Peter L. Larson

Tyrannosaurus rex is everybody’s favorite dinosaur, to the extent that the most horrific predator ever to walk the planet has been converted to a singing, dancing puppet on children’s television. This book is a collection of papers produced for a symposium on the 100th anniversary of the discovery of T. rex (bones now assigned to T. rex had been discovered as early as the 1850s, but the first skeleton with enough pieces to identify was found by Barnum Brown in 1905).

I’m usually not very fond of collections like this, preferring to pick up individual papers of interest rather than an entire volume, but this one is all pretty interesting. Comments culled from the papers, in no particular order:

* As of the date of the book, there were 45 T. rex specimens known - a “specimen” being something more than just an isolated bone or tooth – there’s lots of those. The most complete is the infamous “Sue”, with 73% of the estimated 300 bones in a complete skeleton.

* The first 4 specimens were discovered between 1900 and 1908. The next one wasn’t found until 1967.

* The controversy over “Sue” (her sale for $4M led to the impression that fossils were immensely valuable) and the book and movie Jurassic Park caused an upsurge of popular interest in T. rex, and led to amateur fossil collectors roaming all over looking for their own specimen. Normally, this would been disastrous for paleontology – vertebrate fossils are fragile and often require extensive laboratory preparation (the rule of thumb is 10 days in the lab for every day you spend collecting in the field) – and a horde of enthusiastic but untrained fossil collectors hacking, chipping and blasting away could have destroyed everything they found. However, in this instance amateur collectors were of considerable benefit to paleontology. There’s only one known case of a collector damaging a specimen (that we know of - it is, of course, possible that somebody has his own T. rex in the basement). The major benefit is not so much the number of new specimens discovered but the enlarged geographic range. Prior to the amateur onslaught, all known T. rex skeletons came from the Hell Creek formation in Montana and the Lance formation in Wyoming and the Dakotas, and that is where professionals concentrated their efforts. Amateurs looked in their own backyards and found T. rex all over - Alberta, Saskatchewan, Utah, Colorado (that one came from a housing development in Littleton, and is known as the only T. rex with its own street address) and New Mexico.

* There’s some debate over the number of tyrannosaurid (what used to be called a family and is now called a clade) species. The general consensus is that the “gracile” and “robust” forms of T. rex are male and female, respectively (“gracile” is a relative term here – the animal only weighed 5 tons instead of 6 for the ”robust” form) and Nanotyrannus lancensis is a juvenile T. rex, but some still hold out for two or three species. There’s an Asian species, Tyrannosaurus bataar, which is slightly smaller than the North American form, and a number of things that are in the tyrannosaurid clade but not the genus Tyrannosaurus. All tyrannosaurids are from Asia or North America.

* The recent plethora of specimens has provided considerable new evidence on T. rex biology. A specimen discovered in 2002 had preserved medullary bone; in modern birds, medullary bone is unique to reproductive females – this is part of the evidence that the “robust” form is female.

* A pair of papers debated the significance of T. rex’s minuscule forelimbs (again, “minuscule” is a relative term; although small compared to the total animal, the arms were probably strong enough to rip human-size prey in half). Martin Lockley and his co-authors use a “morphodynamic” or evo-devo argument to claim that the tiny arms are a developmental consequence of the large head – the homeobox genes controlling head, neck and arm development work such that there’s only so much “morphological power” available and if it’s used to develop the head and neck there’s nothing left for the arms (this is a gross oversimplification of the actual paper, and I confess I’m not familiar with morphodynamic theory). Christine Lipkin and Kenneth Carpenter, with exquisite academic politeness, call Lockley et al. complete idiots, and use the DinoMorph computer modeling software to demonstrate that T. rex could have used its arms as “jacks” to stabilize it when moving from a sitting to standing position. DinoMorph software allows the user to model dinosaur bones and joints so that the range of motion at each joint can be computed; one of the interesting things shown with DinoMorph is that none of the carnivorous therapods, tyrannosaurid or not – Allosaurus, Deinonychus, etc. - had a sufficient range of movement in the forelimbs and neck to bring its “hands” to its mouth.

* Theories of T. rex lifestyle have evolved considerably since its discovery. The original concept, made famous by paintings at the American Museum of Natural History by Charles Knight and at the Yale Peabody Museum by Rudolph Zallinger, was that the animal was sluggish and moved in an erect posture, with the tail dragging on the ground. More recent work shows that the tail had been reconstructed as much longer than it actually was, and that the animal probably moved with the body and tail parallel to the ground. T. rex went through a phase when it was considered an obligate carrion feeder; it was assumed that it could not bring its massive body up to a speed sufficient to run down living prey. The most recent work suggests that although T. rex probably would have fed on carrion if it were handy, the animal was built for speed in the 25-40 kph range, and was probably an ambush hunter. A 5-6 ton animal moving at that kind of speed would have had problems if it fell, and every T. rex skeleton more than 10% complete shows evidence of trauma damage to some of the bones. Analysis of bone growth lines shows that the maximum life span for a T. rex was around 30 years, and the animal was sexually mature by about 11 years; thus T. rex had a short but exciting life.

Although, as usual in collections of this sort, individual papers are of uneven quality, the work as a whole is very informative. I’m all psyched to prowl around the Denver formation looking for T. rex teeth.… (más)