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U of T-Yale scientists identify new spiny-headed sea predator

Capinatator is a new species of arrow worm from the Cambrian period

Illustration of Capinatator praetermissus which looks like a flat worn like creature with about 25 spines in each side of its head

Capinatator praetermissus, is a large and exceptionally well-preserved primitive chaetognath (arrow worm). This new species was identified from 508-million-year-old Burgess Shale fossils. Today these predatory marine worms are much smaller and comprise a major type of organism found in plankton – which is the foundation of the marine food web. Illustration: Marianne Collins / ©Royal Ontario Museum.

A team of scientists have identified a small marine predator that once patrolled the ocean floor and grabbed its prey with 50 spines that it deployed from its head.

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The Burgess Shale in British Columbia — home to some of the planet’s earliest animals — is one of the world’s most important fossil sites.  Read more about some of the new species discovered there that are deepening our understanding of early animal evolution

Named Capinatator praetermissus, this ancient creature is roughly 10 centimetres long and represents a new species within the group of animals known as chaetognaths — small, swimming marine carnivores also known as arrow worms. They are known from about 120 species today and represent a separate group within the animal kingdom.

Capinatator is one of the largest chaetognaths known. At more than 500 million-years-old, Capinatator is thought to be a forerunner of the smaller chaetognaths that are abundant in today’s oceans, where they make up a large portion of the world’s plankton and the ocean food chain.

“This new species would have been an efficient predator and a terrifying sight to many of the smallest marine creatures that lived during that time,” said Jean-Bernard Caron, senior curator of invertebrate palaeontology at the Royal Ontario Museum (ROM) and associate professor in the departments of Ecology & Evolutionary Biology and Earth Sciences at the University of Toronto. Caron made the identification with Derek Briggs of Yale University based on 50 specimens from the fossil-rich Burgess Shale in British Columbia.

“This is the most significant fossil discovery about the chaetognath group of animals to date,” said Briggs, Yale’s G. Evelyn Hutchinson Professor of Geology and Geophysics and curator at the Yale Peabody Museum of Natural History. Briggs is lead author of a study published today in Current Biology about this discovery.

During a Royal Ontario Museum fieldwork expedition, led by Des Collins in 1983, several Burgess Shale-type fossils, later identified as Capinatator, were collected on Mount Stephen in the Canadian Rockies. ©Royal Ontario Museum.

According to the researchers, Capinatator’s head configuration is unique. With about 25 spines in each side of its head, the species has nearly double the maximum number of spines found in today’s chaetognaths. This enabled Capinatator to capture prey by closing the two halves of its grasping spines toward each other as it swam.

Briggs and Caron also determined that while it is fairly common to find evidence of chaetognath spines, fossilized chaetognath bodies are extraordinarily rare. Many of the Capinatator specimens in this study included evidence of soft tissues.

Capinatator has up to 25 pairs of spines to help capture prey, almost double the number of spines found in modern forms. Photo: JB Caron / ©Royal Ontario Museum.

“These Burgess Shale fossil specimens preserve evidence of features such as the gut and muscles, which normally decay away, as well as the more decay-resistant grasping spines,” said Briggs. “They show that chaetognath predators evolved during the explosion of marine diversity during the Cambrian Period, and were an important component of some of the earliest marine ecosystems.”

The species name “praetermissus” means “overlooked”. The name Capinatator is derived from “capio,” which means “to grasp,” and “natator,” which means “swimmer.”

This fossil of Capinator is 7.5 cm long and is thought to be an ocean bottom feeder, unlike its tiny modern relatives that live in the water column with other planktonic creatures. This specimen is the most complete showing the spines to the left, and the posterior end of the body to the right, with some evidence of a gut trace running along the middle section of the body. Photo: JB Caron / ©Royal Ontario Museum.

The material for this study, currently held in the ROM’s collections, was collected by the ROM under research and collecting permits provided by Parks Canada. The Burgess Shale fossil sites are located within Yoho and Kootenay National Parks. Parks Canada protects the sites and works with leading scientific researchers to expand knowledge and understanding of this key period of earth history. The Burgess Shale was designated a UNESCO World Heritage Site in 1980.

Research funding was provided by the NASA Astrobiology Institute, the Natural Sciences and Engineering Research Council, the ROM Reproductions Fund, and the Louise Hawley Stone Charitable Trust Publications Fund.

With files from Yale University and Royal Ontario Museum.