Abstract
Vision has revolutionized the way animals explore their environment and interact with each other and rapidly became a major driving force in animal evolution. However, direct evidence of how ancient animals could perceive their environment is extremely difficult to obtain because internal eye structures are almost never fossilized. Here, we reconstruct with unprecedented resolution the three-dimensional structure of the huge compound eye of a 160-million-year-old thylacocephalan arthropod from the La Voulte exceptional fossil biota in SE France. This arthropod had about 18,000 lenses on each eye, which is a record among extinct and extant arthropods and is surpassed only by modern dragonflies. Combined information about its eyes, internal organs and gut contents obtained by X-ray microtomography lead to the conclusion that this thylacocephalan arthropod was a visual hunter probably adapted to illuminated environments, thus contradicting the hypothesis that La Voulte was a deep-water environment.
Highlights
Vision has revolutionized the way animals explore their environment and interact with each other and rapidly became a major driving force in animal evolution
X-ray microtomography (XTM) and thin-sectioning of exceptionally well-preserved specimens from the Middle Jurassic La Voulte Lagerstatte have revealed the anatomy of Mesozoic thylacocephalans with unprecedented resolution, as exemplified here by Dollocaris
Most Mesozoic thylacocephalans had a frontal pair of bulbous compound eyes with an extremely large visual surface (Fig. 1a–c)
Summary
Vision has revolutionized the way animals explore their environment and interact with each other and rapidly became a major driving force in animal evolution. Apposition eyes most certainly evolved much earlier than the Jurassic, we present direct evidence here that the internal organization of the most common modern eye type already existed 160 million years ago With their huge eyes and long prehensile appendages, thylacocephalans are among the most intriguing arthropods of the Palaeozoic and Mesozoic eras (Fig. 1). Thylacocephalans have a remote ancestry dating to the Silurian[18] and possibly earlier[16] and became extinct in the late Cretaceous They are characterized by a segmented body protected by a sclerotized ‘bivalved’ carapace, a pair of large compound eyes and three pairs of powerful head appendages with chelate or spiny tips converging towards the mouth (Fig. 1d). Thylacocephala as a possible malacostracan stem-group is a relevant hypothesis to explore through future cladistic analyses
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