upper and lower tooth whorls.

The curvature of the tooth whorls makes it difficult to understand how they could have been used.

According to the conventional reconstruction, the two tooth whorls were used as scissors, to cut prey between the two whorls, as in this drawing by Ray Troll.

Scissor-tooth model for Edestus.  Credit Ray Troll, www.trollart.com

To me, this model seems unlikely, given the curvature of the tooth whorls. It seems that the outer teeth are nonfunctional, since they can’t come together, so there would be no reason to retain them.

It seems to me that the teeth would be more efficiently used if the entire head was moved up and down, with jaws fixed, to slash large prey. This is a radically new idea. I have submitted an article for publication elaborating on this idea, but I expect that it may be some time before it gets into print.

New vertical-slashing model for Edestus. Drawing by Gary Raham, www.biostration.com, reproduced with permission of Wayne Itano

My new reconstruction of Edestus, showing the pair of symphyseal tooth whorls, in front, used for slashing prey, and flat teeth in the rear for crushing prey. Drawing by Gary Raham, www.biostration.com, reproduced with permission of Wayne Itano.

TNW: I noticed that you referred to Edestus as being a candidate for the "strangest shark of all time." Is Edestus truly a shark? If not, how do you classify it?

WI: I was using "shark" in an informal sense, as the term is not well-defined for many extinct fish. Edestus certainly falls within the class Chondrichthyes, which today comprises 2 subclasses - Elasmobranchii (sharks, including rays) and Holocephali (ratfish). There is some evidence that Edestus (and also Helicoprion) belong to an extinct line that is closer to the Holocephali than to the Elasmobranchii, but this is a matter of debate. It is safe to call Edestus a chondrichthyan, and I try to avoid the word "shark" when I write a technical paper, or maybe keep it in quotes.

TNW:  Tell us a little bit about your research.

WI:  I am interested in many aspects of paleontology, but for the last 22 years I have focused on fossil sharks, particularly ones from the Paleozoic (older than about 250 million years ago). My interest in Paleozoic sharks dates from 1991, when I found a finspine of a Pennsylvanian-aged shark called Ctenacanthus in a roadcut near the town of McCoy, in Eagle County, Colorado. I wrote an article about this find for the newsletter of the Western Interior Paleontological Society (WIPS) in 1992, which you can read by clicking HERE.

Ctenacanthus finspine found near McCoy, Colorado. Scale in cm.  Photo Credit: Wayne Itano

In trying to identify this finspine, I read everything I could find about Paleozoic sharks. Knowing of my interest in the topic, Professor Martin Lockley of the University of Colorado at Denver loaned me a large collection of shark teeth and finspines from McCoy that he and Karen Houck, also of CU Denver, had found in the 1980s. His paleontological interests had by then switched entirely to ichnology (footprints and other fossil traces), and he gave me the opportunity to write up the fossil shark specimens. I published an article on the finspines in 2003 with Houck and Lockley, which you can read HERE, but I haven’t finished with the teeth yet.

My interest in Edestus started when an amateur fossil collector showed me an unusual shark tooth that he had found at McCoy. After a bit of study, I realized that it was a tooth of Edestus, the first known from the entire Rocky Mountain region. This eventually led to my publishing a rather long paper on Edestus in 2012, again with Houck and Lockley, which you can read HERE.

Recently, I have also published three short papers related to Edestus: one on an Edestus tooth from England, one on an Edestus tooth with abnormal serrations, and one on a tooth from China that had mistakenly been identified as Edestus, but which actually belonged to a more “normal” shark called Carcharopsis.

TNW:  Do you have any future expeditions or research papers in the works?

WI:  Lately most of my “field work” has been in museum collections. In the last few years I have been able to view specimens in the collections of the Yale Peabody Museum, the Natural History Museum (London), the British Geological Society, the American Museum of Natural History (New York), and the New Mexico Museum of Natural History and Science. I have several publications in the works, largely based on fossil shark specimens I have seen in those collections.

One area is the taxonomy (classification) of Edestus species. About 15 species of Edestus have been named, but I think that many of these are synonymous. For example, people have named new species based on unusually small or large teeth, but I think they are just teeth of the same species of Edestus but of different ages. There may be as few as 3 valid species of Edestus.

I have another project where I am examining microscopic scratches on Edestus teeth. I am hoping that I can find feeding-related scratches and that their orientation will provide some clues as to whether the scissors-model or the up-down-slashing model is correct.

-Thank you so much, Wayne, for answering some of my questions!  I look forward to hearing more about Edestus in the future!  Thanks again!-

Proterosuchus....or Should I Say "Broterosuchus?"

Before we learn about Proterosuchus, it will be helpful to discuss where this creature comes from.  Proterosuchus is an archosaur, and to understand what an archosaur is, we must first travel back 320 million years into Earth's history: back....to the middle of the Carboniferous Period.  To travel back to that period of Earth's history, click HERE TO SEE A POST I JUST MADE ABOUT THE EVOLUTION OF THE ANIMALS THAT WE ARE TALKING ABOUT RIGHT NOW.  Unless, of course, you are fine with just accepting the idea that the archosaurs are relatives of the dinosaurs, pterosaurs, and crocodilians, in which case you can just skip that post.  I think it's interesting, though, so it might be worth checking out!

Well, that was confusing.  So how does all of this evolutionary rig-a-ma-roll pertain to Proterosuchus?  Well, in his excellent book entitled "Gorgon," paleontologist Peter D. Ward actually talks about that.  Here is that passage from his book:

"During the Triassic a whole new suite of vertebrates populated the land.  The oldest true "ruling reptiles," the stock that would ultimately give rise to the dinosaurs, are found in the oldest rocks of the Triassic.  The most ancient of these is Proterosuchus.  Yet within several million years, there was a variety of these predinosaurs, belonging to a group known as the archosaurs.  From these ancestral stocks the successful lines of crocodiles and crocodile-like animals known as phytosaurs evolved.  From other members of this group came lizards, snakes, and, by the middle of the Triassic, the first true dinosaurs."  

Well, that certainly sums it up quite nicely, don't you think!  Anyways, Proterosuchus was around the size of the extant Komodo dragon, and was one of the largest reptiles alive during its time, in the Early Triassic Period.  Similar in appearance to the modern day crocodiles, it has been theorized that this animal would lie in wait much like the crocodilians, ambushing its prey when it came down to bodies of water to drink.  One bit of evidence that causes some scientists to believe that Proterosuchus hunted like the crocodilians was that the eyes of Proterosuchus were were located on top of its head, again like the crocodilians.

Remains of Proterosuchus are known from both China and South Africa, where it was first discovered by Robert Broom, a famous South African paleontologist, in 1903.  This specimen was discovered in the Karoo Basin, an enormous desert in South Africa where large numbers of fossils have been discovered. 

Fouriesburg on Dwellable

The Archosaurs: A Brief Summary of Reptilian Evolution

320 million years ago, during the Carboniferous Period, the flora and fauna looked quite different than it does today.  Oxygen levels in the atmosphere were much higher, allowing insects to grow to enormous sizes.  Centipedes were the size of snowboards; dragonflies were the size of hawks; and spiders were the size of dinner plates.  There were also no mammals.  Not only that, but there were no reptiles, no dinosaurs, and no birds (which, of course, are dinosaurs).  There were, however, amphibians.  Amphibians, like frogs and salamanders, cannot lay their eggs on dry land, and instead must lay them in pools of water.  This is because the eggs that they lay, unlike those laid by dinosaurs, birds, reptiles, and monotremes (the two egg-laying mammals), have soft-shelled eggs, which allows water to move in and out of them.  They would simply dry up on land!

Around 320 MYA, however, something changed.  Some of these amphibians developed what is known as an "amniotic egg," the type of egg typified by the dinosaurs, birds, reptiles and monotremes.

Around 5 million years after that, around 315 MYA, another major split occurred, this time between the amniotes.  This split resulted in two lineages, the first of which, the synapsids, would one day become the mammals.  The second of these two lineages was the sauropsids.   Within the sauropsids was the group known as the archosaurs.  The archosaurs, in turn, suffered two major splits.  The first split was the crocodiles, alligators and their kin.  They joined with the rest of the reptiles contained within the sauropsids.  The second large split within the archosaurs was another large group, off of which the pterosaurs broke off, before the rest of the group became dinosaurs (and, in turn, birds).  If you look at the family tree below, you can see that the group known collectively as the "reptiles" is what is referred to as a "paraphyletic group."  Put simply, that means that a paraphyletic group consists of "all the descendants of the last common ancestor of the group's members minus a small number of monophyletic groups of descendants, typically just one or two such groups." So for reptiles, that means that the group consists of the last common ancestor of all reptiles (which includes both extant reptiles and the extinct mammal-like reptiles, the precursors of the mammals), including all of the descendants of that ancestor....EXCEPT for the mammals and the birds, which are defined separately.  I feel like I have confused you enough, so I am not even going to get into the whole dinosaur debate.

Top Ten: Extinct Sea Monsters (Part 3 of 5)

 5.  Elasmosaurus - Next up on our trip across time is Elasmosaurus.  One of the largest of the Plesiosaurs ever discovered, Elasmosaurus grew up to 46 feet long, which was about half neck.  Equipped with a fairly small head, Elasmosaurus would have been incapable of going after large prey, so it would have mostly stuck with fish.  Elasmosaurus lived during the Late Cretaceous, a time when much of North America was "Beneath the Waves," under something that we call the "Western Interior Seaway."   Remains of this animal were first uncovered in Kansas, but it almost certainly swam all over the seaway, including in Colorado.

6.  Dunkleosteus - Dunkleosteus, a creature we talked about a few weeks ago in our post about the Coelacanth, is another fascinating animal.  Almost thirty-five feet in length, Dunkleosteus was a member of the Placoderms, a group of armored fish that were only around for about 50 MYA.  A long time, to be sure, but not very long compared to the 400 million year reign of the sharks.  While the Placoderms themselves lived during the Silurian and Devonian Periods, they went extinct during the transition to the Carboniferous Period, at the end of the Devonian.  Dunkleosteus fossils have been discovered in North America, Poland, Belgium, and Morocco.

 COMING UP:

7.  Archelon
8.  Leedsichthys
9.  Tanystropheus
10. Tylosaurus

This post is part of the "Top Ten: Extinct Sea Monsters" series.  For the rest of the posts in this series, click HERE.  

A Look Ahead, Fun Fact 8/3/2012

First off, check out today's post about the tapir, down below!

Next, I decided to spice our "Looks Ahead" up a little, each week I would add in a fun fact or something similar, that I didn't think I would have enough information to devote an entire post to.  So here is your fun fact!

FUN FACT:  For the first season of "Star Wars: The Clone Wars," the popular animated TV show in the same franchise of the classic movies, the producers decided to create a new planet for the premiere episode.  They settled on a small moon that was covered in coral, but no water; somehow, the moon had been drained of its oceans.  They decided to call the moon "Rugosa," after an extinct order of coral, commonly called "horn coral." 

This horn-shape, unique among coral, lived a long time ago, but not in a galaxy far, far away: before the dinosaurs, in fact!  They survived for an incredibly long amount of time, though, from the mid-Ordovician Period (~488 MYA) through to the Late Permian Period, thriving through the Silurian, Devonian and Carboniferous Periods as well.  Although I couldn't find any official confirmation, I assume that the horn-coral went extinct because of the "Great Dying," or the mysterious Permian Extinction, but I am not positive, so don't quote me on that.


Now here's what we have in store for this week:
(4) Saturday:  Ginger Kathrens, Cloud, and the Wild Horses of the Montana Rockies
(5) Sunday:  Animal Spotlight:  The Okapi
(6) Monday:  The Making of Planet Earth:  The Snow Leopard
(7) Tuesday:  Animal Spotlight:  The Red Panda
(8) Wednesday: What Is It?
(9) Thursday:  Animal Spotlight:  The Coati
(10) Friday:  Forget Biker Gangs: The River Otters of India