Mandibulates are an example of evolutionary success, representing over half of all current species on Earth. Today, mandibulates are everywhere: from sea-dwelling crabs to centipedes lurking in the undergrowth or bees flying across meadows, but their beginnings were humbler. During the Cambrian period (539 to 485 million years ago), the first mandibulates were marine animals, most bearing distinct head shields or carapaces. An early mandibulate called Odaraia alata is one of the largest Cambrian arthropods at nearly 20 cm (7.9 inches) in length. First described in 1912, this enigmatic species is characterized by its unique tubular carapace and rudder-like tail fan. In new research, paleontologists reinvestigated Odaraia alata based on new specimens from the famous Burgess Shale.
Artistic reconstruction of Odaraia alata, swimming inverted. Image credit: Danielle Dufault.
Odaraia alata, which lived between 509 and 505 million years ago, has not been revisited since the early 1980s.
Royal Ontario Museum paleontologists Alejandro Izquierdo-López and Jean-Bernard Caron restudied the anatomy of the species based on 150 specimens from the Burgess Shale.
They were able to identify a pair of large appendages with jagged edges near the mouth of Odaraia alata for feeding, clearly indicative of mandibles which are one of the key and distinctive features of the mandibulate group of animals.
In a detailed analysis of its more than 30 pairs of legs, the researchers made another stunning discovery, finding an intricate system of small and large spines.
These spines could intertwine, capturing smaller prey as though a fishing net, suggesting how some of these first mandibulates were able to leave the sea floor and survive in the water column, setting the seeds for their future ecological success.
“The head shield of Odaraia alata envelops practically half of its body including its legs, almost as if it were encased in a tube,” Dr. Izquierdo-López said.
According to the scientists, early mandibulates like Odaraia alata were part of a community of large animals that could have been able to migrate from the marine bottom-dwelling ecosystems characteristic of the Cambrian period to the upper layers of the water column.
These types of communities could have enriched the water column and facilitated a transition towards more complex ecosystems.
“Odaraia alata represents one of the clearest examples of suspension-feeding euarthropods in the Cambrian, highlighting the role of recovering anatomical information to improve ecological reconstructions,” the authors concluded.
“The suspension feeding lifestyle of Odaraia alata further strengthens the increasingly supported notion that Cambrian ecosystems were not limited to the benthos, but had already started to establish food chains throughout the water column, and already had communities of nektobenthic suspension feeders and other pelagic groups.”
The study was published in the Proceedings of the Royal Society B.
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Alejandro Izquierdo-López & Jean-Bernard Caron. 2024. The Cambrian Odaraia alata and the colonization of nektonic suspension-feeding niches by early mandibulates. Proc. R. Soc. B 291 (2027): 20240622; doi: 10.1098/rspb.2024.0622
