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On November 4th, I presented a workshop on evolution at the Arkansas Curriculum Conference. The workshop was sponsored by TIES, the Teacher Institute for Evolutionary Science, an organization dedicated to helping teachers teach evolution, itself sponsored by the Richard Dawkins Foundation for Reason and Science.
Unfortunately, the wifi died right at the beginning of my talk, so the videos embedded in the talk were not able to be played. So for those of you who attended, and for those of you who would like to see the talk, I am posting the powerpoint file here. I know, it is incredibly overdue, but in my defense, the world took a sharp turn into weirdness right afterwards and then we had Thanksgiving. Any of you who are teaches or students also know what a crazy time of year this is. At any rate, here is the powerpoint. I will see about trying to record some audio for it at some point, along with the other talks I have meant to put up. We will see how that goes over the holidays.
If you go to the TIES website, you will see a version of this talk. I have modified it to include more information on fossil formation, which I skimmed over, for the most part, in the workshop itself. I focused more on the slides discussing why learning evolution is important in the first place. It has far more everyday impacts than most people imagine and is well worth understanding even if one believes in creationism or doesn’t care about esoteric biological concepts at all (for instance, if you are a cutting edge software or robotics designer).
In addition, there are a couple of other things I wanted to post. First is an icebreaker activity that TIES provided. In this activity, participants determine whether or not a series of statements about evolution are true or false. In a twist that catches most people off guard, they are ALL false. They are all commonly held beliefs about evolution, but they are all wrong, which makes a good way to start a conversation about the topic.
Here are the statements and a very brief explanation of why they are wrong, as supplied in the document. Further clarifications and discussions are happily supplied upon request.
1. Charles Darwin developed the theory of evolution.
The theory of evolution existed before Darwin; it was Darwin’s Theory of Evolution by Natural Selection that became widely accepted.
2. Living things adapt to their environment.
As a whole, living things are adapted to their environment. Individuals are unchanging, they either live or die based on the traits they are born with.
3. Biologists “believe” in evolution.
Science is not based on belief. The theory of evolution provides a model for scientists to understand the relationships between organisms on the planet.
4. Monkeys will eventually become human.
There are many species of primates and all are adapted to their environment. A chimpanzee would not turn into a human over time anymore than a cheetah would turn into a lion (or vice versa).
5. Evolution is JUST a theory.
Saying that it is “just” a theory implies that it is a guess, or that its not well supported. There is much evidence to support the theory of evolution, as well as direct observation of species change.
6. Only atheists accept the Theory of Evolution.
Scientists of many religions across the world accept evolution, and do not find it incompatible with their faith.
7. If evolution is disproven, creationism must be true.
A problem with logic (disconfirming evidence). Even if you disproved evolution, you would have to develop and support another model of organism diversity. Disproving one, doesn’t
prove the other.
8. No one has ever seen evolution happen.
In organisms that reproduce quickly (like bacteria) changes in species can be directly observed, such as resistances to antibiotics.
9. Order cannot come from disorder, so evolution is false.
Many instances in nature show molecules and substance organizing, such requires energy. The sun provides the energy that ultimately fuels all of life’s processes.
10. There is evidence that dinosaurs lived with humans.
There is no evidence that suggests humans and dinosaurs lived at the same time.
11. Scientists regularly debate that evolution occurs.
Scientists debate elements of evolution, relationships between organisms, and fossils. The only place the evolution debate really happens is in the social settings.
12. Creationism is a valid scientific theory and should be presented with evolution. Creationism violates the scientific principle of natural causality.
13. There are no transition fossils. Museums are filled with fossils that show intermediate species.
14. Carbon dating is not accurate, therefore the age of the earth cannot be determined.
Carbon dating is one of many methods used to date the earth. Taken as a whole, the evidence is overwhelming that the earth is very old.
There is also a dice game that I want to share with you demonstrating how natural selection works, but that will have to wait until next post.
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
For Day 2 of Prehistoric Shark Week on paleoaerie, we are going to take a look at my personal favorite shark. In the late Cretaceous, it was called Scapanorhynchus, the spade snout. But its closest living relative is called Mitsukurina owstoni, also known as the goblin shark. The perfect shark for Halloween.
Scapanorhynchus means spade snout, so named for the elongated, flat snout, the same feature which got the modern shark named goblin. Most of them are small, less than one meter, but can get in excess of four meters. Spade snouts were some of the earliest sharks in Neoselachii, the modern sharks. One of the things this means is that they did not just have straight cartilaginous skeletons, they calcified most parts of the skeleton to reinforce the cartilage. They didn’t make true bone, but the calcium spicules provided more strength for the cartilage.
Goblin shark teeth are long and thin, looking like a mouth full of curved needles. But what most people are fascinated by is the amazing length to which they can protrude their jaws. Modern sharks have what is known as hyostylic jaws, meaning that the jaws are not directly connected to the skull. Instead, they are attached at the back of the jaws on an intermediary bone that allows the jaw to swing forward. All sharks can do this to an extent, but the goblin shark is expecially known for it.
The modern goblin sharks are generally only found in deep water. Its Cretaceous cousins, on the other hand, were widespread in shallow marine areas. Like many fish in the Cretaceous, they seem to have survived the mass extinction even at the end of the Mesozoic by going deep.
This week we will celebrate fossil sharks of the Mesozoic that have been found in Arkansas. Because all of our surface rocks of the period are from the Cretaceous, the sharks are limited to that time. There are other cool sharks from the Paleozoic, but they will have to wait for another time. Hunting for shark teeth in Arkansas can best be done in the chalk formations called the Annona and Saratoga in southwest Arkansas. But you can also find them in several other formations as well.
Many of the sharks found in the Cretaceous in Arkansas have contemporary species. While the species may vary, the genus name is very long-lived. For those who are unaware, scientific names follow a binomial system, with a genus and a species name, the genus being the first name and indicating a group of very closely related species. It is next to impossible to tell the difference between species of sharks just by their teeth unless, and many times even if, one is an expert, so I will be sticking with the genus names.
To begin the week, I present to you Ginglymostoma, the nurse shark.
The scientific name comes from the shape of its mouth. The origin of the name nurse shark is not clear, but it is considered likely to have originated with the Old English word Hurse, for sea floor shark.
Known for its puckered mouth and barbels on the sides of its mouth, nurse sharks spend most of their time near the sea floor scrounging for whatever small animal they can catch. They are very docile and will only bite if provoked. Humans are far too big for nurse sharks to be interested in, so unless one really goes out of their way to annoy a nurse shark, you’re pretty safe, even from the largest ones, which can get over 4 meters.
We have reached the end of Paleo-Animal Fest celebrating the animals that populated the Cretaceous seas of Arkansas 65-120 million years ago. We have seen early crocodilians and gars. We have seen the largest of the predators in the ocean and some of the smallest of creatures populating the seas. Today we are going to wrap it up with an animal famous the world over: elasmosaurs.
Many people today will not know them by that name, but show them a picture of Nessie, the Loch-Ness Monster, and the image they conjure up is the classic elasmosaur, a long-necked marine (which is funny because Loch Ness is a freshwater lake) reptile with big flippers and a small head, essentially looking like a predatory aquatic sauropod. Of course, it probably didn’t hold its head way out of the water like shown in most imaginings, but the general appearance is close.People are frequently pulling things out of the ocean and claiming they are long-lost Mesozoic Monsters from the time of the dinosaurs. Of course, they always wind up being something else.
Sadly, elasmosaurs died out the same time the big dinosaurs died out.But they had a good run, first appearing in the Triassic, close to the beginning of the Mesozoic Era. Elasmosaurs were part of a group called sauropterygians, which first appeared over 200 million years ago.
Here are a couple of illustrations of elasmosaurs. One is by my son, which will be appearing in a booklet I am making about Arkansas during the Cretaceous, as well as a coloring book for kids I am putting together. Some of them really did have amazingly flexible, ridiculously long necks.
Here is one in the expected habitat and following expected behaviors.
Come back next week to celebrate Arkansas Cretaceous Shark Week.
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).