scholarly journals Loss in the making: absence of pelvic fins and presence of paedomorphic pelvic girdles in a Late Devonian antiarch placoderm (jawed stem-gnathostome)

2018 ◽  
Vol 14 (6) ◽  
pp. 20180199 ◽  
Author(s):  
France Charest ◽  
Zerina Johanson ◽  
Richard Cloutier
Keyword(s):  
Elemental Composition ◽  
Developmental Plasticity ◽  
Late Devonian ◽  
Ontogenetic Changes ◽  
Endochondral Bone ◽  
Early Devonian ◽  
Secondary Loss ◽  
Paired Female ◽  
Female Genital

Within jawed vertebrates, pelvic appendages have been modified or lost repeatedly, including in the most phylogenetically basal, extinct, antiarch placoderms. One Early Devonian basal antiarch, Parayunnanolepis , possessed pelvic girdles, suggesting the presence of pelvic appendages at the origin of jawed vertebrates; their absence in more derived antiarchs implies a secondary loss. Recently, paired female genital plates were identified in the Late Devonian antiarch, Bothriolepis canadensis , in the position of pelvic girdles in other placoderms. We studied these putative genital plates along an ontogenetic series of B. canadensis ; ontogenetic changes in their morphology, histology and elemental composition suggest they represent endoskeletal pelvic girdles composed of perichondral and endochondral bone. We suggest that pelvic fins of derived antiarchs were lost, while pelvic girdles were retained, but reduced, relative to Parayunnanolepis . This indicates developmental plasticity and evolutionary lability in pelvic appendages, shortly after these elements evolved at the origin of jawed vertebrates.

scholarly journals Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

2021 ◽  
Vol 100 ◽  
Author(s):  
Alexander J.P. Houben ◽  
Geert-Jan Vis
Keyword(s):  
The Netherlands ◽  
Core Material ◽  
Late Devonian ◽  
Time Interval ◽  
The South ◽  
Early Devonian ◽  
The North ◽  
Depositional Settings ◽  
Palynological Study ◽  
Devonian Age

Abstract Knowledge of the stratigraphic development of pre-Carboniferous strata in the subsurface of the Netherlands is very limited, leaving the lithostratigraphic nomenclature for this time interval informal. In two wells from the southwestern Netherlands, Silurian strata have repeatedly been reported, suggesting that these are the oldest ever recovered in the Netherlands. The hypothesised presence of Silurian-aged strata has not been tested by biostratigraphic analysis. A similar lack of biostratigraphic control applies to the overlying Devonian succession. We present the results of a palynological study of core material from wells KTG-01 and S05-01. Relatively low-diversity and poorly preserved miospore associations were recorded. These, nonetheless, provide new insights into the regional stratigraphic development of the pre-Carboniferous of the SW Netherlands. The lower two cores from well KTG-01 are of a late Silurian (Ludlow–Pridoli Epoch) to earliest Devonian (Lochkovian) age, confirming that these are the oldest sedimentary strata ever recovered in the Netherlands. The results from the upper cored section from the pre-Carboniferous succession in well KTG-01 and the cored sections from the pre-Carboniferous succession in well S05-01 are more ambiguous. This inferred Devonian succession is, in the current informal lithostratigraphy of the Netherlands, assigned to the Banjaard group and its subordinate Bollen Claystone formation, of presumed Frasnian (i.e. early Late Devonian) age. Age-indicative Middle to Late Devonian palynomorphs were, however, not recorded, and the overall character of the poorly preserved palynological associations in wells KTG-01 and S05-01 may also suggest an Early Devonian age. In terms of lithofacies, however, the cores in well S05-01 can be correlated to the upper Frasnian – lower Famennian Falisolle Formation in the Campine Basin in Belgium. Hence, it remains plausible that an unconformity separates Silurian to Lower Devonian strata from Upper Devonian (Frasnian–Famennian) strata in the SW Netherlands. In general, the abundance of miospore associations points to the presence of a vegetated hinterland and a relatively proximal yet relatively deep marine setting during late Silurian and Early Devonian times. This differs markedly from the open marine depositional settings reported from the Brabant Massif area to the south in present-day Belgium, suggesting a sediment source to the north. The episodic presence of reworked (marine) acritarchs of Ordovician age suggests the influx of sedimentary material from uplifted elements on the present-day Brabant Massif to the south, possibly in relation to the activation of a Brabant Arch system.

Late Silurian—early Devonian biogeography, provincialism, evolution and extinction

1985 ◽  
Vol 309 (1138) ◽  
pp. 323-339 ◽  
Keyword(s):  
Late Devonian ◽  
Time Interval ◽  
Early Devonian ◽  
Marine Benthos ◽  
Higher Taxa ◽  
Coal Deposits ◽  
Family Level ◽  
Biotic Events ◽  
Adaptive Radiations ◽  
Extinction Events

There is increasing marine to continental regression from the latest Silurian until the latter half of the early Devonian, when a major transgressive trend is initiated which achieves its maximum in the later middle Devonian and late Devonian. Data suggest a relatively high climatic gradient, but no evidence favouring continental, sea-level glaciation during the late Silurian-early Devonian. Arid climate evidence (marine evaporites, calcretes) shows a well-developed arid belt. Coal deposits are lacking before the late Devonian. Palaeogeography of the time interval is disputed, largely owing to the use of different classes of data - remanent magnetic, lithological, biogeographical. I employ a pangaeic reconstruction because it fits the available lithological and biogeographical data comfortably, but I am under no illusions about its being the ‘correct’ palaeogeography. Rate of phyletic evolution of marine benthos speeds up during the time interval owing to a steadily increasing level of provincialism, that is, cutting up biogeographical entities into smaller entities with consequent smaller populations. There are no major marine adaptive radiations, nor evidence for any marked extinction events during the interval. Few family level and higher taxa become extinct during this time interval; such units as the halysitid corals, pentamerinid brachiopods, and graptoloid graptolites are exceptional. Few adaptive radiations, such as those of the ammonoids and terebratuloids occur during the interval. The absence of other major biotic events during the interval is consistent with its position well within ecologic—evolutionary unit VI (A. J. Boucot, J. Paleont . 57, 1-30, 1983).

Review of the Devonian camerate crinoid Bogotacrinus scheibei Schmidt from Colombia

1987 ◽  
Vol 61 (4) ◽  
pp. 750-757 ◽  
Author(s):  
George C. Mcintosh
Keyword(s):  
North America ◽  
Western Europe ◽  
Lower Devonian ◽  
Appalachian Basin ◽  
Upper Devonian ◽  
Eastern North America ◽  
Late Devonian ◽  
Early Devonian ◽  
Lower Upper

Two recently collected specimens of Bogotacrinus scheibei Schmidt, 1937, from the Devonian (Emsian–Eifelian) Floresta Formation of Colombia reveal that Bogotacrinus is a dicyclic camerate crinoid genus closely related to Pterinocrinus Goldring, 1923 (Lower–Upper Devonian of eastern North America and western Europe), and Ampurocrinus McIntosh, 1981 (Lower Devonian of Bolivia). The new diplobathrid camerate crinoid family Pterinocrinidae, characterized by species with low conical dicyclic cups and rami composed of compound, bipinnulate brachials, is herein proposed to accommodate these three genera. This family originated in western Europe and migrated into the Malvinokaffric and southern Eastern Americas Realms during the Early Devonian and into the northeastern Appalachian Basin by the Late Devonian.

scholarly journals Endochondral bone in an Early Devonian ‘placoderm’ from Mongolia

2020 ◽  
Author(s):  
Martin D. Brazeau ◽  
Sam Giles ◽  
Richard P. Dearden ◽  
Anna Jerve ◽  
Y.A. Ariunchimeg ◽  
...  
Keyword(s):  
Phylogenetic Analyses ◽  
Sister Group ◽  
New Taxon ◽  
Endochondral Bone ◽  
Early Devonian ◽  
Skeletal Tissue ◽  
Bony Fishes ◽  
Computed Microtomography ◽  
Living Species ◽  
X Ray Computed

Endochondral bone is the main internal skeletal tissue of nearly all osteichthyans—the group comprising more than 60,000 living species of bony fishes and tetrapods. Chondrichthyans (sharks and their kin) are the living sister group of osteichthyans and have cartilaginous endoskeletons, long considered the ancestral condition for all jawed vertebrates (gnathostomes). The absence of bone in modern jawless fishes and the absence of endochondral ossification in early fossil gnathostomes appears to lend support to this conclusion. Here we report the discovery of extensive endochondral bone in Minjinia turgenensis, a new genus and species of ‘placoderm’-like fish from the Early Devonian (Pragian) of western Mongolia described using x-ray computed microtomography (XR-µCT). The fossil consists of a partial skull roof and braincase with anatomical details providing strong evidence of placement in the gnathostome stem group. However, its endochondral space is filled with an extensive network of fine trabeculae resembling the endochondral bone of osteichthyans. Phylogenetic analyses place this new taxon as a proximate sister group of the gnathostome crown. These results provide direct support for theories of generalised bone loss in chondrichthyans. Furthermore, they revive theories of a phylogenetically deeper origin of endochondral bone and its absence in chondrichthyans as a secondary condition.

scholarly journals The life cycle in late Paleozoic eryopid temnospondyls: developmental variation, plasticity and phylogeny

Fossil Record ◽  
2021 ◽  
Vol 24 (2) ◽  
pp. 295-319
Author(s):  
Rainer R. Schoch
Keyword(s):  
Life Cycle ◽  
Algal Blooms ◽  
Developmental Plasticity ◽  
Principal Component ◽  
Limiting Factors ◽  
Ontogenetic Changes ◽  
Apex Predators ◽  
Developmental Variation ◽  
Broad Variation ◽  
Range Of Variation

Abstract. Eryopid temnospondyls were large apex predators in Carboniferous and Permian stream and lake habitats. The eryopid life cycle is exemplified by Onchiodon labyrinthicus from Niederhäslich (Saxony, Germany), which is represented by numerous size classes from small larvae to heavily ossified adults. Morphometric and principal component analyses provide new insights into ontogenetic changes in O. labyrinthicus, and comparison with adults of other eryopids documents phylogenetic patterns in the occupation of morphospace. Compared with small specimens of Sclerocephalus spp., immature O. labyrinthicus occupies a neighboring but much larger space, corresponding to a broader range of variation. Adults of Actinodon frossardi map with some juveniles of O. labyrinthicus, whereas other juveniles of the latter lie close to adults of O. thuringiensis, Glaukerpeton avinoffi and Osteophorus roemeri. Morphospace occupation of adult eryopids is partly consistent with cladistic tree topology, which gives the following branching pattern: Actinodon frossardi forms the basalmost eryopid, followed by Osteophorus roemeri, Glaukerpeton avinoffi and the genus Onchiodon (O. labyrinthicus + O. thuringiensis); then Clamorosaurus nocturnus; and finally the monophyletic genus Eryops. The presumably juvenile skull of Eryops anatinus falls well outside the domains of both adult eryopids and immature O. labyrinthicus, showing a unique combination of juvenile and adult features. Instead, Onchiodon langenhani and the Ruprechtice specimens referred to O. labyrinthicus map within the domain of immature O. labyrinthicus. Raised levels of variation in O. labyrinthicus coincide with evidence of a stressed habitat, in which limiting factors were fluctuating salinity, absence of fishes, enhanced competition and seasonal algal blooms. The documented broad variation was possibly caused by developmental plasticity responding to fluctuations in lake hydrology and nutrients in this small, short-lived water body.

Cornwallis Fold Belt and the mechanism of basement uplift

1977 ◽  
Vol 14 (6) ◽  
pp. 1374-1401 ◽  
Author(s):  
J. Wm. Kerr
Keyword(s):  
Sedimentary Cover ◽  
Basic Structure ◽  
Vertical Displacement ◽  
Crystalline Basement ◽  
Normal Faults ◽  
Late Devonian ◽  
Fold Belt ◽  
Early Devonian ◽  
The North ◽  
Sverdrup Basin

Cornwallis Fold Belt is a north-trending anticlinorium more than 650 km (400 mi) long, that extends from the Precambrian Shield to the Sverdrup Basin. It is the folded and faulted sedimentary suprastructure that overlies Precambrian crystalline basement rocks of the Boothia Horst. The horst and fold belt represent lower and intermediate levels of the Boothia Uplift. Evolution of the Cornwallis Fold Belt includes two phases, formation and modification.Formation. The basic structure of the Cornwallis Belt, a relatively simple, steep-sided, north-plunging anticlinorium, was formed in the interval from Proterozoic to Late Devonian time during several discrete phases of deformation that involved a similar stress pattern. These phases can be attributed to pulses of differential vertical uplift of the underlying Boothia Horst. The earliest phases involved periods of gentle arching of the crystalline basement and sedimentary cover in late Proterozoic and early Paleozoic times. The fold belt was formed mainly by the Cornwallis Disturbance (new name) which involved further differential vertical uplift, and comprised several pulses: (1) Early Silurian, mild, affecting only part of the belt; (2) Early Devonian, very strong, affecting the entire belt; (3) late Early Devonian, moderately strong, affecting the entire belt; (4) Late Devonian, moderately strong, affecting the entire belt. Each pulse was a cycle that began with uplift and erosion of the fold belt and shedding of detritus into the adjacent basins, and was followed by broader regional subsidence and the resumption of deposition on the belt. Between pulses of uplift there was regional subsidence, during which the fold belt subsided less than the flanking basins and received less sediments.Differential vertical displacement originated in the crystalline basement, occurring along fault zones that define the Boothia Horst, and are parallel to and controlled by a steep to vertical north-trending foliation. Faults extend into the sedimentary suprastructure comprising the overlying Cornwallis Fold Belt, and change gradually upward from vertical faults to high-angle reverse faults, overturned anticlines, and finally to asymmetric anticlines. Because the fold belt plunges north, this gradational sequence occurs from south to north in the exposed part of the fold belt. Structures formed by early pulses were rejuvenated by later pulses with the same sense of movement.Modification. The basic structure of the Cornwallis Fold Belt was modified by other types of deformation during the interval from Late Devonian to the present. Many of the preexisting faults were reactivated, but with a different sense of movement. During the Late Devonian to Middle Pennsylvanian Ellesmerian Orogeny, southward overriding of upper levels of the sedimentary succession produced folds in the rocks east and west of the Cornwallis Fold Belt which had not been previously deformed and could easily be displaced southward on an underlying décollement surface. The north-trending Cornwallis Fold Belt, however, was an obstacle to southward overriding in which the effects of overriding were reduced. Zones of interference structures developed near the margins, guided by older basement-controlled structures. Left-lateral faults were developed on the western margin and right-lateral movement is probable on the eastern margin.The Cornwallis Fold Belt extends an unknown distance northward beneath the younger rocks of the Sverdrup Basin. These younger rocks were deposited during a long period of northward downwarping that began in mid-Mississippian time. This same downwarping caused an abrupt increase in the northward plunge of the fold belt.During the Cretaceous–Tertiary Eurekan Rifting Episode the Cornwallis Fold Belt was fragmented by block faulting. The horsts form islands, and the grabens form submarine channels, some of which contain thick sections of semiconsolidated Cretaceous–Tertiary sediments. Numerous other normal faults that occur within the fold belt probably formed at this time. Cretaceous–Tertiary faults within the Cornwallis Fold Belt have a rectilinear pattern that was inherited from preexisting structures.

New insights into the origins and radiation of the mid-Palaeozoic Gondwanan stem tetrapods

2018 ◽  
Vol 109 (1-2) ◽  
pp. 139-155 ◽  
Author(s):  
John A. LONG ◽  
Alice M. CLEMENT ◽  
Brian CHOO
Keyword(s):  
Middle Devonian ◽  
Late Devonian ◽  
Early Devonian ◽  
Biogeographic History ◽  
History Of ◽  
Scan Data ◽  
Devonian Age ◽  
High Degree ◽  
Phylogenetic Models

ABSTRACTThe earliest tetrapodomorph fishes appear in Chinese deposits of Early Devonian age, and by the Middle Devonian they were widespread globally. Evidence for the earliest digitated tetrapods comes from largely uncontested Middle Devonian trackways and Late Devonian body fossils. The East Gondwana Provence (Australasia, Antarctica) fills vital gaps in the phylogenetic and biogeographic history of the tetrapods, with the Gondwanan clade Canowindididae exhibiting a high degree of endemism within the early part of the stem tetrapod radiation. New anatomical details of Koharalepis, from the Middle Devonian Aztec Siltstone of Antarctica, are elucidated from synchrotron scan data. These include the position of the orbit, the condition of the hyomandibular, the shape of the palate and arrangement of the vomerine fangs. Biogeographical and phylogenetic models of stem tetrapod origins and radiations are discussed.

scholarly journals The revival of a so-called rotten fish: the ontogeny of the Devonian acanthodian Triazeugacanthus

2015 ◽  
Vol 11 (2) ◽  
pp. 20140950 ◽  
Author(s):  
Marion Chevrinais ◽  
Richard Cloutier ◽  
Jean-Yves Sire
Keyword(s):  
Original Description ◽  
Size Increase ◽  
Late Devonian ◽  
Allometric Growth ◽  
Ontogenetic Changes ◽  
The Past ◽  
Ontogenetic Stages ◽  
Size Series

Since its original description as a chordate, the Late Devonian Scaumenella mesacanthi has been interpreted alternately as a prochordate, a larval ostracoderm and an immature acanthodian. For the past 30 years, these minute specimens were generally considered as decayed acanthodians, most of them belonging to Triazeugacanthus affinis. Among the abundant material of ‘ Scaumenella ’, we identified a size series of 188 specimens of Triazeugacanthus based on otolith characteristics. Despite taphonomic alteration, we describe proportional growth and progressive appearance of skeletal elements through size increase. Three ontogenetic stages are identified based on squamation extent, ossification completion and allometric growth. We demonstrate that what has been interpreted previously as various degrees of decomposition corresponds to ontogenetic changes.

scholarly journals Morphospace saturation in the stem-gnathostomes pteraspidiformes heterostracans: an early radiation of a ‘bottom’ heavy clade

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5249
Author(s):  
Marco Romano ◽  
Robert Sansom ◽  
Emma Randle
Keyword(s):  
Evolutionary History ◽  
Late Devonian ◽  
Gradual Decline ◽  
Early Devonian ◽  
Morphological Disparity ◽  
Anatomical Features ◽  
Early Radiation ◽  
Taxic Diversity ◽  
Shed Light ◽  
Over Time

Ostracoderms (fossil armoured jawless fishes) shed light on early vertebrate evolution by revealing the step-wise acquisition of jawed vertebrate characters, and were important constituents of Middle Palaeozoic vertebrate faunas. A wide variety of head shield shapes are observed within and between the ostracoderm groups, but the timing of these diversifications and the consistency between different measures of their morphospace are unclear. Here, we present the first disparity (explored morphospace) versus diversity (number of taxa) analysis of Pteraspidiformes heterostracans using continuous and discrete characters. Patterns of taxic diversity and morphological disparity are in accordance: they both show a rise to a peak in the Lochkovian followed by a gradual decline in the Middle-Late Devonian. Patterns are largely consistent for disparity measures using sum of ranges or total variance, and when using continuous or discrete characters. Pteraspidiformes heterostracans can be classified as a “bottom-heavy clade”, i.e., a group where a high initial disparity decreasing over time is detected. In fact, the group explored morphospace early in its evolutionary history, with much of the subsequent variation in dermal armour occurring as variation in the proportions of already evolved anatomical features. This Early Devonian radiation is also in agreement with the paleobiogeographic distribution of the group, with a maximum of dispersal and explored morphospace during the Lochkovian and Pragian time bins.

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