This Blog Entry is Dedicated to the Natural History Caucus, Many of Whose Members work in Collections Serving Paleontology: You Help Promote the Enduring Fascination of Kids of All Ages with Dinosaurs, and Deserve the Nation's Thanks for the Careers in Science this Inspires
We all pretty much believe in things like gravity and inertia, even if we cannot do the math behind them. We also tend to believe professional engineers when they make more sophisticated claims about a given metal beam being able to support a skyscraper, or a truck of a certain rating being able to haul a cargo of so many tons at a particular top speed, because we know that these engineers have a firm grounding in the laws of physics that govern those situations. But structural and automotive engineers are not the only ones who can do these calculations and make pretty near exact analyses of what is possible and what is not. These days, vertebrate paleontologists are doing some pretty good biomechanical engineering analysis themselves on the fossil record of predatory dinosaurs. A look at one of the year 2007’s top dinosaur stories gives us some good examples of how things that seem totally conjectural to laypersons such as ourselves, are actually based on calculations of what kind of body structure it would take for dinosaurs to overcome gravity and inertia routinely and thrive daily, millions of years ago.
So Just How Big Were the Big Meat-Eating Dinosaurs & How Do We Know?
One of the biggest stories this year was the announcement by a team led by Xu et al. (2007) from the Chinese Academy of Sciences that they had found a gigantic bird-like dinosaur Gigantoraptor erlianensis. Based on about 16 well preserved bones, including a mandible (basically a jaw), they showed that this animal was about 24 ft. long, about 12 feet high at the hip and weighed about 3,000 pounds. This creature was taller than a giraffe , was longer than the longest living crocodile ever measured, and weighed about as much as a black rhino. Yet, at least in its erect stance, it resembled Sesame Street’s Big Bird, assuming that Big Bird also had very heavily clawed feet and wings that also ended in very serious claws. It was largely meat-and –mollusc eating, but apparently could cross-over into plants. The posture in which it apparently walked (or ran) featured a head held somewhat aloft and forward of the body, shoulders leaning forward (like a charging football player running almost parallel to the ground) with its tail held out stiffly in back (no analogy with the football player there. )
How did the paleontologists infer all this? First, they were able to determine it was bird-like owing to both its wing-like bone structure, certain feather-like patterning on those bones and histological (microscopic bone tissue level ) data that matched it to other bird-like dinosaurs (the latter detail showing the porosity of the bones also explains why even at 3,000 pounds, Gigantoraptor was light, and probably fast on the ground, for its size) . Second, they had samples of more complete skeletal remains from other smaller bird-like ancient animals, so they had a head start by being able to scale up using structural analogies (or “homologies”), when filling in some of the remaining major bio-architectural blanks. Third, the grooving and tilt of the bone surfaces indicated the leaning and standing aspect of the bird-like dinosaur. Fourth its ultimate live weight was calculated using measurements like the major bones’ circumference, length, and the ratios among them: this is not unlike bringing in an a broken auto part to an auto body parts shop and the staff there being able to tell you what kind of car or pick up truck you were driving, and how much it could tow behind itself or carry in its cargo box. Fifth, the jaw structure showed that it was somewhat beak-like, in a kind of rounded goose-like manner, but there were places for teeth in the back. The creature could grab and break off a chunk of prey with the front end and masticate with the back. While this structure is not widely seen in extant animals, it has been found in related dinosaurs. In those other dinosaurs the bones of smaller eaten dinosaurs were found within the predator’s fossilized body frames where the stomach of the predator that ate them would have been located, although a smaller number of specimens showed occasional fossilized plant remains instead. As with many current dinosaur studies, CAT scans and computer graphics were used to help visualize details and help visualize matching “missing pieces.”
So, is Gigantoraptor the biggest meat-eating dinosaur?
A review paper by Therrien and Henderson (2007) suggests that earlier bird-like dinosaurs found by Xu’s team (and by inference a dinosaur like Gigantoraptor ) are probably not going to be the body mass leaders of the carnivorous pack, as it were, because that honor goes to the theropods (the “beast-footed”). This group includes Giganotosaurus/ Carachadontosaurus (Coria & Salgado 1995, Coria & Currie 2006), Spinosaurus (Dal Sasso et al. 2005, Sereno et al., 1996, Sereno et al. 1998), or everyone’s Jurrasic Park movie & museum favorite Tyrannosaurus rex (Henderson & Snively 2004). To get a great and quite accurate size comparison chart that includes these dinosaurs click on the enigmatically authored (“Dinoguy2”) link that follows:
http://en.wikipedia.org/wiki/Image:Largesttheropods.png
Therrien & Henderson suggest that for a vertebrate paleontologist, the luckiest fossil body part to find and begin modeling your theropod is a complete, or near complete skull. They strongly favor the use of a skull-length- based formula for estimating body length (about 97% reliability of prediction) and somewhat different but still skull-length-based formula for estimating body mass or weight (about 87% reliability). The authors’ preferred engineering modeling approach is shown to be the best available when competing methods of estimating body size are tested against dinosaur fossils that are known to be skeletally complete from head to toe and tail. In other words, their formula can be proven to work better than others , because the proof of correlating measurements is already on display “in the skeletal flesh” as it were in the museum to check against.
They also use a kind of structural engineer’s “strength of materials vs. likely stresses” argument that suggests that there probably was an overall upper limit to the size and weight of theropods, based partly on their type of bone structure, and the requirement that they be able to walk , run and hunt on only two feet . Given what is known from fossils found thus far, they suggest that the two very closely related dinosaurs Carcharodontosaurus and Giganotosaurus would have been about 39 feet long and weighed about 14 tons, eclipsing Tyrannosaurus rex in length and overall body size by a small but persistent margin of a few feet and a couple of tons.
If ---- and this is a big if in those author’s eyes, the partial skull of Spinosaurus is as big as some dinosaur reconstructors have made it out to be through their filling in of absent material----- the overall length of Spinosaurus would have been about 42 feet, and the calculated weight a seemingly incredible, and biomechanically hard-to-rationalize 20 tons. Therrien and Henderson posit that as a practical matter a body length of about 39 feet and a weight of 14 tons was about as big as they see as sustainable for these predators before they would simply become too slow to hunt or simply start breaking down of their own weight.
Biomechanics Is at the Core of Vertebrate Size & Motion Studies in the Present as Well as the Past
Are you still unconvinced that these vertebrate paleontologists were not just making it up? Well, it turns out that their predictive biomechanical models of weight-bearing capacity and style of locomotion work very well with living animals, and that these studies of living animals tend to reinforce the reasonable certainty of the paleontologists. In addition, animal biomechanics also works in comparisons of modern man vs. the great apes vs. prehistoric man. Orthopedic surgeons rely on biomechanics when designing replacement knee and hip joints, and collegiate kinesiology brings biomechanics right down to the analysis and enhancement of athletic performance .
Because, in the end, gravity and inertia have been around and working a lot longer than they have been doing arthroplasty, longer than we humans have been around , and yes, even longer than when these large carnivorous dinosaurs roamed (or more likely ran on their hind legs) across the earth.
A Brief Bibliography on the Use of BioMechanics In the Estimation of Size, Strength, Mobility & Speed of Fossil & Contemporary Vertebrates, with special interest in Large Predatory Dinosaurs
Abdel-Rahman RR & Hefzy MS . 1998. Three-dimensional dynamic behavior of the human knee joint under impact loading. Medical Engineering and Physics 20: 276-290.
Alexander RM 1985. Mechanics of posture and gait of some large dinosaurs. Zoological Journal of the Linnean Society 83: 1-25.
Alexander RM. 1988. Elastic mechanisms in animal movement. NY: Cambridge University Press.
Alexander RM . 1989. Dynamics of dinosaurs and other extinct giants. New YorK: Columbia Univesity Press.
Alexander RM. 2006. Dinosaur biomechanics. Proceedings of the Biological Society 272 (1596): 1849-1855.
Anderson JF, Hall-Martin A & Russell DA. 1985. Long bone circumference and weight in mammals , birds and dinosaurs. Journal of Zoology 231: 53-61.
Anyonge, W. 1993. Body mass in large and extinct carnivores. Journal of Zoology 231: 339-350.
Biewener AA. 2002. Walking with tyrannosaurs. Nature 415 (6875): 971-973.
Biewener AA. 2006. Patterns of mechanical energy change in tetrapod gait: pendula, springs and work. Journal of Experimental Zoology: Comparative Experimental Biology 305 : 899-911.
Blob, RW. 2000. Interspecific scaling of the hindlimb skeleton in lizards, crocodilians, felids and canids; does limb bone shape correlate with limb posture? Journal of Zoology 250: 507-530.
Brochu CA. 2003. Osteology of Tyrannosaurus rex: insight from a nearly complete skeleton and high resolution computed tomographic analysis of the skull. Society for Vertebrate Paleontology Memoir 7:1-138.
Carlsoo S. 1972. How man moves: kinesiological studies and methods. New York: Crane, Russak & Co.
Christiansen P & Farina RA. 2004. Mass prediction in theropod dinosaurs. Historical Biology 16: 85-92.
Colbert RH. 1962. The weight of dinosaurs. American Museum Novitates 2076:1-16.
Coria RA & Salgado L. 1995. A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature 377: 224-226.
Coria RA & Curie PJ. 2006. A new carcharodontosaurus (Dinosuaria: Therapoda) from the Upper Cretaceous of Argentina. Geodiversitas 28: 78-118.
Dal Sasso C et al. 2005. New information on the skull of the enigmatic theropod Spinosaurus with remarks on its size and affinities. Journal of Vertebrate Paleontology 25: 888-896.
Damuth J & MacFadden BJ. (eds.) 1990. Body size in mammalian paleobiology. Oxford, UK: Cambridge University Press.
Day JJ et al. 2002. Dinoaur locomotion from a new trackway. Nature 415 (6871): 494-495.
Farlow, JO. 1990. Dynamic dinosaurs. Paleobiology 16: 234-241.
Farlow JO, Smith MB & Robinson JM. 1995. Body mass, bone “strength indicators”, and cursorial potential of Tyrannosaurus rex. Journal of Vertebrate Paleontology 15: 713-725.
Floyd, RT. 2004. Manual of structural kinesiology. Boston: McGraw-Hill.
Gans C. 1974. Biomechanics: an approach to vertebrate biology. Philadelphia: Lippincott.
Henderson DM. 1999. Estimating the masses and centers of mass of extinct animals by 3-D mathematical slicing. Paleobiology 25: 88-106.
Henderson DM & Snively E. 2004. Tyrannosaurus rex en pointe : allometry minimized rotational inertia of large carnivorous dinosaurs. Biology Letters 271: s55-s60.
Hirokawa S. 1993. Biomechanics of the knee joint: a critical review. Critical Reviews in Biomedical Engineering 21: 79-135.
Hoyt et al. 2006. What are the relations between mechanics, gait parameters, and energetic in terrestrial locomotion? Journal of Experimental Zoology : Comparative Experimental Biology 305: 912-922.
Henry HT, Ellerby DJ & Marsh RL. 2005. Performance of guinea fowl Numida meleagris during jumping requires storage and release of elastic energy. Journal of Experimental Biology 208: 3293-3302.
Hurlburt G. 1999. Comparison of body mass estimation techniques using recent reptiles and the pelycosaur Edaphosaurus boanerges. Journal of Vertebrate Paleontology 19: 338-350.
Hutchinson JR. 2004. Biomechanical modeling and sensitivity analysis of bipedal running ability. I. Extant data. Journal of Morphology 262: 421-440.
Hutchinson JR. Biomechanical modeling and sensitivity analysis of bipedal running ability. II. Extinct taxa. Journal of Morphology 262: 441-461.
Hutchinson JR et al. 2006. The locomotor kinematics of Asian and African elephants: changes with speed and size. Journal of Experimental Biology 209: 3812-3827.
Hutchinson JR & Garcia M. 2002. Tyrannosaurus was not a fast runner. Nature 415 (6875): 1018-1021.
Irschick DJ & Jayne BC. 1999. Comparative three-dimensional kinematics of the hindlimb for high-speed bipedal and quadrapedal locomotion of lizards. Journal of Experimental Biology 202: 1047-1065.
Irschick DJ & Jayne BC. 1999. A field study of the effects of incline on the escape locomotion of a bipedal lizard, Callisaurus draconoides. Physiological and Biochemical Zoology 72: 44-56.
Irschick DJ & Jayne BC . 2000. Size matters: ontogenetic variation in the three-dimensional kinematics of steady-speed locomotion in the lizard Dipsosaurus dorsalis. Journal of Experimental Biology 203: 2133-2148.
Irschick DJ et al. 2003. Effects of loading and size on maximum power output and gait characteristics in geckos. Journal of Experimental Biology 206: 3923-3934.
Ivanenko YP et al. Modular control of limb movements during human locomotion. Journal of Neuroscience 27: 11149-11161.
Jungers WL. 1984. Aspects of size and scaling in primate biology with special reference to the locomotor skeleton . Yearbook of Physical Anthropology 27: 73-97.
Katchburian MV et al. 2003. Measurement of patellar tracking: assessment and analysis of the literature. Clinical Orthopedics and Related Research 412: 241-259.
Kontulainen SA et al. 2007. The biomechanical basis of bone strength development during growth. Medicine and Sport Science 51: 13-32.
Marchal F. 2000. A new morphometric analysis of the hominid pelvic bone. Journal of Human Evolution 38: 347-365.
Mazzetta GV, Christiansen P & Farina RA. 2004. Giants and bizarres: body sizes of some southern South American Cretaceous dinosaurs. Historical Biology 16: 71-83.
Musahl V. et al. 2002. Biology and biomechanics. Current Opinion in Rheumatology 14: 127-133.
Nummela A, Kreanen T & Mikkelsson LO. 2007. Factors relating to top running speed and economy. International Journal of Sports Medicine. 28: 655-661.
Piazza SJ. 2005. Mechanics of the subtalar joint and its function during walking. Foot and Ankle Clinics 10: 425-442.
Robson Brown KA, Daviews EN & McNally DS. 2002. The angular distribution of vertebral trabeculae in modern humans, chimpanzees, and the Kebara 2 Neanderthal. Journal of Human Evolution 43: 189-205.
Ruff CB. 2003. Long bone articular and diaphyseal structure in Old World monkeys and apes. II: Estimation of body mass. American Journal of Physical Anthropology 120: 16-37.
Sawyer GJ & Maley B. 2005. Neanderthal reconstructed. Anatomical Record B: The New Anatomist 283: 23-31.
Seebacher F. 2001. A new method to calculate allometric length-mass relationships of dinosaurs. Journal of Vertebrate Paleontology 21: 51-60.
Sereno PC et al. 1996. Predatory dinosaurs from the Sahara and the late Cretaceous: faunal differentiation. Science 272: 986-991.
Sereno et al. 1998. A long-snouted predatory dinosaur from Africa and the evolution of the spinsosaurids. Science 282: 1298-1302.
Smith RJ. 1984. Allometric scaling in comparative biology: problems of concept and method. American Journal of Physiology: Regulatory, Intergrative & Comparative 246: r152-r160.
Smith RJ. 1993. Logarithmic transformation bias in allometry. American Journal of Physical Anthropology 90: 215-228.
Spotila JR et al. 1991. Hot and cold running dinosaurs: body size, metabolism, and migration. Modern Geology 16: 203-227.
Sues HD et al. 2002. Irritator challenger, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology 22: 535-547.
Tocheri MW et al. 2005. A 3-D quantitative comparison of trapezium and trapezoid articular and nonarticular surface areas in modern humans and great apes. Journal of Human Evolution49: 570-586.
Weygand PG et al. 2000. Faster running speeds are achieved with greater ground forces not more rapid leg movements. Journal of Applied Physiology 89: 1991-1999.
Woo SL. 2004. Contribution of biomechanics to orthopedics and rehabilitation: the past, present, and furure. Surgeon 2: 125-136.
Woo SL et al. 2006. Biomechanics of knee ligaments: injury, healing, and repair. Journal of Biomechanics 39 (1): 1-20.
Xu X et al. 2007. A gigantic bird-like dinosaur from the late Cretaceous of China. Nature 447: 844-847.
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