August 29, 2012
Dinosaur names are important. Each moniker is a title that encompasses the various bones and specimens that paleontologists use to bring dinosaurs to life. When I write Tyrannosaurus rex, for instance, the name instantly conjures up an image of a hulking, deep-skulled bone-crusher that roamed western North America during the last two million years of the Cretaceous. A dinosaur’s name conveys a lot of information.
Some names are more mundane than others. Allosaurus is one of my favorite dinosaurs, but her name translates to “different lizard.” Not very inspiring. Alternatively, some dinosaur names can be hard to pronounce. I always pause before I say Amphicoelias to make sure I don’t butcher the sauropod’s name. And, then again, some dinosaur names are unintentionally funny. Pantydraco, anyone?
Just as there are people who are put off by dinosaur feathers, though, some folks are irritated by what they deem “dinosaurs with dumb names.” One of my neighbors over at WIRED, humorist Lore Sjöberg, wrote a brief whine featuring a list of dinosaurs that he thinks should be renamed for dignity’s sake.
Now, there are some dinosaur names that I’m not totally enamored with. While I understand the dinosaur’s symbolic status, Bicentenaria argentina doesn’t exactly roll off the tongue, and the same goes for the unevocative Panamericansaurus (yes, named after Pan American Energy). Then there are the names that appeal to the more puerile portion of my sense of humor. Read the name Texasetes too fast and you may get the dinosaur confused with a part of the male anatomy (not to mention the actual debate over whether the name of Megalosaurus should really be “Scrotum“), and you should always be careful with the pronunciation of Fukuiraptor unless you’re actually trying to insult the allosaur.
But what baffles me is that Sjöberg didn’t pick any of these names. Instead, his list includes the likes of Spinosaurus and Giraffatitan. I get his beef with dinosaurs named after places (Albertosaurus, Edmontosaurus, etc.), and I agree that Gasosaurus was comically unimaginative, but Iguanodon? The second dinosaur ever named, and one of the most iconic prehistoric creatures named for the clue in its teeth that led Gideon Mantell to rightly hypothesize that the dinosaur was an immense herbivore? I have to wonder whether Sjöberg would consider “Iguanasaurus– the original proposed name for the dinosaur–to be a step back or an improvement.
I just don’t get Sjöberg’s contention that Giraffatitan is “terrible” because–*gasp*–the sauropod wasn’t actually a big giraffe. Strict literalism only in naming dinosaurs, please. And, really, what would Sjöberg suggest as a replacement for Spinosaurus? When Ernst Stromer found the theropod, the most distinctive thing about the dinosaur was its enormous vertebral spines. What would you call it? Suchomimus–a cousin of Spinosaurus–is a little more poetic, but I like Stromer’s choice just fine.
There’s no reason to focus on the negative, though. There are plenty of awesome dinosaur names. Yes, yes, Tyrannosaurus rex will always be the best, but I still get a kick out of saying the names of the enigmatic sauropod Xenoposeidon, the dromaeosaur Pyroraptor, the stegosaur Miragaia, the ceratopsian Spinops, and the oviraptorid Khaan (“KHAAAAAAN!“). Not every dinosaur name is easily pronounced (say Willinakaqe ten times fast) or truly encapsulates the nature of the animal, but at least paleontologists aren’t naming species after online casinos. Not yet, anyway.
March 29, 2012
Tenontosaurus is a difficult dinosaur to describe. This beaked herbivore—a distant, roughly 110-million-year-old cousin of the more famous Iguanodon—didn’t have any spectacular spikes, horns, plates, or claws. In short, Tenontosaurus was a vanilla dinosaur, and is probably most famous for being the prey of the “terrible claw” Deinonychus. But there is something very important about the unassuming plant-eater: Paleontologists have collected a lot of them. There are at least 30 complete or partial Tenontosaurus skeletons in museums across the country, including everything from very young dinosaurs to adults. With such a sample size, paleontologists can compare skeletons to dig into the dinosaur’s biology, and University of California at Berkeley paleontologist Sarah Werning has done just that. In a paper just published in PLoS One, Werning details how Tenontosaurus grew up.
The secret to Tenontosaurus growth is in the bones themselves. The microscopic structure of dinosaur bone contains clues to how rapidly the dinosaurs grew and what was happening to them at the time of death. For this study, Werning created slides from sections of Tenontosaurus long bones—the humerus, ulna, femur, tibia and fibula—to tease out the history of each animal and the larger pattern of how the dinosaur changed with age.
During early life, Tenontosaurus grew quickly. “Throughout early ontogeny and into subadulthood,” Werning writes, “Tenontosaurus tilletti is characterized by bone tissues associated with fast growth.” But the dinosaur didn’t maintain this quick pace during its entire life. Sometime in its adolescence, perhaps around the time Tenontosaurus began reproducing, the dinosaur’s growth rate slowed. (Working with colleague Andrew Lee, Werning previously found that Tenontosaurus and other dinosaurs started having sex before they reached full size.) The dinosaur kept growing, but at a much slower rate, until it eventually reached skeletal maturity and its growth all but ceased.
This kind of growth pattern wasn’t unique to Tenontosaurus. Similar and closely related dinosaurs, such as Rhabdodon and Zalmoxes, appear to have grown quickly in their youth before slowing down sometime in their subadult lives. But not all ornithopod dinosaurs grew this way.
Tenontosaurus, Rhabdodon, Zalmoxes and similar dinosaurs were all on branches near the base of a major dinosaur group called the Iguanodontia. This group also contains Iguanodon itself and the full swath of hadrosaurs (think Edmontosaurus and Parasaurolophus). And, as Werning points out, hadrosaurs and the closer kin of Iguanodon grew extremely rapidly. These dinosaurs grew faster than Tenontosaurus and sustained the high growth rates until their skeletons were fully developed—there was no extended period of slow growth as the dinosaurs approached skeletal maturity.
This different pattern might explain why dinosaurs like Edmontosaurus were so much bigger than their archaic cousins. A really big, mature Edmontosaurus could reach more than 40 feet in length, but Tenontosaurus topped out at around 25 feet. Perhaps the rapid, sustained growth rate of the hadrosaurs and their close kin allowed them to attain huge sizes, while the more variable growth rates of Tenontosaurus constrained the dinosaur’s size to the middle range.
As paleontologists study other dinosaurs, perhaps the details of how iguanodontian growth rates shifted will become clearer. And Werning has set an excellent precedent for other researchers delving into dinosaur histology. Not only is her paper open-access, but Werning also uploaded multiple high-resolution images of the Tenontosaurus bone slides to the website MorphoBank. Other scientists can readily download the images and investigate the slides for themselves. I hope the Tenontosaurus images are just the start of what will become on online library of dinosaur histology—a resource that will undoubtedly help researchers further investigate the biology of these amazing animals.
Werning, S. (2012). The Ontogenetic Osteohistology of Tenontosaurus tilletti PLoS ONE, 7 (3) DOI: 10.1371/journal.pone.0033539
December 27, 2011
There is much we still don’t know about dinosaurs. In fact, some aspects of dinosaurs have puzzled paleontologists for well over a century. Among the most frustrating is why the great herbivore Iguanodon had prominent thumb spikes. Despite all the possibly explanations provided for this appendage, none are especially satisfying.
The peculiar false thumb of Iguanodon was originally thought to set into the dinosaur’s nose. When Gideon Mantell first described the animal in 1825, the various bits and pieces of the dinosaur were thought to represent the remains of an enormous, iguana-like reptile. As a result, it seemed reasonable that a conical, bony spike corresponded to the same structure on the snouts of rhinoceros iguanas. This placement made sense within the prevailing view that creatures like Iguanodon were lizards writ large, but the idea was tossed when a series of more complete Iguanodon were found in a Belgian coal mine in 1878. The “horn” actually belonged on a mitten-like hand, opposite a prehensile finger.
But why should Iguanodon have a hand spike? The most popular idea is that the dinosaur used the appendage for defense—an illustration by John Sibbick in The Book of Dinosaurs shows and Iguanodon stabbing its spike into the neck of an attacking allosaurid. The restoration looks more than a little ridiculous. In order to get within poking range, the defending Iguanodon would have to place itself right in front of its assailant, perfectly within the range of the slicing dental cutlery of the carnivore. Such maneuvers would require the attacker to hold still while being prodded. One popular-audience book suggested that the spike might house a venom gland, but there is no evidence for this and, furthermore, the Iguanodon would still have to get within biting range of the attacking theropod to use the weapon.
There are a few other speculative hypotheses. Maybe Iguanodon used the spikes in combat with one another. Or perhaps, as David Norman briefly suggested in his section on basal iguanodontia in the second edition of The Dinosauria, the spike was used for “breaking into seeds and fruits.” These are not unreasonable notions, but there is also no positive evidence to suggest that they are correct, either. The Iguanodon thumb spike is a strange specialization that must have originated for a reason. The question is whether we can test any of these ideas.
Though my own suggestion is not any better than those I have been disappointed by, I wonder if the Iguanodon spike is a Mesozoic equivalent of another false thumb seen among animals today—the enlarged wrist bones of red and giant pandas. Perhaps the Iguanodon thumb spike was an adaptation for stripping foliage from tree branches. The dinosaur could have grasped the branch with the prehensile finger, or flexed the main fingers of the palm around a bough, and run the spike down the branch to remove the greens without having to chew through the less-nutritious twigs. But this hypothesis has problems, too. The false thumbs of pandas flex so that they help the mammals grip bamboo, whereas the Iguanodon spike was rigid. And why would an Iguanodon preferentially select greener browse, especially when supplied with a formidable battery or self-replacing teeth? Furthermore, this idea is difficult to test—a preserved thumb spike wouldn’t show wear from use the same way a fossil tooth would. The Iguanodon spike was surrounded by a tough, keratinous sheath, so the actual wear wouldn’t be seen on the bone itself. A functional model of an Iguanodon hand could help investigate this idea, but even then, direct evidence would be lacking.
Perhaps there isn’t a good modern analog for the Iguanodon spikes. The bones look like they could be used for any number of things, from defense to feeding, but frustratingly, there isn’t any unambiguous indication of what they were used for or why they evolved. Perhaps, to solve this mystery, we need to go beyond the obvious and try to think like a dinosaur.
March 10, 2011
In one short section of his book Parasite Rex, science writer Carl Zimmer asked a simple question: “Did tapeworms live in dinosaurs?” There is no reason to think they didn’t. Both the living descendants of dinosaurs (birds) and their crocodylian cousins harbor tapeworms, Zimmer pointed out, and so it isn’t unreasonable to imagine monstrous, prehistoric tapeworms winding their way through dinosaurian intestines.
The thought of a hundred-foot-long prehistoric tapeworm is fascinatingly repulsive—and even formed the basis of the carrion-eating monster Carnictis in Peter Jackson’s revival of King Kong—but so far, no one has found a trace of one. This doesn’t mean that dinosaurs were parasite-free.
To find a dinosaur parasite, you need to know what to look for and where to look for it. The soft bodies of dinosaur parasites were more likely to decay after the death of their host than become preserved, but like living parasites today, dwellers in a dinosaur’s digestive tract probably produced cysts or eggs that were passed out of the body in the dinosaur’s excrement. Since fossilized feces, called coprolites, have been found for a variety of dinosaurs, they are the best places to look for signs of infestation.
In 2006, George Poinar and Arthur Boucot announced that they had discovered the tell-tale signs of intestinal parasites in an Early Cretaceous dinosaur coprolite found in Belgium. The fossil had come from a coal shaft where over 30 individual Iguanodon skeletons had been found in the late 19th century, although the fossilized scat was probably not left by a herbivore. After studying 280 of the site’s coprolites in 1903, C.E. Bertrand concluded that the trace fossils represented a carnivorous dinosaur, which was supported by fragments of a large theropod also found at the locality.
Analysis of the fossil required its destruction. It was scrubbed, ground down into grains, suspended in hydrochloric acid solution, spun in a centrifuge, placed in hydrous hydrofluoric acid, centrifuged again, and so on, leaving the scientists with a concentrated dino-poo residue that could be readily viewed under the microscope. Traces of a protozoan and three helminth worms were visible.
The parasites appeared to be very similar to organisms that still infest animals today. Tiny protozoan cysts found in the coprolite residue were proposed to be a prehistoric species of Entamoeba—a widespread microorganism that can be harmless or disease depending on species—and eggs from both trematode and nematode worms were recovered that resembe those of still-living varieties. In terms of cyst and egg anatomy, at least, these types of parasites have not changed very much in 125 million years.
Just how these organisms affected their host dinosaur is unclear. Some may have caused illness, while others carried out their life cycles without triggering observable symptoms. Barred from studying the dinosaur that left the scat behind, there’s no way to tell. In another case of dinosaur parasitism, though, the infesting organism had clear, harmful effects on its host.
When large theropod dinosaurs fought, they often bit each other on the face. We know this because of damaged skulls with healed bite marks on them. But some tyrannosaurs had lower jaws perforated by a series of smooth-edged holes that were inconsistent with the damage a bite would have produced. Instead, a 2009 paper by Ewan Wolff, Steven Salisbury, Jack Horner and David Varricchio argued, these holes were created by a microorganism similar to Trichomonas gallinae—a protozoan that causes throat ulcers and opens the same kinds of lesions in the jaws of modern birds.
Once the paleontologists recognized the jaw lesions, they found them in numerous tyrannosaur specimens. Of 61 examined skulls, about 15 percent showed evidence of the pathology, so the microorganism certainly got around. (The Tyrannosaurus known as “Sue” had one of the worst infestations.) How it found new hosts is unknown. Perhaps the microorganism lived in herbivorous dinosaurs, too, and entered the tyrannosaurs when they fed on infested prey. Then again, the behavior of the tyrannosaurs themselves probably made things worse. Face-biting may have transmitted the microorganisms from one individual to another, and some tyrannosaurs may have picked up the parasites when they scavenged their own dead.
There were certainly many more dinosaur parasites than those recognized so far. Finding them is hard work, but there are ways to detect their presence. Who knows? Maybe someone will eventually find Zimmer’s tyrannosaur tapeworm.
POINAR, G., & BOUCOT, A. (2006). Evidence of intestinal parasites of dinosaurs Parasitology, 133 (02) DOI: 10.1017/S0031182006000138
Wolff, E., Salisbury, S., Horner, J., & Varricchio, D. (2009). Common Avian Infection Plagued the Tyrant Dinosaurs PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0007288
February 22, 2010
Dinosaurs as depicted in museums, movies and art today are sleek, brightly-colored and often feathered. This was not always the case. When dinosaurs were first recognized by science at the beginning of the 19th century, naturalists like Gideon Mantell and William Buckland thought they looked like enormous lizards and crocodiles. Iguanodon, as its name might suggest, was thought to be a gigantic version of the tropical lizards, and Megalosaurus was envisioned as a more crocodile-like beast.
Buckland, in particular, was enthralled by these ancient creatures. They were the petrified evidence of a past world that had flourished and been destroyed during a past beyond memory, and (as later recounted by his son Francis) Buckland once described the great Megalosaurus this way:
During this period of monsters there floated in the neighborhood of what is now the lake of Blenheim – huge lizards, their jaws like crocodiles, their bodies as big as elephants, their legs like gate-posts and mile-stones, and their tails as long and as large as the steeple of Kidlington or Long Habro’. Take off the steeple of either church, lay it in a horizontal position, and place legs on it, and you will have some notion of the animal’s bulk. These stories look like fables, but I ask not your indulgence to believe them. There the monsters are, and I challenge your incredulity in the face of the specimens before your eyes; – disbelieve them if you can.
It was impossible not to be fascinated by such creatures, and they were so spectacular that Buckland thought the fossils of these dinosaurs may have inspired myths and legends:
May not the idea of the dragons, curious stories of which are chronicles in various parts of England, owe their origin, in some way or other, to the veritable existence of these large lizards in former ages? To point out the train of ideas or circumstances which led to these ancient dragon stories is of course impossible, particularly as man was not coexistant with Megalosaurus and Co. – still there is a certain shadow of connexion between them.
Buckland left this question open, but over a century and a half later the historian Adrienne Mayor would illustrate that he was on the right track. The mythology of many cultures, from Native American tribes to the Greeks, was heavily affected by the discovery of fossil bones. The Thunderbird, the Cyclops, Griffins, dragons and more were not just figments of our imagination, but early attempts to make sense of strange fossil bones found throughout the world.