May 18, 2009
If late night B-movies have taught me anything, it is that radiation makes things grow very big really, really fast. This is not true, of course, but it is a standard convention of cheesy science fiction, and it is a theme carried on by Leigh Clark’s novel Carnivore.
The story unfolds at a remote Antarctic research station where a team of scientists has brought back a Tyrannosaurus egg they found frozen in ice. At one point someone says “Gosh, we shouldn’t put any of that radioactive waste we have lying around next to that egg or it will grow very fast!” But of course this is just what the human villains of the story do. Before you know it the little Tyrannosaurus is a full-grown terror, gorging itself on the hordes of nameless characters that seem to appear out of nowhere at the outpost.
I would mention the main characters of the novel, but there is not much point. Almost everyone falls prey to the Tyrannosaurus in gruesome fashion. Indeed, Clark’s antagonist is a very messy eater, and it is no wonder that it eats so many people since it can’t seem to keep those it captures in its mouth for very long. If done right the descriptions of blood and gore could have been chilling, but instead the novel jumps from one scene of over-the-top carnage to the next.
Carnivore mostly serves as an excuse to have a Tyrannosaurus munching on scores of hapless victims in the Antarctic, but a more effective thriller is Lincoln Child’s new novel Terminal Freeze. In some ways it is quite similar to Clark’s book (a team of scientists finds a prehistoric killer locked in ice), but Terminal Freeze is more fully developed. The Arctic base where Child’s novel is set is described in vivid detail, making it easy to imagine his monster slinking down the dark, chilled hallways. As it turns out, Child’s creature is not a dinosaur but an unknown kind of mammal, but it is just as terrifying as Clark’s more famous antagonist.
While the idea that dinosaurs (or other monsters) might be preserved alive in ice for millions of years is a bit silly, we do know that dinosaurs inhabited cold habitats within the Arctic Circle. The past year has seen the publication of several papers describing the diversity of dinosaurs in the cold northern reaches of the globe. While novelists still have to figure out how to close gaps of tens of millions of years to bring dinosaurs and humans together, a tyrannosaur trotting through the snow is not such a far-flung idea after all.
March 17, 2009
If you visited what is now Alberta, Canada 75 million years ago, you would have to beware of some formidable predators. The large tyrannosaurids Daspletosaurus and Gorgosaurus prowled the landscape while the smaller sickle-clawed killers Dromaeosaurus and Saurornitholestes stalked their prey in the forest. You might be excused, then, if you missed a smaller feathered predator that weighed about as much as a domestic chicken and was named Hesperonychus.
Announced by paleontologists Nicholas Longrich and Philip Currie this week in the journal PNAS, Hesperonychus is the smallest predatory dinosaur yet known from North America (even smaller than the termite-eating Albertonykus, which Currie and Longrich described last year). It still would have been quite large compared to the mammals of its day, however, and it may have been the scourge of our ancient relatives. This fits with the hypothesis that dinosaur predation on mammals kept mammals small, but as Longrich and Currie point out, it could also mean that the occupation of niches by mammals kept dinosaurs from becoming much smaller.
During the Mesozoic, the time when non-avian dinosaurs flourished, there were no large mammals. One of the biggest was Repenomamus, which was about the size of a small dog and lived during the Cretaceous. It was large enough to eat some baby dinosaurs (which fossil evidence has shown it did) but this was unusual. Most mammals were smaller and ate seeds, insects, and fruit. This means that if there were dinosaurs smaller than Hesperonychus they may have come into competition with mammals for food and places to live in the forest. Rather than coming into such direct competition for resources with mammals it seems that the smallest of theropod dinosaurs were just large enough to see mammals as food.
What is even more surprising is that Hesperonychus does not fit in with any other maniraptoran dinosaurs from North America. When Longrich and Currie studied its bones to determine what kind of dinosaur it was, they found that it was most closely related to the microraptorine dinosaurs from China. This group of feathered dinosaurs, which includes Microraptor and Sinornithosaurus, had not been found in North America before. Not only that, but Hesperonychus is about 45 million years younger than the oldest members of this group in Asia. Therefore it extends the range of the microraptorine dinosaurs over both time and geography, hinting at other tantalizing finds yet to be disinterred from the rock.
March 13, 2009
Fossil trackways have shown paleontologists that some sauropod dinosaurs moved together in herds. But how were their herds organized? Were they made up only of particular age groups or were individuals of different ages all mixed together? In a new paper in Palaeogeography, Palaeoclimatology, Palaeoecology, scientists Timothy Myers and Anthony Fiorillo discuss two different sites that suggest that at least some sauropods segregated their herds by age.
Before discussing the fossil sites in detail, Myers and Fiorillo review some of the problems in inferring behavior from fossil trackways alone. A photo included in the paper, for instance, shows the tracks of a human next to those of a grizzly bear. Was this person walking alongside gentle Ben? No, the tracks had been made hours apart. The same principle holds for fossil tracks. The presence of tracks made by two individuals in the same place does not necessarily mean they were there at the same time. Further evidence would be required to show this was true.
There can be difficulties with evidence from bone beds, too. The fossils from Mother’s Day Quarry in Montana are from a herd of sauropod dinosaurs that may have died during a drought. What is strange, however, is that nearly all the bones are from juvenile and sub-adult animals. Immature animals typically suffer higher death rates than adults during droughts, but the question was whether this site represents a herd of immature animals or simply the immature portion of a larger herd. The lack of adults and the fact that the bones had not been transported after the animals died led Myers and Fiorillo to suggest that the Mother’s Day Quarry site represents an actual herd of immature animals separate from adults.
The Big Bend site in Texas differs in that it consists of three juvenile Alamosaurus that died and were buried together. Like the Montana site, this bone bed represents a single event rather than the accumulation of multiple skeletons over time. The fact that no adult bones are found and that no accumulations of multiple Alamosaurus adults are known suggests that these dinosaurs herded together when young but became more solitary as they became mature.
So what do these two sites mean? Factors that might potentially bias the formation of bone beds must be kept in mind, but they appear to suggest that, in at least some sauropods, juvenile individuals formed groups separate from herds of mature individuals. This may have to do with size. The adults were much, much larger than immature individuals and may have had different dietary needs. This may have segregated herds by age with the younger animals grouping together for protection. This type of age segregation was probably not present in all sauropods, but it may have been prevalent among some of the largest species.
March 2, 2009
You can find dinosaurs in New Jersey, but you have to know where to look. Even though my home state is known for suburban sprawl and peculiar odors today, a little over 65 million years ago much of it was covered by the ocean. Marine crocodiles, plesiosaurs, and gigantic mosasaurs prowled the near-shore waters, and the dinosaurs Hadrosaurus and Dryptosaurus inhabited the land not too far from the ancient beach. When these dinosaurs died, sometimes their bones were washed out into rivers and carried to the boundary of the sea, where they became fossilized along with the remains of marine animals.
Unfortunately some of the most significant fossil sites in New Jersey have been built over or are no longer being examined, but there is one place where anyone can go to find fossils. It is called Big Brook and is well known for the abundance of shark teeth and other small fossils. Every one in a while, though, someone finds a bit of dinosaur bone.
Last December, New Jersey dentist Paul Kovalski found a chunk of brown bone at Big Brook three inches wide by three inches long. It didn’t look like much, but when he took it to the paleontologists at the Academy of Natural Sciences in Philadelphia, they were able to confirm that it came from a dinosaur. It most likely belonged to Hadrosaurus, New Jersey’s state dinosaur and one of the first major dinosaur discoveries in North America.
I have never been to Big Brook, but I’m making plans to make a number of visits there as the weather warms up. I doubt that I will be lucky enough to find any dinosaur bones, but who knows? I just might get lucky.
January 30, 2009
Earlier this month I wrote about a new scientific paper that described an ancient, dinosaur-filled habitat that existed in what is now Siberia. Commenter Naruto raised a point of confusion to many;
I think there is a mistake in this article. The mistake is at the second paragraph, on the last line. “growing understanding that they were not cold-blooded creatures.”, and I think the right one should be “growing understanding that they were cold-blooded creatures.” The “not” shouldn’t be in that line. …
In order to answer this question we have to untangle what phrases like “warm-blooded” and “cold-blooded” really mean, especially since they can be more confusing than helpful.
Let’s start with the “cold-blooded” animals like fish, amphibians, and reptiles. Their body temperatures fluctuate with that of their surrounding environment, which means they are ecothermic. This does not automatically mean that these animals are sluggish, though. If the temperature of their surrounding environment is high enough they can be very active (meaning that they are literally “warm-blooded” in those circumstances), and some of these animals even have special physiological mechanisms that help them maintain a high body temperature. Great white sharks, for instance, are able to keep their body temperature several degrees Celsius above the temperature of the cold coastal waters they inhabit.
The animals we often refer to as being “warm-blooded,” by contrast, are more aptly described as being “endothermic.” This means that they generate their own body heat and often keep it at a relatively high, constant temperature. Living mammals and birds are the main examples of this kind of physiology, but there are some species that can switch between being endothermic and ectothermic. Some small birds and bats are endothermic for part of a day or part of the year but ectothermic during other parts. They are so small and burn energy so fast that if they were not able to switch their metabolisms, they would have to constantly collect food or they would die.
So, were dinosaurs ectothermic, endothermic, or something else entirely? Read more after the jump.