The jaw apparatus of the Late Cretaceous heteromorph ammonoid<i>Pravitoceras</i>

A nearly complete radula with seven elements per row preserved inside of an isolated, bivalved, calcitic lower jaw (= aptychus) of the Late Jurassic ammonite Aspidoceras is described from the Fossillagerst€ atte Painten (Bavaria, southern Germany). It is the largest known ammonite radula and the first record for the Perisphinctoidea. The multicuspidate tooth elements (ctenodont type of radula) present short cusps. Owing to significant morphological differences between known aptychophoran ammonoid radulae, their possible function is discussed, partly in comparison with modern cephalopod and gastropod radulae. Analogies between the evolution of the pharyngeal jaws of cichlid fishes and the ammonoid buccal apparatus raise the possibility that the evolution of a multicuspidate radula allowed for a functional decoupling of the aptychophoran ammonoid jaw. The radula, therefore, represents a key innovation which allowed for the evolution of the calcified lower jaws in Jurassic and Cretaceous aptychophoran ammonites. Possible triggers for this morphological change during the early Toarcian are discussed. Finally, we hypothesize potential adaptations of ammonoids to different feeding niches based on radular tooth morphologies.

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“…; Tanabe et al . ). Crop and stomach contents of different aptychophoran taxa have confirmed this opinion (Lehmann & Weitschat ; Dietl et al .…”

Section: Discussionmentioning

confidence: 97%

Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus

Keupp¹,

Hoffmann

Stevens

et al. 2016

Palaeontology

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“…Additionally, Tanabe et al . (2015) described the jaw apparatus of P. sigmoidale and suggested that the jaw apparatus functioned to bite and cut up prey based on morphological characteristics. Kruta et al .…”

Section: Discussionmentioning

confidence: 99%

Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

Misaki,

Okamoto,

Maeda

2023

Papers in Palaeontology

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The heteromorph ammonite Pravitoceras sigmoidale with extremely twisted retroversal hook and its probable ancestors, Didymoceras awajiense and D. morozumii, occur mainly in the Upper Cretaceous Izumi and Sotoizumi groups in southwest Japan. Their morphological characteristics were investigated in this study. Morphotypes I–II were recognized in D. morozumii. Morphotypes III–V were recognized in D. awajiense. Morphotypes VI–VIII were recognized in P. sigmoidale. Moreover, all morphotypes were recognized in both the dextral and sinistral forms of these three species. Based on the morphological and stratigraphic relationships, it is considered that the evolutionary process of these species is divided into three steps: (1) shift from morphotypes I–II to III; (2) increase in variation from morphotypes III to III–V; and (3) shift from morphotypes III–V to VI–VIII. By comparing these morphotypes based on the ‘growing tube model’ belonging to the moving frame analysis, it is seen that there are no significant gaps of coiling patterns in the evolutionary processes of this lineage. Meanwhile, morphotypes III–V of D. awajiense have a larger morphological variation than morphotypes I–II of D. morozumii and morphotypes VI–VIII of P. sigmoidale. These results, and the radiometric ages from previous studies, suggest that D. awajiense, with considerable variation between ancestor and descendant species, existed in a short interval. It seems that P. sigmoidale occurred after the continuous but rapid and drastic morphological evolution from D. morozumii via D. awajiense.

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“…Specifically for extinct cephalopods like the ammonoids, this kind of technical innovations have been key to the description of structures which would have been rarely found in this group otherwise. Examples include the employment of a wide variety of tomographic techniques such as grinding tomography, X-ray microtomography, synchrotron tomography, and neutron tomography (e.g., Hoffmann et al, 2013;Tajika et al, 2015;Takeda et al, 2016;Kruta et al, 2020;Cherns et al, 2021;Smith et al, 2021;Tanabe et al, 2021), laser-induced fluorescence (Barlow et al, 2021), and digitization techniques such as surface or 3D scanning and photogrammetry (Peterman et al, 2019(Peterman et al, , 2020. Ammonoids are extinct cephalopods that appeared during the Early Devonian and went extinct at the Cretaceous/Paleogene boundary, with a few members eventually surviving into the earliest Paleogene (Landman et al, 2015).…”

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confidence: 99%

Discovery of Ammonoid Jaw Apparatus and Associated Features Using Reflectance Transformation Imaging (Rti)

Morón-Alfonso

Cichowolski

Hoffmann

et al. 2023

PEAPA

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We report on remains of the buccal apparatus and possible associated structures for the Late Cretaceous ammonite Maorites seymourianus from the López de Bertodano Formation (Antarctic Peninsula). This is the first description of these structures for the family Kossmaticeratidae. Further, we discuss the most likely taphonomic processes taking place that allowed this exceptional preservation. Reflectance Transformation Imaging (RTI) technique was employed in this work to better document the faint structures. We briefly provide a review of this method and its potential importance for paleontological studies because it seems that this powerful technique has been largely overlooked by paleontologists.

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The jaw apparatus of the Late Cretaceous heteromorph ammonoidPravitoceras

Cited by 6 publications

References 32 publications

Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus

Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus

Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

Discovery of Ammonoid Jaw Apparatus and Associated Features Using Reflectance Transformation Imaging (Rti)

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