At this point in time, you may well have had enough of articles on the topic of leaving Europe. If that’s the case, you’ll be delighted to know this one is about biogeography and how dinosaurs spread, and has nothing to do with a certain referendum.
Biogeography is the study of species distributions through geological time. It has helped to unravel mysteries like how ostriches, emus and rheas – 3 closely related species of flightless birds – came to live in Africa, Australia and South America respectively. Similar questions vex palaeontologists. So a recent study took a novel approach to understand how dinosaurs spread across the globe during the Mesozoic Era and it found some intriguing patterns.
The Mesozoic Era, which comprised the Triassic, Jurassic and Cretaceous periods, was the age in which dinosaurs roamed the earth. It lasted about 180 million years until it was ended by a large meteor roughly 65 million years ago. During this time the map of the world underwent some pretty major changes. Pangea, the supercontinent made up of all of the world’s major land masses, broke up. First into two, Laurasia (North America, Europe and Asia) and Gondwana (Africa, South America, Australia, Madagascar, India and Antarctica) and eventually into something approaching the world we know today.
All these changes in world geography lead to questions about how and when dinosaur species were able to spread to new areas. Researchers recently tried to answer some of these using a network study for the first time. Network theory involves representing a system as a network of nodes and connections. It has been used in many disciplines from particle physics to biology to sociology but never in this particular field.
This study used fossil records and our knowledge of Mesozoic geography to construct a network. Today’s landmasses were the nodes and connections were established the first time a dinosaur family appeared to spread from one to another. This was the best approach to avoid errors caused by incomplete fossil records for a particular time period or region.
The study made two curious findings. The first was that connections were still being made, albeit at a reduced rate, in the late Cretaceous period when all the continents were separated by oceans and seas. The theory used to explain this finding is that dinosaurs were able to migrate across temporary land bridges. If this sounds implausible to you, remember that this would have happened over tens of millions of years.
To investigate this possibility, another network was constructed with weighted connections between continents. These were based on the depth of the seas separating them. Shallow seas meant strong connections, as this would increase the likelihood of a bridge forming. This network showed a significant correlation with the migration network, lending support to the land bridge theory.
The second unusual finding was that for about 25 million years during the early Cretaceous period all connections involving Europe were outward. This would suggest that during this time there was some kind of exodus from Europe and it has got the scientists flummoxed. Dr Alexander Dunhill, who co-wrote the study, said “This is a curious result that has no concrete explanation. It might be a real migratory pattern or it may be an artefact of the incomplete and sporadic nature of the dinosaur fossil record.”
So, either something very interesting was happening in Europe 125 million years ago or we just need to get digging. Either way this study shows the benefits of thinking outside the box and applying new methods to old questions, you never know what you might discover.
Alexander M. Dunhill, Jordan Bestwick, Holly Narey, James Sciberras.Dinosaur biogeographical structure and Mesozoic continental fragmentation: a network-based approach. Journal of Biogeography, 2016; DOI: 10.1111/jbi.12766
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