Female (top) and male (below) of the ostracod Cypideis salebrosa. Note the male shell is more elongated than that of the female. This is thought to reflect the need to accommodate the large male genitalia (highlighted in blue). A team of researchers studied this specimen and others in the collections of the Smithsonian's National Museum of Natural History to better understand the role of sexual selection in extinction. Their findings were published in Nature on April 11.