Published on December 2nd, 2021 | by David Marshall
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Episode 131/132: Burmese Amber Pt1
Burmese amber is well known for preserving fossils in exquisite details. This amber is dated to around 100 million years old, representing the Albian – Cenomanian ages of the Cretaceous period, so would have been deposited whilst non-avian dinosaurs still walked the land.
Fossils preserved in this amber include representatives from numerous different groups including arachnids, insects, vertebrates, and plants. Whilst the amber itself (as fossilised tree sap/resin) is produced in a terrestrial environment, some marine species have been caught up in amber. This includes such animals as ostracods, snails and surprisingly even an ammonite!
In the first part of this series, we speak to Dr Javier Luque, Harvard University, about the discovery of a crab in amber. We put this discovery in context by first examining what crabs are, before turning our attention to their fossil record. In the next episode, we’ll take a look at the details of the discovery.
Following on from this, we will discuss the political situation in Myanmar and question whether or not working with Burmese amber is currently ethical.
Modern and fossil crabs can live in a number of environments from marine to freshwater and even terrestrial.Some species of crabs can be completely terrestrial as adults, whilst others, such as the arboreal crab, even live on and around trees! Wherever a crab lives, it is important to remember that habitat and even shape doesn’t remain constant throughout its life. During ontogeny (growth to adult form), crabs can go through radical metamorphosis, taking on shapes (morphology) and lifestyles (ecologies) completely different from their adult form.
The Christmas Island red crab is an excellent example of this. This crab is entirely terrestrial, but will lay its eggs in the sea. There the larvae develop through different phases before making the transition back onto land as young crabs.
Megalope stage of the Christmas Island red crab. This instar is still aquatic and looks different to the final adult form. This stage of growth in other species may look even more different to the adult. Image: Chook keeper CC BY-SA 4.0. We find the first fossils of brachyurans (true crabs) in the Jurassic, but the Cretaceous period saw the origins of numerous new crabs during a great ‘Cretaceous crab revolution’. Image: Luque et. al. 2021. Such species from this time include Callichimaera perplexa, which looks fairly bizarre relative to modern crabs.Reconstruction of Callichimaera perplexa. Image: Oksana Vernygora.
Burmese amber is found in Northern Myanmar where it is commercially mined for jewellery and for its fossil inclusions. It can be a lucrative business for dealers, but the return of conflict in 2017 raises ethical questions as to the study of newly excavated specimens. Image: Miners digging and sorting Burmese amber at Noije Bum in the Hukawng Valley in Kachin State. Credit: Sieghard Ellenberger CC BY 2.0Before the most recent political turmoil, a fossil crab measuring just 5mm across (about the size of a lentil) was discovered in amber. Image: Lida Xing (China University of Geosciences, Beijing).The fossil was named Cretapsara athanata which translates as ‘the immortal Cretaceous spirit of the clouds and waters’. Image: Luque et. al. 2021.The fossil is complete, 3D and preserves amazing detail. This indicates that it was entombed in amber whilst still alive. These images were produced using a CT scanner, similar to those used in hospitals. Image: Luque et. al. 2021.The CT scanning was even able to reveal details of the gills within the body of the crabs.
Cretapsara athanata is an incredibly significant fossil. Not only is it the best preserved fossil crab to date, but it is the earliest data point we have for piecing together the terrestrialisation of crabs. If you look at the family tree of the true crabs and their habitats, it is the first crab seen in the fossil record to live in an environment with freshwater influence. The fact it is preserved in fossilised tree resin gives it a very close association to the terrestrial realm. Reconstruction of Cretapsara athanata in an amphibious freshwater habitat. Image: Franz Anthony.Dr Javier Luque in the field looking for Cretaceous crabs. Image: Daniel Ocampo R. (Vencejo Films).Javier collecting fossils in the field.
Unless otherwise stated, images are courtesy of Dr Javier Luque.
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