Anomalocaridids had blade-like filaments across their backs, which scientists think may have functioned as gills. Credit: Esben Horn.
Fossils from Morocco suggest that these giant shrimp were around much longer and grew bigger than we thought.
Anomalocaridids were already believed to be the biggest creatures during the Cambrian period, with previous specimens measuring up to 2 feet (approximately 60 cm). But thanks to the discovery of some well-preserved fossils in Morocco, palaeontologists from Yale University have discovered that these ancient sea creatures grew to much larger sizes than previously believed.
The team of scientists, led by former Yale researcher Peter Van Roy (now at Ghent University in Belgium) and Derek Briggs, director of the Yale Peabody Museum of Natural History, located an anomalocaridid fossil that measures more than one metre.
The study, published in the journal Nature, also suggests that this marine invertebrate was around for longer than previously believed. Anomalocaridids, distinguished by its spiny head limbs, possibly for catching prey, and the circle of plates at the mouth end, were supposed to have died out at the end of the Cambrian period (540-500 million years ago).
However, the giant anomalocaridid fossil dates back to the early Ordovician period (488-472 million years ago) suggesting that these giant predators were around for 30 million years longer than scientists expected. “The anomalocaridids are one of the most iconic groups of Cambrian animals,” Briggs said in the press release.
“These giant invertebrate predators and scavengers have come to symbolize the unfamiliar morphologies displayed by organisms that branched off early from lineages leading to modern marine animals, and then went extinct. Now we know that they died out much more recently than we thought.”
The new fossils also include thousands of examples of soft-bodied marine fauna from the Ordovician period. Hard tissue, such as shells and bones, fossilises and preserves more readily than soft-tissue, providing scientists with an incomplete view of the Ordovician period.
The animals discovered in Morocco lived on a muddy sea floor in deep water and were trapped by sediment clouds that preserved their softer bodies. “The new discoveries in Morocco indicate that animals characteristic of the Cambrian, such as the anomalocaridids, continued to have a considerable impact on the biodiversity and ecology of marine communities many millions of years later,” Van Roy said in the press release.
