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Related Concept Videos

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Diversity of Protists III

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Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...
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The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms never become fossils. Moreover, the fossil record only exhibits fossils that have been discovered. Nevertheless, sedimentary rock fossils of long-lived, abundant, hard-bodied organisms dominate the fossil record. These fossils offer valuable information, such as an organism's physical form, behavior, and age. Studying the fossil record helps...
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Alveolates are a group of organisms recognized by the presence of alveoli, which are cytoplasmic sacs located beneath the cell membrane. While their function remains uncertain, alveoli may help regulate water balance by controlling how much water enters and leaves the cell. In dinoflagellates, these structures may serve as armor plates. There are three major types of alveolates: ciliates, which move using cilia; dinoflagellates, which use flagella for movement; and apicomplexans, which are...
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Amoebozoa represent a diverse group of terrestrial and aquatic protists that utilize lobe-shaped pseudopodia for locomotion and feeding. This characteristic differentiates them from the Rhizaria, which possess threadlike pseudopodia. The primary classifications within Amoebozoa include gymnamoebas, entamoebas, and the plasmodial and cellular slime molds. Phylogenetic evidence indicates that Amoebozoa diverged from a lineage that ultimately gave rise to fungi and animals.Gymnamoebas and...
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Gastrulation establishes the three primary tissues of an embryo: the ectoderm, mesoderm, and endoderm. This developmental process relies on a series of intricate cellular movements, which in humans transforms a flat, “bilaminar disc” composed of two cell sheets into a three-tiered structure. In the resulting embryo, the endoderm serves as the bottom layer, and stacked directly above it is the intermediate mesoderm, and then the uppermost ectoderm. Respectively, these tissue strata...
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Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the...
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Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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A Silurian pseudocolonial pterobranch.

Derek E G Briggs1, Nicolás Mongiardino Koch2

  • 1Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06520, USA; Yale Peabody Museum, New Haven, CT 06520, USA.

Current Biology : CB
|November 7, 2023
PubMed
Summary
This summary is machine-generated.

A newly discovered Silurian fossil, Rotaciurca superbus, is identified as a planktic pterobranch, a type of hemichordate. This finding suggests cephalodiscids, like graptolites, also inhabited the water column, with origins dating to the Cambrian period.

Keywords:
Bertie GroupPaleozoic planktonSiluriancephalodiscidgraptolitehemichordatephylogenyproblematicapterobranch

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Area of Science:

  • Paleontology
  • Marine Biology
  • Evolutionary Biology

Background:

  • Pterobranchs (Hemichordata) are rare sessile marine animals, with fossil graptolites widely used as zone fossils.
  • Living pterobranchs include Rhabdopleura and pseudocolonial cephalodiscids.
  • The Silurian Bertie Group is known for its diverse eurypterid fossils.

Purpose of the Study:

  • To describe and classify a problematic fossil from the Silurian Bertie Group.
  • To determine the phylogenetic placement and lifestyle of the new fossil, Rotaciurca superbus.
  • To estimate the divergence times of hemichordates and pterobranchs.

Main Methods:

  • Morphological analysis of the fossil's tube structures.
  • Phylogenetic analysis to determine evolutionary relationships.
  • Divergence time estimation using relaxed total-evidence clocks.

Main Results:

  • The fossil, Rotaciurca superbus, is identified as a pterobranch, specifically a planktic cephalodiscid with a unique float structure.
  • Phylogenetic analysis places Rotaciurca within the cephalodiscids, necessitating a new family, Rotaciurcidae.
  • Divergence time estimates place the origins of hemichordates and pterobranchs in the earliest Cambrian.

Conclusions:

  • Rotaciurca superbus represents the first known planktic cephalodiscid, indicating invasion of the water column by this group.
  • The discovery provides insights into the ecological roles of pseudocolonial macroinvertebrates in planktic communities.
  • The study refines the evolutionary timeline of hemichordates and pterobranchs, pushing their origins to the Cambrian.