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Christmas Island red crabs (Gecarcoidea natalis) represent a species of veritable crab inhabiting terrestrial regions.
Scientists have ascertained that crabs have undergone evolution to journey from the ocean to the land and then revert numerous instances across the past 100 million years.
A recent investigation, released on Nov. 6 in the publication Systematic Biology, determined that authentic crabs (Brachyura) — comprising 7,600 species distributed among 109 families — have adapted to traverse from oceanic to terrestrial environments somewhere between seven and 17 separate occasions. (True crabs stand apart from other crustaceans that have formulated crab-esque structures).
They also discovered that in two or three instances, crabs even retreated to the ocean from land. “It is unequivocally more difficult to transition from land to water,” declared chief author Joanna Wolfe, an investigator specializing in organismic and evolutionary biology at Harvard University, speaking with Live Science.
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The majority of arthropods departed from the sea uniquely during evolutionary occurrences surpassing 300 million years in the past, through a process known as terrestrialization.
Within the recent study, researchers commenced on a quest to ascertain how routinely and when true crabs forsook the marine setting for the terrain. They gathered three novel datasets concerning 333 species of true crabs originating from 88 families, encompassing both sea and land cohorts.
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Employing the complete crab fossil documentation, the researchers utilized a duo of mapping methodologies: one wherein the crab transitions from an entirely marine setting to terrain directly through intertidal zones like beaches, and another where the species migrates from the fully marine setting to terrain indirectly, via estuaries, freshwater sources, riverbanks, coastal woodlands, and jungles.
Their discoveries authorized the team to categorize each crab species into a spectrum of terrestriality — or the degree of suitability they possess for existence on land. By leveraging techniques initially crafted to analyze the progression of viruses akin to COVID-19, the investigators pinpointed the timeline of true crab evolution.
Their findings propose that true crabs surfaced approximately 45 million years prior to prior estimations and could be traced to the mid-Triassic epoch (spanning 251.9 million to 201.3 million years ago), rendering them coeval with several of the foremost recognized dinosaurs.
Summary of phylogeny and divergence duration approximations for true crabs, colored by taxonomic superfamily.
They abandoned the ocean somewhere between seven and 17 instances due to convergent evolution — occurring when diverse organisms evolve comparable characteristics independently.
They discovered that the majority of crabs can solely subsist within semi-terrestrial habitats, with land-dwelling crabs demonstrated to be concentrated in a single species-dense group of the family tree. “It is a prevalent misconception that crabs are endeavoring to evolve toward perpetual terrestrial existence. The majority of crab species continue to thrive within the ocean,” Wolfe stated.
Carys MatthewsSocial Links NavigationLive Science Contributor
Carys Matthews operates as a freelance scribe for Live Science possessing a fervor for the realm of nature. Formerly the digital head editor of BBC Wildlife and BBC Countryfile Magazine, she composes pieces regarding the outdoors, the natural world as well as fitness and wellbeing. Prior to this engagement, she contributed to several sports and ecological publications within the U.K.
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