Friday, May 31, 2013

The "Lion of the Jurassic" fed like a falcon

People seem to think that giant predatory dinosaurs were absolute monsters. Of course, they were monstrous in size, with some species reaching upwards of 50ft in length. However, just because they attained these great sizes does not mean they were reckless, ruthless killers. The more we discover about the giant theropods, the more we are able to compose a lifelike and accurate picture of their biology. In recent years, technological advances have allowed us to take a look not only at the surface of fossils, but test their strength and stress under conditions which they would have faced in life.

Recently, the juggernaut theropod Allosaurus, the lion of the Jurassic, was the subject of a study on feeding mechanisms. Combining engineering and technology with a biological perspective allowed Eric Snivley and his team from Ohio University to examine the living mechanics of the predator and determine how it would have fed. They determined that, although Allosaurus was a large predator, it had a very light skull, and its muscles were not suited for vigorous shaking as much as they were for plucking and tearing at flesh.

Allosaurus and Falco. Image coutresy of WitmerLab, Ohio University.

A major find from this study was the placement of the longissimus capitis superficialis muscles on Allosaurus' neck. These muscles, Snivley explains, are comparable to "a rider pulling on the reins of a horse's bridle." If a muscle on either side contracts, then the head moves in that direction, allowing the head to shake from side to side. However, if both muscles contract, the head is pulled directly down. On Allosaurus, these muscles were located very low on the skull, and indicated that the animal drove its head into its prey, held it there, and then tore straight back and up ( This feeding strategy can be seen in modern raptors, including kestrels.

The Jurassic Paleodiet
This comparatively delicate method of feeding, along with the animal's lightweight skull, raise some interesting questions. Allosaurus is commonly portrayed hunting and feeding on the huge sauropods with which it shared its environment. It is true that Allosaurus likely hunted with hatchet-like movements of its skull, slashing through skin and muscle and bleeding out its prey; however, I believe that the possibility of Allosaurus hunting adult sauropods is becoming slimmer and slimmer with each new discovery we make.

Although it was the most abundant large carnivore of the late Jurassic (at least in North America and Europe), it probaby did not hunt the most abundant herbivores, which were the sauropods. I'm sure that allosaurs attempted to tackle juveniles frequently, and probably with some success, but the bulk of their prey likely consisted of animals which were much easier to tackle. Small ornithopods, juvenile stegosaurs, and other small herbivores, as well as small carnivores and many non-dinosaurian prey items, were likely higher of a priority to Allosaurus than the titanic sauropods.

Sunday, May 19, 2013

Mock-turtles and Reptilian Otters: The pioneering placodonts

Throughout the Mesozoic, marine life was dominated by reptiles of all shapes and sizes. Some of the most bizarre and striking species lived at the very beginning of the era, during the Triassic period. Among ridiculously long-necked protorosaurs and ichthyosaurs as large as sperm whales lived a family of very bizarre, and extremely specialized, animals known as the placodonts.

Placodonts, meaning "flat teeth," were a family of reptiles which lived across the globe and only survived during the Triassic. They were not giants like so many others; the largest species grew to 3m (10ft) long. They were not superpredators, nor were they diminuitive prey items. In fact, at first glance, there doesn't appear to be anything too exciting about them. But to see what makes placodonts so special, we need to look in their mouths.

The placodont Placodus, a bizarre chimera of marine iguana and sea otter. Reconstruction by Dan Varner.
The placodonts weren't named for nothin'. They were armed with almost stone-like, crushing teeth which were perfect for crushing shellfish. These were the first - and last, for a very long time - reptiles to specialize in eating hard-shelled invertebrates. For a long time, the origins of these very specialized reptiles was unknown. Recently, however, fossils of the most basal placodont known were discovered. This specimen, dubbed Palatodonta bleekeri, lacked the crushing teeth of its later relatives - instead, it had small, sharp, peg-like teeth, perfect for gripping much softer prey (Neenan et. al, 2013). These teeth, in comparison, are nothing special in the world of reptiles.

The basal placodontiform Palatodonta bleekeri. Reconstruction by Jaime Chirinos.
The Triassic, as discussed in a previous post, was an age of extremely rapid radiation, with reptiles of all sorts quickly evolving to fill any and all niches left open by the Permo-Triassic Extinction. In oceans filled with species adapted to feed on fish and cephalopods, the placodonts evolved a niche avoided by all other reptiles: scouring the sea floor for bivalves and other hard-shelled goodies.

The "mock-turtle" Henodus. Despite all similarities, it was a placodont, not even closely related to true turtles. Reconstruction by Jim Robbins.
In their day, the largest placodonts were too large to be preyed upon by most animals in their environment - smaller sharks and fish-eating reptiles were the only others to share the shallow seas in which they swam. However, as marine predators began to evolve, the placodonts had to adapt: many species evolved bony armor. This armor may cause some confusion, as some armored species were so well-protected that, at first, they look just like turtles, which had yet to evolve. Some species, such as the 2m (6ft) Psephoderma, took this armor to even greater lengths, with articulated "suits" of armor which allowed for greater mobility in the water.

Another mock-turtle, Psephoderma, and a nothosaurid. Illustration by Kahless28 on deviantArt.
The placodonts were true pioneers in the world of reptiles. They were the first reptiles to evolve a bony shell, and some of the first animals to exploit a niche which would later be filled by animals such as sea otters. Unfortunately, like so many unique species of the Triassic, they disappeared at the end of the period, paving the way for shellfish-eating sharks, turtles, and a myriad of other sea-going oddities.

James M. Neenan, Nicole Klein, Torsten M. Scheyer. 2013. European origin of placodont marine

reptiles and the evolution of crushing dentition in Placodontia. Nature Communications. March 27, 2013. doi:10.1038/ncomms2633

Thursday, May 9, 2013

The "Dinosaurs" that Weren't: The [brief] Age of Pseudosuchians

Circa 250Ma (million years ago), the Paleozoic Era came to a dramatic close. The devastating Permian-Triassic Extinction, aptly nicknamed the "Great Dying," saw the extinction of over 90% of marine species and 70% of terrestrial species, and was the largest extinction in Earth's history. It may have taken the planet a whopping 10 million years to recover from the event. When the planet did recover, the landscape was not dominated by synapsids or amphibians anymore: this was the great Age of Reptiles, the Mesozoic. But the Mesozoic's most famous inhabitants, the dinosaurs, did not start out as the masters of the earth. In the Triassic, the world belonged to the false-crocodiles.

A psampling of pseudosuchians. Pictured are rauisuchians (top and bottom rows), an aetosaur (middle row, left), and a phytosaur (middle row, right). Illustrations by N. Tamura.

Enter the great clade of Pseudosuchia. One of the two major groups within Archosauria, which also includes dinosaurs and pterosaurs, the pseudosuchians are an incredibly diverse group of reptiles which had their 50 million years of fame at the very beginning of the Mesozoic. In the wake of such a large extinction, the pseudosuchians were the first to fill any and all empty niches. In fact, the pre-dinosaur world was very, well, dinosaurian in appearance: bipedal predatory juggernauts hunted low-lying, heavily-armored herbivores, while enormous crocodile-like hunters stalked the waterways. The shapes and sizes of these Triassic pseudosuchians can be thought of as a sort of biological foreshadowing for species yet to evolve, including theropods, ankylosaurs, and crocodiles.

The fauna of Triassic Arizona. All species pictured, except the ones with the big X's, are pseudosuchians, composing the majority of life on land, as well as major predators in the water.  Reconstruction by Jeff Martz. X's by yours truly.

The Triassic pseudosuchians experienced a period of extremely rapid, and greatly successful, evolution: the small, agile reptiles which had arisen in the beginning of the period had evolved into the dominant terrestrial predators by the middle, and by the end of the period they dominated all aspects of life. In fact, in this relatively short period of time, they had even more diverse habits and appearances than early dinosaurs. A comparison of Triassic archosaurs and phytosaurs revealed that early dinosaurs were half as diverse as other closely-related reptiles, including pseudosuchians, and displayed little difference in their anatomy and habits throughout the period (Brusatte et. al, 2008). 

Clearly, the extinction of the pseudosuchians of the Triassic does not mean they were inferior to their successors. Quite the opposite is true. Had the larger species not gone extinct at the end of the Triassic, it is likely that the pseudosuchians would have maintained their comfortable position as masters of the land. In fact, the body plans of several Triassic pseudosuchians were repeated by dinosaurs much later in history. Rather than competition or lack of resources, it is likely that large pseudosuchians went extinct due to a period of rapid global warming, leaving smaller species that lived in the shadows of increasingly abundant dinosaurs.

Although the dominant pseudosuchians went extinct at the end of the Triassic, suchians in general still thrived. Pictured are Paul Sereno and a variety of crocodylomorphs which once inhabited North Africa during the Cretaceous.

However, not all was lost for the pseudosuchians. One subgroup, Suchia, the "true crocodiles," contains some of the only surviving archosaurs: the crocodylians. The suchians, alongside the dinosaurs, reigned in the Mesozoic, evolving to fill a wide variety of niches, from insect-eaters to marine predators to species large enough to eat large dinosaurs. But even with their extreme diversity during the rest of the Mesozoic, the pseudosuchians would never again be the true masters of the planet in the way they were during the Triassic.


Brusatte, Stephen L., Michael J. Benton, Marcello Ruta, and Graeme T. Lloyd. 2008. “Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs.” Science 321 (5895) (September 12): 1485–1488. doi:10.1126/science.1161833.

Friday, May 3, 2013

Jurassic Park 3D: A some-expenses-spared review

I'm not going to rehash the influence of Jurassic Park, nor am I going to point out its paleontological flaws. I've already done that enough. All I want to say in this post is that Jurassic Park 3D is a living, breathing, reminder as to why the movie was so tremendously popular and not only changed public reception and expectation of recreated dinosaurs, but changed the world of film itself.

As I was talking to my younger brother about JP3D, he made a good point: it is the quintessential "'that's-why-we-go-to-the-movies' movie", as he put it. It's got everything a classic movie needs: thrills, chills, laughs, beauty, depth, dinosaurs... As Lex says after rebooting the park's power, "you name it, we got it!" It's more than just a bunch of CGI an animatronic dinosaurs chasing hapless humans around a tropical island. And even if you can't appreciate the plot elements of JP (I'm aware it's not the greatest movie out there [but definitely in my Top 5, jus' sayin']), the technology behind it is breathtaking.

Even the animatronic dinosaurs still look lifelike in Jurassic Park 3D.
Think about it: Jurassic Park came out in 1993. With minimal retouching of the CGI models, even in 3D, the dinosaurs still are more lifelike than any that have graced the silver screen since its release (the only exceptions, perhaps, being the other JP films). To this day, watching the female tyrannosaur heavily pad its way after the flare that Grant threw is still entirely convincing. When the duo of Velociraptors strut into the kitchen, you feel as if you are right there with them. When I saw that monumental Brachiosaurus for the first time on the big screen, I was just as in awe as the characters in the film.

To this day, Jurassic Park has the ability to make animals long gone from this planet look entirely real, even if they majorly lack on accuracy. Even now, when we have movies made entirely with computers, Jurassic Park holds its own in every aspect, from acting to visual effects. If you haven't seen JP3D yet, you must. It's a real reminder of the power of technology, whether you pay attention to the movie itself or the story behind it.