02861nas a2200265 4500008004100000022001400041245009300055210006900148260001500217300000900232490000700241520206800248653001302316653001802329653001402347653001802361653001802379653001802397100002402415700002702439700001702466700001902483700001502502856007802517 2020 eng d a1471-214800aAncestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan0 aAncestral morphology of Ecdysozoa constrained by an early Cambri c23/11/2020 a1-180 v203 a

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.

10aCambrian10aCycloneuralia10aEcdysozoa10aPalaeobiology10aPanarthropoda10aPhylogenetics1 aHoward, Richard, J.1 aEdgecombe, Gregory, D.1 aShi, Xiaomei1 aHou, Xianguang1 aMa, Xiaoya uhttps://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-020-01720-602849nas a2200205 4500008004100000245010800041210006900149260003200218300000900250520218900259653001302448653002102461653001602482653001602498100001602514700002202530700002102552700001502573856005502588 2020 eng d00aA Cambrian fossil from the Chengjiang fauna sharing characters with gilled lobopodians and radiodontans0 aCambrian fossil from the Chengjiang fauna sharing characters wit bResearch Squarec01/08/2020 a1-133 a

Background: Lobopodians are worm-like animals with simple legs. Probably representing a grade of organization, rather than an explicit clade, some lobopodians are thought to have given rise to both Euarthropoda and Onychophora (velvet worms). Another subset has been referred to as gilled lobopodians, and are characterized by flap-like appendages along the trunk and large, raptorial forelimbs. These animals probably include the ancestors of another important Cambrian group, the Radiodonta: large predatory or filter-feeding stem-arthropods such as Anomalocaris.

Results: Parvibellus atavus gen. et sp. nov. from the Early Cambrian Chengjiang fauna of China is a small fossil preserving a distinct cephalic region bearing a pair of lateral projections and a circular, ventral mouth. The trunk bears eleven pairs of flap-like appendages and a short pair of terminal projections. A circular ventral mouth is also seen in Radiodonta and in some gilled lobopodians. Parvibellus atavus, gilled lobopodians and radiodontans also share the character of flap-like appendages along the trunk. However, the new fossil differs from radiodontans and gilled lobopodians by its small size and the absence of enlarged and/or raptorial frontal appendages. It also differs from gilled lobopodians in lacking ventral lobopod limbs, and from radiodontans in lacking stalked eyes.

Conclusions: Parvibellus atavus expresses a unique combination of characters among Cambrian arthropods, and could be part of an early radiation of nektonic stem-Euarthropoda. Lobopodians have emerged as a diverse grade of proto-arthropods ('worms with legs'), walking on the substrate of the early Palaeozoic seas. The new fossil hints at a similarly diverse fauna of nektonic (swimming) stem-group arthropods in the Cambrian, from which gilled lobopodians and radiodontans may have evolved.

10aCambrian10aChengjiang fauna10aLobopodians10aradiodontan1 aLiu, Jianni1 aDunlop, Jason, A.1 aSteiner, Michael1 aShu, Degan uhttps://www.researchsquare.com/article/rs-47449/v101699nas a2200193 4500008004100000022001400041245007400055210006900129260001500198300000900213490000700222520110900229653001301338653001201351653002101363653001801384100002701402856007601429 2020 eng d a1543-592X00aArthropod Origins: Integrating Paleontological and Molecular Evidence0 aArthropod Origins Integrating Paleontological and Molecular Evid c31/07/2020 a1-250 v513 a

Phylogenomics underpins a stable and mostly well-resolved hypothesis for the interrelationships of extant arthropods. Exceptionally preserved fossils are integrated into this framework by coding their morphological characters, as exemplified by total-evidence dating approaches that treat fossils as dated tips in analyses numerically dominated by molecular data. Cambrian fossils inform on the sequence of character acquisition in the arthropod stem group and in the stems of its main extant clades. The arthropod head problem incorporates unique appendage combinations and remains of the nervous system in fossils into a scheme mostly based on neuroanatomy and Hox expression domains for extant forms. Molecular estimates of arthropod origins in the Cryogenian or Ediacaran predate a coherent picture from the arthropod fossil record, which commences as trace fossils in the earliest Cambrian. Probabilistic morphological clock analysis of trilobites, which exemplify the earliest arthropod body fossils, supports a Cambrian origin, without the need to posit an unfossilized Ediacaran history.

10aCambrian10afossils10amolecular dating10aphylogenomics1 aEdgecombe, Gregory, D. uhttps://www.annualreviews.org/doi/10.1146/annurev-ecolsys-011720-12443702745nas a2200313 4500008004100000022001400041245004600055210004300101260001500144300001600159490000700175520188000182653001302062653002102075653002602096653001502122653001702137653001702154653002602171653001902197653002802216100002402244700001902268700002702287700001802314700001702332700001502349856006702364 2020 eng d a0960-982200aA Tube-Dwelling Early Cambrian Lobopodian0 aTubeDwelling Early Cambrian Lobopodian c27/02/2020 a1529–15360 v303 a

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.

10aCambrian10aChengjiang Biota10aFacivermis yunnanicus10alobopodian10aluolishaniid10apanarthropod10aphylogenetic analyses10asecondary loss10atube-dwelling lifestyle1 aHoward, Richard, J.1 aHou, Xianguang1 aEdgecombe, Gregory, D.1 aSalge, Tobias1 aShi, Xiaomei1 aMa, Xiaoya uhttps://linkinghub.elsevier.com/retrieve/pii/S0960982220301196