A 365-Million-Year-Old Freshwater Community Reveals Morphological and Ecological Stasis in Branchiopod Crustaceans.

Branchiopod crustaceans are represented by fairy, tadpole, and clam shrimps (Anostraca, Notostraca, Laevicaudata, Spinicaudata), which typically inhabit temporary freshwater bodies, and water fleas (Cladoceromorpha), which live in all kinds of freshwater and occasionally marine environments [1, 2]. The earliest branchiopods occur in the Cambrian, where they are represented by complete body fossils from Sweden such as Rehbachiella kinnekullensis [3] and isolated mandibles preserved as small carbonaceous fossils [4-6] from Canada. The earliest known continental branchiopods are associated with hot spring environments [7] represented by the Early Devonian Rhynie Chert of Scotland (410 million years ago) and include possible stem-group or crown-group Anostraca, Notostraca, and clam shrimps or Cladoceromorpha [8-10], which differ morphologically from their modern counterparts [1, 2, 11].

Fate and nature of the onychophoran mouth-anus furrow and its contribution to the blastopore.

The ancestral states of bilaterian development, and which living groups have conserved them the most, has been a controversial topic in biology for well over a hundred years. In recent years, the idea that gastrulation primitively proceeded via the formation of a slit-like blastopore that then evolved into either protostomy or deuterostomy has gained renewed attention and some molecular developmental support. One of the key pieces of evidence for this 'amphistomy' theory comes from the onychophorans, which form a clear ventral groove during gastrulation.

A complete insect from the Late Devonian period.

After terrestrialization, the diversification of arthropods and vertebrates is thought to have occurred in two distinct phases, the first between the Silurian and the Frasnian stages (Late Devonian period) (425-385 million years (Myr) ago), and the second characterized by the emergence of numerous new major taxa, during the Late Carboniferous period (after 345 Myr ago). These two diversification periods bracket the depauperate vertebrate Romer's gap (360-345 Myr ago) and arthropod gap (385-325 Myr ago), which could be due to preservational artefact. Although a recent molecular dating has given an age of 390 Myr for the Holometabola, the record of hexapods during the Early-Middle Devonian (411.