Australasian Science Magazine

By John Long

New techniques are enabling palaeontologists to test hypotheses about major evolutionary transitions.

Recently I spent a few days working with my colleagues at the Australian Synchrotron in Melbourne. We used the facility to get clear 3-D images of our ancient fossil fishes for various research projects. The facility is costly to run, so we utilised the time around the clock, with specimens being changed at all hours of the night to maximise our allocated beam time.

Finally near the end of the 48-hour session, we were almost done. Our last specimen, a 380-million-year-old placoderm fish male’s reproductive clasper, was scanned to the rousing chorus of Beethoven’s Ninth Symphony in the wee hours of the night to much rejoicing by the team.

This approach to research is not new to palaeontology, but an emerging trend in which cutting-edge techniques are increasingly used to extract whole new layers of information from fossils. They can potentially result in exciting and unexpected discoveries.

The incredible fossilised sperm preserved in 16-million-year-old Riversleigh ostracods reported in this column in July was revealed though synchrotron scanning . The synchrotron, though, is really just an elaborate method of imaging fossils in high resolution 3D formats, but other new technologies are now available that enable us to take fossils or data derived from them in exciting new directions.

Two recent palaeontology papers demonstrate how the use of new methods is just as important as finding spectacular new fossils in order to turn palaeontological research from the domain of the interested specialist into a major international breakthrough in science.

Much of mammalian evolution is a based upon fossil teeth and their highly characteristic patterns. A landmark article published in Nature in August by a team of international researchers led by Enni Harjunmaa from Helsinki University, and including Dr Alistair Evans from Monash University, showed that experiments on the development of mammalian teeth can be used to test hypotheses about major evolutionary transitions. By mutating mouse teeth through inserting certain proteins at a particular stage of the isolated tooth’s growth (artificially grown in a petri dish), the teeth would develop with particularly unusual molar patterns. With this technique, experiments can now be designed to test major evolutionary trends in mammalian evolution.

The significance can be easily grasped when in vivo inhibition of certain homeobox gene signals in modern rodent teeth reproduce the same patterns seen only in fossil rodent teeth. This helps to determine the direction of the evolutionary trends, and enables novel interpretations of the significance of patterns in fossil mammal teeth.

Another paper in Science in August shows a truly remarkable trend in dinosaur evolution that helps us better understand the transition from theropod dinosaurs to birds. The research did not involve any field work but undertook an enormous amount of coding of skeletal features from many kinds of dinosaurs and fossil birds. Led by Dr Mike Lee of the South Australian Museum (see pp.20–22) and involving a team of international collaborators, it used a totally new approach to phylogenetic analysis by fine tuning an existing algorithm commonly used in molecular biology with additional code written specifically to tackle palaeontological data sets. The resulting analysis involved some 1529 morphological characters coded for 120 different species of dinosaurs and early birds: with two or three variable states on each coding, that’s up to half a million variable states to be manually coded!

Their research showed that body size in dinosaurs is highly conserved within the theropods, and that the closest theropod relatives to birds get smaller towards the transition. Branches along the line leading to birds then underwent an explosion of morphological characters compared with the rest of the tree. The rates of early bird evolution were calculated to be four times faster than the branching of dinosaur species along the overall tree.

Such methodologies are revolutionary in palaeontology. They allow us to go back and reanalyse many of the major transitions in the evolution of life, and determine the rates of evolution and isolate the potential prime drivers of such events.

I look forward to seeing what will be the next big thing in palaeontology given these new methods are now published and available for other research groups to build upon.

John Long is Strategic Professor in Palaeontology at Flinders University.