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    Ecological effects of competition on pycnodont fishes (Actinopterygii, Neopterygii, Pycnodontomorpha) and its possible role leading to their extinction

    (FWF-Project P 29796-B29)


    Primary Investigator: Univ.-Prof. Dr. Jürgen Kriwet


    Background

    Pycnodont fishes (Pycnodontomorpha) are a monophyletic and ecologically successful clade of extinct ray finned fishes with a fossil record spanning 175 million years from the Late Triassic to middle Eocene (Tintori 1981; Poyato-Ariza & Wenz 2002; Kriwet & Schmitz 2005). They are most commonly associated with shallow water marine habitats but are also found in association with freshwater and estuarine deposits (Longbottom 1984; Poyato-Ariza et al. 1998). A deep, rounded, and laterally compressed body, a frontal flexure of the skull in profile view, a more or less prognathous snout, and elongated dorsal and anal fins, forming together with the caudal fin an effective rudder characterize pycnodonts (Fig. 1). In their body shape they superficially resemble extant coral reef fishes like butterflyfishes (Chaetodontidae), doctorfishes (Acanthuridae), and triggerfishes (Balistidae). Distinctive characteristics of pycnodonts are their molariform teeth, which generally are arranged in well-defined rows on the unpaired vomer (upper jaw) and paired prearticulars (lower jaws) (Fig. 2). This dentition represents an adaptation to shelled prey. Their diversity is strikingly high, with over >600 nominal species in >45 genera of which many taxa are based on teeth and dentitions only (Kriwet, 2001a; 2005). The palaeobiogeography of these fishes suggests they originated in the Tethys Sea initially and then spread worldwide (Kriwet 2008; Martín-Abad & Poyato-Ariza 2013).
    Traditionally considered an order, Pycnodontiformes (Poyato-Ariza & Wenz 2002), they are now accepted to represent a superorder, Pycnodontomorpha, which was considered as a possible sister group candidate to Teleostei (Nursall 2010). However, a more recent analysis by Poyato-Ariza (2015) identified pycnodonts to be the sister group to Halecostomi (Holostei + Teleosteomorpha), which would make pycnodonts the most basal group among neopterygian fishes. Pycnodontomorpha comprises the orders Gyrodontiformes containing the families Gyrodontidae and Mesturidae, and Pycnodontiformes, including all remaining taxa (Nursall 2010). In this application whenever the term pycnodont is used, it refers to the total group Pycnodontomorpha.
    The fact that pycnodonts weathered both the Late Triassic/Early Jurassic and the K/Pg extinction events indicates that these fishes had a particularly successful evolutionary strategy. Indeed, their increasing raw species diversity through the Mesozoic is quite plainly seen in the fossil record (Late Triassic: 4; Early Jurassic: 2; Middle Jurassic: 16; Late Jurassic: 77; Early Cretaceous: 73; Late Cretaceous: 101 [only named and currently as valid considered species listed]). The increase in raw species numbers in the Late Cretaceous is mirrored in the great increase in morphological disparity (Marramà et al. 2016a). The increase in species diversity from the Middle Jurassic onwards indicates the first diversification event in the history of pycnodonts.
    A steep drop in taxon number occurred from the Late Cretaceous to Palaeocene, which might indicate that the K/P boundary event also affected pycnodont fishes. The disappearance of most major lineages well before the K/P boundary, which was used by Kriwet (2001a) to reject an extinction event at this boundary might be related to the so-called Signor-Lipps effect. Most pycnodonts known from the Palaeocene also occur in the Late Cretaceous with the exception of members of Pycnodus, which seemingly originated in the Palaeogene. This pycnodont is the most derived member of Pycnodontomorpha and the last representative of this formerly diverse group in the Eocene before it vanished, too.
    A popular hypothesis regarding the extinction of pycnodonts is the observation that many modern teleost groups common in coral reefs today arose at the same time that pycnodonts were beginning to decline (Bellwood 1996; 2003). Were the pycnodonts simply outcompeted by better-adapted teleosts or could there have been other factors in their extinction?
    During the Mesozoic, pycnodonts also faced competition from shallow water adapted, shell crushing ginglymodian fishes. In this case, however, the ginglymodian fishes (with the exception of Lepisosteidae) perished at the K/Pg boundary. Are there correlated evolutionary trajectories in both groups that enabled them to survive?
    The project applied for here tends to answer two major questions: 1) Are competition patterns within pycnodonts and between pycnodonts, ginglymodians and ecologically similar fishes detectable, and could it explain diversity and diversification patterns within pycnodonts and 2) did the rise of teleosts, particularly Acanthomorpha, lead to the extinction of the pycnodonts in the Eocene? Thus, this project focuses on biotic rather than abiotic effects influencing diversity patterns.

    Goals

    The major goals of this project are to gain deeper insights and a better understanding of the mechanisms that determine the evolutionary history, success, and final extinction of a highly diverse clade of fishes (Pycnodontomorpha). It was demonstrated that pycnodont fishes were very successful, highly diversified and evidently well adapted to the habitats they occupied. It is hypothesized that they were an important and major element of marine as well as continental influenced fish faunas (e.g., Kriwet 2001a). Nevertheless, the reasons for (1) their seemingly rapid diversification in the Early Mesozoic, (2) their subsequent success and thus their possible superiority over other fish groups inhabiting same environments (e.g., Ginglymodi), (3) their habitat use (= facies depending distribution) and possible size aggregations due to ontogenetic shifts, (4) diversity fluctuations in, i.e., relation to abiotic crises (e.g., Cenomanian/Turonian and K/P boundary events, environmental changes) or biotic factors (e.g., competition), and (5) the events triggering their final disappearance more or less simultaneously with the appearance and evolution of teleostean groups, which are considered to be important elements of modern coral-fish assemblages are ambiguous or have not been addressed with rigorous analytical methods up to now. The proposed project intends to find answers to these still not fully understood and varied aspects, which (in addition with already known traits such as feeding kinematics) will help understanding the evolutionary history of this important group and thus has the potential to identify universal evolutionary processes.

    Team

    • Univ.-Prof. Dr. Jürgen Kriwet (PI) Read more
    • John J. Cawley, MSc (Predoctoral Researcher)
    • Fabrizio De Rossi (Student Assistant)

    Publications

    2019
    • Cawley, J.J. & Kriwet, J. 2019. A new pycnodontid fish Flagellipinna rhomboides (Neopterygii, Pycnodontiformes) from the Upper Cretaceous (Cenomanian) of Lebanon, with notes on juvenile form and ecology. Journal of Vertebrate Paleontology, 39: e1614012 (16 pages). Link to article
    • Gouiric-Cavalli, S., Remírez, M., Kriwet, J. 2019. New pycnodontiform fishes (Actinopterygii, Neopterygii) from the Early Cretaceous of the Argentinian Patagonia. Cretaceous Research, 94:45-58. Link to article
    2018
    • Cawley, J.J., Marramà, G., Carnevale, G. & Kriwet, J. 2018. A quantitative approach to determine the taxonomic identity and ontogeny of the pycnodontiform fish Pycnodus (Neopterygii, Actinopterygii) from the Eocene of Bolca Lagerstätte, Italy. PeerJ, 6:e4809 (30 pages). Link to article
    2017
    • Cawley, J.J. & Kriwet, J. 2017. A new pycnodont fish, Scalacurvichthys naishii, gen. et sp. nov., from the Late Cretaceous of the Middle East. Journal of Systematic Palaeontology, 16: 659-673. Link to article
    • Cawley, J.J. & Kriwet, J. 2017. Possible sexual dimorphism in Pankowskichthys (Neopterygii, Pycnodontiformes) from the Cenomanian, Haqel, Lebanon. Research & Knowledge 3: 33-35. Link to article
    • Cawley, J.J. & Kriwet, J. 2017. New information about Late Cretaceous pycnodont fishes (Actinopterygii, Pycnodontiformes) from the Near East. Research & Knowledge 3: 47-48. Link to article
    • Stumpf, S., Ansorge, J., Pfaff, C. & Kriwet, J. 2017. Early Jurassic diversification of pycnodontiform fishes (Actinopterygii, Neopterygii) after the end-Triassic extinction event: Evidence from a new genus and species, Grimmenodon aureum. Journal of Vertebrate Paleontology 37(4): e1344679 (14 pages). Link to article

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