Bushizheia yangi gen. et sp. nov. is a euarthropod species from the Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte, Southwest China. Sclerotised dorsal tergites, sclerotisation of post-frontal head limb appendages, and no isolated cephalic sclerite support the euarthropod affinities of B. yangi gen. et sp. nov. However, the frontal head limbs resemble in morphology the anteroventral raptorial appendage of radiodonts. Although, due to the absence of critical soft anatomy, we cannot elucidate the exact segmental affinities of these raptorial appendages, the possession of 'great appendage'-like frontal head limbs is important for assessing the range of limb morphology evolved by early euarthropods.
We describe Fengzhengia mamingae gen. et sp. nov., a new euarthropod from the lower Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte, Southwest China. Fengzhengia mamingae possesses prominent frontal appendages, stalked, circular eyes, a simple, sub-triangular head shield, and a trunk with 15 tergites, the anterior nine each bearing a single medial axial spine. Limited evidence suggests biramous trunk appendages with paddle-shaped exopods. At the posterior end is a sub-triangular region, possibly a pygidium, articulated with a tail fan. The frontal appendage of F. mamingae resembles those of certain 'great appendage' arthropods and Isoxys. We test the affinities of F. mamingae by parsimony and Bayesian analyses and tentatively suggest that it is an early branch of Deuteropoda. We suggest that F. mamingae may have been a nektobenthic scavenger or predator, and its dorsal exoskeleton is notable for exhibiting defensive spines.
Crayfish are rare in the fossil record and therefore it is important to investigate each occurrence in detail. The only known fossil crayfish from France, Astacus edwardsi Van Straelen, 1928, is known from a replica made by pouring plaster of Paris inside the holotype (consequently destroyed), an external mould extracted from a travertine cavity from the Thanetian of Sézanne. An evaluation of the taxonomic name, A. edwardsi, is provided; A. edwardsi is considered valid in accordance with ICZN rulings. It possesses atypical features for all other astacid genera, thus Emplastron gen. nov. is erected. Emplastron edwardsi gen. et comb. nov. inhabited a warm climate with calm waters, abundant food sources, and an ample supply of calcium carbonate: so much so that it is surprising that it is the only recovered specimen. Despite apparent North American faunal and floral affinities in the vicinity, E. edwardsi is more closely related to European crayfishes than it is to American ones.
Megacheirans, or great‐appendage euarthropods, have featured prominently in discussions regarding the early evolution of the head region in total‐group Euarthropoda. However, several aspects of the ventral morphology of most representatives remain incompletely known given the loss of data associated with fossil compression, coupled with the rarity of some of these taxa. Here, we describe the ventral aspect of head organization of the jianfengiid megacheiran Jianfengia multisegmentalis using micro computed‐tomography, and explore its evolutionary significance. The head consists of a pair of stalked eyes, a pair of great appendages, and four pairs of biramous appendages, all covered by a dorsal head shield. The rostral portion of the head bears a median projection, which we interpret as an anterior sclerite akin to that observed in several other Cambrian euarthropods. The anterior sclerite in J. multisegmentalis articulates with robust stalks with rounded projections in a more adaxial position, and bears the compound eyes. Critically, the ventral side of the head of J. multisegmentalis features a prominent lobe‐shaped hypostome/labrum complex located immediately behind the great appendages, and between the first pair of biramous appendages. This situation is consistent with that observed in Leanchoilia illecebrosa and suggests a conserved, and possibly ancestral, pattern of a six‐segmented head (eyes, great appendages and four biramous limb appendages) with a hypostome/labrum complex for Megacheira. The existence of the hypostome/labrum complex in J. multisegmentalis falsifies the hypothesis that the anterior projections on the head of jianfengiids might be homologues of the euarthropod labrum.
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