Discovering a new species is always exciting, but so is finding a living one that everyone assumed had been lost to time. A small clam, previously known only from fossils, was recently found living at Naples Point, just up the coast from UC Santa Barbara. The discovery appears in the journal Zookeys.
“It’s not that common to find a species alive for the first time from the fossil record, especially in an area as well-studied as Southern California,” said co-author Jeff Goddard, a research associate at UC’s Institute of Marine Sciences. Santa Barbara. “Ours doesn’t go anywhere as far back as the famous Coelacanth or the mollusk Neopilina galatheae – which represent an entire class of animals thought to have become extinct 400 million years ago – but it goes back to the time of all these magnificent animals captured by the pits La Brea Tar Pits’.
On an afternoon low tide in November 2018, Goddard was turning over rocks in search of slugs in Naples when a pair of small, translucent bivalves caught his eye. “Their shells were only 10 millimeters long,” he said. “But when they extended and started waving a shiny leg with white stripes longer than their shell, I realized I had never seen this species before.” This surprised Goddard, who has spent decades in California’s intertidal habitats, including many years specifically at Naples Point. He immediately stopped what he was doing to take close-up photos of the intriguing animals.
With quality images in hand, Goddard decided not to collect the animals, which were rarely seen. After determining their taxonomic family, he sent the images to Paul Valentich-Scott, curator emeritus of malacology at the Santa Barbara Museum of Natural History. “I was surprised and intrigued,” Valentich-Scott recalls. “I know this family of bivalves (Galeommatidae) very well along the coast of America. This was something I had never seen before.”
He mentioned a few possibilities to Goddard, but said he would have to see the animal in person to make a proper assessment. So Goddard returned to Naples Point to claim his clam. But after two hours of combing just a few square meters, he still hadn’t realized his prize. The genre would go on to elude him many times over.
Nine trips later, in March 2019, and almost ready to give up for good, Goddard turned over another rock and saw the needle in the haystack: A single specimen, next to a few small white bare branches and a large tunicate. Valentich-Scott would finally get his sample and the pair could finally get to work on identification.
Valentich-Scott was even more surprised when he put his hands on the shell. He knew it belonged to a genus with a member in the Santa Barbara area, but this shell didn’t match any of them. It raised the exciting possibility that they had found a new species.
“That really started the ‘hunt’ for me,” Valentich-Scott said. “When I suspect something is a new species, I have to go through all the scientific literature from 1758 to the present day. It can be a daunting task, but with experience it can go pretty quickly.”
The two researchers decided to check an interesting reference to a fossil species. They located images of Bornia bivalve from the paper describing the species in 1937. It appeared to match the modern specimen. If confirmed, this would mean that Goddard had not found a new species, but a living fossil species.
It is worth noting that the scientist who described the species, George Willett, estimated that he had excavated and examined perhaps 1 million fossils from the same site, Baldwin Hills in Los Angeles. That said, he never found B. cooki itself. Instead, he named it after Edna Cook, a Baldwin Hills collector who had found the only two known specimens.
Valentich-Scott requested Willett’s original specimen (now classified as Cymatioa cooki) from the Natural History Museum of Los Angeles County. This object, called the “type specimen,” serves to define the species, so it is the ultimate judge of clam identification.
Meanwhile, Goddard found another specimen at Naples Point – a single empty shell in the sand under a boulder. After carefully comparing the specimens from Naples Point with Willett’s fossil, Valentich-Scott concluded that they were the same species. “It was quite remarkable,” he recalls.
Despite its small size and cryptic habitat, all of this raises the question of how the clam escaped detection for so long. “There’s such a long history of shell collecting and molluscology in Southern California — including people interested in the more elusive micromolluscs — that it’s hard to believe that no one has even found our little cutie’s shells,” Goddard said.
He suspects the clams may have arrived here in currents as planktonic larvae, transported from the south during the marine heatwaves of 2014 to 2016. These allowed many marine species to expand their distributions northward, including several that were specifically documented at Naples Point. Depending on the animal’s growth rate and longevity, this could explain why no one had observed C. cooki at the site before 2018, including Goddard, who has been working on bare branches at Naples Point since 2002.
“The Pacific coast of Baja California has large fields of tidal boulders that stretch literally for miles,” Goddard said, “and I suspect that down there the Cymatioa biscuit probably lives in close association with animals that burrow under those boulders.
Paul Valentich-Scott et al, A fossil species found living in southern California, with notes on the genus Cymatioa (Mollusca, Bivalvia, Galeommatoidea), ZooKeys (2022). DOI: 10.3897/zookeys.1128.95139
Provided by University of California – Santa Barbara
Reference: Rare fossil clam discovered alive (2022, November 7) retrieved November 8, 2022 from https://phys.org/news/2022-11-rare-fossil-clam-alive.html
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