February 2025: Megacheiran arthropod

cf. Leanchoilia illecebrosa (Hou, 1987)

Paleozoic: Lower Cambrian, Maotianshan Shale, ca. 520 million years old

Maotianshan Hill, Chengjiang, Yunnan, China

Leanchoilia illecebrosa is a type of primitive arthropod from the early Cambrian period. It is an early representative of the Megacheira, an extinct group of predatory arthropods that were widespread in the seas worldwide from the Early Cambrian to the Late Ordovician. Depending on the author, up to about 20 genera and several families are distinguished. However, the relationships within this large group are partly disputed.

The name Megacheira – in English “big hands” – is based on the peculiar morphology with the often large appendages on the head, which are sometimes reminiscent of arms and were used to catch prey, at least in some genera. In some genera, it has been proven that these appendages were very mobile, which probably made catching prey easier. Some Megacheira species are thought to have fed on smaller arthropods, such as the Bradoriida, a group of small, bivalved arthropods that is also extinct.

See Leanchoilia illecebrosa (Hou, 1987) from the Lower Cambrian of Chengjiang (China); scale: 5 mm.

Adult forms of Leanchoilia illecebrosa were up to 46 mm long; our much smaller specimen may represent an immature animal. In their morphology, Leanchoilia illecebrosa and related species of Megacheira resemble modern crustaceans, but they are only distantly related to them. In fact, the relationship of Megacheira to modern arthropods is not entirely clear. In some studies they are considered as stem-group Euarthropoda (“true arthropods”), others treat them as early Chelicerata, which today includes spiders and scorpions.

Leanchoilia illecebrosa was one of over 80 species of arthropods in the so-called Chengjiang Biota. This biota from southern China, which are around 520 million years old, is extraordinarily well preserved and diverse – almost 200 species have been described since its discovery in 1984. The good preservation has also made it possible to identify internal organs and stomach contents in some species, which helps to understand their relationships, diets and physiology. The otherwise extremely rare preservation of organisms without hard parts (such as jellyfish and worms) also contributes significantly to understanding these early faunas and the evolution of many animal groups.

Thomas A. Neubauer, Munich