Adaptations to squid-style high-speed swimming in Jurassic belemnitids

Abstract

Although the calcitic hard parts of belemnites (extinct Coleoidea) are very abundant fossils, their soft parts are hardly known and their mode of life is debated. New fossils of the Jurassic belemnitid Acanthoteuthis provided supplementary anatomical data on the fins, nuchal cartilage, collar complex, statoliths, hyponome and radula. These data yielded evidence of their pelagic habitat, their nektonic habit and high swimming velocities. The new morphological characters were included in a cladistic analysis, which confirms the position of the Belemnitida in the stem of Decabrachia (Decapodiformes).

Buoyancy mechanisms limit preservation of coleoid cephalopod soft tissues in Mesozoic Lagerstätten

“…Fossil evidence indicates that these animals were active or moderate swimmers drifting in the water column and had a carnivorous lifestyle (Klug et al . ). This, coupled with a metabolism that is likely to have been nitrogen based, suggests that they too would have elevated levels of tissue ammonia.…”

Diversity and morphological evolution of Jurassic belemnites from South Germany

“…Rare anatomical evidences suggest that most belemnites were active predators and good swimmers (Reitner and Urlichs, 1983;Riegraf and Hauff, 1983;Klug et al, 2010Klug et al, , 2016.…”

“…By following the Parento optimality concept recently applied to ammonite shells (Tendler et al, 2015), these different hydrodynamic properties suggest that, combined to modifications of phragmocones, fins, and other soft parts (Klug et al, 2016), the rostral morphotypes could be evolutionary tradeoffs towards one or more specific tasks. The exact identification of respective tasks is beyond the goal of this study, but it is possible that the outlying rostral forms of the morphospace correspond to specialized taxa optimized for singular swimming behaviours.…”

“…1), which are especially abundant in marine sediments of the Jurassic and Cretaceous. These organisms, considered as stem-group decabranchian coleoids Fuchs et al, 2015;Klug et al, 2016) (Fig. 1), composed a large part of the Mesozoic nekton and held a key position in the dynamics of trophic webs (i.e., as predators of small organisms and preys for marine reptiles and chondrichthyans; Massare, 1987;Doyle and MacDonald, 1993;Martill et al, 1994;Walker and Brett, 2002).…”

Dynamic Paleontology

“…A prominent discontinuity occurs in ichthyosaur evolution across the Triassic-Jurassic boundary, with the more "primitive" (and hence more easily killed by large cephalopods) ichthyosaurs occurring before the boundary, and the faster paripelvian (with a reduced pelvis to improve speed and to help them chase their faster cephalopod [belemnite] prey; Klug et al 2016) and presumably more capable ichthyosaurs occurring in the Jurassic and Cretaceous; Thorne et al 2011). A prominent discontinuity occurs in ichthyosaur evolution across the Triassic-Jurassic boundary, with the more "primitive" (and hence more easily killed by large cephalopods) ichthyosaurs occurring before the boundary, and the faster paripelvian (with a reduced pelvis to improve speed and to help them chase their faster cephalopod [belemnite] prey; Klug et al 2016) and presumably more capable ichthyosaurs occurring in the Jurassic and Cretaceous; Thorne et al 2011).…”