Heterostracan vertebrates and the Great Eodevonian Biodiversification Event—an essay

Blieck, Alain

doi:10.1007/s12549-016-0260-1

Cited by 5 publications

(2 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The head, including the gill skeleton, accounts for approximately 25% of estimated total body length, the reconstructed oral aperture is likely to have been in a near-perpendicular plane to the direction of forward movement, the dentition is minimal, and the lower jaw is long and slender ( figure 2b,c). To the best of our knowledge, this is the earliest combination of such features known in any jawed vertebrate, adding to an emerging picture of total-group chondrichthyans as early, nektonic specialists, in contrast with the reconstructed demersal habits of their heavily skeletonized osteichthyan and 'placoderm' contemporaries [74]. Aspects of this character suite occur repeatedly among stem chondrichthyans, suggesting that the familiar gill slit condition of sharks might originate from such early, and apparently multiple, natural experiments in suspension feeding.…”

Section: E Ta N O P Sy Ru S U R a N Ia C A N Th U S D Ip La C A N Th mentioning

confidence: 87%

An early chondrichthyan and the evolutionary assembly of a shark body plan

et al. 2018

View full text Add to dashboard Cite

Although relationships among the major groups of living gnathostomes are well established, the relatedness of early jawed vertebrates to modern clades is intensely debated. Here, we provide a new description of , a Middle Devonian (Givetian approx. 385-million-year-old) stem chondrichthyan from Germany, and one of the very few early chondrichthyans in which substantial portions of the endoskeleton are preserved. Tomographic and histological techniques reveal new details of the gill skeleton, hyoid arch and jaws, neurocranium, cartilage, scales and teeth. Despite many features resembling placoderm or osteichthyan conditions, phylogenetic analysis confirms as a stem chondrichthyan and corroborates hypotheses that all acanthodians are stem chondrichthyans. The unfamiliar character combination displayed by , alongside conditions observed in acanthodians, implies that pre-Devonian stem chondrichthyans are severely under-sampled and strongly supports indications from isolated scales that the gnathostome crown group originated at the latest by the early Silurian (approx. 440 Ma). Moreover, phylogenetic results highlight the likely convergent evolution of conventional chondrichthyan conditions among earliest members of this primary gnathostome division, while skeletal morphology points towards the likely suspension feeding habits of, suggesting a functional origin of the gill slit condition characteristic of the vast majority of living and fossil chondrichthyans.

show abstract

Section: E Ta N O P Sy Ru S U R a N Ia C A N Th U S D Ip La C A N Th mentioning

confidence: 87%

An early chondrichthyan and the evolutionary assembly of a shark body plan

et al. 2018

View full text Add to dashboard Cite

show abstract

“…The comparable VM stress distributions between the chelicerae of Erettopterus bilobus and Pterygotus anglicus suggest that these taxa would have experienced similar stresses while feeding and therefore probably targeted similar prey. Based on the known faunal assemblages that co-occur with these pterygotid species ( Dunlop, Braddy & Tetlie, 2002 ; Miller, 2007b ; Lebedev et al, 2009 ; McCoy et al, 2015 ; Fyffe, Johnson & van Staal, 2016 ; Blieck, 2017 ; Tables S10 and S11 ), coupled with the large body lengths of Er. bilobus (0.7 m) and Pt.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical analyses of pterygotid sea scorpion chelicerae uncover predatory specialisation within eurypterids

Bicknell

Simone²,

Meijden³

et al. 2022

PeerJ

View full text Add to dashboard Cite

Eurypterids (sea scorpions) are extinct aquatic chelicerates. Within this group, members of Pterygotidae represent some of the largest known marine arthropods. Representatives of this family all have hypertrophied, anteriorly-directed chelicerae and are commonly considered Silurian and Devonian apex predators. Despite a long history of research interest in these appendages, pterygotids have been subject to limited biomechanical investigation. Here, we present finite element analysis (FEA) models of four different pterygotid chelicerae—those of Acutiramus bohemicus, Erettopterus bilobus, Jaekelopterus rhenaniae, and Pterygotus anglicus—informed through muscle data and finite element models (FEMs) of chelae from 16 extant scorpion taxa. We find that Er. bilobus and Pt. anglicus have comparable stress patterns to modern scorpions, suggesting a generalised diet that probably included other eurypterids and, in the Devonian species, armoured fishes, as indicated by co-occurring fauna. Acutiramus bohemicus is markedly different, with the stress being concentrated in the proximal free ramus and the serrated denticles. This indicates a morphology better suited for targeting softer prey. Jaekelopterus rhenaniae exhibits much lower stress across the entire model. This, combined with an extremely large body size, suggests that the species likely fed on larger and harder prey, including heavily armoured fishes. The range of cheliceral morphologies and stress patterns within Pterygotidae demonstrate that members of this family had variable diets, with only the most derived species likely to feed on armoured prey, such as placoderms. Indeed, increased sizes of these forms throughout the mid-Palaeozoic may represent an ‘arms race’ between eurypterids and armoured fishes, with Devonian pterygotids adapting to the rapid diversification of placoderms.

show abstract