A species of clam thought to have been extinct for 40,000 years has been found alive

spécimen vivant espèce fossile

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A bivalve mollusc, bapt Simatio cookie, until now only known from Pleistocene fossils. But this tiny clam was recently found alive on a sandy beach off the coast of California.

In November 2018, Jeff Goddard, a research associate at UC Santa Barbara’s Marine Science Institute, came face-to-face with the enigmatic pair of tiny translucent bivalves while searching for sea snails at low tide off the coast of Naples Point. The latter has a shell that is just 10 millimeters long and has a long base with white and shiny stripes. Although southern California bivalve molluscs have been widely studied and documented, Goddard had never encountered this species before.

After taking several pictures of these animals, without disturbing them unnecessarily, he sent these photos to Paul Walendych-Scott, curator emeritus of malacology at the Santa Barbara Museum of Natural History, who was just as amazed as he was. ” I am familiar with this family of bivalves (Galeommatidae) of the coast of America. That’s something I’ve never seen before », He says. Photos are not enough to identify the animal with certainty, it is necessary to capture it to examine it more closely. But months later, after many attempts, Goddard found this strange mollusk specimen.

Similarities in a fossil record

Both researchers were able to begin their identification work. The animal’s particularly distinctive shell raised the possibility that it was a previously undescribed new species. To verify this, Wallendych-Scott carefully examined all scientific literature published from 1758 to the present day. A fossil species, Described in 1937It caught the attention of two researchers in particular.

Sample Simatio cookie
Lateral (A) and ventral (B) view of live specimen taken at Naples Point (length: 7.4 mm). (c, d) Simatio cookie in its natural environment. © B. Walendych-Scott et al.

Examples of bivalves Bornia Cookie, discovered in an article by paleontologist George Willett, that the shell they found was actually very similar. Recall that Willett documented the mollusc fauna when a sewer line was installed in Baldwin Hills in central Los Angeles. The work uncovered a 20- to 30-cm-thick Pleistocene deposit of invertebrate and vertebrate fossils more than a meter below the surface. These deposits date back to 36,000 to 28,000 years ago.

In his publication, the scientist recognized a total of 296 species of molluscs and described two new genera of Galeommatidae bivalves, Rosefordia rayana And Bornia Cookie (Today Simatio cookie), the researchers say. Willett named after Edna Cook, a shell collector who collected the specimens at the time.

type model
Specimen specimen used by George Willett to describe the genus Bornia Cookie In 1937. © P. Valentich-Scott et al.

After comparing their mollusk to the original specimen described by Willett, housed at the Natural History Museum of Los Angeles County, the researchers concluded that it was indeed the same species. At the same time, Goddard found another specimen at Naples Point, an empty shell, which also matched perfectly. Bornia Cookie.

A search that will undoubtedly lead to other models

Finally, researchers have so far found three living specimens of this species: two individuals observed in 2018 and a specimen captured in 2019. C. Cookie Thus joins the list of “Lazarus taxa,” which includes species long thought extinct and then rediscovered. ” Finding a species alive for the first time in the fossil record is not that common. », Goddard observed. How could this mollusk have escaped the attention of experts for so long? ” Southern California has a long history of shell collecting and malacology […] It’s hard to believe that no one has even found the shells of this tiny creature “, he added.

Their preferred habitat is probably further south outside of the Baja California peninsula, which could explain why no one noticed their presence. C. Cookie Before. ” C. Given the cookie’s small size, translucent shell, and secretive habits, it’s no wonder the species’ life events were ignored for more than 80 years. “, write the researchers, thanks to their new description, other individuals of the species will undoubtedly be discovered soon, especially further south, off the coast of Mexico.

According to the two researchers, these clams may have arrived in the form of planktonic larvae via ocean currents from south to Naples Point, particularly during the 2014 to 2016 ocean heat waves. species to extend their range northward, especially to many at Naples Point.

Source: P. Valentich-Scott and J. Goddard, ZooKeys

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