ScienceDaily (May 11, 2010) — Why were the sauropod dinosaurs able to get so much larger than today's terrestrial animals? A research group led by the University of Bonn seems to have solved this puzzle. According to this research Jurassic fast food culture was a key to gigantism. The giant dinosaurs did not chew their food -- they just gulped it down. The results of the researchers' years of work are now being published in the journal Biological Reviews.
Giant dinosaurs did not have any molars but gulped down their food like fast food. Only in this way did they have enough time to meet their intense energy demands, a research group led by Professor Martin Sander at the University of Bonn believes. (Credit: Copyright Frank Luerweg, University of Bonn)
Martin Sander is a spokesman for an international research group which is looking for explanations for this and other paradoxes. The Deutsche Forschungsgemeinschaft (German Research Foundation) has funded the project to date with three million euros. Now the scientists involved have presented the fruits of their work on more than 30 pages in Biological Reviews. For the first time, their research is offering a plausible answer to the question which the group sought to answer six years ago: why the giant long-neck dinosaurs were even able to exist. The researchers also explain why today's terrestrial animals are nowhere near reaching the Jurassic size record. One reason is that we chew. Giant dinosaurs gulped.
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P. Martin Sander 1 , Andreas Christian 2 , Marcus Clauss 3 , Regina Fechner 4 , Carole T. Gee 1 , Eva-Maria Griebeler 5 , Hanns-Christian Gunga 6 , Jürgen Hummel 7 , Heinrich Mallison 8 , Steven F. Perry 9 , Holger Preuschoft 10 , Oliver W. M. Rauhut 4 , KristianRemes 1,4 , Thomas Tütken 11 , Oliver Wings 8 and Ulrich Witzel 12
1 Steinmann Institute, Division of Palaeontology, University of Bonn, Nussallee 8, 53115 Bonn, Germany
2 Institut für Biologie und Sachunterricht und ihre Didaktik, University of Flensburg, Auf dem Campus 1, 24943 Flensburg, Germany
3 Clinic for Zoo Animals, Exotic Pets and Wildlife, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland
4 Bayerische Staatssammlung für Paläontologie und Geologie, University of Munich, Richard-Wagner-Strasse 10, 80333 Munich, Germany
5 Institut für Zoologie, Abteilung Ökologie, University of Mainz, Johann-Joachim-Becher Weg 13, 55128 Mainz, Germany
6 Zentrum für Weltraummedizin Berlin, Institut für Physiologie, Charite-University of Berlin, Arnimallee 22, 14195 Berlin, Germany
7 Institut für Tierwissenschaften, University of Bonn, Endenicher Allee 15, 53115 Bonn, Germany
8 Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung an der Humboldt-Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany
9 Institut für Zoologie, Morphologie und Systematik, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
10 Institut für Anatomie, Abteilung für Funktionelle Morphologie, University of Bochum, Universitätsstrasse 150, 44801 Bochum, Germany
11 Steinmann Institute, Division of Mineralogy, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
12 Institut für Konstruktionstechnik, Fakultät für Maschinenbau, University of Bochum, Universitätsstrasse 150, 44801 Bochum, Germany
Correspondence to * E-mail: martin.sander@uni-bonn.de
Re-use of this article is permitted in accordance with the Terms and Conditions set out at http://www3.interscience.wiley.com/authorresources/onlineopen.html
KEYWORDS
Dinosauria • Sauropoda • gigantism • Mesozoic • long neck • phylogenetic heritage • evolutionary innovation
ABSTRACT
The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.
We review the biology of sauropod dinosaurs in detail and posit that sauropod gigantism was made possible by a specific combination of plesiomorphic characters (phylogenetic heritage) and evolutionary innovations at different levels which triggered a remarkable evolutionary cascade. Of these key innovations, the most important probably was the very long neck, the most conspicuous feature of the sauropod bauplan. Compared to other herbivores, the long neck allowed more efficient food uptake than in other large herbivores by covering a much larger feeding envelope and making food accessible that was out of the reach of other herbivores. Sauropods thus must have been able to take up more energy from their environment than other herbivores.
The long neck, in turn, could only evolve because of the small head and the extensive pneumatization of the sauropod axial skeleton, lightening the neck. The small head was possible because food was ingested without mastication. Both mastication and a gastric mill would have limited food uptake rate. Scaling relationships between gastrointestinal tract size and basal metabolic rate (BMR) suggest that sauropods compensated for the lack of particle reduction with long retention times, even at high uptake rates.
The extensive pneumatization of the axial skeleton resulted from the evolution of an avian-style respiratory system, presumably at the base of Saurischia. An avian-style respiratory system would also have lowered the cost of breathing, reduced specific gravity, and may have been important in removing excess body heat. Another crucial innovation inherited from basal dinosaurs was a high BMR. This is required for fueling the high growth rate necessary for a multi-tonne animal to survive to reproductive maturity.
The retention of the plesiomorphic oviparous mode of reproduction appears to have been critical as well, allowing much faster population recovery than in megaherbivore mammals. Sauropods produced numerous but small offspring each season while land mammals show a negative correlation of reproductive output to body size. This permitted lower population densities in sauropods than in megaherbivore mammals but larger individuals.
Our work on sauropod dinosaurs thus informs us about evolutionary limits to body size in other groups of herbivorous terrestrial tetrapods. Ectothermic reptiles are strongly limited by their low BMR, remaining small. Mammals are limited by their extensive mastication and their vivipary, while ornithsichian dinosaurs were only limited by their extensive mastication, having greater average body sizes than mammals.
(Received 9 September 2009; revised 13 March 2010; accepted 16 March 2010)
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