100 million years ago, a coral reef in Northern Spain was providing a comfy home for a diverse variety of little crustaceans called decapods. The order Decapoda consists of crustaceans with ten legs, and includes many of what we consider today to be shellfish delicacies: crabs, lobsters, and shrimp, to name a few. But in prehistoric times, before humans were around to broil or sauté up a decapod dinner, many different species existed who would become the forerunners of modern crustaceans.
From 2008 to 2010, Adiël Klompmaker, a researcher in the Department of Geology at Kent State University and the Florida Museum of Natural History (University of Florida), collected decapod fossils from the abandoned Koskobilo quarry in Spain together with a team of researchers from the U.S., the Netherlands, and Spain. A recent study by Klompmaker published in the journal Cretaceous Research describes eight new crustacean species that were found there. The quarry was once a coral reef; a hotspot of diversity that provided abundant resources for plants and animals that lived in and around it.
Among the 36 species found in the Koskobilo quarry, the researchers uncovered two of the oldest spider crabs yet discovered, Cretamaja granulata and Koskobilius postangustus. Spider crabs are marine crabs with pointed heads, thick bodies, and long, gangly legs. Today, there are nearly 1000 species of spider crabs, representing a good portion of the 15,000 existing decapod species (De Grave ea. 2009). They can vary in size anywhere from less than one centimeter in length (like the European long-beaked spider crab, Macropodia rostrata) to a 13-foot leg-span (Macrocheira kaempferi, the Japanese giant crab.) The discovery in Spain leaned more towards the smaller size: Cretamaja granulata was 15 millimeters in length for the central part of the crab (known as the carapace). The fossil shows it had a pear-shaped carapace from which extended two diverging spines. The discovery lengthened the evolutionary timeline of spider crabs by millions of years.
The reef that accommodated these little crustaceans went extinct ~100 million years ago along with the animals in it. It appears these decapods needed the rich resources the reef provided to live: few of them have been found in the region that date back to after the reef died out. The Koskobilo reef was one of the most diverse and decapod-friendly environments during the Cretaceous period, which lasted from 145 to 66 million years ago. Klompmaker compared the crustacean diversity with that of 19 other areas around the world from Cretaceous period and this reef in Spain housed the most variety of species. The study also provided further evidence that reefs are much more conducive to species diversity than other ocean areas—they have abundant food, places to hide from predators, and nooks and crannies in which organisms can make a home. Fortunately, reefs today also bear a high level of diversity as they did in ancient times, but scientists are still wary about the effects humans and climate change may have on these reefs and the species that live in them.
“Today’s decapods can adapt to a new environment without reefs, migrate elsewhere or go extinct,” Klompmaker said. “By documenting what happened in the past, we may provide clues as to what could happen to decapod crustaceans such as crabs, shrimp and lobsters in today’s deteriorating reefs.”
Adiël Klompmaker of Kent State University and the Florida Museum of Natural History .
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