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Three years ago, a ten year old boy was visiting a monastery in Colombia. Being a curious boy, he looked around at his surroundings. He could have done like others have done for centuries and not paid that much attention to the stones upon which he walked, but he didn’t. He noticed a curious fossil fish in one of the flagstones. Most people, if they noticed it at all, would have simply given it a passing nod of interest. He, on the other hand, took a picture of it and sent it to the local Paleontology Research Center to see if they knew what it was.
Firstly, I amazed they even had a local paleontology research center, most places don’t. Secondly, it is amazing that the boy took the time to bring it to their attention. Thirdly, it is amazing that someone there noticed what they had and brought it to the attention of the needed experts. All these amazing, unusual occurrences have resulted in an article in the January 31 edition of the Journal of Systematic Paleontology detailing the new fossil species discovered by that boy. Sadly, no one knows how to contact him to let him know about the publication. The researchers have his name and email, but have apparently been unable to contact him to give him his copy of the paper about his fish.
The fish he discovered was named Candelarhynchus padillai, after the Monastery of LaCandelaria near Ráquira, Colombia, where it was found. The stone for the flagstone came from a nearby quarry. According to the authors of the paper, the rocks in the quarry corresponding to the flagstones were “fossiliferous, finely laminated, light to dark grey, indurated mudstones ofthe lower-middle Tuonian San Rafael Formation…” The rock strata also contained numerous plankton, ammonites, clams, and crabs; so quite a rich fauna. The Turonian is 89.8-93.9 Mya, according to the latest GSA time scale, so we are talking roughly 92 Mya.
The fossil is excellently preserved, with slabs containing both part and counterpart, meaning that when they split the slab, pieces and impressions were left on both sides. The whole body can be seen, with nice detail around the head, as well as impressions of the soft tissue portions of the fins. At 27 cm (just over one foot), it is a decent-sized fish. It’s a thin fish, with a long skull full of tiny, conical teeth. It was clearly a fast-swimming predator, and likely prey for a lot of larger species.
The reports on the fish said that it does not have any living relatives. That is true, in a way, but also not. The specific family the phylogenetic analysis placed it in is Dercetidae, an extinct family that all died out in the Cretaceous. However, if we look a bit broader, it is in the Order Aulopiformes. This order is mostly known for a variety of mostly deep water fish known as lizard fishes, which is why all the news reports of this find have said Candelarynchus was a “lizard fish.” Even though it is in the same Order, it is not in the same family as any of the modern lizard fish.
But the title of this post mentioned Arkansas and I have thus far not done so. Vernygora reports that current analyses of fossil aulopiforms include three main families: the Dercetidae, Halecidae, and the Enchodontidae. One of the most prominent Cretaceous fish from Arkansas is Enchodus, commonly called the “saber-toothed herring.”
This is a terrible name because Enchodus has nothing to do with herrings. It was at one time considered part of Salmoniformes, making it closer to salmon. However, more recent analyses have consistently placed it in Aulopiformes, specifically within the Enchodontidae, making it closer to lizard fish. This makes a good deal of sense to me because, if you add the fangs from a payara, commonly known as the vampire fish, onto a lizard fish, you have pretty good idea of what Enchodus was like.
Fossil lizard fish then were quite abundant in the Late Cretaceous in both worldwide range and diversity. They may not be the most recognized fish today, but they have a long history and make for great fossils that can be found in a lot of places, including southwestern Arkansas.
Greetings and welcome to the final day of Prehistoric Shark Week! All week we have covered sharks that swam in Arkansas during the Cretaceous Period. The dinosaurs get all the press, but we had a diverse marine ecology during that time. Last week, we met a few of the non-shark denizens, such as mosasaurs, elasmosaurs, and more. This week, we have seen nurse sharks, goblins, sand tigers, and an array of rays, skates, and angel sharks. We wrap up the festival of marine animals with the question that everyone wants to know. Where did the most famous sharks of all time, the Great White and Megalodon, come from and how does Arkansas play into this?
The Great White, or simply White Shark, is named Carcharodon carcharias, meaning sharp tooth pointer, although more popularly named for its white belly, is well known as the largest living predatory fish in the sea, reaching up to and, probably over, 20 feet. Megalodon, listed either as Carcharocles megalodon or Carcharodon megalodon, depending on whether or not one believes it is directly related to or convergent with White Sharks, is the largest known predatory fish ever, reaching sizes up to three times that of the White Shark. It appeared in the fossil record about 16 Mya, but went extinct 1.6 Mya (contrary to what a fictitious documentary on the Discovery Channel claimed).
During the Cretaceous, the southwestern part of the state was covered by the Western Interior Seaway, which for us, was essentially equated to having the Gulf coast not just on our doorstep, but flooding it. Those waters were warm, rich in nutrients, and a hotbed of marine life. In those waters, a few sharks of interest made their home.
All of the sharks we will be talking about are lamniform sharks. These sharks are known for being at least partially endothermic, meaning they used their core muscles to create their own heat and maintain an elevated body temperature, giving them the ability to be active hunters even in cooler waters. Of course, it also meant they were hungrier, needing more food, keeping them always on the prowl. This is what allows the White to be such a fearsome hunter today, giving it the power and energy to breach completely out of the water during attacks.
Squalicorax is an extinct shark of the time that is commonly thought to have resembled Whites. These sharks got up to five meters, although they were typically around two meters. Squalicorax is also called the Crow Shark, which some people have speculated it got that name from evidence of its scavenging. However, squalus means shark (and is the scientific genus name for dogfish) and corax means crow, so the name Squalicorax literally means crow shark. Now as to why it was named that way to begin with, no one knows because when Agassiz named it in 1843, he didn’t leave a record as to why. They hunted and scavenged a wide range of animals, everything from turtles to mosasaurs. Unfortunately, the relationships between Squalicorax and other lamnids is uncertain, so whether or not it could have been ancestral to anything, much less Whites or megalodons, is unknown at present.
Another candidate is a shark named Isurus hastalis, an Oligocene shark that lived 30 Mya. Isurus also includes the modern day mako shark. However, a researcher by the name of Mikael Siverson concluded that the Isurus teeth were not makos, but worn down teeth similar to modern Whites. So he changed the name to Cosmopolitodus. It has also been suggested that these sharks originated from a shark called Isurolamna, which lived in the paleocene 65-55 Mya.
A more recent view, and one which I back (with freely admitted bias because it allows me to say they evolved from Arkansas sharks:) ), is that both Whites and megolodons evolved from an extinct lamnid called Cretolamna, the Cretaceous lamna. This shark had large, strong teeth and was very successful. It had a worldwide distribution and lived from the Cretaceous to the Paleocene. Cretolamna fossils have not been reported in Arkansas thus far, but they were a member of the family Cretoxyrhinidae, of which the shark Serratolamna was a member. The teeth of Cretolamna and Serratolamna are extremely similar, as one might expect from genera in the same family. However, Serratolamna teeth have serrations and Cretolamna does not, making Serratolamna teeth closer in shape to the White Shark. Serratolamna did not have the same worldwide distribution and did not last as long as long as Cretolamna, though. It is impossible to tell which one was directly ancestral to the later sharks, but Cretolamna, due to its more cosmopolitan range, has gotten the nod. It was named first and is much better known than Serratolamna, giving it an edge when people find and identify fossil shark teeth. Thus, it is not a big stretch to say that Serratolamna, or a very close relative, eventually evolved into Carcharodon carcharias as well as Carcharocles (or Carcharodon) megalodon.
I hoped you have enjoyed Prehistoric Shark Week and the previous week of Cretaceous Arkansas marine predators. Let me know if there is another group that you think deserves special consideration for a celebratory week.
For Day 4 of Prehistoric Shark Week, I would like to mention another modern day shark that has been around since the Cretaceous: the sand tiger sharks. Tomorrow, I will discuss a couple of Cretaceous sharks that may be the ancestors of the two most famous sharks in the world – the Great White and the giant Megalodon.
The Sand tiger is a common shark in the Cretaceous sediments, or at least, their teeth are, which means they were probably pretty common back then. The teeth tend to be long and thin, with two small cusps on either side of the large, center blade. Elasmo-branch.org reports that the center blade is smooth-edged with a strongly bilobed root, large bulge in the center of the root (aka lingual protruberance), and nutrient foramen in the center.
There are actually two sharks that are often called sand tigers in the Cretaceous rocks. One is Carcharias holmdelensis, the Cretaceous version of Carcharias taurus, the modern day sand tiger shark. Also going by the name grey nurse shark, amid several others, sand tigers are large-bodied sharks that will eat pretty much anything, but since it is a fairly slow and placid shark most of the time, it doesn’t seem to go after anything that requires a lot of effort. They are known for gulping air to allow themselves to float in the water column without expending much effort. So although they look scary, they appear to be too lazy to live up to appearances.
The other shark that gets called a sand tiger, is Odontaspis aculeatus, one of the ragged toothed sharks, which also go by the name sand tiger. These sharks were until recently in the same family as Carcharias, but have since been pulled out into their own family. They are very similar, as one might has guessed from the numerous times these sharks have been grouped and split over the years. As Elasmo-research.org put it, “Chaos reigned until Leonard Compagno examined museum specimens from all over the world, corrected misidentifications and sorted out synonyms.”
For Day 3 (a little late, yes) of Prehistoric Shark Week, I want to bring to your attention the diversity of chondrichthyans that have opted for a flatter bauplan.
Sharks are generally split into two groups, the galeomorphs, which are mostly the more typical torpedo-shaped sharks, including the sharks that most people think of when they envision a shark. The other group is the squalimorphs. These sharks lack an anal fin and many of them have developed a penchant for flatter bodies and broad pectoral fins, and in some cases pelvic fins as well (although not all, such as the dogfish and frilled sharks). Up until recently, the batoids, otherwise known as skates and rays, were considered part of this group, the consensus being that they were a more specialized type of squalimorph shark that had taken flat to an extreme. But the most recent molecular studies have indicated that they are a group unto themselves. The batoids have a long fossil history, with a number of ray teeth found in the Cretaceous deposits of Arkansas, particularly the eagle ray family Myliobatidae. Their teeth are typically flat rectangles on top with a comb-like surface below. Another type of ray that can be found are the guitarfish, or Rhinobatos casieri. These pectoral fins of these fish extend to their head, giving them a triangular shaped front end of a more traditional shark-like back end.
Skates and rays are generally very docile and would not be very threatening, spending their time scrounging about on the sea floor for benthic (living in or on the sea floor) invertebrates and the occasional fish. The same can’t be said for the last member of this group, the sawfish. Armed with a rostrum (its elongated snout) with teeth out to the side, the fish looks like it has a chain saw for a nose. The sawfish will swim into a school of fish and thrash its rostrum rapidly back and forth, spearing and stunning several fish, which it can then gobble up. They can also use it to dig up clams and crabs from the sediment. While they won’t attack humans, any human who provoked one may easily wind up perforated by the rostrum, probably not deadly but certainly painful. Most modern sawfish reach a respectable two meters, but the largest species, the green sawfish (Pristis zijsron) can top seven meters (24 feet). This is as large as the Cretaceous versions. Modern sawfish are typically put into the family Pristiformes. The Cretaceous ones are in their own family, called Sclerorhynchiformes and are not directly related, in that the Cretaceous ones are not thought to be ancestral to the modern ones. They are both put into the group Pristirajea, so they are thought to at least be related. But with the uncertainties in the relationships of the modern fish, the relationships with fossil forms are necessarily less certain. In any case, Arkansas sports several different species from this group, including Schizorhiza stromeri, Sclerorhynchus sp., Ischyrhiza mira, Ischyrhiza avonicola, and Ptychotrygon vermiculata. We were postively awash in sawfish.
The true squalimorph sharks that have shown up in the Arkansas Cretaceous rocks are best represented by the Angel shark (Squatina hassei), which looks like an early rendition of a skate, so it is little wonder that most researchers viewed skates and rays as simply more specialized versions of these sharks. Nevertheless, it appears this is case of convergence, not homology (similarity due to relationship). If it is homologous, it isn’t directly so. It is possible both groups had a common slightly flattened ancestor and each took their own route from there.
All of these fish are pretty docile hunters, scrounging around the sea floor for benthic organisms, all those animals that make their home in or on the sea floor sediments. They spend their time digging around the sand for crabs, clams, and other invertebrates, the occasional fish. When threatened by the presence of a predator, they hide on the bottom, using their shape to help them blend in with the seafloor. Neither the ones today or the ones in the Cretaceous would have bothered a human swimming around them.
Becker, Martin A., Chamberlain, John A., Wolp, George E. 2006. Chondricthyans from the Arkadelphia Formation (Upper Cretaceous: Upper Maastrichtian) of Hot Spring County, Arkansas
Welcome to Day 4 of Paleo-Animal Fest, celebrating the creatures populating the Arkansas seas during the Cretaceous. Today we are going to look at a fish that has survived for an amazingly long time. They first appeared in the Late Cretaceous and have survived to the present day, still thriving. You can find them in many freshwater lakes and rivers, especially brackish and hypoxic (low oxygen) waters, even into marine waters on the occasion. They are a tough predator in many ways, from their durability in the fossil record to their physical defenses and their intimidating jaws. I am of course talking about gars.
Gars are piscivorous, meaning they eat other fish. The most common description of them is “voracious predator.” They are known for their tooth-filled jaws, scales of armor, and their fight. Their typical mode of attack is a lightning-quick sideways bite. Gar fishermen are often called “not right in the head.”
Gars can be found in many places within North America, but their fossils can be found all over the world. The vast majority of the fossils have been identified as Lepisosteus, which includes the longnose, shortnose, spotted, and Florida gar. However, most of their fossils are isolated scales, which makes it difficult to impossible to tell what type of gar it is from. So I am going to go with most people’s favorite gar, Atractosteus spatula, the alligator gar (pictured above). It is the biggest one reaching almost 3 meters. Another impressive armored, ancient fish that is still around is the sturgeon, which can get a lot bigger, but are nowhere near as impressive in the teeth department.
There are not a lot of skeletons of gars with heads and tails, but there are a lot of body pieces covered in scales. Gar scales are thick, rhomboid-shaped ganoid scales, meaning they are covered in what is effectively enamel. The scales form an excellent armor, making handling them hard on the hands. They are so tough and dense, in fact, that the scales have been used as arrowheads and make even CT scans on gars hard to impossible to get decent views. On the plus side, this results in them having excellent preservational potential and can be found quite commonly. The scales make the fossils really stand out and readily identifiable to at least the group Lepisosteiformes.
By far, the most complete and detailed description of gars ever published is by Lance Grande, the universally acknowledged leading world expert on fossil fish, called “An empirical synthetic pattern study of gars (Lepisosteiformes) and closely related species, based mostly on skeletal anatomy. The resurrection of Holostei.” Special publication 6 of the American Society of Ichthyologists and Herpetologists, published in 2010. This is a massive tome, amassing almost 900 pages of detailed observation on gars. This book is a companion to a similar volume he did on bowfins. I can honestly say I have never seen a more thorough job on any group such as this in my life. Every time I look at it, I think wow, all this on just gars? This would make any scientist proud to have one of these capping their life’s work and this doesn’t even begin to touch the work put out by Grande. I am in awe.
Monday was a goniopholid crocodilian. Tuesday was mosasaurs, the largest of the marine predators. For day 3, we’re going to the other end of the scale.
What is a picture of a rock outcrop doing here? This is a picture of the Saratoga Chalk, courtesy of the Arkansas Geological Survey. Look at it this way, and it is tons of chalk, the same that they used to make for blackboards when they used the real thing.
But look at it under a microscope and you open up an entirely new world. For chalk is not just a rock. It is a rock made of trillions of shells of microscopic organisms that live in the oceans.
Two kinds of microorganisms make up most of the chalk. The Saratoga is primarily noted for its abundance of foraminifera, (forams for short) one-celled organisms that form shells, or tests, out of minerals dissolved in the sea water. The ones that make up chalk and limestone form theirs out of calcium carbonate. It is unclear what they are related to, but one thing is clear. They have developed a huge diversity in their over 500 million years of existence.
I find forams fascinating because of their wonderful diversity. Here is another picture posted on the blog “Letters from Gondwana.” The article is a nice description of forams if you want more information on them.
The other group that is commonly found in chalk is called the coccolithophores. These are very tiny, once-celled plants found in the ocean and make up one of the largest groups of phytoplankton. They also make shells of calcium carbonate, but instead of a shell like the forams, they create their home with a few dozen intricately formed scales.
The coccolithophore Gephyrocapsa oceanica. Wikipedia.
When the cells die, the scales scatter and become tiny grains of calcium carbonate which, when piled up on the ocean floor with all the other debris from the oceans, can form those particles of chalk that you used to clean off the blackboard.
Both of these groups prefer shallow, warm seas. Go to the Bahamas or the Persian Gulf and you will get an idea of the environments that are admirably suited to making modern day chalk, as well as getting a good idea of what Arkansas was like 100 million years ago.
Continuing our celebration of marine animals of the Cretaceous found in Arkansas, here is a picture of a mosasaur. It is from the Dallas (Perot) Museum of Nature and Science. They have a great display of several different mosasaurs. You can also see one on display at the natural history museum located at the University of Texas at Austin.
Mosasaurs were the apex predators of their time, which was in the Late Cretaceous. Tyrannosaurs may have ruled the land, but mosasaurs ruled the seas. The first mosasaurs appeared in the early Cretaceous, but by the end, they dominated the oceans. Unfortunately for them, they only had a 20 million year or so run at the top before the mass extinction at the end of the Mesozoic Era wiped them out along with the dinosaurs.
Mosasaurs were not related to dinosaurs, other than also being reptiles. They were most closely related to the group of lizards that include the monitor lizards, such as the Nile monitor and Komodo Dragon. They were fast predators with a powerful tail to move them through the water. Mosasaurs were so adapted to the water that they bore live young and were not able to walk on land, although they did still have to surface for air like every other reptile. Recent research has found they were endothermic (warm-blooded), unlike their competitors, giving them an edge by allowing them to sustain higher activity levels. It also meant they had to eat more often, making it necessary for them to be effective hunters. Research has also indicated they were countershaded, with a lighter belly than the back, much like many sharks of today. They had a varied diet, with some species specializing in different prey, so over the whole group, they pretty much ate everything in the ocean.
Mosasaur bones have been found in many places throughout southwest Arkansas, which was covered by the Western Interior Sea during the Cretaceous. Two species have thus far been recognized. Platecarpus was fairly small, only 4-5 meters (13-16 feet), but were noted for some exceptionally preserved fossils that retained the impressions of a tail fluke, allowing paleontologists for the first time to see what their tails looked like. The other species is Mosasaurus itself, a huge predator that reached lengths of 15-18 meters (50-60 feet).
Welcome back to the new school year. Some of you will be excited to be back, seeing old friends, making new ones, and learning new things. Some of you will be sad to see summer end. Many of you will be doing both at once. Others of you of course aren’t in school and don’t care about it, but if you are here, you are nevertheless interested in learning cool new stuff. So it is a time for a celebration of the natural world.
Shark Week is a big summer event on the Discover Channel. It is probably their biggest viewer draw all year. Who doesn’t like learning about sharks and seeing them in all their awe-inspiring glory? Additionally, if one is keeping up with the weather, southern Louisiana is currently being deluged, with Baton Rouge and surrounding areas practically getting washed away.
So I thought this would be a good time for Paleoaerie to hold its own version of Shark Week. I can’t do a series of tv specials, so I am going to extend my Paleo Shark week over two full weeks. All this week I will be putting up short posts on marine creatures that swam in the oceans of southern Arkansas during the Cretaceous. Every day will be a new post on something that would make your swim…interesting. Next week will truly be Paleo Shark Week. Every day next week will be highlighting a different shark that would be swimming in the Cretaceous waters of southern Arkansas.
To kick things off, I will start with this creature.
This is a crocodylomorph, meaning that it is in the same group that includes crocodiles and alligators. Specifically, it is a member of the family Goniopholididae. Species in this group were, at least superficially, similar to modern crocodilians. They were semi-aquatic hunters living in marsh and swamp lands. They wouldn’t look out of place with the modern alligators swimming around Arkansas today, except that they probably couldn’t compete effectively with alligators, who are better adapted for the lifestyle than they were. They lived throughout much of the Mesozoic, from the early Jurassic to the Late Cretaceous, when the more modern forms replaced them.
Goniopholids are what is known as mesosuchians, which means “middle crocodiles”. Mesosuchians, as the name suggests, were more derived than the earliest crocodyliforms, such as the protosuchians, although less derived than modern-day crocodilians. Mesosuchians is not a formal name, but an informal and decidedly paraphyletic (i.e. not a valid cladistic grouping because it leaves out some descendants) name to designate those crocodyliform species showing the early characteristics and those that show the characteristics of the modern crocodilians. Here is a phylogenetic tree put out by Chris Brochu in 2001, showing the general relationships within the crocodylomorphs. The names on the left side of the long main line include everything from that point on, e.g. Crocodymorpha includes “sphenosuchians” and everything below it, but not the Aetosauria and above. Mesosuchians plus Eusuchia (which does include all modern groups) can correctly be called Mesoeucrocodylia, but that hardly helps us specify the group.
Mesosuchians include a wide variety of animals with a large number of species. They include terrestrial animals like the carnivorous boar croc Kaprosuchus and the herbivorous Simosuchus, as well as the more typical semi-aquatic pholidosaurs, which include the super croc Sarcosuchus, one of the largest crocodylomorphs ever, reaching almost 40 feet.
Sarcosuchus may not have been quite as big as Deinosuchus though. Deinosuchus was an alligatoroid (within the larger alligator family, but not a modern alligator), which potentially reached upwards of 40 feet, but may have been heavier set. Sarcosuchus lived in the early Cretaceous at the same time as Goniopholis in Arkansas, but lived in Africa and South America. Deinosuchus, on the other hand, lived int he Late Cretaceous right here in Arkansas. While we have no bones to prove this, we do know they lived in Texas and Mississippi, as well as many other places in the United States. The environment would have been suitable for them, so there is no reason to think they did not live here as well.
Wow. I can not believe that I have not posted anything here since Halloween. My New Year’s Resolution is to not let that happen again. I have no excuses. But as was said on the Syfy show The Expanse, “We can not change the things we’ve done, but we can all change the things we do next.”
For this post, I want to relate the trip I took to Arkadelphia just before the Christmas holidays to visit the Goza Middle School on the invitation of one of their science teachers, Trent Smith. That trip will benefit many people in the future, and it also provided a chance to see some Arkansas geology and paleontology that may prove interesting to fossil enthusiasts.
This all started with an email I got from Trent Smith, who had found some fossils he wanted help identifying. After looking at the attached photo, I tentatively identified most of them as specimens of Exogyra ponderosa, a common oyster from the Cretaceous Period. There also appeared to be a goniatite ammonoid, a Cretaceous Period cephalopod, or squid relative. I could not be sure just from looking at the pictures, so I offered coming down to take a look at them in person. Trent was amenable to that and after a few emails back and forth, we arranged to not only look at his fossils, but talk to his eighth grade science class while I was there. It turned out that the school was interested in me talking to multiple classes, which all told was about 160 students. They suggested I could either give one talk to all of them at once, or I could do multiple talks to individual classes. I much prefer the smaller groups where people can get a more hands on experience with the fossils and have more opportunity for students to ask questions, so I opted to give several talks. I wound up giving seven talks, with two of the talks to combined classes. So I had the opportunity to speak with a lot of students.
When I got there, Trent helped me bring in my boxes and took me to his room to start setting up. Goza Middle School students are fortunate to have great science teachers who are passionate about science and education. Trent’s classroom fossil collection was by far the largest fossil collection I have ever seen in a public school classroom. They have a good variety of most of the invertebrate fossils that can be found in Arkansas. They also had a fabulous nautiloid ammonoid 4″ across or more. I had a shell of a modern Nautilus, a genus of the only extant ammonoids, so the students were able to compare a modern version with one over 70 million years old.
For each class, I gave a short introduction to the fossils that can be found in the state, which is much more diverse than most people realize. I also gave them a quick demonstration of the immense expanse of time we were discussing. I have a timeline that stretches eighteen feet and covers 600 million years. People are usually suitably impressed with that timeline, but when I tell them how much space our civilization represents on the timeline, they are stunned. At that scale, all of human recorded civilization is approximately the width of one human hair. Afterwards, we let the students look at the fossils I brought and ask questions. The students were more reluctant to get out of their seats and approach the front table than the younger kids I usually talk to, which I found interesting and speaks to how quickly we train our students to sit and listen without interaction. But once they got over their training, they enjoyed being able to handle the fossils and examine them close up. The students were uniformly polite and well behaved and were a pleasure to talk with. Midway through, the teachers treated me to a tasty potluck lunch.
If everything was left at that, it would have been a great trip and I would be happy to return, but they really went above and beyond. In addition to lunch and a small donation (I have generally not asked for payment for classroom visits in the past and as a result, getting paid for it almost never happens, but getting paid means I can go to more classes so is greatly appreciated), they provided me with even more. They gave me my first two Paleoaerie shirts, which they designed and they did a fantastic job. On the front of both shirts is a dinosaur foot that looks like the foot of Arkansaurus, the only dinosaur bones ever found in the state, and my name, Dr. Daniel. On the back of one shirt, it has the dinosaur foot with the words PALEONTOLOGY above it and DIGGING UP KNOWLEDGE below it. On the back of the second shirt, it says PALEOAERIE.ORG followed by my three statements of what guides my efforts: The universe is endlessly amazing, knowledge is useful only when it is shared, and you can’t really know something unless you understand how and why we think we know it. The shirts are going to be my uniform for future talks.
After school was over, Trent showed me a spot he has collected fossils from on Wp Malone Road, just west of I-30. According to the Arkansas Geological Survey’s geologic map of the Arkadelphia quadrangle, the area is listed as being in the Nacatah Sand, an Upper Cretaceous formation consisting of a mix of unconsolidated sediments deposited in a nearshore marine environment. However, the marl, a limey clay, we found in the creek looked more like it came from the Marlbrook Marl, a formation that lies underneath the Nacatah and separated from it by the Saratoga Chalk formation. The Saratoga Chalk is not thick in this area, so it is quite easy to go from the Nacatah to the Marlbrook in a very short distance. In this particular locale, the Marlbrook is close by and it is likely that what we found was washed downstream to where we found it. As I recall, Trent mentioned that fossils were more common the farther upstream one went, which would support this idea. The Marlbrook Marl, when fresh, is a blue-gray lime clay, or marl, laid down in nearshore, shallow marine environments, just like the Nacatah Sand, but without the sand contribution. The upper part of the Marlbrook is also famous for being extremely fossiliferous and this site was no exception. I initially attempted to collect what I found, but very quickly realized there were so many shells that it was impossible to carry them all. The great majority of what we found were shells of Exogyra ponderosa, but the numbers would have allowed us to quickly fill a crate with specimens. We also found a few snail shells (of what type I am not sure) and a terebratulid brachiopod, but the numbers of everything else did not begin to compare with the shells of Exogyra. On other trips, Trent collected numerous Exogyra shells and gave me two boxes full of shells. Thanks to him, I will be able to supply many Arkansas classrooms with actual Arkansas Cretaceous fossils.
This area is a nice place to collect. As long as one is on public land (or with the permission of the land owner), you can collect any of the invertebrates you want, so you can feel free to collect Exogyra shells here. But the Marlbrook also contains more than just oysters, brachiopods, and snails. It has also yielded mosasaurs and even the occasional elasmosaur. There is even the possibility that a dinosaur was washed out to sea and could be found there. So if you collect in this area and find some bones, give me a call.
Many thanks to Trent Smith and the whole of Goza Middle School, not just for your hospitality, but for living the statement of Dr. Scott the Paleontologist on Dinosaur Train: “Get outside, get into nature, and make your own discoveries.”
National Fossil Day is today. The Museum of Discovery is having their second annual National Fossil Day event this Saturday. In celebration of these events, I am reviewing important fossils of Arkansas. Last post I stated my picks for the most famous fossils of Arkansas. This time I will discuss what I think are the most common fossils in particular regions of the state.
In the Ozarks, you can find an abundance of marine fossils. There are ammonoids, bryozoans, brachiopods, clams, corals, echinoids, and many others. The Pitkin limestone is so chocked full of Archimedes bryozoans that it is sometimes referred to as the Archimedes limestone. But overall, I have to go with crinoids as the most commonly found fossil in the Ozarks. Crinoids lived throughout the Paleozoic Era, making them potential finds throughout the region. They survived even up to the present day in deep marine settings, but in the Paleozoic, they lived throughout the shallow marine realm, which is where fossils are most common.
Known as sea lilies today due to their plant-like appearance, they are actually echinoderms, making them relatives of sea urchins and sea stars. While not common today, they were quite abundant during the Paleozoic. Most of the fossils of crinoids are of their stems, which look like stacks of circles with the centers punched out, sort of like flattened rings. But occasionally, you can find the tops of the crinoids with the body (called a calyx) and the arms still intact. These are rare because, like all echinoderms, the body is made of plates that fall apart into indistinguishable fragments shortly after death.
You will not find many fossils in the Ouachitas, but two types of fossils are commonly found there, conodonts and graptolites. Conodonts are the toothy remains of the earliest vertebrates. Unfortunately, you can place several of them on the head of a pin, so unless you are looking at rocks under a microscope, you probably won’t see them. That leaves graptolites, which can be found in several places fairly easily. Unless you know what you are looking at, they can be easy to miss. On black shale, they often appear as pencil scratches that are easy to overlook. But look closely and you will see that many of them look like tiny saw blades. These are what remains of animals we call today pterobranchs. These animals are the closest an animal can get to being a chordate, the group that includes vertebrates, without actually being one. So the Ouachita mountains have fossils that bracket that hugely important transition from spineless to having a backbone.
For the third choice, one could always argue for shark teeth, which are commonly found in southwest Arkansas, but can be found most anywhere in the state. But if we limit our discussion to the southwest part of the state, the easiest to find on the basis of quantity and size I think has to go to Exogyra ponderosa. These are Cretaceous aged oysters known for their thick shells adorned with a curled hornlike shape. They are big, sturdy, and can be found by the thousands. One can only imagine that the Cretaceous was a great time to be an oyster. At that time, southwest Arkansas was beachfront property. with lots of shoreline and shallow marine deposits of sand, shale, limestone, and the famous Cretaceous chalk deposits. Dinosaurs walked along the beach, marine reptiles like mosasaurs and elasmosaurs plied the waters, along with sharks and fish of all kinds. And between them lay mountains of oysters.
You may notice that I left out pretty much all of eastern Arkansas. That is because that region of the state is covered in fairly recent Mississippi river sediment, so you don’t find that many fossils in that part of the state. Some have been found, such as the Hazen mammoth, mastodons, sea snakes, and the occasional giant ground sloth or whale, but the fossils are few and far between. So while they have several fascinating fossils, they aren’t going to show up on anyone’s list of commonly found fossils.
So those are my choices. Do you have other suggestions?