Being that Netflix temporarily suspended my account as someone has been swiping the outgoing discs from my mailbox, my wife and I have been getting our movies from our local library as of late. Most fall into categories of “Seen it too many times on TBS/TNT/WPIX between 1990-1995″, “Strange Indie Film that thinks it’s funny when it’s not”, and half the “documentary” section is made up of National Geographic specials on Egypt, but there are a few good Cary Grant and Hitchcock films to keep us entertained (sometimes, in the case of North by Northwest, you get both at the same time!). There’s only so many times I can watch Bringing Up Baby in any given month, however, so last night I picked up Chased By Dinosaurs (a “sequel” to the Walking With Dinosaurs series) and it was as painful as I had expected.
The point of the 3 part documentary series is to have “naturalist” Nigel Marvin actually walk with dinosaurs, getting so close that if the creatures were real he would be “half the man he used to be” in a quite literal sense. I don’t want to be too unkind to Nigel, but the only programs I’ve seen him in have been the “Walking With” series and as host of Shark Week a few years back, and he seems part of the current breed of “naturalists” like Jeff Corwin and even Steve Irwin that need to chase down, harass, and touch the wildlife rather than act as a guide or host to the natural world as David Attenborough does. I’ll most likely write about how idiotic the escapades of today’s television naturalists are at some later time, but during the course of the program I found myself rooting for the dinosaurs, hoping Nigel would be picked off by Sarcosuchus or Giganotosaurus.
The CGI in the programs was essentially par for the course, the use of puppets for close ups being much less realistic than one would hope (as in the case with Nigel’s encounter with Mononykus), but the Tarbosaurus vs. Therizinosaurus sequence was some of the better CGI work I’ve seen in the series (despite the fact that even though Tarbosaurus gets slashed across the face, it simply wanders off with no gaping wound or even bleeding). I’ve long been interested by Therizinosaurus, often presented as only an arm in most of the books I was able to find as a child. It seems that since then more skeletal material has been found, but even so it seems that much of the appearance of the creature is still inferred from its close relatives, namely Beipiaosaurus. Regardless of how correct the BBC team was in reconstructing the animal, the living thing must have been a wonder to behold, plus it would help to see what it did with claws that were longer (but less robust) than those of any other known dinosaur. Speaking of giant-clawed dinosaurs, the program reminded me of one of the great dinosaur mysteries still enveloping an animal named Deinocheirus, the only remains of the animal being a single set of massive arms ending in “blunt” claws. Some have suggested this animal was an apex predator, using such huge arms to rip into prey, while other have suggested it was a giant form of Ornithomimid dinosaur, which typically have quite long arms in relation to their body size. As appealing as it may be to think of these arms as belonging to a predator (and they may) it seems more likely that the owner was an Ornithomimid, the arms of the Carnosauria being shorter and more robust with a tendency to become shorter as body size increases. Think of it this way; if you’re a huge predator with a mouth full of dagger-like teeth, that’s a lot of weight you need to carry around and reducing the size of the arms (along with increasing the size of holes in the skull) is one way of coping with the weight problem. It could be argued that Deinocherius wouldn’t need to have a large head if it was equipped with such massive claws, but if that was the case it would need to “undo” some of the adaptations inherited from its ancestors who clearly show a trend towards more massive heads and shorter arms. Until more material is found we will simply not be able to tell with 100% accuracy, but I think biomechanics and what we know of dinosaur evolution at this time should make anyone skeptical that Deinocherius is more closely allied to the Carnosauria than the Ornithomimids.
As with the other BBC-made prehistoric programs, the disc came with a companion documentary to back-up its depiction of “packs” of Giganotosaurus attacking Argentinosaurus. The prospect of large predatory dinosaurs hunting cooperatively has enthralled many a paleo-artist, but up until recently we didn’t have much hard evidence that predators got together other than to mate. While the documentary, made for the Horizons program, employed some terrible cut-and-paste CGI from the Walking With… series (including dousing an Allosaurus green and calling it Giganotosaurus) and inappropriate music at times, the actual paleontology aspects were interesting. When the documentary finally got around to it, the narrator introduced us to Phil Currie, one of the go-to guys if you want to know something about predatory dinosaurs (especially Tyrannosaurids). Although controversy still surrounds the find, Currie did painstakingly track down a site discovered by Barnum Brown that contained at least 10 Albertosaurus skeletons of varying age (with little associated fossil material from other dinosaurs) telling us they died as a group. How they lived, however, is another matter and is open to speculation and I would be curious to see if there was any bite-mark riddled skeleton of a large herbivore nearby. Large predators that are often anti-social may gather together if a large source of food is available, but then again this does not seem to explain the varying ages and proximity of the skeletons, the prevailing view (prior to this discovery) being that these animals should want to avoid each other as much as possible.
Perhaps Albertosaurus had a family pattern similar to that of leopards or cheetahs, the young staying with the mother until a certain age and then being “kicked out” to do their own hunting, the fossil association being a family group before such a split. Indeed, perhaps the more inexperienced, younger dinosaurs did not participate in the hunt at all, their participation being more of a liability than an asset. Of the Tyrannosaurs Albertosaurus is among the most lightly built and long legged, suggesting it was perhaps a more active, faster predator than its southern relative Tyrannosaurus rex. At present, there is simply no way to know, the fossil evidence being the most certain and possible hunting behavior resting on so many inferences and hunches that we can’t possibly know what actually occurred; active hunting behavior doesn’t fossilize (outside of, perhaps, fossil trackways).
The documentary also mentioned a relative of Giganotosaurus named Mapusarus, discovered in an aggregation of several individuals in Argentina. Unfortunately, the details of such finds are not readily available to me, but although a joint paper by the discoverer Rodolfa Coria & Currie suggest the find might represent some sort of predator trap, it could also very well be gregarious or social behavior. The ages/sizes/life stages of the animals are not mentioned in any resource I’ve yet seen, but perhaps it is family social behavior with the growing carnosaurs later being kicked out; such an assemblage does not automatically mean these animals hunted together or even cooperatively. Even so, this was enough proof for the BBC team to back-up their idea that Giganotosaurus possibly tailed a young or sick Argentinosaurus (remember, this animal would be about a hundred feet long and many, many tons), biting at it until the animal bled to death. Such behavior does make sense, great white sharks employing a similar “strike-and-wait” technique on large elephant seals as to not be hurt in the process of the kill, but there is no way for us to know for sure. Could it also be possible that because Argentinosaurus was so big that when the large ones died for whatever reason there was enough flesh to support many predators for a long amount of time (the amount of time a 70 foot + carcass could support a group of predators depending upon the metabolism of the predators), or that this “social behavior” is centered around scavenging kills (thus explaining why we find little of any herbivores close by, the bones of the deceased giants torn away from each other and destroyed)?
Like I mentioned earlier, when studying fossils we are at a disadvantage because we only have the traces of what once was a living animal, and the further we get from anatomy the more speculative and shaky ideas get. Morphology and cladistics are pretty sound, and the environment of the animals can be determined to some degree. The interaction of animals/plants and environment moves up a level in speculation, however, and after that (but tied to it) comes behavior, which is also tied to coloration/appearance. We can infer some things about where an animal lived or how it may have acted, but while trying to figure out how predatory dinosaurs is hunted and interesting, there’s not much substance to it. This isn’t me saying “Bad scientist, no thinking for you!” but we need to keep what we know, what we can know, and what we can only imply in perspective if we are to be honest about findings and research.
Why is this important? Well yesterday the book The Hunters or the Hunted? arrived at my door and I had time to read the introduction before my Behavioral Biology class. It seems that in the latter part of the 20th century, a scientist named Dart looked at the bone assemblages in fossil caves in Africa, those known to be inhabited by Australopithecenes especially. What Dart suggested from the crushed and badly mangled bones was that Lucy’s kin were headhunters, using bones as blades and bludgeons, killing many antelope and even each other. Dart went to great lengths to show how each of the damage patterns he saw was related to tool-use among the “ape-men”, going out of his way to try and disprove any alternate hypotheses. Today, we know that Dart was terribly wrong and he far over-estimated the cultural and intellectual ability of Australopithecus, but he still put a lot of time, energy, and study into what he believed to be genuine evidence of behaviors now understood to be non-existent at the time. Especially with the discovery of “Selam”, it seems that we are finding that these creatures had some important features that set the stage for future evolution but were not truly “ape-men”, one step away from being the leopard-skin wearing barbarians of film and comic fame. Such is a lesson we must learn in science; if we are trying too hard to find what we want to see, we could very well make our own illusions.