Arthropods (they of a hard outer-skeleton, like crustaceans, spiders, and insects) very often have larval phases that are completely different from the adults — such as caterpillars and butterflies. Allegedly, one of the reasons crabs have been so successful is that their larval life habits (diet, locomotion, etc.) are decoupled from their adult life habits.
Most ancient fossils display a suite of “primitive” features, consistent with their early evolution and allowing them to be distinguished from their modern descendants. But the fossil described in this paper, despite its age, possesses a very modern morphology, indistinguishable from many crab larvae living today. “It’s amazing, but if we did not know this was a 150-million-year-old fossil, we might think that it came from today’s ocean,” Dr. Martin said. “This came as quite a surprise to all of us.”
A friend, reading this, asks, wouldn’t these people be better off not to think about evolution at all? Maybe nature doesn’t care much about evolution and isn’t interested in fulfilling tenured profs’ predictions.
True crabs (Brachyura) are the most successful group of decapod crustaceans. This success is most likely coupled to their life history, including two specialised larval forms, zoea and megalopa. The group is comparably young, starting to diversify only about 100 million years ago (mya), with a dramatic increase in species richness beginning approximately 50?mya. Early evolution of crabs is still very incompletely known. Here, we report a fossil crab larva, 150?mya, documented with up-to-date imaging techniques. It is only the second find of any fossil crab larva, but the first complete one, the first megalopa, and the oldest one (other fossil ca. 110?mya). Despite its age, the new fossil possesses a very modern morphology, being indistinguishable from many extant crab larvae. Hence, modern morphologies must have been present significantly earlier than formerly anticipated. We briefly discuss the impact of this find on our understanding of early crab evolution. – Joachim T. Haug, Joel W. Martin, Carolin Haug. A 150-million-year-old crab larva and its implications for the early rise of brachyuran crabs. Nature Communications, 2015; 6: 6417 DOI: 10.1038/ncomms7417 (paywall)
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