Admissions > PhD by research > Research Projects > Origin and early evolution of the vertebrate skeleton

Origin and early evolution of the vertebrate skeleton

Supervisor: Professor Philip Donoghue

 The skeleton represents one of the few defining characters of vertebrates (1) and yet relatively little is known concerning its early evolution. In large part, this is because the organisms in which the skeleton first evolved are now long extinct and have no descendents that could serve as suitable proxies for study. However, because the skeleton is invariably mineralized it is predisposed to fossilization, such that there is an abundant fossil record of the extinct groups in which the vertebrate skeleton, as we known it from sharks, bony fishes, tetrapods and humans, was established as an embryological and structural entity. This fossil record has been the subject of long term study, but it has only recently begun to be interpreted in light of embryological principles and phylogenetic hypotheses (2-4).

Although the vertebrate skeleton is generally considered to be a single coherent system, it is actually a chimaera of a number of distinct systems that have their own embryological and evolutionary histories. Much has been learned about the evolution of the skull from histological study its extensive fossil record (4), but the evolution of component tissues, such as bone, cartilage, enamel and dentine, remain poorly understood, for wont of appropriate methods of analysis. Furthermore, and perhaps somewhat paradoxically, almost nothing is known about the evolution of that most characteristic of vertebrate characters, the vertebral skeleton and its associated endoskeleton. In large part, this occurs because the vertebral skeleton is the last major system of the vertebrate skeleton to emerge within vertebrate phylogeny (5).

 The project will entail the anatomical and histological study of dermoskeletal, endoskeletal and vertebral elements among the stem-gnathostomes, a spectrum of jawless and jawed vertebrates that represent the first vertebrates to possess skeletal tissues and which record the sequential assembly of the entire vertebrate skeleton (4, 6).  The tissues comprising the skeleton will be compared to dermoskeletal and endoskeletal tissues in living jawed fishes, such as the sharks, rays and boney fishes. Methods of analysis will include conventional thin-sectioning and analysis using light and scanning electron microscopy. However, a substantial focus of the project will be the use of synchrotron radiation X-ray tomographic microscopy (SRXTM) – a state-of-the-art and high resolution alternative to medical CT scanning that generates virtual computer models of the tissues that can be dissected as effectively as the tissues of living animals (7).

 The results of this study will provide the first comprehensive understanding of vertebrate skeletal tissues and of the the evolution of the vertebrate endoskeleton, its homologies to endoskeletal structures in living osteichthyans (bony fishes, including ourselves), and evolution of the tissues comprising the endoskeleton. As such, it will be of relevance to palaeontologists, skeletal anatomists and developmental biologists, with whom the student could actively integrate, should they so wish. 

Training

Training will be provided, the operation of light and scanning electron microscopes, and of SRXTM. Training will be provided in in histological techniques and methods of conventional light and scanning electron microscopy, SRXTM and computed tomography. In addition to preparing the student for a career in palaeontology and evolutionary biology, it will provide additional transferable technical skills that would be of benefit within any future scientific or computationally-based career.

 References

  1. A. Graham, Current Biology 14, R956 (2004).
  2. M. M. Smith, B. K. Hall, Biological Reviews 65, 277 (1990).
  3. P. C. J. Donoghue, I. J. Sansom, J. P. Downs, Journal of Experimental Zoology - Part B: Molecular and Developmental Evolution 306B, 278 (2006).
  4. P. C. J. Donoghue, I. J. Sansom, Microscopy Research & Technique 59, 352 (2002).
  5. C. Gans, R. G. Northcutt, Science 220, 268 (1983).
  6. P. C. J. Donoghue, M. A. Purnell, Trends in Ecology & Evolution 20, 312 (2005).
  7. P. C. J. Donoghue et al., Nature 442, 680 (Aug, 2006).

 

Last updated: 1/11/11