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

Abstract

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]. Here we report the discovery of an ephemeral pool branchiopod community from the 365-million-year-old Strud locality of Belgium. It is characterized by new anostracans and spinicaudatans, closely resembling extant species, and the earliest notostracan, Strudops goldenbergi [12]. These branchiopods released resting eggs into the sediment in a manner similar to their modern representatives [1, 2]. We infer that this reproductive strategy was critical to overcoming environmental constraints such as seasonal desiccation imposed by living on land. The pioneer colonization of ephemeral freshwater pools by branchiopods in the Devonian was followed by remarkable ecological and morphological stasis that persists to the present day.

Placoderm Assemblage from the Tetrapod-Bearing Locality of Strud (Belgium, Upper Famennian) Provides Evidence for a Fish Nursery

“…The tetrapod remains were found in association with very abundant flora [2], a putative insect [3–5], continental crustaceans [6–9] as well as sarcopterygian [10–12] and as yet undescribed acanthodian and actinopterygian fishes. The placoderm assemblage has been recently described and includes the antiarch Grossilepis rikiki , the groenlandaspidid Turrisaspis strudensis and the phyllolepidid Phyllolepis undulata [13,14].…”

A New Chytridiomycete Fungus Intermixed with Crustacean Resting Eggs in a 407-Million-Year-Old Continental Freshwater Environment

“…Branchiopods were another dominant component of this ecosystem, the fossils being frequently disarticulated but without decay induced by fungi or traces of damage caused by other organisms. As recently suggested for the branchiopods from the Upper Devonian [48], temporary pools were likely an environment devoid of predators. In modern aquatic ecosystems parasitic chytrids are the dominant parasites [50].…”

“…The resemblance of the Rhynie Chert spiny structures to anostracan cysts provides a circumstantial argument for an anostracan identity for Lepidocaris . Resting eggs have recently been identified in branchiopods from the Upper Devonian (Famennian), including species of Notostraca and Spinicaudata [48]. The former, measuring ca 71 μm, are closer in size to the Rhynie Chert specimens than are extant branchiopod resting eggs.…”

Functional morphology of amplexus (clasping) in spinicaudatan clam shrimps (Crustacea, Branchiopoda) and its evolution in bivalved branchiopods: A video-based analysis

“…The assumed male of the Devonian Lepidocaris has a pair of large clasper-like first maxillae (Scourfield, 1926;Walossek, 1993;Olesen, 2009), and spinicaudatans with two pairs of preserved claspers have been found from both the Carboniferous and the Jurassic (Wentang and Yanbin, 1990;Orr and Briggs, 1999). Clasper structures have not been recognized in the even older (late Devonian) spinicaudatan fauna of Strud, Belgium (Gueriau, 2016), but this is probably due to vagaries of preservation. Outside Branchiopoda claspers are, among others, found in the crustacean group Ostracoda (Cohen and Morin, 1990;Martens, 2000), which resembles clam shrimps in having a bivalved carapace.…”