Adorned with fins down the sides of its body, a distinct head with long antennae, massive jaw structures inside its mouth and growing to more than 30 cm (11.8 inches) in length, Timorebestia koprii was one of the largest animals in the Early Cambrian oceans.
Reconstruction of Timorebestia koprii in the pelagic ecosystem preserved in Sirius Passet; other species shown in the foreground are Kiisortoqia, Siricaris, Kerygmachela, Pauloterminus, Kleptothule, and Isoxys; further in the background are two radiodonts: Tamisiocaris and an amplectobeluid. Image credit: Robert Nicholls / BobNichollsArt.
Timorebestia koprii lived in the Early Cambrian oceans, more than 518 million years ago.
The animal’s fossilized remains were found at the Sirius Passet fossil locality in North Greenland.
“We have previously known that primitive arthropods were the dominant predators during the Cambrian, such as the bizarre-looking anomalocaridids,” said Dr. Jakob Vinther, a paleontologist at the University of Bristol.
“However, Timorebestia koprii is a distant, but close, relative of living arrow worms, or chaetognaths. These are much smaller ocean predators today that feed on tiny zooplankton.”
“Our research shows that these ancient ocean ecosystems were fairly complex with a food chain that allowed for several tiers of predators.”
“Timorebestia were giants of their day and would have been close to the top of the food chain. That makes it equivalent in importance to some of the top carnivores in modern oceans, such as sharks and seals back in the Cambrian period.”
Inside the fossilised digestive system of Timorebestia koprii, Dr. Vinther and colleagues found remains of a common, swimming arthropod called Isoxys.
“We can see these arthropods was a food source many other animals,” siad Dr. Morten Lunde Nielsen, a paleontologist at Korea Polar Research Institute, the University of Bristol and British Geological Survey.
“They are very common at Sirius Passet and had long protective spines, pointing both forwards and backwards.”
“However, they clearly didn’t completely succeed in avoiding that fate, because Timorebestia munched on them in great quantities.”
Holotype of Timorebestia koprii. Image credit: Park et al., doi: 10.1126/sciadv.adi6678.
“Arrow worms are one of the oldest animal fossils from the Cambrian. While arthropods appear in the fossil record about 521 to 529 million years ago, arrow worms can be traced back at least 538 million years back in time,” Dr. Vinther said.
“Both arrow worms, and the more primitive Timorebestia, were swimming predators. We can therefore surmise that in all likelihood they were the predators that dominated the oceans before arthropods took off.”
“Perhaps they had a dynasty of about 10-15 million years before they got superseded by other, and more successful, groups.”
“Timorebestia is a really significant find for understanding where these jawed predators came from,” said Oxford University’s Dr. Luke Parry.
“Today, arrow worms have menacing bristles on the outside of their heads for catching prey, whereas Timorebestia has jaws inside its head.”
“This is what we see in microscopic jaw worms today — organisms that arrow worms shared an ancestor with over half a billion years ago.”
“Timorebestia and other fossils like it provide links between closely related organisms that today look very different.”
“Our discovery firms up how arrow worms evolved,” said Dr. Tae Yoon Park, a palentologist at the Korean Polar Research Institute.
“Living arrow worms have a distinct nervous centre on their belly, called a ventral ganglion. It is entirely unique to these animals.”
“We have found this preserved in Timorebestia and another fossil called Amiskwia.”
“People have debated whether or not Amiskwia was closely related to arrow worms, as part of their evolutionary stem lineage.”
“The preservation of these unique ventral ganglia gives us a great deal more confidence in this hypothesis.”
The team’s work was published in the journal Science Advances.
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Tae-Yoon S. Park et al. 2024. A giant stem-group chaetognath. Science Advances 10 (1); doi: 10.1126/sciadv.adi6678