Ontogeny in Dysalotosurus lettowvorbecki (Dinosauria: Ornithischia)
Final Report Abstract
Ontogeny is a central aspect of the life history of any animal, and understanding of ontogenetic processes is key to our understanding of almost any other aspect of biology, from ecology via taxonomy to evolution. However, in palaeontology, ontogenetic data is usually very limited, since many fossil animals, especially fossil vertebrates, are often known from few or even only a single individual. Thus, the rare occurrence of growth series in fossil vertebrates is of greatest importance for our understanding of the biology and evolution of the respective group. The small to medium-sized ornithopod dinosaur Dysalotosaurus is known from more than 100 individuals of different growth stages that come from a single locality, and is thus an ideal taxon for the study of ontogeny in an ornithischian dinosaur. This project thus had the objective to analyse ontogenetic changes in this dinosaur, using a range of modern techniques, including qualitative anatomical investigations, morphometrics, and bone histology. Furthermore, the results were to be put in an evolutionary context to investigate the affect of ontogeny on the evolution of ornithopod dinosaurs. A re-analysis of the available data on the find of the remains of Dysalotosaurus confirmed that the animals most probably represent a mass-death event of a single population of this taxon. Investigation of the cranial ontogeny of Dysalotosaurus revealed several expected patterns, such as the lengthening of the snout, a relative decrease of the size of the orbit, and an elevation of the posterior skull region. With the lengthening of the snout, the number of teeth increases during ontogeny. Interestingly, many of these changes are also observed in the evolution of ornithopods, in which the generally larger, more derived taxa have longer snouts, relatively smaller orbits, and more teeth than more basal taxa. This indicates that peramorphic heterochronic changes played a major role in the evolution of ornithopod dinosaurs, most probably in connection with an increased adaptation towards a strictly herbivorous diet. In the postcranium, the ossification patterns and rather few changes of proportions of single elements (other than an increased robustness of most elements during ontogeny) indicate that Dysalotosaurus was a precocial animal that showed a reptile-like, indeterminate growth strategy. These findings were supported by the histological studies, which showed no evidence of a cessation of growth in even the largest individuals, but welldeveloped articular ends of the bones of even the smallest animals preserved. The histological analysis indicates that Dysalotosaurus reached sexual maturity rather early in ontogeny, at less than 50 % adult size. Furthermore, bone histology is remarkably variable between different elements of the skeleton and often even between different areas within a single element, indicating that caution is needed when interpreting growth patterns from a single or few histological samples.
Publications
- 2007. Dryosaurus lettowvorbecki – A hoard of options. Hallesches Jahrbuch für Geowissenschaften Beiheft 23: 137-139
Hübner, T. R.
- 2008. Dysalotosaurus lettowvorbecki – Implications of its cranial ontogeny for ornithopod dinosaurs. Journal of Vertebrate Paleontology 28(3): 93A
Hübner, T. R.
- 2009. On the postcranial ontogeny and paleobiology of the ornithopod dinosaur Dysalotosaurus lettowvorbecki. Journal of Vertebrate Paleontology 29(3): 118A
Hübner, T. R.
- 2010. A juvenile skull of Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia) and implications for cranial ontogeny, phylogeny and taxonomy in ornithopod dinosaurs. Zoological Journal of the Linnean Society, 160: 366-396
Hübner, T. R. & Rauhut, O. W. M.
- 2011. Ontogeny in Dysalotosaurus lettowvorbecki. PhD Thesis. Ludwig- Maximilians-Universität München. 318 pp
Hübner, T. R.
