杏吧原创

Most early animals of the Cambrian period 鈥� about half a billion years ago 鈥� were small enough to fit in the palm of your hand. But a new Cambrian predator named this week was a giant in comparison, growing to half a metre long. Named Titanokorys gainesi, the impressive invertebrate is a reminder of just how much is left to uncover in the fossil record of Cambrian life.

Described by palaeontologists and , both at the Royal Ontario Museum in Canada, the new fossils were uncovered in 506-million-year-old rock at Marble Canyon in Kootenay National Park, British Columbia, Canada, in 2014.

鈥淭hey [the fossils] were somewhat enigmatic at that time, and were shelved for the time being,鈥� Moysiuk says. But the discovery of a better fossil in 2018 helped show that those remains were something we hadn鈥檛 seen before.

To date, Caron and Moysiuk have identified a dozen specimens of T. gainesi. The species was an invertebrate with a large, rounded head shield that gave it the appearance of a sci-fi spacecraft. There is no creature quite like this alive today.

In fact, T. gainesi is categorised as a member of an early animal group called the radiodonts 鈥� evolutionary cousins of early arthropods, often distinguished by their segmented, grasping appendages for capturing prey, and pineapple slice-shaped mouths. Some radiodonts grew even larger than T. gainesi; one species that lived 25 million years later 鈥� Aegirocassis benmoulai 鈥� .

We have found broadly similar creatures in Kootenay before. In 2019, Caron and Moysiuk described a smaller invertebrate from the same fossil site and named it Cambroraster falcatus. This had specialised grasping appendages suited to sifting through sediment for tiny morsels, a trait that Titanokorys shares.

While the two are probably distinct species, Joanna Wolfe at Harvard University says caution is needed given that the larvae or early life stages of some arthropods seem different from the adult forms. With many new Cambrian species being named from various fossil sites, it is possible some might represent the same species at different developmental stages.

Nevertheless, the anatomy of the new fossil species indicates that T. gainesi moved along the ancient sea bottom. 鈥淭he very broad head carapace of Titanokorys resembles the form of some modern organisms adapted to life near the sea bottom, like horseshoe crabs,鈥� says Moysiuk. Different radiodont species have appendages adapted to different uses, Wolfe notes, from stabbing to sifting. The fact that Titanokorys and Cambroraster lived alongside each other and fed in similar ways hints that the Cambrian reef sediments were rich in tiny morsels.

The Cambrian animals found at Kootenay look distinct from a famous set of fossilised animals found in another set of Canadian Cambrian rocks known as the Burgess shale, as well as from similar Cambrian fossil sites in China, the western US and elsewhere.

鈥淭he Burgess shale is still arguably the best window into the Cambrian seas,鈥� Moysiuk says, but there are more fossil sites that share similar forms of preservation, as well as species, at other places around the world. 鈥淛ust like in modern oceans, we would expect to see many different environments even in relatively close proximity,鈥� notes Wolfe.

Each fossil site offers a different snapshot in space and time, meaning that there are probably many more bizarre Cambrian species awaiting discovery in the delicate Cambrian rock.

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