Home » Posts tagged 'Mesozoic'
Tag Archives: Mesozoic
Prehistoric Shark Week, Day 5: From Whence the Great White?
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?
A collection of galeomorph sharks that made their home in Cretaceous Arkansas and much of the world’s oceans, appropriately scaled.
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.
Squalicorax. www.elasmo-research.org
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.
Possible evolutionary sequence of the Great White. http://www.elasmo-research.org
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.
Serratolamna gafsana. Wikipedia. Photo by Hectonichus.
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.
Day 4 of Paleo-Animal Fest
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.
This thing looks like a prehistoric crocodile. My.core.com/~garman/garanglershome.htm
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.
Ganoid scales
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.
Lepisosteus simplex. FossilMuseum.net
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.
Taphonomy Tuesday
Taphonomy 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).
The 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 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. http://www.oceansofkansas.com
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.
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 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. Tolweb.org
Nautilus. Arkive.com
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. Biologycorner.com
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.
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.
The 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.
Myths and Misconceptions #1: Allosaurus rex, or That is NOT a Dinosaur
When I worked at the Denver Museum of Nature and Science as a volunteer in the educations collection (if you ever get the chance to volunteer at a museum, do it, it was a lot of fun and very educational), I happened upon a man with a young boy by his side, whom I presume was his son, looking at an impressive skeleton. I thought how great it was the man took time to bring his son to the museum. But when the boy asked what the skeleton was and the man answered, “Allosaurus rex,” my opinion of the experience dropped. I’m still glad he brought the boy to the museum, but it could have been so much better.
Allosaurus rex? Actually, a blue whale. Definitely NOT a dinosaur. Also, not DMNS. Really, the London Natural History Museum. Photo by author. Click to enlarge.
So what was wrong with what he said? There is no such creature as an “Allosaurus rex.” There is an Allosaurus and there is a Tyrannosaurus rex, but not the two together. It also did not help that the man was standing directly in front of the plaque that read, “Fin whale.”
Much has been written on what a dinosaur is and what is not, but considering the extreme levels of confusion in the general populace, I thought it worth discussing it here. Not everything that is a big skeleton and/or extinct is a dinosaur. In addition to the above whale, I have heard dimetrodons, pterosaurs, saber-toothed cats, mammoths, giant rhinos, mosasaurs, modern elephant skeletons and many other things called dinosaurs, when in reality, NONE of the previous creatures qualify as dinosaurs.
So, if none of those are dinosaurs, what is? What are some of the things people think about when they try to define dinosaurs? The first thing that most people think about is a giant, scaly reptile. However, some dinosaurs were the size of chickens, so not all of them were big. Many also had feathers, so the scaly motif is not altogether correct either. They are reptiles, but unlike anything most people would consider a reptile today.
Quetzalcoatlus northropi. UT Museum. Not a dinosaur either. Photo by author.
Other traits people often use to distinguish dinosaurs are that none of them were aquatic and none of them flew. These aren’t really true either. Some will say they only lived in the Mesozoic Era and died out at the end of the Cretaceous Period 65 million years ago. Again, false. It is true that most animals considered dinosaurs did indeed live only in the Mesozoic Era, but not all died out at the famous K-T extinction event. Some of you may be thinking to yourselves the author has no idea what he is talking about. Nevertheless, as we will see, some dinosaurs are quite at home in both air and water, especially the ones that lived past the Mesozoic.
Even if all these things were true about dinosaurs, none of it really matters. These traits are all distinguishing characteristics that are generally true about most dinosaurs, but not necessarily true about all. What defines an organism is not the same as the diagnosis. Definitions are done by evolutionary relationships. Diagnoses tell us how we can recognize them, what distinguishing characteristics can be used. However, distinguishing characteristics do not necessarily describe all the members of the group. For instance, one might distinguish all members of a family by their last name, but if people get married and change their last name, they do not suddenly stop being a member of the family. A daughter, for example, is defined by who her parents are, not by what name she has. Likewise, her distinguishing characteristics tell us who she is as an individual and can give us clues to her family relationships, but her definition as a daughter depends solely on her relationship to her parents.
The discredited and completely unaccepted haemothermia hypothesis: Mammals and birds are both warm-blooded; therefore, they must be related. I.e., superficial similarities can be misleading. Image from wikipedia.
I should note here that it wasn’t always this way. Back in the old days, organisms were grouped by similarity, who looked like whom, so at that time, there was really no difference between definition and diagnosis. But as people studied organisms more closely, they found that a lot of times, superficial similarities masked deeper differences, which indicated they weren’t really related at all. So for most of the last century, scientists have tried to find real, evolutionarily related groupings to build something akin to a geneology of life. To do so, it became evident that definitions and diagnoses of groups had to be different, so for the last couple of decades, definitions have been based on relationships and diagnoses based on characteristics. This system of classification by defining groups according to their relationships is called phylogenetic systematics.
So, how then do we define a dinosaur? The standard modern definition of a dinosaur has been stated as the most recent common ancestor of Triceratops and modern birds and all of its descendants (Padian, 1997). Note this means that all birds are, by definition, dinosaurs. So it is obvious that some dinosaurs are quite small (e.g. hummingbirds), flew (most birds), and could reasonably be called aquatic (e.g. penguins). The reason for this is because the earliest birds are clearly closely related to animals, such as Velociraptor and its close relatives, which are indisputably dinosaurs. If one took a picture of Archaeopteryx which had no feathers to a bunch of elementary school kids and asked them to identify it, the general answer is that it is obviously a dinosaur, but put feathers on it and they call it a bird. They are thus both correct answers. Dr. Thomas Holtz has proposed a slightly different definition: the most recent common ancestor of Megalosaurus and Iguanodon and all of its descendants. Both definitions encompass the same groups of animals as far as our understanding goes, but Holtz’s definition includes the dinosaurs that were first discovered, so is considered by many to be a superior definition.
Dinosaur family tree, by Nobu Tamura (paleocritti.com). Click to enlarge. Note on trees like this, the branches can be pivoted on their branch points without changing relationships (e.g.,it makes no difference whether you say “your brother and sister” or “your sister and brother”), so anything in Saurischia is equally related to anything in Ornithischia. Thus, it doesn’t really matter what animal in each group you choose as the representative of each group as long as the groups as a whole remain intact.
Unfortunately, scientists don’t always talk about these terms correctly either, making the whole process confusing. Michael Benton, a leading paleontology researcher with numerous well-respected publications, got it wrong when he defined dinosaurs according to synapomorphies in The Complete Dinosaur. While synapomorphies are used in developing modern classifications, they are used for diagnoses, not definitions of groups, which Dr. Benton assuredly knows (as evidenced by the fact he normally states it correctly in his other works), but when someone is as prolific as Dr. Benton, the occasional error is bound to slip in now and then.
Synapomorphies are very important in figuring out relationships. Unlike any old similarity, synapomorphies are shared, derived characteristics, meaning that the character is the same in the organisms being compared because they share a common ancestor, i.e. they are derived from the same source. Of course, because it requires knowledge of the common ancestor, synapomorphies can only be identified AFTER one has a hypothetical relationship. Thus, to discover strong relationships, scientists will create (mathematically, using a computer because it is way too complex to try doing by hand for anything beyond a few species), all the possible relationships between all the organisms under consideration and then map all the characteristics they can onto every possibility. The relationships requiring the fewest inconsistencies and providing the simplest explanation is considered the most likely. Inconsistencies can occur due to convergent evolution (organisms not closely related developing similar characteristics due to similarities in environmental constraints) or homoplasies (characteristics changing back to a previous form), but with examination of enough characteristics, good relationships usually appear. Of course, the more data you can put into the analysis, the better the results normally get, which is why we continue to study and try to find new fossils and collect more data (and who wouldn’t want more fossils?).
This is all well and good, but how then do we recognize a dinosaur when we see one? Dr. Benton provided a good list of skeletal characteristics, which really won’t mean a lot to people who are not very familiar with skeletons and scientific terminology (but a basic description can be found here and Wikipedia has a surprisingly in depth description). Nevertheless, there are some generalities we can make. If we exclude birds, we can say the non-avian dinosaurs (that we know of) died out at the end of the Cretaceous Period. They all carried their legs underneath their bodies like mammals (and birds of course) and were decidedly unlike other reptiles. None were fliers, although the most bird-like ones got close, and none were aquatic, although some did indeed at least go wading. But remember, these are generalities and if we find a dinosaur with flippers, as long as it otherwise appears related to other known dinosaurs, it will still be a dinosaur. But if it does not fall within the relationships defined above, it will not be a dinosaur, no matter how much it may look like one.
I don’t have an online source for the Padian article, so here is the reference.
Padian, K. 1997. Dinosauria: Definition. pp. 175-179. In Currie, P.J. and K. Padian (eds.) Encyclopedia of Dinosaurs. Academic Press.
Dinosaur Odyssey: a Journey You Should Take.
Dinosaur Odyssey: Fossil Threads in the Web of Life
By Scott D. Sampson
Publication date 2009 (hardback) 2011 (paperback). 332 pg. University of California Press. ISBN: 978-0-520-24163-3.
Suitable for junior high students and up.
Author: Dr. Sampson is best known these days as Dr. Scott the Paleontologist, from Dinosaur Train on PBS KIDS (a children’s show I can recommend). But he doesn’t just play one on TV, he is a real-life paleontologist, and a well-respected one at that, best known for his work on late Cretaceous dinosaurs in Madagascar and the Grand Staircase-Escalante national Monument. He is Chief Curator at the Denver Museum of Nature and Science. He has a blog called Whirlpool of Life and can be found on Facebook. Dr. Sampson has had a longstanding interest in public science education, particularly about connecting children with nature. That interest is clearly evident in Dinosaur Odyssey.
This book has been out a few years, but its main message is more deeply relevant now than ever before. This book is not really about dinosaurs. It is about the interconnectedness of all things. Dinosaurs are simply a fascinating hook for discussing ideas about evolution and ecology. If you are looking for a book that just talks about dinosaurs, look elsewhere. But if you want a book that puts dinosaurs in context as part of a complete and ever-changing ecosystem, if you want to learn about the Mesozoic world as a stage upon which dinosaurs are only a part, however awe-inspiring and prominent, of a much larger web of life, this book is for you. In Dr. Sampson’s hands, dinosaurs are not skeletons of bizarre creatures, they are living organisms interacting with others, changing and being changed by their environment. In a similar vein, our ideas about them are neither set in stone nor idle speculation, they are dynamic and changing, based on new discoveries and scientific understanding, circling ever closer towards a deeper understanding.
The book is written for someone with decent reading ability, but not a dinosaur aficionado. No real prior scientific knowledge is required, simply a desire to learn about the natural world. For those who want more, or find some of the terminology daunting, there is a wealth of notes and references at the end, along with a substantial glossary. The book begins with a short history of the scientific study of life and Sampson’s personal experiences searching for dinosaurs in Madagascar, which led to some of his thinking for the book as an introduction to what follows. Throughout the book, he uses his personal experiences to enrich the scientific discussions, making it a personal story, not just an academic one. Chapter two is an ambitious glimpse at the history of the universe until the dinosaurs appear, along with a short discussion of the geological principles forming the foundations of our understanding of geologic time. Chapter three introduces the dinosaurs, defining what is meant when a scientist talks about dinosaurs and the different groups of dinosaurs. Along the way, he discusses what species are, how they are named, and how we figure out relationships, although not in detail, just enough for a non-science person to understand the broad concepts. Chapter four discusses the physical world of the Mesozoic in terms of plate tectonics and how the movement of the continents shaped the world and thus the evolutionary history of dinosaurs. He even discusses the role of the atmosphere and oceans in climate. Chapter five builds the basics of ecosystems and nutrient flow, chapter six provides a background in evolutionary theory, chapter seven discusses how dinosaurian herbivores adapted to changing plant communities and how the dinosaur and plant communities may have co-evolved, each influencing the other. Chapter eight adds predators to the mix and chapter nine finishes the ecological chain with decomposers. Chapters ten and eleven discuss sexual selection and metabolism in dinosaurs.
Michael Skrepnick contributed several paintings for the book, such as this one of Daspletosaurus attacking an Einiosaurus herd.
The chapters to this point built up how dinosaurs fit into the ecosystem and the workings of evolutionary theory. The next three chapters then take that information and discuss the dinosaurs rise to prominence in the Triassic, development of dinosaur ecosystems in the Jurassic, and their ultimate development through the Cretaceous period. Chapter fifteen, as might be expected, discusses the extinction ending the Mesozoic Era and the dominance of dinosaurs as major players on the world stage.
One might think the book would end at this point. But Sampson has one final chapter to go, which is probably the most important message in the book. He finishes the book by discussing why dinosaurs are important today. We are facing an extinction event equal to the end of the Cretaceous in terms of biodiversity loss, yet few people seem to notice just how comparatively depauperate our global ecosystems are becoming. Because dinosaurs draw peoples’ attention, they are the perfect tool to discuss evolutionary and ecological issues. In this chapter, Sampson discusses how to use dinosaurs to reach people and teach them about our own ecosystems, how we are affecting it and the problems we are facing. In this way, looking at our past through a dinosaurian lens can help us find our way forward.
In the final analysis, this book is a must-read for anyone interested in the natural world and how it works, especially if they love dinosaurs.
Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages.
By Dr. Thomas Holtz, Jr. Illustrated by Luis V. Rey.
Publication date 2007. 427 pg. Random House. ISBN: 978-0-375-82419-7.
Author: Dr. Holtz, self-proclaimed “King of the Dino Geeks,” or as I like to call him Dr. Tyrannosaur, is a well-known and respected paleontologist who’s understanding of all things tyrannosaur is unparalled. As a senior lecturer at the University of Maryland and the Faculty Director of the Science & Global Change Program for the College Park Scholars, he has extensive teaching experience. I have had the pleasure of attending several of his talks at meetings of the Society for Vertebrate Paleontology and he has always been informative and interesting and his students have always been very positive about him.
Illustrator: Luis Rey is an accomplished and respected artist, known especially for his paleo art. He has won the Society of Vertebrate Paleontology Lazendorf Award, given to outstanding artists and his artwork can be seen in several museums, books, and other outlets. He is known for very colorful dinosaurs with close attention to anatomical detail. He makes huge efforts to bring dinosaurs to life as actual, living creatures with as much accuracy as possible. A few have criticized his artwork for being too fanciful, in that he draws wattles and other structures on dinosaurs for which we have no hard evidence. But these structures are extremely difficult to preserve in fossils and their living relatives do have them. Matt Wedel, a noted dinosaur researcher in his own right (although he studies sauropods, not theropods like Dr. Holtz) has said, “If you go bold, you won’t be right; whatever you dream up is not going to be the same as whatever outlandish structure the animal actually had. On the other hand, if you don’t go bold, you’ll still be wrong, and now you’ll be boring, too.” Luis Rey has never been called boring.
I decided to start off my reviews with this book, even though it has been out since 2007, because I think every school should have it. There are good reasons it won “Outstanding Science Trade Books for Students K to 12: 2008 by the National Science Teachers Association. It is called an encyclopedia and it does have chapters describing all the various dinosaur groups, but it is so much more. It is not a small book and here is my only real criticism of the book. Despite its title, it is not quite a book for all ages (School Library Journal rated it Grade 5 and up and it would take an exceptional 5th grader to read it). If you are looking for a book to read to little kids, look somewhere else. It is called an encyclopedia for a reason. Nevertheless, with that caveat in mind, if you are looking for a book to give your dinosaur-obsessed kid who can read well, this book is for you. It is not just for kids though. Adult dinosaur enthusiasts will like it too.
What I like best about this book is that it does not simply focus on the dinosaurs. There are plenty of books that will give you an A-Z description of dinosaurs. Holtz gives the reader a feel for what paleontology is and how it works. The goal of this book is to explain why we think what we do about them, how we know what we know. He starts off the book discussing how science, particularly as it applies to paleontology. He then has a chapter on the field’s history, followed by three chapters of geology and geologic time to put everything into perspective. Chapters 5-9 discuss how paleontologists find fossils and attempt to reconstruct what they looked like and how they are related to each other. It is not until chapter 10 that he even starts talking about dinosaurs themselves and that chapter simply explains how they are related to other vertebrates. Chapters 11-35 are the meat of the book that everyone would expect. This is where he discusses the amazing diversity of dinosaurs. The last five chapters discuss dinosaur behavior and metabolism and how we approach topics like this that are not so easy to see in the fossils. The last three chapters then put the dinosaurs in context of time and ecology. Contrary to popular opinion, dinosaurs did not all live at the same time. They spanned a vast length of time and these chapters give the reader some sense of what the earth was like during the major time periods, who lived when and what other animals they lived with. The last chapter ends predictably with a discussion of extinction, but rather than just say the asteroid killed them all off, Holtz discusses some of the complications of that hypothesis, finishing off with how life continued after the asteroid impact (including the dinosaurs, who were only mostly dead, not completely dead, a few made it through and thrived as birds). At the end of the book is a series of tables listing all the dinosaurs, including where and when they lived and their estimated size and weight.
Holtz doesn’t go it alone either. Scattered throughout the chapters are inserts from other researchers (such as Dr. Kristi Curry Rogers shown here) explaining various topics related to their own research, so the reader gets the perspective of many paleontologists, not just the author’s.
A serious bonus for this book is that Dr. Holtz has attempted to keep the book as current as possible by posting online corrections necessitated by new research, which you can find here.
As a final word, the book is superbly illustrated with numerous drawings, both in monotone and vivid color, by Luis Rey. There are no images of actual fossils, which some have criticized the book for, but my personal feeling is that the book was not designed to be a textbook for dinosaurs. It was designed to show the dinosaurs as living animals, not simply as their bones. There are plenty of other places one can find that. This book is for a view of what they were like alive and most importantly, why we think they were like that shown here and how we study them.
For other reviews of this book, try here, here, here, and here, among others. All illustrations above can be found within the book, as well as the linked sites for Luis Rey and Dr. Rogers.
paleoaerie 