All the shells from marine creatures are empty, so the organisms were long dead by the time they were engulfed; the outer shell of the ammonite is broken away and the entrance of the shell is full of sand. The amber also contains additional sand.
“There is a diverse assemblage (at least 40 individuals) of arthropods in this amber sample from both terrestrial and marine habitats, including Isopoda, Acari (mites), Araneae (spiders), Diplopoda (millipedes), and representatives of the insect orders Blattodea (cockroaches), Coleoptera (beetles), Diptera (true flies), and Hymenoptera (wasps). The incomplete preservation and lack of soft body of the ammonite and marine gastropods suggest that they were dead and underwent abrasion on the seashore before entombment,” researchers write.
The most plausible scenario is that the resin-producing tree lay on or right next to a sandy beach. The flying insects were trapped in amber while it was still on the tree, flying too close and getting stuck. As the resin slowly flowed down the tree trunk, it trapped more and more organisms. As it reached the floor, it finally encased some unfortunate marine creatures that were washed ashore.
“The shells may record an exceptionally high, perhaps storm-generated tide, or even a tsunami or other high-energy event. Alternatively, and more likely, the resin fell to the beach from coastal trees, picking up terrestrial arthropods and beach shells and, exceptionally, surviving the high-energy beach environment to be preserved as amber,” researchers write.
At any rate, it was a spectacular chain of events that culminated with just the right conditions to preserve this stunning piece of amber for about a hundred million years.
It’s not exactly clear how old the piece of amber is. Researchers suspect it is 99 million years old since that is the date of the layer it was found in, but it could be even older.
The team also used X-ray micro-computed tomography (micro-CT) to obtain high-resolution three-dimensional images of the ammonite including its convoluted shell sutures, which are very important for determining the species of ammonite.
The study “An ammonite trapped in Burmese amber” was published in Proceedings of the National Academy of Sciences