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A recent study conducted by palaeontologists at the Royal Ontario Museum (ROM) sheds light on the evolution and ecological role of Odaraia, a unique marine organism reminiscent of a taco, which thrived during the Cambrian period. Fossils gathered by the ROM have confirmed that Odaraia featured mandibles, allowing scientists to classify it as part of the mandibulate group. This marks a significant step forward in understanding the animal’s place in the tree of life, particularly after it had remained an enigma among arthropods since its discovery in the Burgess Shale over a century ago. The findings of the study, titled The Cambrian Odaraia alata and the colonization of nektonic suspension-feeding niches by early mandibulates, were published in the journal Proceedings B.
The researchers identified a pair of sizable appendages equipped with sharp, jagged edges located near the mouth of Odaraia, strongly suggesting the presence of mandibles, a key characteristic of mandibulates. This discovery positions Odaraia as potentially one of the earliest representatives of this significant animal group. Additionally, an examination of its over 30 pairs of legs unveiled a sophisticated arrangement of small and large spines. According to the study’s authors, these spines might have interlocked, enabling Odaraia to trap smaller prey akin to a fishing net, illustrating how early mandibulates ventured off the seafloor and into the water column, laying the groundwork for their subsequent ecological expansion.
“The head shield of Odaraia covers nearly half of its body, including its legs, creating a tube-like form,” explained Alejandro Izquierdo-López, the lead author of the study, who performed his research as a PhD student at the University of Toronto while based at ROM. “Earlier descriptions from the 1980s highlighted its morphology, yet the limited fossil record back then left two crucial questions unanswered: Is Odaraia truly a mandibulate? And what was its feeding mechanism?”
Measuring almost 20 cm in length, the authors point out that early mandibulates like Odaraia were integral to a community of larger organisms that could migrate from bottom-dwelling habitats typical of the Cambrian era to the upper layers of the water column. Such communities may have enhanced the richness of the water column and paved the way for more intricate ecosystems.
The Cambrian fossil record chronicles a pivotal divergence of animal groups dating back over 500 million years. During this era, key evolutionary innovations emerged, such as eyes, legs, and shells, all contributing to the initial diversification of numerous animal taxa, including mandibulates—one of the principal groups of arthropods known for their jointed limbs.
Mandibulates exemplify remarkable evolutionary success, comprising over half of all extant species today. They inhabit diverse environments, from marine species like crabs to terrestrial types like centipedes and bees. However, their origins were significantly more modest, with the earliest mandibulates being marine organisms, often characterized by distinct head shields or carapaces.
“The Burgess Shale has provided a wealth of knowledge in paleontology,” remarked Jean-Bernard Caron, the Richard Ivey Curator at ROM and co-author of the study. “Our ongoing research at the ROM on remarkable fossil specimens, including Tokummia and Waptia, has already expanded our understanding of early mandibulate evolution. Still, some species, such as Odaraia, have remained quite mysterious.”
The Royal Ontario Museum is home to the world’s largest collection of Cambrian fossils from the renowned Burgess Shale in British Columbia. The remarkable preservation of these fossils provides insights into structures, organisms, and ecosystems that would ordinarily not survive the fossilization process. However, mandibulates are infrequently found within these records, as most fossilized remains preserve only hard structures like skeletons or the mineralized exoskeletons of trilobites, which are features that mandibulates lack.
For over four decades, Odaraia has been celebrated as one of the most notable organisms from the Burgess Shale, recognized for its distinctive taco-shaped carapace, pronounced head and eyes, and a tail resembling a submarine’s keel. Visitors can view Odaraia specimens at the Willner Madge Gallery, Dawn of Life, within the Royal Ontario Museum.
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