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Taphonomy Tuesday

Slide1Taphonomy Tuesday? What the heck is taphonomy, you ask? Taphonomy is the study of burial processes and all the changes that take place betwixt death and being collected as a fossil. One might also include the effect of sexiness in what fossils get studied and forgotten about, way more people are interested in tyrannosaurs than fossil mosquitos, for instance. Change comes to all things and paleoaerie is no exception. You may have noticed that the answer to Monday’s mystery fossil did not get posted on the blog last week, although it was posted on the Facebook page. That will be rectified today. But first, a couple of pieces of news.

Mystery Monday and Fossil Friday will be suspended for the summer so I can work on other aspects of the website. I would like to make some different posts and add more to the site. however, for those of you who are primarily interested in the fossils, they will return along with school, teachers, and homework, although hopefully a bit more fun than either doing or, even worse, grading homework (trust me, having been both a student and teacher, grading is almost always more painful than doing the assignments). In the meantime, you can look forward to more varied posts, the addition of a couple of things, such as a techno page for recommended apps and multimedia and an Amazon store in which you can peruse recommended items (and in a small way support the work of paleoaerie, which while free to you, is not to me). So I hope you will stick with me through these Darwinian changes and avoid the pitchforks and torches (ed. note: in keeping with the medieval theme of the picture, I thought about saying burning faggots, but so few people these days know that in olden times, faggot simply meant a bundle of sticks, language too evolves).

modlogoThe other big news is that I have started a collaboration with the Museum of Discovery in Little Rock to host a celebration of National Fossil Day in October. I am really looking forward to it and, between me and the museum educators at the MoD, we have a lot of ideas for things to do. I hope everyone can come out and enjoy the festivities and learn about fossils in Arkansas and beyond firsthand.


Platecarpus skull fossil at Plano West Senior High Photo Credit:Wesley Kirpach. Wikimedia Commons.

Now, for that fossil…Did any of you recognize this as the skull of a mosaaur, specifically that of Platecarpus? To picture a mosasaur, imagine a komodo dragon, replace the feet with flippers, and compress the tail so it is taller than it is wide (aka laterally compressed) so it looks more fish-like than lizard-like, and you have a pretty good view of a mosasaur. There is a reason for that. Komodo dragons are part of a group of lizard called monitor lizards, which are thought to be close relatives of mosasaurs and so are likely an excellent model for what the ancestral animal of mosasaurs looked like before they became aquatic.

Platecarpus. Wikimedia.

Platecarpus. Wikimedia.

Platecarpus was a carnivorous marine reptile that swam in the Cretaceous seas. While dinosaurs like Tyrannosaurus rex and Triceratops roamed the land, Platecarpus and its relatives patrolled the oceans. This is one of the most common mosasaurs, so much of what we know about them comes from fossil of this genus. It was smaller than many of the other mosasaurs. Some, like Kronosaurus, could reach up to 17 meters, but Platecarpus only averaged around 4-7 meters. Its name means “flat wrist,” alluding to the flippers, although it hardly distinguishes them from other mosasaurs in this regard. What did make them stand out from the other mosasaurs was a relatively shorter snout with eyes that faced more forward, so it probably had better stereoscopic vision, that is, it had better depth perception than most others of its kind. This may be why it had a shorter snout, to prevent the snout from blocking its field of view. Like other mosasaurs, Platecarpus had two rows of teeth on its palatine bones, forming the roof of its mouth. This arrangement actually isn’t all that unusual in lizards and snakes, it is really common in fish. The teeth (all of them, not just the palatal teeth) were pointed and conical, although not as sharp as some of its kin, indicating it went after small, soft prey, like small fish and soft invertebrates like squid or perhaps even jellyfish. They could have gone after larger prey like crocodilians do, but unlike crocodilians which have a strong skull capable of withstanding the forces of ripping a prey item apart, Platecarpus had a much weaker skull which would likely not have stood up to the stresses of the crocodilian death roll (this is when they grab a limb and spin until the limb is ripped off, the moral of the story is of course, never dance with a gator). The overall shape of Platecarpus is stockier than most mosasaurs. This would have had the effect of decreasing surface area relative to body weight, which could have increased its metabolism by holding in heat better.

KUVP1001. Mike Everhart.

KUVP1001. Mike Everhart.

One of the things that makes Platecarpus as a genus so interesting is the fossils that have been found with soft tissue preservation. In one, along with parts of the skin, parts of the trachea (windpipe) were preserved. Originally, they were interpreted as part of a dorsal fin, thus all the early pictures of mosasaurs with fins along their backs. However, it was quickly discovered what the traces really were. To his credit, Williston, the scientist who had reported in 1899 the traces as a dorsal fins was the one who published another short paper three years later saying he had made a mistake and the fossil really showed the cartilaginous rings found in trachea. The tracheal rings have also been interpreted as showing the branching point between the two lungs, which is important because it answered a question about their origins. Every researcher agrees that mosasaurs are lepidosaurs, the group including lizards and snakes, but what wasn’t known was whether or not mosasaurs were derived from aquatic lizards or from snakes. The discovery of a trachea showing two lungs confirms the origin within lizards (snakes only have one lung). It may still be that snakes evolved from mosasaurs, but that is not very likely.

The other piece of soft tissue that has been found is the outline of the tail showing a lobe on the tail forming a very shark-like tail. Until this time, many people had thought the mosasaur swam with an eel-like motion, but the tail and the deep caudal fins indicate a much faster shark-like swimming motion. This in turn has caused people to reevaluate the view they were slow ambush predators, supporting a more active predatory forager. Whether or not other mosasaurs had this fin is currently unclear, so there may have been specializations within this group not seen in the larger mosasaur family. Another such example is the discovery of what has been interpreted as thicker eardrums, which may have allowed them to dive to deeper depths.

Tail fluke preserved around skeleton. Credit: (top) Photograph (by Johan Lindgren), (centre) sketch indicating the bones and skin structures preserved (by Johan Lindgren), and (bottom) life reconstruction (by Stefan Sølberg) of Prognathodon sp.

Tail fluke preserved around skeleton. Credit: (top) Photograph (by Johan Lindgren), (centre) sketch indicating the bones and skin structures preserved (by Johan Lindgren), and (bottom) life reconstruction (by Stefan Sølberg) of Prognathodon sp.

The southwestern corner of Arkansas was at the edge of the Late Cretaceous Western Interior Seaway, so we have several fossils of them in places like Clark, Hempstead and Howard counties, although you can find them all over the world in the right type of rocks. You can find them in the Brownstone and Marlbrook Marl Formations. These formations are indicative of warm, shallow seas, much like the Bahamas today, which considering the locations, shouldn’t come as too much of a surprise to people. If you were taking a nice vacation on the warm Cretaceous beaches 80-85 million years ago, you might have tried fleeing into the water to avoid the dinosaurs on the beach, but you would have been no safer in the water.

I would like to thank Rachel Moore, who supplied a lot of the research involved in putting this post together.

The ethics of fossil collecting


Today’s Google doodle celebrates the 215th birthday of Mary Anning. She was one of the first people to help usher in the modern age of paleontology as a science and was the prime worker on the Jurassic Coast near Dorset, England, probably the most important fossil site for marine reptiles in the world. The Natural History Museum of London calls her “the greatest fossil hunter ever known..” Among other finds, she is credited for finding the first correctly identified skeleton of an ichthyosaur, the first complete specimens of a plesiosaur, the first pterosaur outside Germany, and identifying coprolites as fossil feces. Until that time, they were called bezoar stones, indigestible masses found within the digestive system. They were rumored to be an almost universal antidote for poisons and were used as such in J.K. Rowling’s Harry Potter series. The first woman to receive a eulogy at the London Geological Society, an honor given only to distinguished member scientists (she wasn’t even a member because the society did not accept women at the time, they just took her work and published it under their names), Mary Anning was widely sought after by researchers in her time for her expertise.

This brings up an interesting debate. It is hotly debated what role commercial fossil dealers have in paleontology. The current majority consensus as presented by the Society for Vertebrate Paleontology is that they should be stopped because all the fossils they collect are sold, almost always, to private collectors, thereby removing them from scientific study. Fossils that are not in the public trust (like a museum) are not accessible to other scientists to study, so all the knowledge that may be gleamed from their study is lost to the public. They explicitly state this in their bylaws. Section 6, Article 12 states: “The barter, sale or purchase of scientifically significant vertebrate fossils is not condoned, unless it brings them into, or keeps them within, a public trust. Any other trade or commerce in scientifically significant vertebrate fossils is inconsistent with the foregoing, in that it deprives both the public and professionals of important specimens, which are part of our natural heritage.”


The tyrannosaur named Sue. Wikipedia.

They have a point. Few fossils collected by commercial fossil dealers ever get scientifically studied. Who knows how many priceless and important fossils are locked away in someone’s private collection. Museums do not have the resources to compete with private competitors to buy fossils except in the rarest of occasions and even then, it depends on the finances and good will of private individuals willing to donate to the museum for that purpose. The tyrannosaur named Sue sold at auction for $7.6 million to the Field Museum in Chicago, who needed the help of the California State University system, Walt Disney Parks and Resorts, and McDonald’s, along with numerous individual donors to raise the money. Researchers collecting fossils must always be on their guard to protect their dig sites due to the common occurrence of thieves stealing fossils from their dig sites to sell them. Many paleontologists have stories of finding a skeleton at the end of the season and having no time to collect it, only to come back the next season to find someone has collected the sellable parts and not uncommonly have smashed the rest. Even if the fossils find their way to a public institution where they can be studied, most commercial fossil collectors do not take sufficient notes about location and all the details at the site to make the find reliable enough to study well. It is often said that a fossil without provenance data has little more worth than having no fossil at all and for good reason. If you don’t know where a fossil came from, there is little you can say about it and it is impossible to place it in context with other fossils.

On the other hand, commercial fossil collectors say that without them, most of the fossils they collect would have eroded away and been gone completely with no record of them ever having existed at all. There simply aren’t enough paleontologists and money in academia to collect all the fossils they do and they are right. The tyrannosaur Sue is a great example of a dinosaur fossil that may not ever have been found if it were not for commercial fossil dealers. What makes this point important for this essay is that Mary Anning was a commercial fossil dealer. She funded her research and supported herself by selling fossils. Without the income she received from fossil sales, she would never have been able to make the discoveries she did.

Possibly the only known photograph of Mary Anning and she is not even credited in the photo, which is called The Geologists. 1843, Devon. Salt print by William Henry Fox Talbot. Photograph: The National Media Museum, Bradford

Possibly the only known photograph of Mary Anning and she is not even credited in the photo, which is called The Geologists. 1843, Devon. Salt print by William Henry Fox Talbot. Photograph: The National Media Museum, Bradford

So who is right? Maybe they both are. It is undeniable that unscrupulous poachers and fossil dealers steal and destroy priceless fossils which never enter the public and academic consciousness, but it is also undeniable that commercial fossil dealers have contributed greatly to our knowledge of paleontology. The AAPS, Association of Applied Paleontological Sciences, an organization representing commercial fossil dealers, advocates for responsible collecting, having a professional academic work with commercial fossil dealers so any finds can be studied. Their position would indeed help bridge the gap between the academic and the commercial dealer. However, this requires the benevolence of the collectors and many, possibly most, are uninterested in letting academics study their fossils. While the fossils may be able to be studied during the time they are found and prepared (removing the encasing rock and putting the pieces together), most of the study comes after this point. A fossil in private hands can easily become lost and access is at the mercy of the owner. A museum, on the other hand, is required to maintain records of the fossils and provide access to anyone who wants to study them.

paleo_images0.Par.11277.Image.150.355.1So what is to be done? Currently, it is illegal to collect vertebrate fossils on Federal land. The reasoning is that Federal land is owned by everyone. As such, anything on Federal land must be protected for all citizens, making collections for private sale not in the interests of the country as they take fossils out of the public trust and therefore inaccessible to the public. States have their own rules, some make it illegal, others have no specific laws concerning fossil collections. On private land, there are no restrictions. Any fossils found on private property are the property of the land owner and they can do whatever they want.

What is the correct answer? That depends on your point of view. Certainly the collective point of view has changed through time. What do you think?

Mystery Monday

Mystery Monday

For today’s Mystery Monday fossil, see if you can identify this creature.

Fossil Friday

It’s Friday, time for the answer to Monday’s mystery fossil. Were you able to identify it?

enchodusoceansofkansasThese fossils are from a fish called Enchodus, the “saber-fanged herring.” Teeth of Enchodus are commonly found in the Cretaceous-aged rocks in southwestern Arkansas, especially near Malvern and Arkadelphia in the Arkadelphia and Marlbrook Marl Formations, up into the Paleocene rocks of the Midway Group a bit farther north. In other places you can even find them in rocks of Eocene age, although you will have much better luck in the Cretaceous rocks. At this time, southern Arkansas was shallow to coastal marine. Go to the Bahamas, imagine Enchodus, mosasaurs, plesiosaurs, and plenty of sharks in the water around the islands and you would have a good picture of the landscape back then. They were abundant at the end of the Mesozoic Era and survived the asteroid impact that rang the death knell for many animals, including the non-avian dinosaurs. But they never regained their prominence as a key member of the marine ecosystem, eventually dying out completely in the Eocene sometime around 40 million years ago (the Eocene lasted from 55 to 34 million years ago).


The fish reached sizes over 1.5 meters, which makes them on the large side, but not really big, considering there were mosasaurs in the same waters that surpassed 10 meters. Still, with fangs longer than 5 cm, they would not have been fun to tangle with. They were clearly effective predators on smaller fish and possibly soft animals like squid. At the same time, fossils have been found showing they were themselves prey for larger predators, such as sharks, the above-mentioned mosasaurs, plesiosaurs, and even flightless seabirds such as Baptornis. Baptornis was a toothed, predatory bird, but as it only reached 1 meter or so, it would have only been able to hunt young Enchodus. So like many of us today, Baptornis was always up for a good fish fry.

Hesperornis, a larger version of Baptornis, and a few Enchodus feeding on some herring-type fish. Picture by Craig Dylke.

Hesperornis, a larger version of Baptornis, and a few Enchodus feeding on some herring-type fish. Picture by Craig Dylke.

Enchodus is often called the “saber-fanged herring,” although it is unrelated to herrings. So what then was it? Herrings are what is known as forage fish, meaning they are mostly prey items of larger fish and other animals. Most of the fish called herrings are in the family Clupeidae in the groups Clupeiformes, which includes such well-known fish as sardines and anchovies. Enchodus, on the other hand, has been placed into the group Salmoniformes, which includes trout, char, and of course, salmon. When one typically thinks of trout and salmon, one doesn’t think of bait fish, they think of the fish that eat the bait fish. Thus, Enchodus would better better described as a fanged salmon (they were a bit large to call them fanged trout).



Mystery Monday

Mystery Monday

Time for another Mystery Monday. Teeth like this are reasonably common in Arkansas rocks of a particular age. See if you can tell what it is.

Puma concolor, The Ghost Cat of Arkansas

I have a special treat today. I am pleased to announce our first guest post on paleoaerie. John Svendsen found a set of puma fossils when he was in high school. Today, he shares with us what he has learned about them since that time.

“Masters of stealth, they seldom step from the shadows.”


For many years people have reported sightings of mountain lions and pumas in Arkansas yet the Arkansas Game and Fish Commission has repeatedly disputed such claims.  Rather the AGFC believes that any such sightings are simply of feral mountain lions released from captivity that should be shot on sight.   Why would the AFGC deny the obvious – that living, breeding mountain lions can be found in the state?  As noted by Bryan Hendricks (2009), if the AGFC acknowledges the presence of a sustainable population of wild mountain lions in Arkansas, then it will be compelled to draft a management plan to assure their survival. That means the agency will have to devote money and manpower to compile a population estimate, and then hold meetings to get public input for management options.  By virtue of the mountain lions endangered status, a management plan would likely seek to increase or maintain its population – obviously,  deer and turkey hunters and livestock farmers would feel at risk having this predator protected by law and would seek litigation or legislation to assure that they can continue to kill mountain lions on sight.

Fortunately there was a time tens of thousands of years ago when mountain lions roamed the state without fear of man.  This ancient pre-historic cat roamed the hills and savanna of North America for millions of years in the company of dire wolves, saber-tooth tigers, giant sloths, peccaries and cave bears.  Just as these mammals became extinct so did the mountain lion and by the late Pleistocene (approximately 10-12,000 years ago) no mountain lions survived in North America.  Fortunately a few mountain lions from South America migrated northward and reestablished living populations throughout much of North America.  The mountain lions we see today in Arkansas are the ancestors of this small migrating band from South America.

The mountain lion, known scientifically as Puma concolor, occupies a vast range of ecological zones as diverse as desert, tropical rain forest and alpine steppes (Kurten, 1976).  Cats such as P. concolor are poorly represented in the fossil record and taxonomic research on felids is somewhat incomplete.   Much of what is known about their evolutionary history is based on mitochondrial DNA analysis and still there are substantial confidence intervals in suggested dates and lots of room for error (Culver et. al, 2000).    We do know however that pumas come from a very long line of evolution with episodic bursts of development and diversification that can be traced 40 to 60 million years ago through the late Tertiary period.

These prehistoric creatures are large cats with powerful bodies.  Males can weigh 250lbs. (103 kg) with a length of 4.5 feet and a 3 foot tail. It is the second largest cat in the Americas, after the Jaguar, and it is the fourth heaviest cat in the world, after the Tiger, Lion, and Jaguar.  It is a solitary cat and rarely is seen in the presence of other cats except during breeding and the raising of a litter.  It is an apex predator and is specialized for the task:  binocular vision, acute sense of smell and sight, retractable claws, strong canine teeth and masseters, and powerful forearms and legs allowing it to leap 40 feet, jump 15 feet high and pounce from a height of 5-story building.  Few animals are capable of outrunning, alluding or surviving a puma attack — fortunately they prey chiefly on the weak and injured and thus strengthen the gene pool of those on which they prey.

ImagePuma fossils are rare in the fossil record of Arkansas and have only been identified from:  Conard Fissure and Svendsen Cave (see Figure 1).   Conard Fissure is a geologic feature in Northern Arkansas where a deposit of Pleistocene fossils were discovered in 1903 when Waldo Conard was searching through fissures and crevices on his land in search of lead.  In one of these fissures he found a “bone mine” with thousands of bones preserved in limestone – thirty-seven genera and fifty one species, of which nearly half are extinct.  The original excavation of the fissure was performed by Barnum Brown, the initial discoverer of Tyranosaurus rex, and yielded an assortment of small animals and rodents but also larger mammals including peccary, deer, bear, wolves and foxes.    This entombment of a wonderful assemblage of mammal is accounted for by the fact that the fissure long remained open and was inhabited in the late Irvingtonian (240,000-300,000 years BP) by many carnivorous animals.

puma2bSvendsen Cave yielded the remains of a puma following its discovery in 1974 by two young spelunkers, John Svendsen and Ola Eriksson who were still in high school at the time (Pluckette, 1975). The cave is developed in dolomitic limestone of the Everton Formation and contains over a mile of mapped passage and three stream systems.  The skeletal remains were encased in a travertine ledge only 500 feet from the entrance of the cave (see Figure 3) but passage to the remains included a low strenuous crawl and squeeze, a siphon and two climbs.  The puma is presumed to have entered the cave from an entrance now unknown and may have been washed to the depositional site.

puma3Svendsen Cave proved to be a marvelous find as the remains were chiefly intact and materials that were recovered included:  partial skull with teeth, partial left mandible with teeth, left humerus, scapula, ribs, and vertebrae (see Figures 4-6).  No exact date can be assigned to the Svendsen puma albeit antiquity is evident given mode of occurrence and lack of metastable materials in the skeletal remains.  At the depositional site, the bone-bearing travertine is undergoing dissolution and the sediments are being removed by a nearby stream.   Thus a climatic regimen of less than the present level of precipitation which allowed formation of the travertine ledge is indicated for the cave area during deposition of the puma (Pluckette, 1975).   Given the dimensions of the dentition, mandible and humerus obtained from the site a dating of the Middle Pleistocene, Ionian stage (781 to 126 thousand years ago), is presumed albeit the fossils could be much older.


puma5puma6No other sites in Arkansas have been discovered which have yielded prehistoric fossils of the P. concolor albeit more are likely waiting to be found in the future.


P. concolor is still a resident of Arkansas.  In most of North America P. concolor is currently classified as an endangered species and protected, whereas in Arkansas it is currently legal to shoot and kill P. concolor upon sight as the Arkansas Game and Fish Commission has declared, “All cougars (mountain lions) in Arkansas are considered to be escaped pets or the feral progeny of escaped pets and hence it is legal to kill such animals.”  The future of this magnificent big cat lies at the mercy of people who must preserve its natural environment and allow it free passage.


Brown, B. 1908.  The Conrad Fissure, a Pleistocene bone deposit in northern Arkansas; with descriptions of two new genera and twenty new species of mammals.  Am. Mus. Nat. Hist. Mem. 9: 155-208.

Culver M1, Johnson WE, Pecon-Slattery J, O’Brien SJ.  2000.  Genomic ancestry of the American puma (Puma concolor).  Journ. of Heredity.  91:  186-197.

Hendricks, B. 2009. “Arkansas sportsman: AGFC not lying just avoiding furball over big cats.” Arkansas Democrat-Gazette. Feb. 8, 2009.

IUCN, 2010. “The IUCN Red List of Threatened Species” (On-line). Mammals. Accessed March 29, 2011 at

Johnson, W.E.,  Eizirik, E., Pecon-Slattery, J., Murphy, W.J., Antunes, A., Teeling, E. and O’Brien, S. J.  2006. The Late Miocene radiation of modern Felidae: A genetic assessment. Science 311:73-77

Kurten, B. 1965.  The Pleistocene felidae of Florida.  Bull. Florida State Mus. 9(6):  215-273.

Kurten, B.  1976.  Fossil Puma (Mammalia:  Felidae) in North America.  Netherlands Journ. of Zoo.  2694):  502-534.

O’Brian, S. J., and Johnson, W. E. 2005. Big Cat Genomics. Ann. Rev. Genomics Hum. Genet. 6: 409-29

Pluckette, W. L. 1975.  An occurrence of the Puma, Felis concolor, from Svendsen Cave, Marion County, Arkansas.  Ark. Acad. Of Sciences, Vol. 29, p. 52-53.

Turner, A. 1997. The Big Cats and Their Fossil Relatives: an Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.

Young, S.P. and Goldman, E.A.  1946.  The puma, mysterious American cat.  Am. Wildlife Inst. 358 p.

The answer to last week’s Mystery Monday

The answer to last week’s Mystery Monday fossil was supposed to be posted last Friday, which didn’t get done. I am going to have to make some changes in the schedule or change the way I do things because I simply don’t have the time to post a new fossil and give a full discussion of it every week and do anything else. So if you have any suggestions on how you think changes would be best done, let me know. I could cut back to every two weeks; still give a fossil every week, but not go into much discussion of what it is each week; or some other possibility. Let me know your preferences.

At any rate, for the last Mystery Monday fossil, I posted this little fossil.


What we have here is a little goniatite ammonoid that has been pyritized, meaning that the shell has been replaced with pyrite. This type of fossilization is pretty common. As the bacteria eat the organism, some of them will release sulfur, which then combines with the hydrogen in the water to form hydrogen sulfide. When it precipitates out of the water, it usually does so as pyrite. In some cases, like in this one, the pyrite crystals can replace the organism so well that it makes a detailed copy of the original. For obvious reasons, this type of fossilization is called replacement, in which the original oranism is replaced with a mineral, be it calcium carbonate, iron, opal, quartz, or in this case, pyrite.

So what are goniatite ammonoids? Ammonoids are part of the group (often called phylum, but for various reasons the specific rank of the group is often no longer used) Mollusca; which includes snails, (gastropods), clams (Bivalvia, meaning two shells, or less commonly, Pelecypoda, meaning hatchet foot), and the Cephalopods.

Cephalopod diversity.

Cephalopod diversity.



Cephalopods include the squids and octopuses, as well as the Nautilus, which is what concerns us here. If you aren’t familiar with a nautilus, think of a squid inside a spiral shell. Squids used to have shells, either long, straight ones or curved and coiled ones. The only one left of these shelled squid is the nautilus. However, you can still see the remnant of the shell in an internal structure called a squid pen, or in the case of cuttlefish, the cuttlebone. In either case, they are the last vestiges of the external shells we see in the nautilus and the ammonoids.

Squid anatomy.

Squid anatomy.

During the Paleozoic and Mesozoic Eras, ammonoids were much more common and much more diverse. During the Jurassic and Cretaceous Periods during the Mesozoic, the type of ammonoids that were most common were the more familiar fossils known as ammonites. Goniatites were much earlier and lived during the Paleozoic.

Nautilus shell. Wikimedia.

Nautilus shell. Wikimedia.

How does one tell the difference between the different types of ammonoids? Look at the internal partitions. These partitions, called septae, separate the chambers within the shell. As the animal grows, it adds material to the edge of the shell, making it larger and larger at that end. Once the shell gets big enough, the animal will create a new partition in the back, separating the current body chamber from the earlier, smaller one. A small hole is left in the septae so the siphuncle, a thin tube, can pass through, connecting all the previous chambers. The siphuncle could then be used to pump water or gas in and out of the chambers so they could be used as ballast, allowing fine control of their buoyancy.

ammonoidags1The septae in the nautiloids (the group of ammonoids containing the modern nautilus) are all very smooth, forming a nice curve. The nautiloid septae curve inwards, whereas the ammonoids curve outwards to some extent. Ammonoid septae are also much more complex. Goniatites, the earlier forms, had simple wavy septae. Ceratitic ammonoids created septae in which the waves were more jagged, with what often looks like little saw-toothed crenulations. The later ammonites (many people call all of them ammonites, but this term more properly only refers to the more derived subset) had very complex septae, showing several smaller wave patterns overlaid upon the larger wave.


Ammonoids were very common in the Paleozoic and Mesozoic and were found throughout the oceans of the time. They typically lived in shallow marine environments all over the world. They also evolved rapidly, so new species tended to appear and disappear on a fairly regular basis. This abundance, diversity, and rapid turnover make them prime index fossils. Index fossils are those fossils which are useful for dating the rock layer and correlating the layer from one spot to another. Using index fossils allows us to piece together a complete sequence of events even if there is no one place that has the entire sequence of rocks preserved. As a result, any fossils that can be used as index fossils become very important to people trying to figure out the history of life on earth, such as this little ammonoid. If you want to find one for yourself, look in almost any of the limestone or chert formations in the Ozark mountains. There are plenty.