An “extremely rare” marine organism discovered in a 99-million-year-old piece of amber is helping researchers put together what ancient ecosystems once looked like during the time of the dinosaurs.
The fingernail-sized ammonite was found in a hunk of amber along with at least 40 other individual organisms that once lived on land or in the sea during the mid-Cretaceous period. Related to modern squids, the spiral-shelled ancient predator is a rare example of sea life trapped in amber that is only produced by trees on the land.
“Aquatic organisms are rarely found in amber, but when they occur they provide invaluable evidence for the better understanding of amber taphonomy and past ecosystems,” wrote the authors in the Proceedings of the National Academy of Sciences.
High-resolution 3D images obtained through X-ray micro-computed tomography (micro-CT) show that the shell was a juvenile Puzosia (Bhimaites), a subspecies of ammonites with a smooth, whorled shell. But how did a locomotive ancient mollusk wind up in tree resin along with ancient mites, spiders, millipedes, cockroaches, and wasps only found on land? The researchers believe that the resin most likely flowed from a conifer tree that was once found in an estuarine, coastal landscape. As gravity towed seeping resin down the tree, any bugs or land-based animals in its way would have been encased. Eventually, the resin would have reached the beach where it would have surrounded any marine organisms in its path. However, no soft tissue was found in the ammonite shell or four other marine shells also within the amber, indicating that the animals were likely dead by the time they were smothered in resin.
Altogether, the authors note that it helps paint a picture of an ancient landscape in what is now Myanmar.
“Our discovery indicates that the Burmese amber forest was living near a dynamic and shifting coastal environment,” concluded the authors. Holes bored into the amber by marine bivalves suggest that it was still soft when it reached the brackish nearshore environment, further adding to the theory that trees were in close proximity to the shore.
The authors note that dating amber can be controversial because amber pieces can be reworked and redeposited in younger deposits – that’s where the help of preserved marine organisms come into play.
“The amber-bearing strata can be dated from palynofloras, ammonites, and radio-dating evidence, but the amber could be older. Marine inclusions can help date ambers,” wrote the authors. “The present discovery is another interesting example of dating using fossils present inside the amber.”