With over 15,000 extant species, Decapoda—or ten-legged crustaceans such as crabs, shrimp, lobsters, and relatives— are among the most speciose and economically important group of crustaceans. Despite of their diversity, anatomical disparity, and remarkable fossil record extending back to the Late Paleozoic, the origins of Decapoda and their phylogenetic relationships with eumalacostracans remains elusive and inconclusive. Molecular dating suggests that decapods originated in the Late Ordovician (~450 Mya), but no reliable fossil crown groups are found until the Late Devonian. Moreover, there is no consensus on which lineages belong to stem groups, obscuring our understanding of the roots of the ten-legged decapod body plans as a whole, and how they relate to other non-decapod crustaceans. We present new, exceptional fossils from the Late Devonian of Czech Republic and Poland that belong to †Angustidontida, an odd shrimp-looking crustacean with a combination of anatomical features unlike those of any crown eumalacostracan known—extinct or extant. Our phylogenetic analyses, including representatives of all major lineages of crown eumalacostracans plus †Angustidontida, identify angustidontids as the only known stem-group decapod, and give hints about the transformation series, polarity of change, and evolutionary pathways leading to the modern decapod body plans seen today.

中文翻译：

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特殊的晚泥盆世节肢动物记录了十足目甲壳类动物的起源

拥有超过 15,000 种现存物种，十足目——或十足甲壳类动物，如螃蟹、虾、龙虾和亲戚——是甲壳类动物中最特殊和经济上最重要的一类。尽管它们的多样性、解剖学差异和可追溯到晚古生代的显着化石记录，但十足目动物的起源及其与真鲨目动物的系统发育关系仍然难以捉摸且没有定论。分子测年表明十足目动物起源于晚奥陶世（~450 Mya），但直到晚泥盆世才发现可靠的化石冠群。此外，对于哪些谱系属于茎群还没有达成共识，这使我们对十足类十足目身体计划的根源以及它们与其他非十足目甲壳类动物的关系的理解变得模糊不清。我们呈现新的，来自捷克共和国和波兰晚泥盆世的特殊化石，属于 †Angustidontida，一种外观奇特的虾类甲壳类动物，具有多种解剖学特征，不同于任何已知的已灭绝或现存的冠真甲藻。我们的系统发育分析，包括冠真角鲨属和 †Angustidontida 的所有主要谱系的代表，将 angustidontids 确定为唯一已知的干群十足目动物，并提供有关转化系列、变化极性和导致现代十足目动物身体计划的进化途径的提示今天看到了。