scholarly journals A molecular palaeobiological hypothesis for the origin of aplacophoran molluscs and their derivation from chiton-like ancestors

2011 ◽  
Vol 279 (1732) ◽  
pp. 1259-1268 ◽  
Author(s):  
Jakob Vinther ◽  
Erik A. Sperling ◽  
Derek E. G. Briggs ◽  
Kevin J. Peterson
Keyword(s):  
Molecular Phylogeny ◽  
Molecular Clock ◽  
Sister Group ◽  
Crown Group ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Paraphyletic Assemblage

Aplacophorans have long been argued to be basal molluscs. We present a molecular phylogeny, including the aplacophorans Neomeniomorpha (Solenogastres) and Chaetodermomorpha (Caudofoveata), which recovered instead the clade Aculifera (Aplacophora + Polyplacophora). Our relaxed Bayesian molecular clock estimates an Early Ordovician appearance of the aculiferan crown group consistent with the presence of chiton-like molluscs with seven or eight dorsal shell plates by the Late Cambrian (approx. 501–490 Ma). Molecular, embryological and palaeontological data indicate that aplacophorans, as well as chitons, evolved from a paraphyletic assemblage of chiton-like ancestors. The recovery of cephalopods as a sister group to aculiferans suggests that the plesiomorphic condition in molluscs might be a morphology similar to that found in monoplacophorans.

What the Ur-crustacean Looked Like

2020 ◽  
pp. 1-20
Author(s):  
Stefan Richter ◽  
Christian Wirkner
Keyword(s):  
Larval Development ◽  
Olfactory System ◽  
Marine Species ◽  
Sister Group ◽  
Central Complex ◽  
Compound Eyes ◽  
Last Common Ancestor ◽  
Crown Group ◽  
Nauplius Larva ◽  
Paraphyletic Assemblage

Crustaceans are a paraphyletic assemblage within arthropods. Hexapoda (insects) are nested within crustaceans, with the Remipedia the most likely sister group to Hexapoda. Together, crustaceans and hexapods comprise the monophyletic Tetraconata (also called Pancrustacea). Herein, we “reconstruct” the last common ancestor of crown group Tetraconata, calling it the ur-crustacean. We base our reconstruction on knowledge of extant crustaceans. We tentatively suggest that the ur-crustacean displayed certain characters: The ur-crustacean was a free-living marine species with a distinct head and equipped with two pairs of sensory limbs (antennule and antenna), mandibles, and two more pairs of mouthparts (maxillule and maxilla). We suggest that no further segments were fused to the head and that no maxilliped was present. The ur-crustacean may or may not have possessed a carapace. Its brain was complex, with an extended olfactory system, possibly a central complex, and a lateral protocerebrum containing at least two optical neuropils. The protocerebrum was connected to a nauplius eye as well as to compound eyes. The ur-crustacean might have had a uniformly segmented trunk posterior to its five-segmented head or (less probably) may have possessed two tagmata, a limb-bearing thorax and a limb-less abdomen. It had a heart that might have extended right through the trunk independently of tagmatization. Its thoracopodal appendages were true arthropodal (consisting of podomeres) with a protopod (probably subdivided into coxa and basis), an exopod, and an endopod. Larval development started with a nauplius larva (probably an orthonauplius).

Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation

2019 ◽  
Vol 484 (1) ◽  
pp. 61-65
Author(s):  
R. M. Antonuk ◽  
A. A. Tretyakov ◽  
K. E. Degtyarev ◽  
A. B. Kotov
Keyword(s):  
Complex Formation ◽  
Central Asian Orogenic Belt ◽  
Early Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Central Asian ◽  
Geochronological Study ◽  
Three Stages ◽  
Late Neoproterozoic ◽  
Quartz Monzodiorites

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

The fossil record of Phasmida (Insecta: Neoptera)

2000 ◽  
Vol 31 (4) ◽  
pp. 473-480 ◽  
Author(s):  
Erich Tilgner
Keyword(s):  
Dominican Republic ◽  
Molecular Clock ◽  
Fossil Record ◽  
Sister Group ◽  
Baltic Amber ◽  
Molecular Clock Dating

AbstractA review of the Phasmida fossil record is provided. No fossils of Timema Scudder are known. Euphasmida fossils include: Agathemera reclusa Scudder, Electrobaculum gracilis Sharov, Eophasma oregonense Sellick, Eophasma minor Sellick, Eophasmina manchesteri Sellick, Pseudoperla gracilipes Pictet, Pseudoperla lineata Pictet and various unclassified species from Grube Messel, Baltic amber, and Dominican Republic amber. The oldest documented Euphasmida fossils are 44-49 million years old; molecular clock dating underestimates the origin of the sister group Timema by at least 24 million years.

New Monoplacophora (Mollusca) from Late Cambrian and Early Ordovician of Missouri

1986 ◽  
Vol 60 (3) ◽  
pp. 606-626 ◽  
Author(s):  
Bruce L. Stinchcomb
Keyword(s):  
New Species ◽  
New Genus ◽  
New Genera ◽  
New Genus And Species ◽  
Upper Cambrian ◽  
Early Ordovician ◽  
New Family ◽  
Late Cambrian ◽  
Lower Ordovician ◽  
A New Species

Fourteen new species and six new genera of the molluscan class Monoplacophora are described from the Upper Cambrian Potosi and Eminence formations and the Lower Ordovician Gasconade Formation of the Ozark Uplift of Missouri and some new biostratigraphic horizons are introduced. A new superfamily, the Hypseloconellacea nom. trans. Knight, 1956, and a new family, the Shelbyoceridae, are named. The genus Proplina is represented by five new species: P. inflatus, P. suttoni from the Cambrian Potosi Formation, P. arcua from the Cambrian Eminence Formation and P. meramecensis and P. sibeliusi from the Lower Ordovician Gasconade Formation. A new genus and species in the subfamily Proplininae, Ozarkplina meramecensis, is described from the Upper Cambrian Eminence Formation. Four new monoplacophoran genera in the superfamily Hypseloconellacea and their species are described, including: Cambrioconus expansus, Orthoconus striatus, Cornuella parva from the Eminence Formation, and Gasconadeoconus ponderosa, G. waynesvillensis, G. expansus from the Gasconade Formation. A new genus in the new family Shelbyoceridae, Archeoconus missourensis, is described from the Eminence Formation and a new species of Shelbyoceras, S. bigpineyensis, is described from the Gasconade Formation.

Tectonic controls on late Cambrian-Early Ordovician deposition in Cordillera oriental (Northwest Argentina)

2020 ◽  
Vol 109 (6) ◽  
pp. 1897-1920 ◽  
Author(s):  
Romain Vaucher ◽  
N. Emilio Vaccari ◽  
Diego Balseiro ◽  
Diego F. Muñoz ◽  
Antoine Dillinger ◽  
...  
Keyword(s):  
Early Ordovician ◽  
Northwest Argentina ◽  
Late Cambrian

scholarly journals Jaw elements in Plumulites bengtsoni confirm that machaeridians are extinct armoured scaleworms

2019 ◽  
Vol 286 (1907) ◽  
pp. 20191247 ◽  
Author(s):  
Luke A. Parry ◽  
Gregory D. Edgecombe ◽  
Dan Sykes ◽  
Jakob Vinther
Keyword(s):  
Phylogenetic Analysis ◽  
Early Evolution ◽  
The Body ◽  
Common Origin ◽  
Discrete Elements ◽  
Crown Group ◽  
Total Group ◽  
Early Ordovician ◽  
Jaw Apparatus ◽  
Competing Hypotheses

Machaeridians are Palaeozoic animals that are dorsally armoured with serialized, imbricating shell plates that cover or enclose the body. Prior to the discovery of an articulated plumulitid machaeridian from the Early Ordovician of Morocco that preserved unambiguous annelid characters (segmental parapodia with chaetae), machaeridians were a palaeontological mystery, having been previously linked to echinoderms, barnacles, tommotiids (putative stem-group brachiopods) or molluscs. Although the annelid affinities of machaeridians are now firmly established, their position within the phylum and relevance for understanding the early evolution of Annelida is less secure, with competing hypotheses placing Machaeridia in the stem or deeply nested within the crown group of annelids. We describe a scleritome of Plumulites bengtsoni from the Fezouata Formation of Morocco that preserves an anterior jaw apparatus consisting of at least two discrete elements that exhibit growth lines. Although jaws have multiple independent origins within the annelid crown group, comparable jaws are present only within Phyllodocida, the clade that contains modern aphroditiforms (scaleworms and relatives). Phylogenetic analysis places a monophyletic Machaeridia within the crown group of Phyllodocida in total-group Aphroditiformia, consistent with a common origin of machaeridian shell plates and scaleworm elytrae. The inclusion of machaeridians in Aphroditiformia truncates the ghost lineage of Phyllodocida by almost a hundred million years.

Sign in / Sign up

Export Citation Format

Share Document