Saturday, November 7, 2009

Contemplating the Functional Morphology In Vertebrates and the Latest Research

While off-line and continuing my "Paleo Quest" in between tweets and posts, I continued my research, when I could, through browsing the internet and watching some entertaining and enlightening documentaries which cover the latest research in Paleontology. Doing so, I managed to see two documentaries on NatGeo and one on PBS (KET here in Kentucky.). The two documentaries on NatGeo are entitled "Bizarre Dinosaurs," which is a documentary based off the National Geographic article of the same name, and "Dinosaurs Decoded," which explains Horner and his colleague from Berkeley, Mark Goodwin's theories that, if they hold true, then approximately 1/3 of all Dinosaur taxa would be wiped out! In other words, 1/3 of these species do not exist!! This is a case of Mistaken Identitiy, they claim. I'll get to these in a second. The PBS program was the first of a three-part miniseries of episodes on their successful show Nova, entitled "Becoming Human," which includes the latest fossil finds and knowledge about Human evolution, as well as Chimpanzee and Human divergence. However, this post is about functional Morphology in Vertebrates (in other words, body plan/ Anatomy) , more specifically the Dinosauria. In this case, this would include the two National Geographic documentaries I mentioned.

The nice thing about these two documentaries is their extensive coverage of the group, including the odds and ends, as well their use of Diagrams and Models in addition to interviews with key experts, like Dr. Horner, Dr. Sereno, Dr. Bakker, Dr. Holtz, Dr. Witmer, among others. Now, lets go throught the oddities of the documentaries one by one.

"Bizarre Dinosaurs"

The name says it all and it nicely covers the some of the odd ones of the Dinosaur World. The following list are of the Animals covered in the documentary and what they said about them:

  • Amargasaurus- this sauropod is truly bizarre with it being the only sauropod/titanosaur genus to have a double row of elongated "spines" on it's back, large enough to have supported a skin sail, similar to the Spinosaurus aegyptiacus.
  • S. aegyptiacus- I found this part to be the most interesting as not only did the show talk about the basics of this animal, but commented on it's truly bizarre morphology, the crocidilian snout and the large single row of spines jutting from the middle vertebrae of the spinal column, which most likely supported a sail as well. Oddly enough, Horner admitted to the true diet of this theropod, when they referrenced it's appearance in the failure, Jurassic Park III. His reasoning for selecting the Spino and not, say...Giganotosaurus carolinii or T. rex, yet again, was, one, it was the largest theropod known, and second was he was tired of T. rex "hogging the glory." They, then, commented on it's bizarre "sail." Covered were the ideas of thermal regulation while fishing, and/or display.
  • Nigersaurus- "The Jurassic Lawn Mower/ Vaccuum cleaner" as I'd like to call him. This sauropods most bizarre feature is it's head! Clearly this looks like it's the offspring of a Diplodocus and a vaccuum cleaner, making me infer it's a diplodocid. The teeth and the jaws of this animal or in such a bizarre layout that it possibly combed the low growing vegetation.
  • Dracorex hogwartsia- or "juvenile Pachy." This pachycephalosaurid is so named because it looks like something out of a fantasy film, specifically a dragon. The odd skull doesn't seem to be real! Well it is, but what exactly is it? "Hogwarts' Dragon King" is one of those taxa that Horner and Goodwin believe to be a stage in the life of a related pachy. So, is it's own species/genus or is it the growth stage of another animal. (Will cover this soon....)
  • Deinocheirus- Bizarre as it only known from a gargantuan pair of menacing arms and that is it!! Ornithomimid? Herbiverous? Carniverous? Omniverous? We don't know! This theropod is about as mysterious it gets!
  • Epidendrosaurus- Tiny, cute, but bizarre! This little theropod, and I Do Mean Little, is bizarre as it apparently had large eyes, making it nocturnal, and an elongated index finger, possibly to fish for insects in the barks of trees.
  • Masiakasaurus- This small theropod is bizarre, though sadly not in the documentary, but the article, was bizarre in that it had it's four front dagger-shaped teeth curved out of it's mouth and looked like hooks at the end of it's jaws.
  • Carnotaurus sastrei- This large Cretaceous theropod is bizarre for it's bull-like face, from which it gets it's name. The function of the horns was purely social and used for display and identification between members of the family. It was portrayed in Michael Crichton's The Lost World as possessing the ability to blend into it's environment like a chameleon.
As you can see, they're all pretty bizarre. The next documentary I'll mention in this lengthy post is "Dinosaurs Decoded." This documentary covered the research published in the journal PLos One. And, as stated above, according to these findings on Dinosaur growth patterns and how their morphology changed as they grew and matured. Fragmentary bone, once thought to belong to a pachycephalosaur was identified by Mark Goodwin of Berkeley and collegue of Horner as a infant Triceratops. The main reasons behind a lot of these claims between the Tyrannosaurs, the Certopsians and Pachys covered in the documentary was not of whether bones in the skeleton were fused or not, as many bones in the skull of some adult species aren't fused, allowing a kinetic skull when eating (i.e. T. rex had many bones in it's skull that had not fused so that to handle struggling prey, could twist and turn and not break off it's teeth. These gaps were filled with either cartilage or muscles to the skull could "flex" when the animal was eating.), but instead, microscopic sutures that had not closed in some specimens and taxa as they would be in an adult animal. Personally, I find it quite an interesting hypothesis. This leads me back to Dracorex hogwartsia, as well as Stygimoloch, and Pachycephalosaurus.  Observing tiny slices of bone in each species has led to the finding of open sutures in Dracorex and Stygimoloch, indicating these animals were not full grown adults,but, according to Horner and Goodwin, they are merely stages of development in Pachycephalosaurus. How? What are the significance of sutures? Open sutures in the bone allow more room for the animal to grow. This has led Horner and Goodwin to apply these ideas and methods on Tyrannosaurus rex, Nanotyrannus lancensis, and other tyrannosaurs. Horner believes that the Nano may be a teenage T. rex. Is he right? Well.....there's not way for sure. However, there is a chance that the Nano may merely be a growth stage of T. rex or another tyrannosaur species.

However, there's more to growth than that. It's true that fused bones in an animal don't necessarily mean the animal is full grown. Sutures are a good way to tell, however, that doesn't necessarily mean anything either. Now, I know I'm no Ph.D, yet, but think about it. There may be some taxa that reach adulthood but continue growing through out their entire life. Therefore, they would still have open sutures. To truly tell an age and when they stopped growing when they matured is to count the growth rings as well as look for sutures under a microscope.

In my personal opinion, I agree that dinosaur juveniles and their adult counterparts were not Mesozoic "Dr Evils and Mini-Me's" of each other here. More research definitely still needs to be done.

On another note, I would like to comment on the habitual nature of Paleontologists, Biologists and Zoologists that think "black & white," if you wil about the functions of some animals with strange morphologies and appendages. A prime example are the plates of Stegosaurus. My hypothesis is that they were for sexual display, family member/sex identification and thermal regulation, along with other taxa with bizarre appandages like Spinosaurus aegyptiacus' sail and Amargasaurus. There's also the old question about the functionality of the front limbs of the tyrannosaurs. Sure, there obviously was the trade off with the larger head and more muscular neck, along with powerful jaws, and the shrinking of the seemingly vestigial fore-limbs. However, when paleontologists discuss function, they say it's "either this OR that" which is just NOT a good way to think in this field! I believe they were used in number of different ways from courtship, mating, and consuming prey. They might have even helped the animal get up in the morning or something. The arms may have been used to pick itself up if it tripped on the hunt. And, if injujured and can't hunt, the family would have taken care of the injured member. The limbs could have been used for grooming as well, as proposed by Dr. Robert T. Bakker.

My point is that the majority of paleontologists are too "black and white," if you will in their thinking, instead of "grey." In other words, they need to stop thinking that something is "either/or." The thinking is too extreme left and right wing with no middle ground. At least, that's what all this research and thinking has taught me. Hopefully, I will learn more about this when I continue my "Paleo Quest" and my own personal research in my spare time between posts and tweets.