99-Million-Year-Old Ammonite Found in Burmese Amber
An international team of paleontologists has found a piece of amber containing the beautifully preserved ammonite, several marine and land organisms that lived 99 million years ago (Cretaceous period).
The ammonite-bearing piece of amber was obtained from a mine located near Noije Bum Village, Tanaing Town, northern Myanmar. It is 33 mm long, 9.5 mm wide, and 29 mm high, and its mass is about 6 g.
The specimen was analyzed by Professor Bo Wang from the Nanjing Institute of Geology and Palaeontology and his colleagues from China, France, the United Kingdom and the United States.
The researchers used X-ray micro-computed tomography to obtain high-resolution 3D images of the ammonite, including its sutures, which are diagnostically important for ammonites.
They found that the ammonite belongs to Puzosia, an ammonite genus that first appeared in the Upper Albian age of the Cretaceous period (between 113 and 100 million years ago) and ranged through the Cenomanian age (between 100 and 94 million years ago).
“The ammonite is a juvenile, has a maximum preserved diameter of 12 mm, and appears to retain the original aragonitic shell, on the basis of its appearance in reflected light,” they said.
“Its presence in the amber supports a late Albian-early Cenomanian age for the amber deposit. This discovery represents a rare example of dating using amber inclusions.”
The team also found at least 40 individuals of arthropods in the amber sample from both land and marine habitats, including crustaceans, mites, spiders and millipedes, and several individuals of insects, including cockroaches, beetles, true flies and wasps.
“But how did the ammonite, an extinct sea-dwelling relative of squid, and other marine creatures get preserved in a piece of amber that also contains land-based animals? The ammonite and sea snail shells offer possible clues,” the paleontologists said.
“The shells are all empty with no soft-tissue, so the organisms were long dead by the time they were engulfed by resin. 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.”
“The most likely explanation is that a sandy beach covered with shells was located close to resin-producing trees. The flying insects were trapped in the resin while it was still on the tree.”
“As the resin flowed down the tree trunk, it trapped organisms that lived near the foot of the tree. Reaching the beach, it entombed shells and trapped the slaters living there.”
The discovery is reported in a paper in the Proceedings of the National Academy of Sciences.
Tingting Yu et al. An ammonite trapped in Burmese amber. PNAS, published online May 13, 2019; doi: 10.1073/pnas.1821292116