Category Archives: Paleontology

I am a paleontologist

I love the science of paleontology for many reasons. The science combines so many other areas of study into one bundle, such as geology, biology, functional morphology, evolution, stratigraphy, and systematics.

Not only that, dinosaurs and other prehistoric animals are just fun! And being fun, paleontology is a great way to introduce people to science in an engaging way. How many young people start their interest in science by learning about dinosaurs, and say they want to be a paleontologist when they grow up–a bunch!

Well, someone shared this video with me and I love sharing it with you. Enjoy! (you may need to scroll down).

Why dinosaurs are not extinct

In the twenty plus years I have been involved in paleontology I have been witness to a revolution within science. The revolution has been quiet, not noticed by most of the public. Like any good revolution, the battles of this revolution took place between two camps, the “traditionalists” and the “radicals” who were out to change things. And this shift is illustrative of how science as a whole moves from one way of understanding to a brand new way of looking at the world. It is, in fact, a paradigm shift that has profoundly changed biology and paleontology forever.

At issue is how we explore and classify the relationships of all living things. The traditional view, the one that I was taught as a young student, was the classification of living things into the taxonomy originally begun by Carl Linnaeus. This system started with a group, and then sought to put things into the group. For example, one can make the observation that animals that look like “dogs” could be grouped together, so you would start with the idea of a dog-group and look for animals that should be included.

You might put foxes, wolves, domestic dogs into the group, and call it the dog family. You might also note that “cats” could likewise be grouped, and do the same thing, creating a cat family. In this view, the families were equal in rank—and there could be no overlap. An animal would be included in only one of the equal-ranked families. Any animal was included in only one class, for example Amphibia, Reptilia, Aves, or Mammalia.

The equal-ranked heirarchy of classifications worked well enough when we mainly were concerned with modern animals. Clearly, birds look different than mammals and reptiles, so it seemed evident they belonged in their own class. But this classification scheme, however well it served us as a place to start, is myopic about how evolution actually operates—how organisms actually evolve. This is understandable since it was started 100 years before evolution as a theory was established.

In trying to shoehorn life into the system, we repeatedly ran into problems as we expanded our knowledge of the diversity of living things and our understanding that the history of life is a complex branching bush. We knew that early tetrapods (organisms with four limbs) gave rise to the early amphibians that crawled out on land, and that they in turn evolved into reptiles, mammals and birds. But despite this branching within tetrapods, the class ranks were forced to be exclusive, so somewhere in evolutionary history was an “amphibian” that had to become a “reptile,” and a “reptile” that had to become a “bird.”

The many transitional forms in the fossil record increasing became impossible to classify. These intermediate animals had to be forced into one class or another. Increasingly, it became evident that many times the criteria used to put an organism into one class were the whims of an individual scientist, and another equally qualified expert with different opinions might place the same animal in a different class with equal validity.

The origin of birds was for a long time a great mystery to paleontologists. Birds are a pretty unique and specialized group, and while we knew that they originated from reptiles somehow, exactly how and when was unclear. One early paleontologist noted that dinosaurs had many features in common with birds, but the early concepts of what dinosaurs were like distracted most scientists from comparing them too closely. After all, the common conception of dinosaurs was as big, lumbering, dim-witted, swamp-dwelling beasts. The bird ancestor must have been light, fast moving, and energetic.

However, dinosaur research over the last thirty years has completely changed our view of them. Evidence from many lines, including things like footprints and the cellular structure of the bones, all point to dinosaurs as being very dynamic creatures. With this new view, the notion that birds were linked to dinosaurs became clear too. Now, we have dinosaur fossils with feathers, and birds with teeth and dinosaur tails to attest to their close relationships. In fact, birds are most closely related to the meat-eating raptor-like dinosaurs of Jurassic Park fame.

To go along with the revolution in our view of dinosaurs was that revolution in science that I mentioned above–the emergence of a new way to understand the interrelationships of life on Earth. This new model accommodated the myriad branching events that life actually experienced in order to produce the great variety of living things. So, instead of starting with a conception of the group and looking for members, this new concept looked at the branching patterns evident in life, and then sought to apply names.

Below is an illustration of the branching pattern of selected tetrapods, those vertebrates with four well developed limbs. As the first tetrapods gave rise to new and different groups, the branches split off. An early tetrapod gave rise to amphibians and the other animals above it on the chart (mammals, turtles, etc.). A later tetrapod developed traits related to the production of eggs and young that we recognize as the Amniota. Some of those early amniotes went off on an evolutionary trajectory that we can recognize as being the early mammals, and all the diversity that resulted from them. And so it goes up along the branches.

Branching pattern of the tetrapods, mostly the land vertebrates

We now explore the branches and can apply names to the groups that we find to be meaningful. For example, in the illustration below we can call everything in the box a reptile. Note that it includes things that used to be called reptiles, turtles, lizards, snakes, crocodiles, and dinosaurs, but now also includes birds.

Group that includes all the reptiles

Likewise, if we draw a line around the dinosaurs, they also include the birds. This view of life tells a more complete evolutionary history and retains the branches, letting the animals “fall where they will.” We do not pull birds out of their relationships and give them special consideration. Instead of birds being equal in rank with reptiles, they are included among them. This upsets the tradition that being a bird is somehow equally important to being a reptile, but better reflects the reality of descent, without forcing nature into earlier human conventions of naming and grouping. Of course, birds are a group within their own right, and we could zoom in to explore their branching pattern, but it does not change the group to which they belong.

Group of dinosaurs

This leads to another startling statement. Below I have highlighted the groups that are extant (still around today).

Groups of tetrapods that are alive today (extant)

Because of our grouping scheme, birds are included in the dinosaur group, so dinosaurs are not really extinct! They live among us today flitting about, singing their mating songs in the trees. It is funny how things can change in science. Twenty years ago scientists would have told you the dinosaurs were all extinct, and today we say the opposite. I love scientific progress–it can be so startling.

Fossil tells a new tail

Mosasaurs lived in the world’s oceans during the Late Cretaceous, the last Period from the Age of Dinosaurs (see the geologic time scale). They are close relatives of modern snakes and lizards, and during the Cretaceous they become fully aquatic sea monsters, growing to tremendous sizes, and were the top predators of their environments.

Their fossil remains occur in great numbers in the marine chalk deposits of the Central Plains, and numerous specimens have been preserved in museums all over the world (see posts on the chalk formation and on rock formations in general). Yet despite the great numbers of specimens collected, we still have much to learn about these great beasts.

For example, examination of their bones shows that they are elongate animals, with enlarged tails for propelling their bodies through the water. Their limbs are modified into flippers, useful in controlling the direction and orientation of their bodies in the fluid medium. So, it is clear that they are primarily tail-swimmers.

Early restorations based upon this evidence imagined a tail sort of like a modern crocodile, a thick tail that was slightly compressed laterally, making it taller than thick, but remaining relatively snake-like. Early restorations of the skeleton articulated the tail as a long chain of vertebrate, continuous from base to tip without any remarkable difference along the way.

Here is an illustration of the skeleton of the mosasaur Platecarpus from a classic work on mosasaurs (Williston 1898). Note the rod-like straightness of the back.

Mosasaur Platecarpus from Williston

And here is an artist’s illustration of Tylosaurus, the largest of the mosasaurs, from Mike Everhart’s Book, Oceans of Kansas, showing the tail with a slight thickening near the end, but mostly being straight (Everhart 2005, recommended in the Boneblogger store).

Mosasaur Tylosaurus from Oceans in Kansas by Mike Everhart

However, frequently the skeletons of mosasaurs were found preserved in the rock with the last third of the tail bent downward, away from the main axis of the base of the tail. And this was not just found in a few skeletons, but it was found frequently enough that scientists speculated, at least in conversations with each other, that perhaps the down turned tip was not an artifact of preservation, but maybe meant something.

Well, a newly described mosasaurs fossil, which has exceptional preservation, provides the answer. This specimen collected in Kansas and now at the L.A. County Museum, preserves not only the bones, but also impressions of skin, impressions of internal organs, and even some of the body outline. The bones of the tail are clearly down-turned, giving the authors of this new study enough confidence to state what has been quietly talked about before—mosasaurs had a bi-lobed tail fluke (Lindgren et al. 2010).

Mosasaur Platecarpus showing revised body outline

It only takes a single fossil to help overturn past notions about prehistoric life. The next big discoveries are out there, in the rocks and sitting in the museum drawers, waiting to be examined in detail. What will we find next?

Everhart, M. J. 2005. Oceans of Kansas: A Natural History of the Western Interior Sea. Indiana University Press, Bloomington.

Lindgren, J., M. W. Caldwell, T. Konishi, and L. M. Chiappe. 2010. Convergent evolution in aquatic tetrapods: insights from an exceptional fossil mosasaur. PLoS ONE 5(8):e11998.

Williston, S. W. 1898. Mosasaurs. University of Kansas Geological Survey 4(1):81-347.

Science in dinosaur movies: Jurassic Park, then and now

The 1993 movie Jurassic Park, based on the book by Michael Crichton and directed by Steven Spielberg, is seen by most enthusiasts as the best dinosaur movie that Hollywood has produced. It set a high-water mark in the genre for many reasons: it took dinosaurs seriously as a topic, and did not portray the animals simply as ridiculous extras; and the movie was amazing for its visual effects. For any movie from Jurassic Park onward, your dinosaurs had better look real, scary, and believable.

Jurassic Park was also important in that it showed dinosaurs more or less accurately, consulting with real paleontologists in its making, and working to utilize the latest and greatest views on dinosaurs. This is not to say that they did not put in a Hollywood spin, or as I have called it in the past, “Spielbergize” some of the dinosaurs, but as a paleontologist I could really see that the ideas were not completely out of the blue. In fact, Spielberg foreshadowed some of the findings about dinosaurs that were to come.

I want to review some of the key features of Jurassic Park as they were thought of in Hollywood in 1993 and compare that with the state of the art today.

Dinosaur DNA

The entire premise of Jurassic Park is that DNA from extinct species was collected and cloned in order to bring the animals back to life. Are we any closer to being able to do this? Well, not really.

The complete DNA code of any single species is very long and complex, and it is very unlikely that any DNA molecule will survive intact for millions of years. We cannot even clone species that are modern or recently extinct with much success, and we have access to their DNA. The technical difficulties of getting DNA intact, knowing how to put that DNA together on chromosomes, knowing how to trigger the genes on the chromosomes to turn on and off during development, means that even if we could somehow get a complete dinosaur DNA sequence, we could not make a living animal.

However, there have been some amazing advances in molecular paleontology, where protein fragments and amino acids have been shown to be able to survive within fossil bone for an extraordinarily long time, much to the surprise of scientists who assumed that fossilization would destroy the tissues at the molecular level. Making predictions is difficult, especially about the future. Who knows what discoveries await us, but for now, the current best answer is that we will never be able to clone a dinosaur. (See Mammoth protein designed to be cool for more on molecular paleontology).

Excavation Scene

Early in the movie we are treated to a scene of a paleontology excavation as modern paleontologists dig into the past to understand dinosaurs. As with any profession, portrayal in a movie is not often close to reality. Cop movies do not realistically show what it is like to be a cop. Lawyer and doctor movies stretch the true on those professions, and the excavation scene was the one where me and my professional colleagues got a good laugh.

We see the field crew effortlessly dusting sand away from crisp fossil bone. We see the team firing off seismic charges to send waves into the rock to visualize complete dinosaur skeletons underground, just waiting to be effortlessly dug out. Oh boy. This is so far from the truth.

We cannot simply use a type of remote sensing technology to visualize unexposed fossils, however there are a few technologies that people have tried to use. Sometimes the minerals that fill fossil bone have a higher concentration of radioactive elements, and so mapping the concentration of radioactivity over a site has helped to locate concentrations of fossils in those cases. There is a technology called ground-penetrating radar which under certain circumstances could be applied to fossils, but its use is limited. The main problem with both of these techniques is that to find fossils underground, you have to be able to tell them apart from the surrounding rock, and too often the fossils are very similar to the rock that encases them.

Fossils are still found the old fashioned way—by looking for bones weathering out on the surface, and digging around them in hopes that something more is there.

And of course, it is not as simple as dusting them off. Fossils are often enclosed in a hard matrix of rock, which can take many hours of tedious labor to remove. Frequently in the field the fossils are exposed enough to understand how they are laid out, and then removed in giant blocks to be worked on back in the museum lab for the next several years.

Velociraptor

The undeniable stars of the movie were the “raptors.” As shown, they were cunning and relentless killers, bent upon creating havoc for their human character counterparts. In the movie, the velociraptors were shown to be about as tall as an adult human and perhaps 12 feet long nose to tail. That was an exaggeration to say the least.

Real velociraptors have been excavated in Central Asia, and are not known from North America as fossils. However, there are Velociraptor relatives known from this continent. But in life, real velociraptors were only about half the size shown in the movie, maybe the size of a mid-sized dog.

However, Spielberg did not know it, but his velociraptors did not have to be exaggerated in size if he had just said that they were a dinosaur species that was discovered in 1991, and named in 1993—Utahraptor (Kirkland et al. 1993). The same year that Jurassic Park was released also saw the emergence of Utahraptor, a dinosaur that much better fits the dinosaur shown on film. It was discovered in North America, as was suggested for Velociraptor in the movie, and was the size of the animals shown in the film. So, in a way, Spielberg was showing a real dinosaur, just not the one he thought.

Tyrannosaurs Running

It might be a close call as to which was more popular in the movie, Velociraptor or the seminal favorite dinosaur Tyrannosaurus. Who did not thrill to see the giant animal trash Jeeps, eat lawyers, and run amuck? In a harrowing scene, tourists of Jurassic Park are chased at top speed by the Tyrannosaurus and only just manage to escape in their vehicle.

Could Tyrannosaurus almost outrun a Jeep? Well, likely not.

Large animals today do not run well. The heavier an animal is, the more force there is on the animal’s joints and bones, and running compounds the effects of those forces. Modern elephants cannot run, but rather trot. They can move quickly, but they are too large to achieve a full-scale run.

How to kill Tyrannosaurus, from Farlow, Smith, and Robinson, Journal of Vertebrate Paleontology, vol 15(4).

Likewise, tyrannosaurs were very large and heavy animals, and there are physical constraints based upon the strength of their bones and joints. And unlike an elephant, Tyrannosaurus supported all their weight upon two legs, teeter-tottered over their hips. Running would have placed tremendous stresses on the hip joint.

Also, unlike an elephant, the large head of a tyrannosaur was extended out over the ground, as much as 15 feet above the surface, and they did not have forelimbs of any size to speak of. This means that if they did get up to a significant running speed and were to stumble, their heads would fall with great force to the ground without any way to break the fall. In short, if they did run and fall they would bash their brains out on the ground. Running, in this case, would be fatal.

Venomous dinosaurs

In Jurassic Park, the dinosaur Dilophosaurus was portrayed as being able to spit blinding venom into its victim’s eyes. The suggestion that a dinosaur was venomous was groundbreaking. Earlier this year there was a report of the discovery of a venom delivery system in a raptor dinosaur, Sinornithosaurus (Gong et al. 2010), seeming to once again make Spielberg a paleontological prognosticator.

However, it does not seem likely that the interpretation of Sinornithosaurus as being venomous will stand up to further scrutiny. Secondary investigations of the fossils suggest that characters which were viewed as supporting a venom delivery system are actually not what they were first thought (Gianechini and Agnolin 2010), so it looks like we still have to wait to find a venomous dinosaur, much less one that can spit!

Jurassic Park stands as one of the greatest dinosaur movies. From a paleontology stand point, while the movie is fiction several interesting propositions were shown, and this is, after all, what drives our curiosity to explore.

Dinosaur movies at Amazon

References:

Gianechini, F. A., and F. L. Agnolin. 2010. A reassessment of the purported venom delivery system of the bird-like raptor Sinornithosaurus. Paläontologische Zeitschrift.

Gong, E., L. D. Martin, D. A. Burnham, and A. R. Falk. 2010. The birdlike raptor Sinornithosaurus was venomous. Proceedings of the National Academy of Sciences 107(2):766-768.

Kirkland, J. I., R. Gaston, and D. Burge. 1993. A large dromaeosaur (Theropoda) from the Lower Cretaceous of eastern Utah. Hunteria 2(10):1-16.

Shark bites in the Cretaceous Sea

One of the most exciting things in paleontology is being able to definitively establish the interaction of two species from the fossil record. It is thrilling to picture a moment in time, millions of years ago, when two animals were at the same place, at the same time, and be able from fossil evidence to glean something about their interaction and behavior.

One dramatic example of this is finding a fossil with clear evidence that it was bitten by a shark. During the Late Cretaceous, North America was cut in half by an interior sea that extended the Gulf of Mexico across the mid-continent to connect with the Arctic Ocean in the north, effectively creating two land masses where today there is one.

In this last period from the Age of Dinosaurs, fantastic and strange creatures swam the seas. Today, the sediments from that ocean are exposed in badlands across much of western Kansas, Nebraska, and South Dakota. These geologic formations, like the Niobrara Formation, preserve a rich record of the ocean life, and clearly show what a scary ocean it was.

Tylosaurus model from the Carnegie Collection

Giant marine lizards thrived in the sea. These beasts, close relatives of modern snakes and lizards, were called mosasaurs. There were several kinds that likely had different modes of life, some making use of resources close to the surface, and other species specializing in deep-water feeding, with the largest of them reaching 50 feet in length. They were joined by another group of marine reptiles called plesiosaurs. Plesiosaurs occur in two basic body plans, with the unimaginative names of long-necked and short-necked for obvious reasons.

Long-necked plesiosaur Styxosaurus

The long-necked plesiosaurs have been described as looking like a turtle with a snake threaded through its shell. They had a stocky, turtle-like body, enormously long necks capped by a remarkably small head, and stumpy tails. They had four large flippers that helped to propel them through the water as well.

Short-necked plesiosaurs had large heads attached to short, thick necks. The long-necked forms most likely specialized in eating smaller fish with their small heads, maybe using their long necks to “snake” their way amongst their prey before being noticed. The short-necked forms obviously ate large prey, as evidenced by their massive heads and powerful jaws. (You can find models of both long and short-necked forms, as well as mosasaurs as part of the collection of dinosaur toys).

Living alongside these giants of the sea were animals that we would easily recognize, at least for their general body plan—these were the sharks. There was a significant amount of shark diversity in the Interior Sea as well, from relatively small forms that likely ate near the sea floor, to mid-sized forms that ate smaller fish and scavenged on dead carcasses, to several very large species that rivaled the modern great white shark in size and ferocity.

On occasion, when finding remains of fish or the marine reptiles, we find evidence of those remains having been bitten by sharks. The most compelling evidence is when teeth are found embedded in the fossil remains, but also punctures and tooth scratches can be a telltale sign.

Several plesiosaurs have been found as partial skeletons, with bites in several areas of their body, suggesting that after they died and settled to the ocean floor their carcass was scavenged by mid-sized sharks.

Cretoxyrhina bites the back of a mosasaur in the Late Cretaceous. Painting by Dan Varner.

And in one dramatic example, the great white of the Kansas seas bite the back of a mosasaurs, cutting a section of vertebrae completely out of the giant lizard. The section of back, with its included vertebrae, was later spit out by the shark after having been mostly digested. The gristly remains settled to the ocean floor to lie there for millions of years before being found and placed in a museum.

Today we are fascinated by tales of shark attack, with the movie Jaws being a prime example. You can learn about these dangerous animals in another post, but perhaps it gives you some comfort to know that the denizens of the ancient seas also were subject to shark bites!

Additional information about this specimen can be found at Oceans of Kansas.

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