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The Cambrian of Arkansas

Our tour of Arkansas fossils and geology should begin, like any tour, at the beginning. The oldest rocks found in Arkansas in which fossils may be found were formed in the Cambrian Period, the earliest part of the Paleozoic Era. When the Paleozoic Era was first named, it began with the rocks containing the oldest known fossils. We now know of fossils far older than that. Nevertheless, it marks a good starting point for rocks in which fossils become commonly found and are easily recognizable. So while Arkansas does not have the earliest fossils, we do have fossils dating back through most of the history of life once hard parts developed.

Painting by D.W. Miller of the Cambrian world as seen in the Burgess Shale

The Cambrian Period started about 540 million years ago and lasted until 485 million years ago. During that time, while the land was mostly barren, the seas were full of life. Much of what people know about the Cambrian comes from the Burgess Shale in Canada, possibly the best known example of a lagerstätten, a fossil site rich in either fossil diversity or exceptional preservation, of which the Burgess Shale has both. From the Burgess Shale and other localities, we know that the Cambrian saw the rise of most of the major groups of animals we see today. In addition to the comb jellies, sponges, algae and anemones, brachiopods and bristle worms, velvet worms and crinoids; the Cambrian also arthropods of several kinds, most in particular the trilobites, the first chordates like Pikaia, and bizarre creatures like Anomalocaris and Hallucigenia.

The rise of such a diversity of animal life during the Cambrian has been termed the Cambrian Explosion, leading some people to assume it appeared suddenly and without precedent. In truth, the Cambrian “explosion” took tens of millions of years and was preceded by a diverse fauna known as the Ediacaran or Vendian fauna, which first appeared almost 100 million years earlier. The end of the “Garden of Ediacara” and the rise of the Cambrian fauna is thought to have come about due to the evolution of the first predators, necessitating hard shells for defense and hard claws and teeth to kill prey. Collier Shale

Purple represents area Collier Shale can be seen.

The only place in Arkansas to find Cambrian rocks is in the Collier Shale, which was formed in the Cambrian through the Lower Ordovician.

Outcrops for the Collier Shale are limited to a small set of ridges in the Ouachita Mountains, within Montgomery County between Caddo Gap and Mt. Ida, just to the east of state Highway 27. However, most of this area is part of the Ouachita National forest and is ILLEGAL TO COLLECT anything without a permit.

Continental shelf. Encyclopedia BritannicaThe Collier Shale is a large unit at least 1000 feet thick formed mostly of gray to black clay shale that was intensely crumpled during the formation of the Ouachitas. Interspersed within the shale are thin layers of black chert, which together indicate a deep water environment. However, there are also thin layers of dark gray to black limestone, which contain pebbles of chert, limestone, quartz, and even sandstone. It is thought that these layers initially formed in shallower water on the continental shelf before some event caused them to slide off the continental slope into the abyss.

Housia sp. British Columbia

Housia sp. British Columbia

The Collier Shale is not known for abundant fossils, but it does have some. In the Cambrian section of the formation, several genera of trilobites have been found, chiefly of the groups known as Asaphida and Ptychopariida. For more information on trilobites and the different types, try the and websites. The trilobite genera found in the Collier Shale have been from what is known as the Elvinia and Taenicephalus Zones. These are specific groups of trilobite genera that, when found together, allow the age of the rocks to be determined using correlative dating. These groups, or assemblages, of genera have been found in other parts of the world in rocks that have been able to be dated using rigorous and independent methods, such as radiometric dating. We know that rocks elsewhere in the world containing these fossils are roughly between 490 and 500 million years old, indicating the rocks forming this part of the Collier Shale are the same age. This conclusion is supported by fossils in the rock units overlying this part of the Collier matching those found in rock units over similar rock units of known age elsewhere. The trilobites in the Collier are found in the lower part of the formation. The upper part of the Collier contains fossils known as conodonts, but they are Ordovician in age and will be discussed later.

11_01_Irvingella_spTrilobite images from and The Cambrian painting by Miller can be found at, along with more Cambrian information. The map of the Collier Shale can be found at and  the continental shelf image is from

Hart, W. D., J. H. Stitt, S. R. Hohensee, and R. L. Ethington. 1987. Geological implications of Late Cambrian trilobites from the Collier Shale, Jessieville area, Arkansas.  Geology 15:447–450.

Hohensee, S. R.; Stitt, J. H. 1989. Redeposited Elvinia zone Upper Cambrian trilobites from the Collier Shale, Ouachita Mountains, west-central Arkansas. Journal of Paleontology 63(6): 857-879

Loch, J.D. and J.F. Taylor. 2004. New trilobite taxa from Upper Cambrian microbial reefs in the central Appalachians. Journal of Paleontology 78(3):591-602. Online publication date: 1-May-2004.

UPDATE: I thought I would add a little more information about the “Cambrian Explosion,” or as Dr. Donald Prothero calls it, the “Cambrian slow fuse.” The reason for this is because of how long it really took for multicellular life to develop. We have evidence for the earliest life going back over 3.5 billion years, but the earliest agreed upon multicellular life appeared in the Ediacaran fauna (Grypania is a possible multicellular organism dating back 2.1 billion years, but may not be a true multicellular organism and really a colonial organism). Timescale of the Cambrian Diversification EventThe diagram to the right (click to enlarge) is from Prothero’s book, Evolution: What the fossils Say and Why it Matters, and reproduced on a review he wrote of another book. In the diagram, he shows the Ediacaran as starting about 600 million years ago, but now most researchers peg that to about 635 million years ago, so the slow fuse is actually even longer than he shows.  The Collier Shale in Arkansas is in the late Cambrian, so as you can see, several other groups are already present. The fact that we have thus far only found trilobites means that we may yet find more diverse types of fossils, so keep looking (and if you find anything, let us know)!

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.

luis1Illustrator: 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.

luis2What 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.

curryrogersHoltz 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.

luis3As 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.

Forum Friday

Our first few posts here on Paleoaerie have discussed what we are about, why and what we are planning.  Over on Facebook, we’ve discussed a lot of things that may be of interest to readers.  We have discussed how to reach kids, why teaching how science works matters to everyone and certain TV shows and books that don’t think so or do it badly, as well as some that do it well. We noted interesting goings-on at the Museum of Discovery.

We found informative videos and free online courses on dinosaurs, evolution, the genetics of evolution, and human evolution. We found fossil databases, museum collections, and maps of the earth through time. We examined software available to teach science methods and concepts, use 3D modeling in class, upcoming TV shows, Next Generation Science Standards apps, as well as discussing the use of iPads in class. We found a request for scientists willing to work with classes. We even found card games of interest and the Whirlpool of Life.

We’ve discussed the role of evolution in pathogen virulence in disease, antibiotics and cancer, and how it can help manage fisheries .  

We’ve covered the evolution of weird sharks, giant viruses, early mammals, and the earliest eukaryote. We learned about tyrannosaurs and why they weren’t scavengers, how dinosaurs grew feathers,  lost their tails evolving into birds, what is and is not a dinosaur, and using dinosaurs to teach anatomy. We learned about exhibiting extinctions and what they mean to ecosystem health, surviving them, as well as de-extinctions. We learned when teeth evolved, the use of half a sucker, how carnivores become herbivores, and the evolution (or not) of intelligence. We learned about the role of chance in evolution and the haphazard way evolution builds things. We met Mouseunculus and found out just how big a billion really is.

We saw science art, art and science, and art in technology. We talked about Darwin and Wallace, asking scientists about their research, and the process of science correcting itself. And that’s not all.

Roman forum. Image from Wikipedia

We’ve said a lot, but a communication is not a one-way street. I’ve referred to Paleoaerie as “we” many times. Thus far, it’s mostly been “I” that has done the communicating. But let’s change that dynamic. Every couple of weeks or so, we will have Forum Friday. What’s a forum, you ask? Forums were originally a “marketplace or public square of an ancient Roman city” (Merriam-Webster). But more importantly, they were places people gathered to discuss things of interest to them, or simply just to converse and connect with others. Paleoaerie is more than what I bring to it. To really work, others need to contribute. Forum Fridays is a designated space for you to tell me what you want to see, what you want discussed, provide feedback and discussion on topics presented during the week. So let’s talk. I have one simple question: What do you want? (I promise, my name is not Morden, it will turn out better that it did for Ambassador Mollari).

But what have you done for me lately?

“No matter who you are, engaging in the quest to discover where and how things began tends to induce emotional fervor—as if knowing the beginning bestows upon you some form of fellowship with, or perhaps governance over, all that comes later. So what is true for life itself is no less true for the universe: knowing where you came from is no less important than knowing where you are going.” Neill DeGrasseTyson. In the Beginning“. Natural History Magazine. September 2003.

Now that we’ve covered just what this blog is all about and why, it’s time to give you a more detailed look at what we propose to do and what you will find here. On this site, you will find blog posts, links to a variety of websites providing resources and information that have been either put together or verified by content experts, contact information for people that may be of use, and collections of material that are free to use.  In the future, we hope to include material created by students and teachers that have been submitted for public dissemination.

The blog on the website will provide essays on several topics. The first and most common will be reviews of books, videos, games, and other resources, both online and off. Because few teachers can afford to go out and buy books for their classroom on a regular basis, they often rely on donations or library book sales to stock their book collections, so reviews will cover a variety of books, both old and new. As a parent myself, I have seen books in classrooms and ones used by teachers that were more than twenty years old. A few are still great books, a lot are either woefully out of date or were terrible to begin with and should be expunged. Hopefully, these reviews will help guide people to books that have quality information in them that are suitable to classrooms. Some books, like The Complete Dinosaur, 2nd edition or The Dinosauria, 2nd edition, are fantastic books, but are in many places rather technical and probably not something most teachers would stock in their classes (although they would have a happy home in a high school library).

Arkansas's only dinosaur.

Arkansas’s only dinosaur.

Another series of essays will cover the fossils and geologic history of Arkansas. Arkansas has a variety of fossils, from trilobites and bryozoans, fossil oysters and shark teeth, to saber-toothed cats, mastodons, whales, and even dinosaurs. One series will cover individual fossils highlighting the different types of fossils. If we get funding, we will include a 3D interactive image with every fossil we can. Another series will cover Arkansas through time. We have rocks from the Cambrian to the modern. Each essay will cover a selected time period, tell you where in Arkansas you can find rocks of that age, what type of environments they represent, and what sort of fossils you might find in them. It will take a long time, but should be an exciting series to write and as much fun to read. A third paleontologic series will cover common myths and misconceptions of dinosaurs, other prehistoric animals, and paleontologic concepts.


A simplified image of the Arkansas geologic map, available at

New resources will be added to the website as they become available. Pending funding, a series of teacher workshops are planned, with as much of the material as possible available for free download. Interactive lessons made using SoftChalk, Articulate, or other programs will be added. Additionally, other people are encouraged to design materials that, after being checked for accuracy, will be made available to everyone. The more people participate, the better and more useful the site will be. From teacher-designed tools to student presentations, all accurate and topical material will find a home here.

Education is more than just the transference of information. It is a discussion. An important part of this website will be to put people in touch with each other. Posting information by others is just one part. Discussions of how to teach difficult topics will be another. An important goal of this website is to connect scientists with educators in both formal and informal environments with parents, students and anyone else with an interest in learning more. Together, we can get more questions answered as we find ever more questions to ask. Change may be scary, but refusing to change is to be doomed to failure. Finding the right path forward, the right change, means we keep asking questions and helping each other find the answers.


Neil DeGrasse Tyson, Reddit IamI, 2012.

So what’s the problem and what do you plan to do about it?

In the first post, I outlined why I think evolution is important and a few reasons why I think people refuse to accept it. In this post, I will discuss a little more about why it is not taught much in Arkansas and the rest of the United States and what you can expect from this website to help change that.

Teachers make a difference in the classroom, what they teach and what they believe affects their students. Thus, it is disconcerting that only 28% of public school biology teachers consistently teach evolution according to the National Research Council science standards, with 13% actively teaching creationism, despite it being illegal. A full 60% ignore the topic altogether. This perhaps explains why the United States trails most other countries in science aptitude. Arkansas is on average a conservative state, with lower than average income and education levels, and so it is no surprise that Arkansas is below average in science aptitude as well.

So why do so many educators fail to teach evolution in their classes, particularly in Arkansas? There are several reasons. Educators often avoid teaching or only give a cursory introduction to these subjects out of personal ignorance and/or religious beliefs. Many of those who do teach it are unaware they are teaching highly inaccurate and out of date material and must contend with outright hostility from school administrators and parents who do not themselves understand or accept evolution. More than 20% of Arkansas secondary teachers are teaching out of their certified field and the requirements for certification are low to begin with (Arkansas is not alone in this and in fact is only marginally higher than the national average). For example, elementary teachers are often not required to have had any science beyond the minimum standards for their college education degree. Home schooling is also becoming more prevalent, with education provided by parents or informal educators with typically little training in either science or education. It’s also not enough to simply know the facts. There is a long path from the content to education. Getting students to learn accurate information requires passing through a number of filters. Even before that can happen, people have to realize that what they intuitively believe may not be right and their gut feelings may be wrong.

Educational path from content to youth. Content is filtered through the imperfect knowledge and abilities of educators in structured activities or other sources, which may or may not be accurate. Education is heavily influenced by the degree of parental involvement, which may be positive or negative, and is filtered through prior beliefs, which are themselves heavily influenced by parental beliefs. Image by Joe Daniel

Educational path from content to youth. Content is filtered through the imperfect knowledge and abilities of educators in structured activities or other sources, which may or may not be accurate. Education is heavily influenced by the degree of parental involvement, which may be positive or negative, and is filtered through prior beliefs, which are themselves heavily influenced by parental beliefs. Image by Joe Daniel

How can we combat this problem? We cannot expect educators with little training in schools or homes that are cash-strapped and lacking resources to do a good job on their own. So we help them by providing resources they can access online for free (preferably) or small fees (if necessary). The internet is full of resources to fill every need and educators in the know can access myriad sources of knowledge and lesson plans. But the key to this is “in the know.” The internet is also full of misleading and false information. How is an educator that feels insufficiently prepared (be that learning the material, just looking for new ways to teach it, or wanting to provide additional resources for students and parents) to sort through the chaff and find the kernels of quality material? That’s where we come in, we can help them be “in the know.”

The Philosopher Diogenes searches for an honest man,1607 (woodcut) by English School, (16th century); Bibliotheque des Arts Decoratifs, Paris, France;

The Philosopher Diogenes searches for an honest man,1607 (woodcut) by English School, (16th century); Bibliotheque des Arts Decoratifs, Paris, France;

This website is designed to provide information on resources that have been checked by content experts, so educators, parents, and students may be able to rely on the information.  The website will take no position on religion, as it has no bearing on the science and the science is what this is all about. In addition to information on the science itself, information on educational methods, lesson plans, and available resources will be provided. We will help connect scientists with the rest of the public (scientists are people too). We hope to be a lantern in the darkness of confusion, a sieve to separate the gold from the fool’s gold. In the next blog post, I will cover just exactly how we plan to do that.

Greetings and Welcome!

Dinosaurs! In all the natural world, there is little that excites the imagination of most people as much as dinosaurs. They were big, bold, awe-inspiring and terrifying. Dinosaurs were giant reptilian monsters that ruled the earth until a giant meteor hit and wiped them all out, or a world-wide flood drowned them all.

At least, that is what many people imagine. For many people, their understanding of dinosaurs is vastly incomplete and outdated. For many others, it is wildly incorrect. For the vast majority, their view of dinosaurs is a tiny sliver, the smallest glimpse of the wonders dinosaurs truly represent.

This website is not really about dinosaurs, although we will talk about dinosaurs from time to time. We are really here to talk about evolution, to serve as a portal to resources available to teachers, students, parents, and the general public. So why start with dinosaurs? Because dinosaurs are endlessly fascinating, it is easy to start a conversation about dinosaurs. But like dinosaurs, the public view of evolution is incomplete, distorted, and in many cases, completely wrong.

Evolution is not well accepted in the United States. Most people will say it conflicts with their religious beliefs, but there are far too many people who share the religion and accept evolution for me to think religion is really why people do not accept evolution. I think it is a combination of four factors. 1) A fundamental misunderstanding of the nature of science and how it works. 2) They don’t understand what evolution really means because of how badly it generally gets taught, if it is taught, and the lies and distortions swirling about. 3) It is really hard to conceive of the vastness of time represented by the age of the earth. People simply are not used to thinking in terms of millions and billions of years. The monumental scale is beyond their experience. 4) But the biggest reason, I think, and the most important, is fear. If there is one thing people are afraid of and hate more than anything else, above even those of rival political parties, is change and uncertainty. Change is, without a doubt, stressful.

Evolution is the scientific embodiment of change and uncertainty in the living world. It is all about change, so of course evolution is frightening to many people. But life IS change. People are born, they grow old and die. The telegraph gave way to land-line phones, which gave way to smart phones and texting. We went from a nation in which only white male landowners could vote to one in which any adult was allowed to vote. We have witnessed the revolutions of the home computer and the internet; magnetic tapes to mp4 files in the cloud; letters to wireless communication supporting diverse, interconnected, social media networks. We have gone to the moon and back and sent probes out of the solar system. Life changes all around us every day and these changes we have witnessed are nothing compared to what is before us. The rate and scale of change is increasing and we have to prepare for that. We either embrace change and learn to adapt to it or we can try to deny it, resist it, and become roadkill, forgotten memories of a bygone era. If we want our children to succeed, we have to teach them to accept and deal with change or we are dooming our children and ourselves to failure.

Science literacy is crucial for understanding many of the most serious problems affecting society today and the unprecedented changes taking place in our society and the world as a whole. Evolutionary theory in particular forms the foundation of all modern biological thought and impacts our understanding of such diverse areas as medicine, climate change effects, agriculture, water and sewage treatment, sanitation, and overall ecology. As Dobzhansky famously stated, “Nothing in biology makes sense except in the light of evolution.”

But I have never understood the fear of evolution. Ignoring the practicalities of why understanding evolutionary theory is important to understand, it is just a grand way of viewing the world. Darwin said it well:

There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved. On the Origin of Species, 1860.

There truly is grandeur in the history of life on earth as seen through an evolutionary lens. Life is a marvel to behold. In the next post, I will discuss what this site is all about and what you can expect to find here (and why dinosaurs, in addition to they are just cool). I will go more in depth on the resources you may find here and the sorts of blog posts I will make, which will range from reviews and recommendations of books and other media, both old and new, descriptions of Arkansas fossils and geology, and myths and misconceptions. But for now, I invite you to come with me as we journey into the history of life on earth (and most especially in Arkansas). Learn about the fascinating creatures that once lived here and how the current ones came to be, how they live together in a living world, how and why we think what we do; and perhaps most importantly, learn ways to help others learn as well.  As John Boswell portrays so magnificently at the Symphony of Science, it really is the greatest show on earth.