Words By Sam Ashby
In a first for palaeontology, new fossil findings suggest some dinosaurs migrated across oceans to reach Triassic Africa.
Our knowledge on the distribution and behaviour of extinct species is constantly changing. Recent findings in palaeobiology include new species of seals and walruses, and a review of shark fossils at Brighton’s Booth Museum revealed a new species of toothless pterosaur. Perhaps the most notable discovery this month, however, suggests some dinosaurs may have been adept swimmers.
In their 2020 paper, Longrich et al. describe the fossilised remains of a new hadrosaur in Morocco. Hadrosaurs, of the family Hadrosauridae, were large, herbivorous ornithischians that inhabited North American and Central European woodlands. Referring to enlarged rostral bones and a flattened snout, hadrosaurs are often termed the duckbilled dinosaurs (Figure 1).
The findings have been attributed to the late Maastrichtian age of the late Cretaceous period (66 to 72 million years ago). Most peculiar about this finding, was its location. Previous palaeontological findings concluded hadrosaur distribution to be limited to Laurasia, a Triassic supercontinent incorporating North America and Asia. Gondwana, made up of today’s Africa, South America, Australasia, and Antarctica, was dominated by sauropod herbivores and ‘pug-faced’ carnivores (such as carnotaurus and majungasaurus).
Gondwanan Africa was an island with no land masses known to connect with Laurasia. With no previous records of hadrosaurid remains found in Africa, and no evidence suggesting land bridges, Longrich et al. were faced with the most parsimonious explanation. In scientific research, parsimony refers to the ideal that the simplest explanation should be accepted. In this case, the only feasible, albeit highly improbable, solution is aquatic migration.
Migration via drifting on debris might pose an alternative explanation, but this has only been observed in much smaller species. In fact, duckbills may have been quite capable of swimming long distances; other hadrosaurs of the sub-family Lambeosaurinae possessed large, camel-like, padded feet with crude webbing and a prehensile tail strengthened by lateral tendons.
Despite their aquatic capabilities, aquatic A. odysseus migration may not have occurred had it not been for ideal currents of the Tethys Sea (Figure 2). Nonetheless, these hadrosaurs may have swum 500km along this route.
Dr Nicholas Longrich of the University of Bath’s Milner Centre for Evolution, described these fossils as “about the last thing in the world you would expect, … completely out of place, like finding a kangaroo in Scotland.”
In their paper published in Cretaceous Research, Longrich et al. conclude their research: “ocean dispersal, no matter how improbable, becomes the only viable hypothesis. Importantly, over millions of years, highly improbable, once-in-million-years events become likely, even probable”. The nomenclature of this novel species, Ajnabia odysseus, alludes to its unexpected discovery; the Arabic term “Ajnabi” translating to “foreigner” with Odysseus, the ancient Greek idol, also renown for an impressive journey overseas.
References:
Long, N.R., Suberbiola, X.P., Pyron, R.A. & Jalil, N. (2020) The first duckbill dinosaur (Hadrosauridae: Lambeosauridae) from Africa and the role of oceanic dispersal in dinosaur biogeography. Cretaceous Research, doi: 10.1016/j.cretres.2020.104678.
Mateo, P., Keller, G., Punekar, J. & Spangenberg, J.E. (2017) Early to late Maastrichtian environmental changes in the Indian Ocean compared with Tethys and South Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology, 478, 121-38.
