A mostly complete and moderately well-preserved fossilized specimen is thought to represent the first Triassic horseshoe crab found in North America, according to a study published in the December 2017 issue of the journal Neues Jahrbuch für Geologie und Paläontologie by paleontologist Dr. Allan Lerner from the New Mexico Museum of Natural History and Science and colleagues.
Vaderlimulus tricki. The specimen came from a locality in the Olenekian Thaynes Group near Paris, Idaho, the United States. Image credit: New Mexico Museum of Natural History and Science.
Despite their common name, horseshoe crabs are not really crabs (crustaceans), and are more closely related to spiders and scorpions.
They live primarily in and around shallow ocean waters on soft sandy or muddy bottoms, and occasionally come onto shore to mate.
There are only four species of horseshoe crabs alive today, and their populations are decreasing.
Modern horseshoe crabs are often considered ‘living fossils’ due to having shown little apparent change in physical appearance over a vast period of geologic time.
The fossil record of these animals dates back at least 470 million years ago, but their fossils are generally rare.
“When horseshoe crab fossils are found they are often new to science,” Dr. Lerner and co-authors said.
Drawing of Vaderlimulus tricki. Image credit: New Mexico Museum of Natural History and Science.
Dubbed Vaderlimulus tricki, the newfound fossil represent a new genus and species of horseshoe crabs.
“The genus is named Vaderlimulus because the animal’s head shield resembles the helmet worn by Darth Vader from the Star Wars film series,” the researchers explained.
Vaderlimulus tricki lived approximately 245 million years ago during the Early Triassic epoch.
“Dinosaurs and mammals were just beginning their evolutionary development during the Triassic, but horseshoe crabs were already ancient by that time,” the paleontologists noted.
The ancient creature belonged to the extinct family Austrolimulidae and had unusual body proportions.
“Members of this family were expanding their ecological range from marine into freshwater settings during the Triassic and often exhibit body modifications that provide them with a bizarre appearance by modern standards,” Dr. Lerner and colleagues said.
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Allan J. Lerner et al. 2017. First fossil horseshoe crab (Xiphosurida) from the Triassic of North America. Neues Jahrbuch für Geologie und Paläontologie 286 (3): 289-302; doi: 10.1127/njgpa/2017/0702
