Why Do Things Keep Evolving Into Crabs?

About this film

Crustaceans exhibit a remarkable evolutionary trend known as carcinization, where various species independently evolve into crab-like forms. This phenomenon raises questions about the advantages of the crab's morphology, which appears to confer significant evolutionary success. Experts such as Dr. Jo Wolfe, Dr. Javier Luque, and Dr. Katie Collins contribute to the research surrounding this topic, while illustrations by Franz Anthony highlight ancient crab-like creatures. The episode is produced in collaboration with PBS Digital Studios, showcasing the ongoing fascination with evolutionary biology.

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Crab

Crabs are decapod crustaceans, either the Brachyura or various groups within the closely related Anomura, characterised by having a heavily armoured shell, their tail segments concealed under the body, the ability to run sideways, and the habit of hiding in rocky crevices. They do not form a single natural group or clade, but have convergently evolved multiple times from the ancestral decapod body plan through carcinisation, the process of creating this set of characteristics. As a group, they are thus polyphyletic, meaning they have multiple evolutionary origins.

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Evolution

Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as genetic drift and natural selection act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation.

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Biodiversity

Biodiversity is the variability of life on Earth. It can be measured on various levels, for example, genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth—it is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.

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Dinosaur

Dinosaurs are a diverse group of warmblooded reptiles of the clade Dinosauria. They existed through most of the Mesozoic era, first appearing early in the Triassic period. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

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Dinos

In the typology of ancient Greek pottery, the dinos is a mixing bowl or cauldron. Dinos means 'drinking cup', but in modern typology is used for the same shape as a lebes, that is, a bowl with a spherical body, often accompanied by a wheel-turned stand. It has no handles and no feet. Literary references to such vessels are known from the Iliad, and examples have been found from between the seventh and fifth centuries BCE. Ancient artists who painted dinoi include the Dinos Painter, the Gorgon Painter, the Berlin Painter, Exekias and Sophilos.

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