scholarly journals Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Richard J. Howard ◽  
Gregory D. Edgecombe ◽  
Xiaomei Shi ◽  
Xianguang Hou ◽  
Xiaoya Ma
Keyword(s):  
Feeding Strategy ◽  
Phylogenetic Analyses ◽  
Morphological Diversity ◽  
Early Cambrian ◽  
Ancestral State ◽  
Crown Group ◽  
Stem Group ◽  
Chengjiang Biota ◽  
Fossil Records ◽  
Experimental Decay

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.

scholarly journals Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota, and the evolution of seriation in Ecdysozoa

2021 ◽  
pp. jgs2021-060
Author(s):  
Xiaomei Shi ◽  
Richard J. Howard ◽  
Gregory D. Edgecombe ◽  
Xianguang Hou ◽  
Xiaoya Ma
Keyword(s):  
Phylogenetic Analyses ◽  
Sensu Stricto ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Content Type ◽  
Link Type ◽  
Stem Group ◽  
New Material ◽  
Supplementary Material ◽  
Chengjiang Biota

Cricocosmiidae is a clade of palaeoscolecid-like worms from the Chengjiang Biota, China (Cambrian Stage 3). In contrast to palaeoscolecids sensu stricto, which exhibit tessellating micro-plate trunk ornamentation, cricocosmiids possess larger, serially repeated sets of trunk sclerites bearing resemblance to lobopodian trunk sclerites (e.g., Microdictyon spp.). Cricocosmiidae were therefore proposed as stem-group Panarthropoda in some studies but are recovered as stem-group Priapulida in most phylogenetic analyses. The affinity of cricoscosmiids within Ecdysozoa is therefore of much interest, as is testing the homology of these seriated structures. We report four new specimens of the rare cricocosmiid Tabelliscolex hexagonus, yielding new details of the ventral trunk projections, sclerites and proboscis. New data confirm T. hexagonus possessed paired ventral trunk projections in a consistent seriated pattern, which is also reported from new material of Cricocosmia jinningensis (Cricocosmiidae) and Mafangscolex yunnanensis (Palaeoscolecida sensu stricto). Even when the seriated sclerites and ventral projections of cricocosmiids are coded as homologous with the seriated trunk sclerites and paired appendages, respectively, of lobopodian panarthropods, our tree searches indicate they are convergent. Cricocosmiidae is nested within a monophyletic “Palaeoscolecida sensu lato” clade (Palaeoscolecidomorpha nov.) in stem-group Priapulida. Our study indicates that morphological seriation has independent origins in Scalidophora and Panarthropoda.Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosionSupplementary material:https://doi.org/10.6084/m9.figshare.c.5551565

scholarly journals A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora

2015 ◽  
Vol 112 (28) ◽  
pp. 8678-8683 ◽  
Author(s):  
Jie Yang ◽  
Javier Ortega-Hernández ◽  
Sylvain Gerber ◽  
Nicholas J. Butterfield ◽  
Jin-bo Hou ◽  
...  
Keyword(s):  
South China ◽  
Cambrian Explosion ◽  
Suspension Feeding ◽  
Early Cambrian ◽  
Early Paleozoic ◽  
Crown Group ◽  
Morphological Disparity ◽  
Stem Group ◽  
Velvet Worms ◽  
Mode Of Life

We describe Collinsium ciliosum from the early Cambrian Xiaoshiba Lagerstätte in South China, an armored lobopodian with a remarkable degree of limb differentiation including a pair of antenna-like appendages, six pairs of elongate setiferous limbs for suspension feeding, and nine pairs of clawed annulated legs with an anchoring function. Collinsium belongs to a highly derived clade of lobopodians within stem group Onychophora, distinguished by a substantial dorsal armature of supernumerary and biomineralized spines (Family Luolishaniidae). As demonstrated here, luolishaniids display the highest degree of limb specialization among Paleozoic lobopodians, constitute more than one-third of the overall morphological disparity of stem group Onychophora, and are substantially more disparate than crown group representatives. Despite having higher disparity and appendage complexity than other lobopodians and extant velvet worms, the specialized mode of life embodied by luolishaniids became extinct during the Early Paleozoic. Collinsium and other superarmored lobopodians exploited a unique paleoecological niche during the Cambrian explosion.

scholarly journals Cambrian stem-group annelids and a metameric origin of the annelid head

2015 ◽  
Vol 11 (10) ◽  
pp. 20150763 ◽  
Author(s):  
Luke Parry ◽  
Jakob Vinther ◽  
Gregory D. Edgecombe
Keyword(s):  
Anterior Segment ◽  
Character State ◽  
Early Cambrian ◽  
Primitive Character ◽  
Burgess Shale ◽  
Crown Group ◽  
Middle Cambrian ◽  
Stem Group

The oldest fossil annelids come from the Early Cambrian Sirius Passet and Guanshan biotas and Middle Cambrian Burgess Shale. While these are among the best preserved polychaete fossils, their relationship to living taxa is contentious, having been interpreted either as members of extant clades or as a grade outside the crown group. New morphological observations from five Cambrian species include the oldest polychaete with head appendages, a new specimen of Pygocirrus from Sirius Passet, and an undescribed form from the Burgess Shale. We propose that the palps of Canadia are on an anterior segment bearing neuropodia and that the head of Phragmochaeta is formed of a segment bearing biramous parapodia and chaetae. The unusual anatomy of these taxa suggests that the head is not differentiated into a prostomium and peristomium, that palps are derived from a modified parapodium and that the annelid head was originally a parapodium-bearing segment. Canadia , Phragmochaeta and the Marble Canyon annelid share the presence of protective notochaetae, interpreted as a primitive character state subsequently lost in Pygocirrus and Burgessochaeta , in which the head is clearly differentiated from the trunk.

scholarly journals Discussion on ‘Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa’ by Shi et al. 2021 (JGS, jgs2021-060)

2021 ◽  
pp. jgs2021-111
Author(s):  
Martin R. Smith ◽  
Alavya Dhungana
Keyword(s):  
Bayesian Approach ◽  
Early Cambrian ◽  
Content Type ◽  
Animal Body ◽  
Link Type ◽  
Stem Group ◽  
Cambrian Radiation ◽  
Supplementary Material ◽  
Chengjiang Biota

Exceptionally preserved fossils are key to reconstructing the origin of the modern animal body plans in the Cambrian radiation. The Panarthropod phyla Euarthropoda, Onychophora and Tardigrada have roots in a ‘lobopodian’ grade typified by broadly cylindrical organisms with sclerotized dorsal plates and paired ventral projections. A similar anatomical configuration has been taken to link certain palaeoscolecid worms with the earliest ecdysozoans. Shi et al. (2021) contend that these similarities evolved convergently, and that palaeoscolecids are priapulan relatives with little bearing on the panarthropod evolution.Here we show that this conclusion holds only under a particular treatment of inapplicable character states with known shortcomings. When inapplicable tokens are handled more rigorously, palaeoscolecids are most parsimoniously reconstructed as stem-group panarthropods with homologous dorsal plates and ventral projections – highlighting the degree to which the treatment of inapplicable data can influence fundamental evolutionary conclusions. As the position of palaeoscolecids depends so strongly on the underlying methodology, and is highly uncertain under a Bayesian approach, we consider it premature to exclude the possibility that panarthropods evolved from a grade of palaeoscolecids with dorsal plates and ventral projections.Supplementary material:https://doi.org/10.6084/m9.figshare.16419522

scholarly journals The evolutionary history of Stomatopoda (Crustacea: Malacostraca) inferred from molecular data

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3844 ◽  
Author(s):  
Cara Van Der Wal ◽  
Shane T. Ahyong ◽  
Simon Y.W. Ho ◽  
Nathan Lo
Keyword(s):  
Phylogenetic Analyses ◽  
Sister Group ◽  
Molecular Data ◽  
Recent Common Ancestor ◽  
Ancestral State ◽  
Crown Group ◽  
Most Recent Common Ancestor ◽  
History Of ◽  
The Tropics ◽  
Age Constraints

The crustacean order Stomatopoda comprises seven superfamilies of mantis shrimps, found in coastal waters of the tropics and subtropics. These marine carnivores bear notable raptorial appendages for smashing or spearing prey. We investigated the evolutionary relationships among stomatopods using phylogenetic analyses of three mitochondrial and two nuclear markers. Our analyses recovered the superfamily Gonodactyloidea as polyphyletic, withHemisquillaas the sister group to all other extant stomatopods. A relaxed molecular clock, calibrated by seven fossil-based age constraints, was used to date the origin and major diversification events of stomatopods. Our estimates suggest that crown-group stomatopods (Unipeltata) diverged from their closest crustacean relatives about 340 Ma (95% CRI [401–313 Ma]). We found that the specialized smashing appendage arose after the spearing appendage ∼126 Ma (95% CRI [174–87 Ma]). Ancestral state reconstructions revealed that the most recent common ancestor of extant stomatopods had eyes with six midband rows of hexagonal ommatidia. Hexagonal ommatidia are interpreted as plesiomorphic in stomatopods, and this is consistent with the malacostracan ground-plan. Our study provides insight into the evolutionary timescale and systematics of Stomatopoda, although further work is required to resolve with confidence the phylogenetic relationships among its superfamilies.

scholarly journals Mitochondrial Metagenomics Reveals the Ancient Origin and Phylodiversity of Soil Mites and Provides a Phylogeny of the Acari

2019 ◽  
Vol 37 (3) ◽  
pp. 683-694 ◽  
Author(s):  
Paula Arribas ◽  
Carmelo Andújar ◽  
María Lourdes Moraza ◽  
Benjamin Linard ◽  
Brent C Emerson ◽  
...  
Keyword(s):  
Phylogenetic Analyses ◽  
Mitochondrial Gene ◽  
Mixed Forest ◽  
Morphological Diversity ◽  
Terrestrial Ecosystems ◽  
Great Promise ◽  
Ancestral State ◽  
Early Diversification ◽  
Critical Nodes ◽  
Minimum Age

Abstract High-throughput DNA methods hold great promise for phylogenetic analysis of lineages that are difficult to study with conventional molecular and morphological approaches. The mites (Acari), and in particular the highly diverse soil-dwelling lineages, are among the least known branches of the metazoan Tree-of-Life. We extracted numerous minute mites from soils in an area of mixed forest and grassland in southern Iberia. Selected specimens representing the full morphological diversity were shotgun sequenced in bulk, followed by genome assembly of short reads from the mixture, which produced >100 mitochondrial genomes representing diverse acarine lineages. Phylogenetic analyses in combination with taxonomically limited mitogenomes available publicly resulted in plausible trees defining basal relationships of the Acari. Several critical nodes were supported by ancestral-state reconstructions of mitochondrial gene rearrangements. Molecular calibration placed the minimum age for the common ancestor of the superorder Acariformes, which includes most soil-dwelling mites, to the Cambrian–Ordovician (likely within 455–552 Ma), whereas the origin of the superorder Parasitiformes was placed later in the Carboniferous-Permian. Most family-level taxa within the Acariformes were dated to the Jurassic and Triassic. The ancient origin of Acariformes and the early diversification of major extant lineages linked to the soil are consistent with a pioneering role for mites in building the earliest terrestrial ecosystems.

scholarly journals 40 new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds.

2022 ◽  
Author(s):  
Juan Benito ◽  
Albert Chen ◽  
Laura E. Wilson ◽  
Bhart-Anjan S. Bhullar ◽  
David Burnham ◽  
...  
Keyword(s):  
Morphological Evolution ◽  
Phylogenetic Analyses ◽  
Three Dimensional ◽  
Ontogenetic Changes ◽  
Crown Group ◽  
Postcranial Morphology ◽  
Stem Group ◽  
New Information ◽  
The 19Th Century ◽  
Future Work

Ichthyornis has long been recognized as a pivotally important fossil taxon for understanding the latest stages of the dinosaur-bird transition, but little significant new postcranial material has been brought to light since initial descriptions of partial skeletons in the 19th Century. Here, we present new information on the postcranial morphology of Ichthyornis from 40 previously undescribed specimens, providing the most detailed morphological assessment of Ichthyornis to date. The new material includes four partially complete skeletons and numerous well-preserved isolated elements, enabling new anatomical observations such as muscle attachments previously undescribed for Mesozoic euornitheans. Among the elements that were previously unknown or poorly represented for Ichthyornis, the new specimens include an almost-complete axial series, a hypocleideum-bearing furcula, radial carpal bones, fibulae, a complete tarsometatarsus bearing a rudimentary hypotarsus, and one of the first-known nearly complete three-dimensional sterna from a Mesozoic avialan. Several pedal phalanges are preserved, revealing a remarkably enlarged pes presumably related to foot-propelled swimming. Although diagnosable as Ichthyornis, the new specimens exhibit a substantial degree of morphological variation, some of which may relate to ontogenetic changes. Phylogenetic analyses incorporating our new data and employing alternative morphological datasets recover Ichthyornis stemward of Hesperornithes and Iaceornis, in line with some recent hypotheses regarding the topology of the crownward-most portion of the avian stem group, and we establish phylogenetically-defined clade names for relevant avialan subclades to help facilitate consistent discourse in future work. The new information provided by these specimens improves our understanding of morphological evolution among the crownward-most non-neornithine avialans immediately preceding the origin of crown group birds.

scholarly journals A primitive starfish ancestor from the Early Ordovician of Morocco reveals the origin of crown group Echinodermata

2017 ◽  
Author(s):  
Aaron W. Hunter ◽  
Javier Ortega-Hernández
Keyword(s):  
Phylogenetic Analyses ◽  
Radial Symmetry ◽  
Early Evolution ◽  
Phylogenetic Position ◽  
Crown Group ◽  
Brittle Stars ◽  
Major Clade ◽  
Early Ordovician ◽  
Stem Group ◽  
Successful Group

AbstractThe somasteroids are Ordovician star-shaped animals widely regarded as ancestors of Asterozoa, the group of extant echinoderms that includes brittle stars and starfish. The phylogenetic position of somasteroids makes them critical for understanding the origin and early evolution of crown group Echinodermata. However, the early evolution of asterozoans, the origin of their distinctive body organization and their relationships with other Cambrian and Ordovician echinoderms, such as edrioasteroids, blastozoans, crinoids, and other asterozoans, remain problematic due to the difficulties of comparing the calcitic endoskeleton of these disparate groups. Here we describe the new somasteroidCantabrigiaster fezouataensisfrom the Early Ordovician (Tremadocian) Fezouata Lagerstätte in Morocco.Cantabrigiastershares with other somasteroids the presence of rod-like virgal ossicles that articulate with the ambulacrals, but differs from all other known asterozoans in the absence of adambulacral ossicles defining the arm margins. The unique arm construction evokes parallels with non-asterozoan echinoderms. Developmentally informed Bayesian and parsimony based phylogenetic analyses, which reflect the homology of the biserial ambulacral ossicles in Paleozoic echinoderms according to the Extraxial-Axial Theory, recoverCantabrigiasteras basal within stem group Asterozoa. Our results indicate thatCantabrigiasteris the earliest diverging stem group asterozoan, revealing the ancestral morphology of this major clade and clarifying the affinities of problematic Ordovician taxa. Somasteroids are resolved as a paraphyletic grade within stem and crown group Asterozoa (starfishes), whereas stenuroids are paraphyletic within stem group Ophiuroidea (brittle stars).Cantabrigiasteralso illuminates the relationship between Ordovician crown group Echinodermata and its Cambrian stem lineage, which includes sessile forms with incipient radial symmetry such as edrioasteroids and blastozoans. The contentious Pelmatozoa hypothesis (i.e. monophyly of blastozoans and crinoids) is not supported; instead, blastozoans represent the most likely sister-taxon of crown group Echinodermata.Author summaryStarfish and brittle stars, collectively known as asterozoans, constitute a diverse and ecologically successful group of echinoderms that first appear in the fossil record some 480Ma. However, the early evolution of asterozoans, the origin of their distinctive body organization, and their phylogenetic relationships with Cambrian echinoderms remain largely unresolved. We describeCantabrigiaster fezouataensisgen. et sp. nov., a primitive asterozoan from the Fezouata Lagerstätte, Morocco, with a unique endoskeletal arm organization that reveals the ancestral morphology of this major clade. Bayesian and parsimony based phylogenetic analyses indicate thatCantabrigiasteris the earliest diverging stem group asterozoan, and resolve the phylogenetic position of Ordovician asterozoans such as somasteroids. Our analyses clarify the origin of crown group echinoderms relative to their problematic Cambrian stem group representatives.

scholarly journals An early Cambrian polyp reveals an anemone-like ancestor for medusozoan cnidarians

2021 ◽  
Author(s):  
Yang Zhao ◽  
Luke Parry ◽  
Jakob Vinther ◽  
Frances S. Dunn ◽  
Yujing Li ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Fossil Record ◽  
Soft Tissues ◽  
Common Ancestor ◽  
Last Common Ancestor ◽  
Early Cambrian ◽  
Crown Group ◽  
Sessile Polyp ◽  
Animal Evolution ◽  
Chengjiang Biota

Extant cnidarians are a disparate phylum of non-bilaterians and their diploblastic body plan represents a key step in animal evolution. Anthozoans (anemones, corals) are benthic polyps, while adult medusozoans (jellyfishes) are dominantly pelagic medusae. A sessile polyp is present in both groups and is widely conceived as the ancestral form of their last common ancestor. However, the nature and anatomy of this ancestral polyp, particularly of medusozoans, are controversial, owing to the divergent body plans of both groups in the extant lineages and the rarity of medusozoan soft tissues in the fossil record. Here we redescribe the enigmatic Conicula striata Luo et Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. We show that C. striata possessed features of both anthozoans and medusozoans. Its stalked polyp and fully encasing conical, annulated organic skeleton (periderm) are features of medusozoans. However, the gut is partitioned by ~28 mesenteries, and has a tubular pharynx, resembling anthozoans. Our phylogenetic analysis recovers C. striata as a stem medusozoan, indicating that the enormously diverse medusozoans were derived from an anemone-like ancestor, with the pharynx lost and number of mesenteries reduced prior to the origin of crown group Medusozoa.

scholarly journals An exceptionally preserved euarthropod with unique feather-like appendages from the Chengjiang biota

2021 ◽  
Author(s):  
Dayou Zhai ◽  
Mark Williams ◽  
David J. Siveter ◽  
Derek J. Siveter ◽  
Thomas H.P. Harvey ◽  
...  
Keyword(s):  
Soft Part ◽  
Three Dimensional ◽  
Ct Scanning ◽  
Early Cambrian ◽  
Micro Ct ◽  
Burgess Shale ◽  
Terminal Seta ◽  
Stem Group ◽  
Chengjiang Biota

AbstractMicro-CT scanning of the Cambrian euarthropod Chuandianella ovata reveals unprecedented three-dimensional soft-part details. It has an elongate uniramous antennule and a short uniramous second appendage, followed by ten homonomous biramous appendages, each comprising a short paddle-shaped exopod and a unique feather-like endopod with at least 27 podomeres each of which bears a long blade-like endite with a short terminal seta. Based on its carapace and previously known soft-part anatomy C. ovata was compared with the Burgess Shale mandibulate euarthropod Waptia. However, Waptia has recently been shown to bear specialized head appendages that are interpreted as a mandible and maxillula, posterior to which are four appendages each with five-segmented endopods. In contrast, we interpret Chuandianella as an ‘upper’ stem-group euarthropod that possessed neither a differentiated mandible nor a maxillula. Chuandianella further demonstrates that early Cambrian ‘upper’ stem-group euarthropods were experimenting with a range of different limb arrangements and morphologies.

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