Thursday, July 18, 2013

Giant theropods will NIBBLE YOU TO DEATH

Sorry for the lack of updates for a while, everyone! I've been keeping busy with summer class and work, but now I finally have a bit of free time and will start writing again.

More often than not, the fossils of truly gigantic sauropods are found in the same formations as equally gargantuan theropods. There is no doubt that these predators fed on sauropods once in a while but, being extinct and all, it's extremely difficult to determine just how they fed. Most depictions show allosaurs and carcharodontosaurs leaping onto the backs of unsuspecting saurpods, or clamping their toothy jaws around the herbivore's neck.

When the sizes of contemporary sauropods and theropods are compared, we notice something: sauropods were friggin' HUGE. Even those theropods which are theorized to have been pack-hunters would struggle with taking down an adult super-sauropod. Of course, this doesn't mean that the carnivores were forced to starve; there were plenty of smaller, more easily-subdued critters to eat. Facing an animal which weighed as much as an entire herd of elephants could not only fail, it poses a serious risk of injury and even death to the hunters. How, then, could a predator get a taste of sauropod without risking fatal injuries?

The contemporary giants Tyrannosaurus rex and Alamosaurus sanjuanensis. You can see that, as big as T. rex was, the sauropod is tremendously bigger.

Welcome to the wonderful world of flesh-grazing!
The cookiecutter shark is a species of shark which barely reaches 2ft in length. However, its main prey includes animals which are monumentally larger than it is, including, among other things, whales, seals, dolphins, tuna, and other large sharks. How does such a tiny creature eat such big meals?

It manages to do so because it doesn't prey upon the entire animal. The cookiecutter shark rasps small plugs of skin from its prey, which not only provides it with a meal, but also leaves the rest of the animal alive for repetetive feedings. If you think about it, killing an animal which is much larger than yourself is not only dangerous, it is wasteful: if an allosaur was to take down a giant sauropod by itself, there is no way it could eat the entire animal. Even a pack would leave remains, which would be picked up by other carnivores or simply left to rot.

Even the modestly-sized (for a sauropod) Camarasaurus may have been a bit too much to handle for an adult Allosaurus.

Recent analyses of theropod skull biomechanics show that even large predators had relatively fragile skulls. In a recent post, I summarized a study of Allosaurus feeding mechanics which showed that the animal fed with rapid, jerking motions of its head like a modern falcon. A previous study, concerning Allosaurus' "hatchet" method of feeding, showed that running agape directly at the side of a giant sauropod would not only inflict minimal damage to the sauropod, it would break the jaw and possibly the neck of the Allosaurus.  The hatchet-like hunting method would be much more effective on smaller animals.

Even Tyrannosaurus displays certain features of its skull which indicate rapid, birdlike head motions. Perhaps, as these giants ran alongside titantic sauropods, they could quickly strip morsels of meat from the sides of their prey and run off unnoticed. This would not only leave the prey alive for future feedings, it would greatly reduce the possibility of risk or failed attacked by the predators.

The Case of the Leaping Acrocanthosaurus
Fossilized footprints from the carcharodontosaur Acrocanthosaurus atokensis are particularly well-known throughout Texas, where it once dwelled beside the super-sauropod Sauroposeidon proteles. One preserved trackway shows the footprints of the predator trailing a dozen or so of these sauropods, and in one segment of the track, the Acrocanthosaurus appears to have leaped onto the side of one of them. However, the tracks of the sauropod do not appear to change in speed or direction, suggesting that the predator did not hang onto the herbivore for very long, if at all.

As if the Tyrannosaurus/Alamosaurus comparison wasn't startling enough, there's a snowball's chance in Hell that a lone Acrocanthosaurus could ever take down an adult Sauroposeidon. The possible "attack" footprints are shown below the skeletals.
Perhaps this is evidence of Acrocanthosaurus not viciously attacking Sauroposeidon, but simply snagging a strip of meat from its side before parting from the herd. It is certainly much more plausible than an Acrocanthosaurus actually bringing down one of the giants, especially when the sizes of both animals are compared...

Being an apex predator means that you have the size and tenacity to eat basically every bit of flesh in your environment. None of these giant theropods would have had trouble finding something to eat. The question at hand is whether or not they were bold enough to tackle such monumental prey as the biggest of the sauropods, or whether their main quarry were smaller animals. And, while sauropods could certainly fend for themselves, it is very possible that unnoticed bits of muscle and skin could be torn off once in a while.

Monday, July 15, 2013

What do you get when you cross a turtle, a seahorse, and a beaked whale?

Turns out, you would get the newly-described turtle dubbed Ocepechelon bouyai. Hailing from the latest Cretaceous of Morocco, this turtle was far from out of place: at the time, North Africa was covered in a shallow sea that hosted a variety of strange marine reptiles, including sea snakes and mosasaurs, as well as other species of turtle. But nothing could even come close to the weirdness of Ocepechelon.

Dorsal (left) and ventral views of the holotype skull of Ocepechelon bouyai. From Bardet et. al, 2013.

All we know of the turtle thus far is its skull, but skulls are often the most revealing fossils, especially when they're as outlandish as that of Ocepechelon. Measuring 70cm long, it is clear that this turtle was a giant, definitely one of the largest to ever live. But what makes the skull particularly unique is its shape and, thus, its function: although it is very long, it tapers into a very slender and narrow mouth, the opening of which measures only 6cm in diameter.

Lateral view of the holotype skull of Ocepechelon. From Bardet et. al, 2013.

This pipe-like tube of a mouth is reminiscent of animals which aren't even slightly related to turtles, namely beaked whales*, pipefish and seahorses. All of these animals have tiny mouths when compared to the size of their heads, and all feed on tiny prey using suction as their primary hunting method. It would appear that, without any adaptations to pin down, grasp, or pierce prey items, Ocepechelon was also a suction-feeder, spending its time close to the surface of the open Cretaceous seas, sucking in jellies and cephalopods which lingered nearby.

*Also strangely similar to whales is the position of Ocepechelon's nostrils: they are located far back on the skull, as far as turtles go. This also suggests it spent more time at the surface of the water.

Ocepechelon bouyai, in the flesh. I... Uh, I don't really know... What to say. It's just a weird, weird creature.
We often think of turtles as relicts of a bygone era, unchanged by the ages, deserving of that oft-misunderstood title of "living fossils." However, over the course of their 250-million-year-old history, it is more than clear that turtles have evolved into an incredibly diverse group. Surely Ocepechelon is the tube-mouthed figurehead of turtle diversity.

Bardet, Nathalie, Nour-Eddine Jalil, France de Lapparent de Broin, Damien Germain, Olivier Lambert, and Mbarek Amaghzaz. 2013. “A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique Among Tetrapods.” PLoS ONE 8 (7) (July 11): e63586. doi:10.1371/journal.pone.0063586.

For more on giant, weird turtles, see...

Friday, July 12, 2013

A Brief History of Caenagnathids in Film and Television

"Skinny hands and new jaws," a caenagnathid panoply. Reconstructions by Qilong, from deviantArt.

The family Caenagnathidae derives its name from the Latin "recent jaws," as the great Charles H. Sternberg (the pater familis of a family of historic paleontologists), assigned the fossilized jaw he discovered to an advanced Cretaceous bird. It's not such an uncommon phenomenon to misidentify particularly birdlike non-avian dinosaur fossils as birds; the same has happened with a variety of alvarezsaurs, the tiny short-armed anteater theropods, as well as troodontids and other families of coelurosaurs. Of course, if we were able to observe caegnathids and other coelurosaurs in the flesh, they would even act like big birds, so the confusion is totally understandable.

Anyway, the caenagnathids were a very bizarre bunch, even compared to other oviraptors. To start, they were completely toothless, a feature not found in many non-avian theropods. This indicates a varied diet - the caenagnathids were probably herbivorous, though their toothlessness allowed them to take anything, including small prey. As most species were fairly large to absolutely gigantic in size, the likelihood for herbivory is high. Cliched though it is, it's likely that the caenagnathids had a diet similar to large extant ratites such as ostriches and cassowaries. And, like the cassowary, the caenagnathids display another odd feature - a large, bony crest on the top of their heads. Like so many bizarre skeletal features found on extinct species, we're not quite sure what the crest was used for, but it likely had some function in heat dispersal, call amplification, or courtship.

On to my main point: being as bizarre and obscure as they are, it's always a treat to see caenagnathids portrayed in documentaries and [a] movie. However, out of the variety of caenagnathids which have been discovered, only two genera have been portrayed so far: the gargantuan Gigantoraptor and, in the upcoming Walking With Dinosaurs 3D, Epichirostenotes*. 

*Although the genus has not been confirmed, Epichirostenotes was a contemporary of Pachyrhinosaurus and Edmontonia, which can also be seen in the available trailers.

The Gigantoraptor of Dinosaur Revolution, complete with
wattles and glossy feathers. You go, DR!
It makes sense that Gigantoraptor was the first to be portrayed; like Tyrannosaurus, it's the biggest of its family, which, in pop culture, gives its automatic popularity. The big beast has been reconstructed in two documentaries, Dinosaur Revolution and Planet Dinosaur (both from 2011). In both, oddly, it was depicted performing elaborate courtship displays. I only say "oddly" because, while it totally makes sense that they did engage in such displays, we have no direct evidence of any sort of courtship behavior. It just makes me wonder how both production companies making the documentaries ended up having the same animals doing basically the same thing independently of each other. Anyway, I have to say that I much prefer DR's Gigantoraptor; they even gave the male this awesome wattle clearly* based on that of a Temminck's tragopan. The 'raptor from Planet Dinosaur was a li'l too reptilian for me and looked like a big ol' rubber chicken.

A pair of Gigantoraptor performing a courtship display from
Planet Dinosaur (2011). I wasn't too impressed with these guys. Meh.
*Clearly. Jeez, I sound like such a bird snob sometimes.

A couple of days ago, yet another preview for the upcoming philm phenomenon Walking With Dinosaurs 3D was released. Although a lot of it is reused footage from the first trailer, a few interesting bits popped out (including the fact that it will probably be narrated by a pachyrhinosaur... ugh.). Among these bits was a dinosaur which I, and many others, was surprised to see: a caenagnathid, presumably representing the genus Epichirostenotes of the 72-million-year-old Horseshoe Canyon Formation. I'm especially excited to see this animal on the big screen, even though the it is portrayed in the trailer biting at some young pachyrhinosaurs in the dead of night. I don't support this notion that they were nocturnal predators, but to be fair, this is the first I've ever seen this idea and it is a movie.

Epichirostenotes from the new WWD3D trailer, seen here as a creepy nocturnal baby-killer, which it probably was not.

Tuesday, July 9, 2013

True Blood (from a mammoth)

Frozen woolly mammoths Mammuthus primigenius are exciting and very revealing discoveries when they are found. They usually reveal important clues on their ecology and biology, as well as their growth cycle; we know of frozen mammoths ranging from infants to elderly individuals. Because of the subzero temperatures of their final resting place (the north of Russia, generally), they are remarkably well-preserved, with internal organs, skin, and hair all frozen in time.

A test tube of mammoth blood. Hoooooly crap. Photograph by Semyon Grigoriev.

This week, something even more startling was recovered from one of these frozen titans. Liquid blood. This isn't an internet scam or a too-good-to-be-true hoax: a small test tube of liquid blood from the sample was collected, and will be analyzed to determine just how it managed to stay liquid for 10,000 years. The mammoth, a female, was found with the lower half of her body very well preserved, though the upper half was visibly gnawed on by other animals. This indicates that she probably died in a bog or swamp, becoming stuck in deep water or mud.

What does this liquid blood imply? Could this fuel the increasingly common idea to clone extinct animals if we can? And what would we be able to do with a cloned mammoth? Only time will tell how this startling new discovery fuels the future for extinct animals.