Sébastien Olive

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 (411.5–391 Myr ago, Pragian to Givetian stages) is exceptionally sparse and based on fragmentary remains, which hinders the timing of this diversification. Indeed, although Devonian Archaeognatha are problematic, the Pragian of Scotland has given some Collembola and the incomplete insect Rhyniognatha, with its diagnostic dicondylic, metapterygotan mandibles. The oldest, definitively winged insects are from the Serpukhovian stage (latest Early Carboniferous period). Here we report the first complete Late Devonian insect, which was probably a terrestrial species. Its ‘orthopteroid’ mandibles are of an omnivorous type, clearly not modified for a solely carnivorous diet. This discovery narrows the 45-Myr gap in the fossil record of Hexapoda, and demonstrates further a first Devonian phase of diversification for the Hexapoda, as in vertebrates, and suggests that the Pterygota diversified before and during Romer’s gap.

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]. 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.

Garrouste et al. reply

replying to T. Hörnschemeyer et al. Nature 494, 10.1038/nature11887 (2013)Since the nineteenth century, Devonian insects have repeatedly proven to be something else, the sole exception being Rhyniognatha. Recently the Devonian insect Strudiella devonica has been denied by Hörnschemeyer et al., who could not “confirm the presence of a mandible or of mandibular teeth”.

Devonian Antiarch Placoderms from Belgium Revisited

Anatomical, systematic, and paleobiogeographical data on the Devonian antiarchs from Belgium are reviewed, updated and completed thanks to new data from the field and re-examination of paleontological collections. The material of Bothriolepis lohesti is enhanced and the species redescribed in more detail. An undetermined species of Bothriolepis is recorded from the Famennian of Modave (Liège Province), one species of Asterolepis redescribed from the Givetian of Hingeon and another one described from the Givetian of Mazy (Namur Province). Grossilepis rikiki sp. nov. is recorded from the Famennian tetrapod-bearing locality of Strud (Namur Province) and from the Famennian of Moresnet (Liège Province). It is the first occurrence of Grossilepis after the Frasnian and on the central southern coast of the Euramerican continent. Its occurrence in the Famennian of Belgium may be the result of a late arrival from the Moscow Platform and the Baltic Depression, where the genus is known from Frasnian deposits. Remigolepis durnalensis sp. nov. is described from the Famennian of Spontin near Durnal (Namur Province). Except for the doubtful occurrence of Remigolepis sp. in Scotland, this is the first record of this genus in Western Europe. Its occurrence in Belgium reinforces the strong faunal affinities between Belgium and East Greenland and the hypothesis of a hydrographical link between the two areas during the Late Devonian.

Stratigraphy and depositional environments of the Late Famennian (Late Devonian) of Southern Belgium and characterization of the Strud locality

The Famennian (Upper Devonian, c . 372 to 359 Ma) strata of Belgium have recently received much attention after the discoveries of early tetrapod remains and outstandingly preserved continental arthropods. The Strud locality has yielded a diverse flora and fauna including seed-plants, tetrapods, various placoderm, actinopterygian, acanthodian and sarcopterygian fishes, crustaceans (anostracans, notostracans, conchostracans and decapods) and a putative complete insect. This fossil assemblage is one of the oldest continental – probably fresh-water – ecosystems with a considerable vertebrate and invertebrate diversity. The study of the palaeoenvironment of the Strud locality is crucial because it records one of the earliest and most important phases of tetrapod evolution that took place after their emergence but before their terrestrialization. It raises the question of environmental and ecological conditions for the Devonian aquatic ecosystem and the selection pressures occurring at the onset of tetrapod terrestrialization. The present study characterized the fluvial facies of the Upper Famennian sedimentary rocks of Strud and the surrounding areas. The exceptional preservation of arthropods and plants in the main fossiliferous layers is explained by rapid burial in the fine-grained sediment of the quiet and confined flood plain environment. Newly investigated fossiliferous sections in the Meuse–Samson area led to the description and correlation of key sections (Strud, Wierde and Jausse sections, complemented by the less continuous Haltinne, Huy and Coutisse sections). Moreover, the investigated sections allowed a review of the age of the fossiliferous horizon, which is now definitely considered to be Late Famennian in age.

A new placoderm fish (Acanthothoraci) from the Early Devonian Jauf Formation (Saudi Arabia)

ABSTRACT An exceptionally well-preserved new acanthothoracid (placoderm fish) presenting complete endocranium and skull roof, from Saudi Arabia (Qasr Limestone Member, Jauf Formation), Early Devonian in age, is described as Arabosteus variabilis n. gen., n. sp. Compared to other Acanthothoraci, the new taxon exhibits a skull roof variable in its dermal plate distribution (e.g., a supernumerary plate: the posterior central plate) and sensory line pattern. Even the different specimens of this taxon show such variability between them. Arabosteus variabilis n. gen., n. sp. enlarges the scope of our knowledge of Acanthothoraci and Placodermi in general. Traditionally, the Arthrodira, one of the historically earliest described groups, provide the standard reference model for the placoderm skull roof pattern. The interpretation of the acanthothoracid skull roof pattern of the Saudi taxon from an arthrodiran model and the establishment of homologies is impossible to resolve unless based on prior assumptions (e.g., hypothesis of fragmentation or fusion for the paranuchal plate complex). The lateral line system of A. variabilis n. gen., n. sp. is unstable (e.g., presence or absence of the postmarginal sensory line canal) making it ambiguous to define bone homology and terminology. Consequently spatial distribution of skull roof plates has been retained for such a task with a minimal reference to the instable features of the sensory line groove distribution.

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

The placoderm fauna of the upper Famennian tetrapod-bearing locality of Strud, Belgium, includes the antiarch Grossilepis rikiki, the arthrodire groenlandaspidid Turrisaspis strudensis and the phyllolepidid Phyllolepis undulata. Based on morphological and morphometric evidence, the placoderm specimens from Strud are predominantly recognised as immature specimens and this locality as representing a placoderm nursery. The Strud depositional environment corresponds to a channel in an alluvial plain, and the presence of a nursery in such environment could have provided nutrients and protection to the placoderm offspring. This represents one of the earliest pieces of evidence for this sort of habitat partitioning in vertebrate history, with adults living more distantly from the nursery and using the nursery only to spawn or give live birth.

A New Species of Groenlandaspis Heintz, 1932 (Placodermi, Arthrodira), from the Famennian (Late Devonian) of Belgium

ABSTRACT A new species of the phlyctaeniid arthrodire genus Groenlandaspis from the upper Famennian of Belgium is described. The remains of Groenlandaspis potyi, sp. nov., consist of dissociated thoracic armor elements, but the specimen designated to be the holotype displays the median dorsal, anterior, and posterior dorsolateral plates in articulation. Though incomplete, the new species is characterized by an equilateral triangle-shaped median dorsal plate, a protruding posterodorsal apron of the posterior dorsolateral plate behind the overlap area for the median dorsal plate, and an overall lack of ornamentation. Groenlandaspis potyi, sp. nov., constitutes the second occurrence of a Groenlandaspis species in continental Europe after the description of Groenlandaspis thorezi from upper Famennian quarries of Belgium. Another probable new species of Groenlandaspis is also described, though of unknown locality and horizon; it can, however, be deduced to be from the upper Famennian of Belgium without more precision. Together with some unpublished material of groenlandaspidids from the Famennian tetrapod-bearing locality of Strud, this material highlights the richness of Groenlandaspididae diversity in Belgium. The discovery of Groenlandaspis potyi, sp. nov., in Belgium reinforces the Famennian global distribution of this genus during this period. Also, because these organisms have been considered as nonmarine indicators, this material is another argument pleading for close relationships between Euramerica and Gondwana around the Frasnian—Famennian boundary.

The growth of the skull roof plates in Arabosteus variabilis (Acanthothoraci, Placodermi) from the Early Devonian Jauf Formation (Saudi Arabia): Preliminary results

The skull roof growth of Arabosteus variabilis (Acanthothoraci), from the Pragian-Early Emsian of Saudi Arabia is studied on the basis of well-preserved growth lines on the dermal plates. A clear tendency towards growth in length, i.e. allometry in length, can be observed for all studied skull roof plates of Arabosteus variabilis as well as for the skull roof in general. Each studied plate displays particular growth shaping the skull roof according to its position in the skull roof pattern, e.g., the preorbital plate controls the shape of the part of the orbit and the nuchal plate retains the relative proportions in the skull roof during growth.