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. 2016 Jan;12(1):20150877.
doi: 10.1098/rsbl.2015.0877.

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

Christian Klug  1 , Günter Schweigert  2 , Dirk Fuchs  3 , Isabelle Kruta  4 , Helmut Tischlinger  5
Affiliations

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

Christian Klug et al. Biol Lett. 2016 Jan.

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).

Keywords: Belemnitida; Coleoidea; Decabrachia; Jurassic; nekton; phylogeny.

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Figures

Figure 1.
Figure 1.
Key specimen of Acanthoteuthis speciosus Münster 1839, Tithonian, Solnhofen, Germany, SMNS 67751. (a) Specimen under white light, counter slab with radula. Phosphatized buccal mass and fins well visible. (b) Drawing of cephalic cartilage, statocysts with statoliths and oesophagus. (c) UV-image of phosphatized radula. (d) Drawing of the radula (counter slab) after the photos in (c). (e) Drawing of the complete specimen. (f) UV-image of the specimen (slab); the brightest luminescence is produced by phosphatized parts, the slightly bluish luminescence by calcitic parts (arm hooks, buccal mass, statoliths). R, rhachidian tooth; L, lateral tooth (1, 2); M, marginal tooth; Mp, marginal plate.
Figure 2.
Figure 2.
Reconstruction of Acanthoteuthis. Length of animal between 250 and 400 mm; mantle length 100–250 mm. (a) Reconstruction with large fins as in specimen HT 76/122 (electronic supplementary material, figure S3). (b) Reconstruction with small fins corresponding to the extent of the rostrum as in specimen SMNS 67751 (figure 1). (c) Anatomy of Acanthoteuthis focusing on the parts preserved in SMNS 67751 (figure 1). (d) Phylogram of the shortest tree obtained by a heuristic search (tree bisection and reconstruction), 500 boostraps [17]. Character matrix based on [18] with own data including the information obtained from our new specimens (see the electronic supplementary material, table S1). Outgroup: Nautilidae. Note the position of the Belemnitida in the stem of Decapodiformes. no. MPTs, number of most parsimonious trees.
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