Work news

[Lt. Killer M]

Long overdue, it is now time for me to bore you all the near-death with my work. DINOSAURS!



Yesterday, a very (!) short summary of the results of our Research Group appeared in Science:

Sauropod Gigantism

How did sauropod dinosaurs reach body sizes that remain unsurpassed in land-living animals?
P. M. Sander & M. Clauss


Sauropod dinosaurs were the largest animals ever to inhabit the land (see the figure). At estimated maximum body masses of 50 to 80 metric tons, they surpassed the largest terrestrial mammals and nonsauropod dinosaurs by an order of magnitude. With body lengths of more than 40 m and heights of more than 17 m, their linear dimensions also remain unique in the animal kingdom. From their beginnings in the Late Triassic (about 210 million years ago), sauropods diversified into about 120 known genera. They dominated ecosystems for more than 100 million years from the Middle Jurassic to the end of the Cretaceous, setting a record that mammalian herbivores will only match if they can double their current geological survival time. Thus, sauropods were not only gigantic but also, in evolutionary terms, very successful. Recent advances bring us closer to understanding the enigma of their gigantism (1–3). Extrinsic causes have repeatedly been advanced to explain the success of sauropod dinosaurs and the gigantism seen in the dinosaur era. However, physical and chemical conditions in the Mesozoic (250 to 65 million years ago) were probably less favorable for plant and animal life than they are today; for example, atmospheric O2 concentrations were much lower (4). The variation of other factors (such as land mass size, ambient temperature, and atmospheric CO2 concentrations) through time is not tracked by variations in sauropod body size (2,5). Thus, the clue to sauropod gigantism must lie in their unusual biology (see the figure). Sauropods had an elephantine body supported by four columnar legs and ending in a long tail. From the body arose a long neck bearing a small skull. Sauropods exhibit diverse oral, dental, and neck designs, indicating dietary niche differentiation; this variety makes reliance on any particular food source (6) as the reason for gigantism unlikely. However, one evolutionarily primitive character truly sets sauropods apart: In contrast to mammals and advanced bird-hipped dinosaurs (duck-billed and horned dinosaurs), they did not masticate their food; nor did they grind it in a gastric mill, as did some other herbivorous dinosaurs (7). Because gut capacity increases with body mass (8), the enormous gut capacity of sauropods would have guaranteed the long digestion times (6) necessary
for degrading unchewed plant parts, even at a relatively high food intake. The lack of a masticatory apparatus allowed sauropod heads to remain small and was one rerequisite for their long neck to evolve. This neck would ave provided access to food out of reach of other animals (9) with little foraging movement of the whole body, while probably also functioning as a display organ and hence being subject to runaway sexual selection (10). In herbivorous mammals and evolutionarily advanced bird-hipped dinosaurs, in contrast, a disproportionate evolutionary increase in the size of the head and the masticatory apparatus relative to the rest of the body set a mechanical limit to the evolution of very long necks. In addition, the vulnerability of a long neck (10) makes its evolution unlikely without protection from predation by superior body size. The long neck and large body size pose particular physiological problems. Large body size in endothermic animals is associated with a major problem of dissipating excess body heat. A long neck also means that a large volume of air must be moved in the windpipe during ventilation before fresh air reaches the lung. These problems appear to have been solved by an evolutionary innovation shared by sauropods and theropods (meat-eating dinosaurs) and their descendants, the birds: a highly heterogeneous avian-style respiratory system (11) with cross-current gas exchange in the lung and air sacs that pneumatized the vertebrae of the neck and the trunk and filled large parts of the body cavity. Compared to mammalian or reptilian lungs, this system overcame the problem of the long windpipe of sauropods (11) and also probably helped to dissipate excess body heat via the visceral air sac surfaces (11, 12). For selective advantages conferred by large body size to be effective (13), this large body size must be reached quickly by the individual. Uniquely among amniotes, sauropods grew through five orders of magnitude from a 10-kg hatchling to a 100,000-kg fully grown individual. Bone histological evidence indicates that this growth took place at rates comparable to those of large terrestrial mammals (14, 15); reproductive maturity was reached in the second decade of life and full size in the third decade of life (15), as predicted from demographic models that show higher ages at first reproduction to be incompatible with long-term population persistence (16). Such high growth rates are seen only in animals with a basal metabolic rate (BMR) of mammals and birds (17). For sauropods, rather than assuming a constant metabolic rate throughout the animals’ life, an ontogenetic decrease in BMR has been suggested (12, 18). Such a decrease would reconcile rapid growth rates in juveniles with problems resulting from gigantic body size (such as overheating and high food requirements) in adults. Considering the costs of a high BMR, it may have evolved early on in sauropods, as an adaptation for the high growth rates necessary for reaching very large body size. At the population level, egg-laying and the associated production of many small offspring (19), in contrast to the one-offspring strategy of mammalian megaherbivores, is a key characteristic of sauropod reproductive biology and of the dinosaur ecosystem (20, 21). This strategy may have guaranteed longterm survival of gigantic species (20). In mammals, large body size increases the risk of chance extinction by reducing population density and increasing population recovery time: With increasing body size, fewer offspring are produced, and these take longer to mature. The retention of the primitive feature of egg-laying might have alleviated this constraint through much higher population recovery rates than in large mammals (21). Thus, we suggest that the unique gigantism of sauropods was made possible by a combination of phylogenetic heritage (lack of mastication, egg-laying) and a cascade of evolutionary innovations (high growth rate, avian-style respiratory system, and a flexible metabolic rate). Although modern mammals evolved a high growth rate independently, the comparison with sauropods identifies the mastication of food (inherited from small insectivorous ancestors), overheating caused by an inadequate cooling mechanism, and giving birth to live offspring as the major factors limiting the potential body size of mammalian herbivores (see the figure). Recent modeling studies found a high metabolic rate to be incompatible with gigantic body size because of the problem of heat dissipation (22, 23); however, these models assumed metabolic rate to have remained constant throughout life. In addition, one of the studies (23) suffers from poor bone histologic constraints on sauropod growth rates, as does a study (24) arguing against fast growth in sauropods. Compared to other dinosaurs, the long bones of sauropods rarely preserve growth marks, probably because bone tissue was deposited too rapidly to record them (15). Histologic growth rate studies using skeletal elements other than long bones may provide more reliable estimates. Theropod dinosaurs such as Tyrannosaurus rex are similarly outsized compared to mammalian carnivores (1) as sauropods are compared to mammalian herbivores. Thus, there may be links between sauropod gigantism and meat-eating dinosaur gigantism. One such link may be the mode of reproduction. Egg-laying of sauropods must have made large amounts of food available to predators in the form of many small, little-protected young sauropods. In contrast, mammalian megaherbivors withhold this food source from carnivores by rearing very few, well-protected offspring. This greatly decreased resource base may limit maximum body size of carnivores today (21). Further progress in understanding dinosaur gigantism will come from a conservation biology approach that models the carrying capacity of Mesozoic ecosystems based on the juvenile-biased population structure of dinosaurs (19, 20). Such an approach, which goes beyond the reconstruction of an individual’s metabolism (14, 15, 22, 23), will be much more informative regarding resource limitations, population growth potential, and body size evolution of dinosaurs.

[Lt. Killer M]

References and Notes
1. G. P. Burness, J. Diamond, T. Flannery, Proc. Natl. Acad.
Sci. U.S.A. 98, 14518 (2001).
2. M. T. Carrano, in Amniote Paleobiology: Perspectives on
the Evolution of Mammals, Birds, and Reptiles, M. T. Carrano, R. W. Blob, T. J. Gaudin, J. R. Wible, Eds. (Univ.
of Chicago Press, Chicago, 2006), pp. 225–268.
3. P. M. Sander, O. Mateus, T. Laven, N. Knötschke, Nature
441, 739 (2006).
4. R. Berner, J. M. VandenBrooks, P. D. Ward, Science 316,
557 (2007).
5. D. W. E. Hone, T. M. Keesey, D. Pisani, A. Purvis, J. Evol.
Biol. 18, 587 (2005).
6. J. Hummel et al., Proc. R. Soc. B 275, 1015 (2008).
7. O. Wings, P. M. Sander, Proc. R. Soc. B 274, 635 (2007).
8. M. Clauss, A. Schwarm, S. Ortmann, W. J. Streich, J.
Hummel, Comp. Biochem. Physiol. A 148, 249 (2007).
9. A. Christian, G. Dzemski, Fossil Rec. 10, 38 (2007).
10. P. Senter, J. Zool. 271, 45 (2007).
11. M. J. Wedel, Paleobiology 29, 243 (2003).
12. S. F. Perry, A. Christian, T. Breuer, N. Pajor, J. R. Codd,
J. Exp. Zool. A.
13. L. N. Cooper, A. H. Lee, M. L. Taper, J. R. Horner, Proc. R. Soc. B, 10.1098/rspb.2008.0912 (2008).
14. G. M. Erickson, K. C. Rogers, S. A. Yerby, Nature 412, 429 (2001).
15. P. M. Sander, Paleobiology 26, 466 (2000).
16. A. E. Dunham, K. L. Overall, W. P. Porter, C. A. Forster, in Paleobiology of the Dinosaurs. GSA Special Paper 238,
J. O. Farlow, Ed. (Geological Society of America, Boulder,
CO, 1989), pp. 1–21.
17. T. J. Case, Q. Rev. Biol. 53, 243 (1978).
18. J. O. Farlow, in The Dinosauria. 1st Edition, D. B.
Weishampel, P. Dodson, H. Osmolska, Eds. (Univ. of California Press, Berkeley, CA, 1990), pp. 43–55.
19. P. M. Sander, C. Peitz, F. D. Jackson, L. M. Chiappe,
Palaeontographica A 284, 69 (2008).
20. C. M. Janis, M. Carrano, Acta Zool. Fenn. 28, 201 (1992).
21. J. Hummel, M. Clauss, Evol. Ecol. Res. 10, 925 (2008).
22. F. Seebacher, Paleobiology 28, 105 (2003).
23. J. F. Gillooly, A. P. Allen, E. L. Charnov, PLoS Biol. 4, 467 (2006).
24. T. M. Lehman, H. N. Woodward, Paleobiology 34, 264
(2008).
25. The research of P.M.S. and M.C. was supported by the
German Research Foundation (grant FOR 533). This is
contribution number 46 of the DFG Research Unit 533
”Biology of the Sauropod Dinosaurs: The Evolution of
Gigantism.“

Sorry, c&p means that the formatting went to ape-shit.

Also, a nice figure in the paper that I can't upload atm.

[mauer]

Yeah, I was going to read it.

However, it didn't have the nice breaks between sentences or paragraphs.

I could not be arsed.

Thank you sir for you effort.

[akots]

I can quietly e-mail pdf to anyone interested, just let me know.

Nice paper , cannot be arsed to understand it thoroughly though.

[Beam]

If I read it well BMR is a key factor for this gigantism giving enough time? Has any Sloth read this paper?

[socralynnek]

Does the last paragraph mean that you are simulating Jurassic Park or that you are building it...? ;-)

Sounds interesting although I guess I didn't understand some parts correctly.

But dinosaurs are cool!

[Pastorius]

Aaaaaa! Wall of text


RUN FOR YOUR LIVES!

[Lt. Killer M]

sorry, mauer, but I could not be arsed to reformat it when all it takes is a PM:

PM me (or akots) for the PDF, obviously


I wish we could build Jurassic Park, but all that is possible is a complex simulation.

[digger760]

Explain this sentance a bit more:
"This neck would ave provided access to food out of reach of other animals (9) with little foraging movement of the whole body, while probably also functioning as a display organ and hence being subject to runaway sexual selection"

in particular what runaway sexual selction means.

I'd also like to point out the typo "ave".... very uncharacteristic of you killer.

It is infact quite an intersting read.

[grahamiam]

Nice read. I'll take a pdf as I'd like to see the figures. Thanks!