scholarly journals The scleritome of Paterimitra : an Early Cambrian stem group brachiopod from South Australia

2009 ◽  
Vol 276 (1662) ◽  
pp. 1651-1656 ◽  
Author(s):  
Christian B Skovsted ◽  
Lars E Holmer ◽  
Cecilia M Larsson ◽  
Anette E.S Högström ◽  
Glenn A Brock ◽  
...  
Keyword(s):  
Anterior Margin ◽  
South Australia ◽  
Early Cambrian ◽  
Filter Feeding ◽  
Filter Feeder ◽  
Open Cone ◽  
Life Habit ◽  
Stem Group ◽  
Hard Substrates

Early Cambrian tommotiids are problematic fossil metazoans with external organophosphatic sclerites that have been considered to be basal members of the lophophorate stem group. Tommotiids are almost exclusively known from isolated or rarely fused individual sclerites, which made previous reconstructions of the actual organism highly conjectural. However, the recent discovery of the first articulated specimens of the tommotiid Eccentrotheca revealed a tubular sclerite arrangement (scleritome) that limited the possible life habit to sessile filter feeding and thus further supported a lophophorate affinity. Here, we report the first articulated specimens of a second tommotiid taxon, Paterimitra from the Early Cambrian of the Arrowie Basin, South Australia. Articulated specimens of Paterimitra are composed of two bilaterally symmetrical sclerite types and an unresolved number of small, asymmetrical and irregular crescent-shaped sclerites that attached to the anterior margin of the symmetrical sclerites. Together, the sclerites form an open cone in which the symmetrical sclerites are joined together and form a small posterior opening near the base of the scleritome, while the irregular crescent-shaped sclerites defined a broad anterior opening. The coniform scleritome of Paterimitra is interpreted to have attached to hard substrates via a pedicle that emerged through the small posterior opening (sometimes forming a tube) and was probably a sessile filter feeder. The scleritome of Paterimitra can be derived from the tubular scleritome of Eccentrotheca by modification of basal sclerites and reduction in tube height, and probably represents a more derived member of the brachiopod stem group with the paired symmetrical sclerites possibly homologous to brachiopod valves.

An Early Cambrian radula

2008 ◽  
Vol 82 (3) ◽  
pp. 543-554 ◽  
Author(s):  
Nicholas J. Butterfield
Keyword(s):  
Early Cambrian ◽  
Feeding Apparatus ◽  
Strong Case ◽  
Stem Group ◽  
Hard Substrates ◽  
Anterior Posterior

Microscopic teeth isolated from the early Cambrian Mahto Formation, Alberta, Canada, are identified as components of a molluscan radula, the oldest on record. Tooth-rows are polystichous and lack a medial rachidian tooth-column. Anterior-posterior differences in tooth-row morphology are interpreted as ontogenetic and correspond broadly to the diversity of isolated teeth, some of which correspond closely with those of extant aplacophoran molluscs. Associated pock-marked cuticular fragments are interpreted as having supported multiple biomineralized sclerites/spines in the manner of a modern chiton girdle. On the assumption that the cuticle and radula derive from the same species, there is a strong case for identifying this fossil as an aculiferan (aplacophoran + polyplacophora) mollusc, possibly a stem-group chiton. Similarities between the Mahto radula and the feeding apparatus of Wiwaxia and Odontogriphus are shown to be superficial. Terminal wear on some of the Mahto teeth indicate that they were used to scrape hard-substrates.

scholarly journals The early Cambrian tommotiidKulparina rostratafrom South Australia

2015 ◽  
Vol 89 (6) ◽  
pp. 920-932 ◽  
Author(s):  
Christian B. Skovsted ◽  
Glenn A. Brock ◽  
Lars E. Holmer ◽  
Timothy P. Topper ◽  
Cecilia M. Larsson
Keyword(s):  
South Australia ◽  
Early Cambrian ◽  
Filter Feeding ◽  
Feeding Mode ◽  
Mode Of Life

AbstractThe early Cambrian (Terreneuvian, Stage 2) tommotiidKulparina rostrataConway Morris and Bengtson in Bengtson et al., 1990 is revised. The pyramidal sclerites ofK. rostrataare shown to be bilaterally symmetrical and homologues of the symmetrical S1 sclerites ofPaterimitra pyramidalisLaurie, 1986. The scleritome ofK. rostratais also shown to include flattened asymmetrical sclerites that were originally described under the nameEccentrotheca guanoBengtson in Bengtson et al., 1990 and which correspond to the L-sclerites ofPaterimitra. A modified tubular scleritome and a sessile filter-feeding mode of life is envisaged forKulparina rostrata.

scholarly journals The Early Cambrian tommotiid Micrina , a sessile bivalved stem group brachiopod

2008 ◽  
Vol 4 (6) ◽  
pp. 724-728 ◽  
Author(s):  
Lars E Holmer ◽  
Christian B Skovsted ◽  
Glenn A Brock ◽  
James L Valentine ◽  
John R Paterson
Keyword(s):  
Sister Group ◽  
Simple Type ◽  
Early Cambrian ◽  
Filter Feeding ◽  
Stem Group ◽  
Sessile Organism ◽  
Phylogenetic Model

The tannuolinid Micrina belongs to the tommotiids—a common and widely distributed, but poorly understood, group of Early Cambrian fossil metazoans with multiple external organophosphatic sclerites. Recent findings of sessile articulated tommotiid scleritomes indicate that previous reconstructions of tommotiids as slug-like bilaterians with a dorsal cover of sclerites require detailed re-evaluation. Comparative ultrastructural work has already indicated that the tommotiids might be a sister group to the Brachiopoda, with Micrina representing the most derived and brachiopod-like bimembrate tommotiid. Here we further develop and strengthen this controversial phylogenetic model with a new reconstruction of Micrina , where the two types of sclerites—mitral and sellate—belong to a near bilaterally symmetrical bivalved sessile organism. This new scleritome configuration was tested by recreating an articulated bivalved Micrina from isolated mitral and sellate sclerites; both sclerites have muscles that would have enabled movement of the sclerites. The mitral and sellate sclerites of Micrina are considered to be homologous with the ventral and dorsal valves, respectively, of organophosphatic linguliform brachiopods, indicating that a simple type of filter-feeding within an enclosed bivalved shell had started to evolve in derived tannuolinids. The new reconstruction also indicates that the phylogenetic range of ‘bivalved’, sessile lophophorates is larger than previously suspected.

scholarly journals A Cambrian fossil from the Chengjiang fauna sharing characters with gilled lobopodians and radiodontans

2020 ◽  
Author(s):  
Jianni Liu ◽  
Jason A. Dunlop ◽  
Michael Steiner ◽  
Degan Shu
Keyword(s):  
Cephalic Region ◽  
Early Cambrian ◽  
Unique Combination ◽  
Filter Feeding ◽  
Stem Group ◽  
Velvet Worms ◽  
Early Palaeozoic ◽  
Early Radiation

Abstract 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 atavusgen. 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.

Life habit and enrolment in Calymenacea (Trilobita) and their significance for classification

1985 ◽  
Vol 76 (2-3) ◽  
pp. 307-318 ◽  
Author(s):  
W. Hammann
Keyword(s):  
Functional Analysis ◽  
Filter Feeder ◽  
Life Habit ◽  
Behavioural Patterns

ABSTRACTThe life habit of Neseuretus is reconstructed on the basis of functional analysis and compared with that of other Calymenacea. Neseuretus, like all Calymenidae, was probably a filter feeder, burrowing downward into the sediment, where it rested hidden in a U-shaped attitude. Homalonotidae developed frontal burrowing and Bathycheilidae probably lived on the sediment. These calymenid families have different enrolment and behavioural patterns. Enrolment structures are developed, analysis of which leads to an understanding of phylogeny. Bathycheilidae maintained an unspecialised spiral enrolment. Flexicalymeninae and Calymeninae developed an advanced spiral enrolment, while a pseudosphaeroidal enrolment was achieved along independent lines in Kerfornellinae and Homalonotidae.

scholarly journals Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event

2016 ◽  
Vol 113 (25) ◽  
pp. 6945-6948 ◽  
Author(s):  
Luis A. Buatois ◽  
Maria G. Mángano ◽  
Ricardo A. Olea ◽  
Mark A. Wilson
Keyword(s):  
Late Ordovician ◽  
Hard Substrate ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Continuous Increase ◽  
Late Cambrian ◽  
Unconsolidated Sediment ◽  
Underlying Causes ◽  
Hard Substrates ◽  
Shed Light

Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal–substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.

scholarly journals Early Cambrian chronostratigraphy and geochronology of South Australia

2018 ◽  
Vol 185 ◽  
pp. 498-543 ◽  
Author(s):  
Marissa J. Betts ◽  
John R. Paterson ◽  
Sarah M. Jacquet ◽  
Anita S. Andrew ◽  
Philip A. Hall ◽  
...  
Keyword(s):  
South Australia ◽  
Early Cambrian

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 A new early Cambrian bradoriid (Arthropoda) assemblage from the northern Flinders Ranges, South Australia

2014 ◽  
Vol 25 (1) ◽  
pp. 420-437 ◽  
Author(s):  
Marissa J. Betts ◽  
Timothy P. Topper ◽  
James L. Valentine ◽  
Christian B. Skovsted ◽  
John R. Paterson ◽  
...  
Keyword(s):  
South Australia ◽  
Early Cambrian ◽  
Flinders Ranges

Ediacaran scavenging as a prelude to predation

2018 ◽  
Vol 2 (2) ◽  
pp. 213-222 ◽  
Author(s):  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Microbial Mats ◽  
South Australia ◽  
Trace Fossil ◽  
Localized Source ◽  
Oxygen Levels ◽  
Stem Group ◽  
Ediacara Biota ◽  
Ecological Innovation ◽  
Large Predators ◽  
Ancient Ecosystems

Predation is one of the most fundamental ecological and evolutionary drivers in modern and ancient ecosystems. Here, we report the discovery of evidence of the oldest scavenging of shallowly buried bodies of iconic soft-bodied members of the Ediacara Biota by cryptic seafloor mat-burrowing animals that produced the furrow and levee trace fossil, Helminthoidichnites isp. These mat-burrowers were probably omnivorous, stem-group bilaterians that largely grazed on microbial mats but when following mats under thin sands, they actively scavenged buried Dickinsonia, Aspidella, Funisia and other elements of the Ediacara Biota. These traces of opportunistic scavengers of dead animals from the Ediacaran of South Australia represent a fundamental ecological innovation and a possible pathway to the evolution of macrophagous predation in the Cambrian. While the Ediacaran oceans may have had oxygen levels too low to support typical large predators, the Helminthoidichnites maker lived in and grazed on microbial mats, which may have provided a localized source of oxygen.

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