Jaw apparatuses of Jurassic Aspidoceratidae (Ammonoidea) and Cope's rule in evolution of aspidoceratid ammonites (comment on "Giant Middle Jurassic (Bathonian) cf. Laevaptychus sp. of the Aztlán section, Hidalgo State, central Mexico" by C.Esquivel-Macías, P.Zell, J.A.Moreno-Bedmar and K.Flores-Castro [Journal of South American Earth Sciences, 110, 103302]). (December 2021)

• Record Type: Journal Article
• Authors: Rogov, Mikhail A.; Mironenko, Aleksandr A.
• Is Part Of: Journal of South American earth sciences. Volume 112:Part 1(2021)
• Publication Date: 2021-12
• Subjects: Aptychi -- Ammonites -- Evolution -- Aptychophora; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2021.103529
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: Comments are provided on a published paper on Middle Jurassic Laevaptychus from central Mexico [C.Esquivel-Macías, P.Zell, J.A.Moreno-Bedmar and K.Flores-Castro, Giant Middle Jurassic (Bathonian) cf. Laevaptychus sp. of the Aztlán section, Hidalgo State, central Mexico, Journal of South American Earth Sciences, 110, 103302]. This article describes an interesting finding of large-sized ammonite lower jaws (aptychi referred to Laevaptychus paragenus), claimed as the largest Jurassic aptychi ever known. However, the age of these specimens was erroneously defined due to misidentification of an associated ammonite specimen as Bathonian Procerites . Although poorly preserved, this ammonite shows typical features of the Kimmeridgian genus Idoceras . The Kimmeridgian age of these occurrences is in agreement with findings of Laevaptychus, as this is one of few aptychi formal genera, which belongs to a single ammonite family (Aspidoceratidae). Aspidoceratids appeared in the late Callovian and during the evolution of this lineage maximum sizes of adult specimens and the relative whorl height gradually increased up to Kimmeridgian - Tithonian; only prior to their extinction in early Berriasian, aspidoceratids became uncommon and smaller in size. Laevaptychi are thick-valved aptychi, which have high preservation potential while compared with other aptychi of Jurassic ammonites and their host shells. Giant laevaptychi reported in previous publications (the largest of which reaches 35 cm in length) are briefly reviewed. In adult aspidoceratids the maximum length of aptychi is slightly less than the maximum whorl height. Thus, taking into account the size of the largest aspidoceratid ammonites (up to 85 cm in diameter), the estimated length of the largest laevaptychi can be expected to be ~35–40 cm, which is close to their known record. Highlights: Age of Laevaptychus findings in Mexico revised. Review of shell and aptychi size oscillations through evolution of aspidoceratid ammonites is provided.