Ammonoid Buccal Mass and Jaw Apparatus

Tanabe, Kazushige; Kruta, Isabelle; Landman, Neil H.

doi:10.1007/978-94-017-9630-9_10

Cited by 55 publications

(78 citation statements)

References 75 publications

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“…Knowledge of the internal anatomical features of ammonites is largely limited to the preservation and study of mineralized or sclerotized elements belonging to the buccal apparatus such as the upper and lower jaws and radula (Tanabe et al . ). Nevertheless, some features interpreted as buccal elements are still enigmatic due to their unconventional morphology and could possibly belong to other parts of the animal.…”

Section: Scaphitid Species In Which Hook‐like Structures Occurmentioning

confidence: 97%

Enigmatic hook‐like structures in Cretaceous ammonites (Scaphitidae)

Kruta

Bardin²,

Smith³

et al. 2019

Palaeontology

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In the last few decades, hook‐like structures have been reported in the Mesozoic ammonite family Scaphitidae. Despite their exceptional preservation and debates about their function, no detailed reconstruction has been available until now. For the first time, we describe the composition and details of the morphology of these structures found in the body chambers of six specimens of the Campanian ammonite Rhaeboceras halli (Meek & Hayden) using high resolution x‐ray imaging. The hook‐like structures are composed of a thin layer of brushite. The base of each hook is open on one side forming an internal cavity, now filled with sediment. The tips of the hooks end in one or two cusps or, rarely, exhibit a blunt end. We used geometric morphometrics to capture the morphological disparity of the bicuspidate morphotypes comprising 98% of the hooks. Principal component analysis revealed chirality among the hooks and a cluster analysis recognized five morphologies. Contrary to the previous interpretation of these structures, we conclude that they are not radular teeth. They are much larger and more variable in size and shape than any known ammonite radulae and completely out of proportion with respect to the size of the jaw. The chirality, the hook‐like shape, and the absence of a size relationship between the hooks and the body chambers in which they occur, lead us to propose that these hooks could represent elements of the brachial crown related to copulatory behaviour. If so, these would be the first reported remnants of brachial crowns in ammonites.

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Section: Scaphitid Species In Which Hook‐like Structures Occurmentioning

confidence: 97%

Enigmatic hook‐like structures in Cretaceous ammonites (Scaphitidae)

Kruta

Bardin²,

Smith³

et al. 2019

Palaeontology

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“…The new material is important because Devonian ammonoid mouth parts have been described previously mainly from the Frasnian gephuroceratids (Woodward ; Trauth –1936; Matern ; Clausen ; Tanabe et al . ), only rarely from Famennian ammonoids (Frye & Feldmann ; Korn ) and more often from the Carboniferous (Closs , ; Mapes ; Bandel ; Tanabe & Mapes ; Doguzhaeva et al . ; Doguzhaeva ; Landman et al .…”

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confidence: 99%

The oldest Gondwanan cephalopod mandibles (Hangenberg Black Shale, Late Devonian) and the mid‐Palaeozoic rise of jaws

et al. 2016

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It is widely accepted that the effects of global sea‐level changes at the transition from the Devonian to the Carboniferous are recorded in deposits on the shelf of northern Gondwana. These latest Devonian strata had been thought to be poor in fossils due to the Hangenberg mass extinction. In the Ma'der (eastern Anti‐Atlas), however, the Hangenberg Black Shale claystones (latest Famennian) are rich in exceptionally preserved fossils displaying the remains of non‐mineralized structures. The diversity in animal species of these strata is, however, low. Remarkably, the organic‐rich claystones have yielded abundant remains of Ammonoidea preserved with their jaws, both in situ and isolated. This is important because previously, the jaws of only one of the main Devonian ammonoid clades had been found (Frasnian Gephuroceratina). Here, we describe four types of jaws of which two could be assigned confidently to the Order Clymeniida and to the Suborder Tornoceratina. These findings imply that chitinous normal‐type jaws were likely to have already been present at the origin of the whole clade Ammonoidea, i.e. in the early Emsian (or earlier). Vertebrate jaws evolved prior to the Early Devonian origin of ammonoids. The temporal succession of evolutionary events suggests that it could have been the indirect positive selection pressure towards strong (and thus preservable) jaws since defensive structures of potential prey animals would otherwise have made them inaccessible to jawless predators in the course of the mid‐Palaeozoic marine revolution. In this respect, our findings reflect the macroecological changes that occurred in the Devonian. [Correction added on 28 July 2016 after first online publication: In the Abstract, the sentence “Vertebrate jaws probably … in the Early Devonian” was amended]

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“…For all Ammonoidea, such a summary looks different. According to Tanabe et al (2015), five major types of ammonoid jaws are recognised: Throughout the long period of intense study of the Middle-Late Jurassic ammonites, anaptychus-or rhynchaptychus-type jaws have never been found in these groups, let alone the normal-(probably better ''palaeoaptychus''-) type. The evolutionary changes in ammonoid jaws most likely occurred somewhat independently from the changes in shell morphology and ornamentation, which are the basis for the taxonomy of this subclass.…”

Section: Discussionmentioning

confidence: 99%

“…The history of studies of ammonoid aptychi, interpreted as their lower jaws or paired opercula, or both at the same time, is almost 200 years old and has been cited in numerous publications (see Parent et al 2014or Tanabe et al 2015 for reviews). Many attempts have been made to classify aptychi, and numerous parataxa with binominal names have been proposed (e.g., Trauth 1927;Měchová et al 2010;Vašíček et al 2012), but currently the mainstream thought accepts the existence of only two distinct groups of aptychi-like remains in the Jurassic-aptychi sensu stricto and anaptychi.…”

Section: Introductionmentioning

confidence: 99%