@article {1395, title = {Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan}, journal = {BMC Evolutionary Biology}, volume = {20}, year = {2020}, month = {23/11/2020}, pages = {1-18}, type = {Research article}, abstract = {

Background: Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas.

Results: Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia\ +\ Panarthropoda\—i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians.

Conclusions: Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors.

}, keywords = {Cambrian, Cycloneuralia, Ecdysozoa, Palaeobiology, Panarthropoda, Phylogenetics}, issn = {1471-2148}, doi = {https://doi.org/10.1186/s12862-020-01720-6}, url = {https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-020-01720-6}, author = {Howard, Richard J. and Edgecombe, Gregory D. and Shi, Xiaomei and Hou, Xianguang and Ma, Xiaoya} } @article {211, title = {A Tube-Dwelling Early Cambrian Lobopodian}, journal = {Current Biology}, volume = {30}, year = {2020}, month = {27/02/2020}, pages = {1529{\textendash}1536}, abstract = {

Facivermis yunnanicus [1, 2] is an enigmatic worm-like animal from the early Cambrian Chengjiang Biota of Yunnan Province, China. It is a small (\<10 cm) bilaterian with five pairs of spiny anterior arms, an elongated body, and a swollen posterior end. The unusual morphology of Facivermis has prompted a history of diverse taxonomic interpretations, including among annelids [1, 3], lophophorates [4], and pentastomids [5]. However, in other studies, Facivermis is considered to be more similar to lobopodians [2, 6, 7, 8]\—the fossil grade from which modern panarthropods (arthropods, onychophorans, and tardigrades) are derived. In these studies, Facivermis is thought to be intermediate between cycloneuralian worms and lobopodians. Facivermis has therefore been suggested to represent an early endobenthic-epibenthic panarthropod transition [6] and to provide crucial insights into the origin of paired appendages [2]. However, the systematic affinity of Facivermis was poorly supported in a previous phylogeny [6], partially due to incomplete understanding of its morphology. Therefore, the evolutionary significance of Facivermis remains unresolved. In this study, we re-examine Facivermis from new material and the holotype, leading to the discovery of several new morphological features, such as paired eyes on the head and a dwelling tube. Comprehensive phylogenetic analyses using parsimony, Bayesian inference, and maximum likelihood all support Facivermis as a luolishaniid in a derived position within the onychophoran stem group rather than as a basal panarthropod. In contrast to previous studies, we therefore conclude that Facivermis provides a rare early Cambrian example of secondary loss to accommodate a highly specialized tube-dwelling lifestyle.

}, keywords = {Cambrian, Chengjiang Biota, Facivermis yunnanicus, lobopodian, luolishaniid, panarthropod, phylogenetic analyses, secondary loss, tube-dwelling lifestyle}, issn = {0960-9822}, doi = {10.1016/j.cub.2020.01.075}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0960982220301196}, author = {Howard, Richard J. and Hou, Xianguang and Edgecombe, Gregory D. and Salge, Tobias and Shi, Xiaomei and Ma, Xiaoya} }