This ancient sea creature fossilized in tree resin. How'd that happen?
In what may be a first of its kind, a lump of amber has preserved the shell of an ammonite and other shoreline life in stunning detail.
Ninety-nine million years ago in what's now Myanmar, a glob of tree resin oozed onto a beach. Today, the resulting fossilized lump of amber is giving scientists an astonishing glimpse into life on a Cretaceous coastline.
In a study published Monday in the journal PNAS, researchers led by Chinese paleontologist Tingting Yu reveal what is likely the first known record of an ammonite found in amber. These extinct marine mollusks were ancient relatives of octopuses and squid, and they didn't venture on land. Finding an ammonite shell in a land-formed fossil is therefore as eyebrow-raising as finding dinosaur remains on the bottom of an ancient seafloor.
“Amber—ancient resins from trees—commonly traps only some terrestrial insects, plants, or animals,” says study coauthor Bo Wang, a paleontologist at the Nanjing Institute of Geology and Paleontology. “It’s very rare to find some sea animals in amber.”
Researchers suspect that this resin came from a tree on the shoreline, and that it picked up a discarded ammonite shell and other flotsam as it tumbled into the sand. The fossil also contains other aquatic life—marine snails and relatives of today's pillbugs—as well as denizens of the coastal forest's leaf litter, including mites, flies, beetles, a spider, a parasitic wasp, a millipede, and a cockroach.
“This extraordinary assemblage, a true and beautiful snapshot of a beach in the Cretaceous, is just mind-blowing,” says Jann Vendetti, a paleontologist at the Natural History Museum of Los Angeles County who wasn't involved with the study. While the ammonite is perhaps the most visibly startling find, the real treasure may be having such diversity of life in a single sample from this time period.
“The idea that there’s a whole community of organisms in association—that may prove more important in the long run,” adds study coauthor David Dilcher, a paleontologist and emeritus professor at Indiana University Bloomington.
Shell of a find
The study is the latest to shed light on the ammonites, a group of shelled mollusks that lived during the age of dinosaurs, with roots going back to more than 400 million years ago. The group died out 66 million years ago alongside the nonavian dinosaurs, but by that time, they had achieved global distribution and had become dazzlingly diverse. Like their modern mollusk cousins, ammonite species probably adapted to living at many depths—and came in many sizes. Some stayed just a fraction of an inch wide, while other kraken-like giants grew to more than eight feet across.
If you had goggles, flippers, and a time machine, you'd likely see ammonites everywhere in Cretaceous waters, bobbing through ancient coral reefs alongside fish and marine reptiles, such as the dolphin-like ichthyosaurs and large mosasaurs.
“If you were scuba-diving in a shallow marine setting, you absolutely would have seen ammonites,” says Jocelyn Sessa, a paleontologist at Drexel University who specializes in fossil mollusks. “They would be as common as seeing some snails crawling around.”
High-resolution scans revealed the ammonite's internal structure. Researchers think the ammonite belongs to the subgenus Puzosia (Bhimaites), which emerged more than a hundred million years ago and lived until at least 93 million years ago.