Biodiversity of †pycnodonts (Actinopterygii) during the Cenomanian–Turonian (Upper Cretaceous)

ABSTRACT

By comparing the morphological variability of two groups of pycnodonts, the Coccodontoidea and the Nursalliini, the author demonstrates that in the Late Cretaceous these two groups had adopted completely different blauplans. Throughout the Cretaceous and the Eocene, the Nursalliini maintained the typical shape of the pycnodonts, rounded and flattened. The Cocodontoidea expressed 21 new species that belonged to 17 new genera, across which there was extraordinary biodiversity. The typical body plan was almost abandoned, and elongated, and somewhat very tapered, forms emerged (Stenoprotome), which lived alongside very short and very high fish. Indeed, this period produced the shortest and the highest fish that have ever lived (Maraldichthys). Indeed, while the more highly variable groups (Coccodontoidea) represented a punctiform episode in the evolutionary history of pycnodonts, remaining confined to the arm of Tethys (central Lebanon) and to the time period corresponding to the lower upper Cenomanian, the morphologically more conservative groups (Nursalliini) colonised the seas of the entire planet from the Cretaceous to the Eocene, even surviving the great mass extinction period corresponding to the Mesozoic-Cenozoic passage. Thus, the enormous biodiversity of Coccodointoidea did not represent a selective advantage over the environmental crisis at the end of the Cretaceous.

KEYWORDS:

• Pycnodonts
• biodiversity
• Coccodontoidea
• Nursalliini

Note on materials and methods

The material used for this work is part of the ‘Luigi Capasso Public Collection’ (LCPC). This is a Public Collection that was established two centuries ago and is protected by the Italian State. It is legally registered by two Decrees of the Ministry for Cultural Heritage, such as the no. 14, dated 11 October 1999, and no. 6259-A, dated 29 April 2020, both according to Italian law 1089/39 for the protection of the National Cultural Heritage. The specimens of this Collection were publicly accessible for studies on the basis of Article 30 of Italian law N ° 42/2004. I report below the inventory numbers of the individual specimens illustrated in the figures of this paper: Figure 2.1 = S.291; Figure 2.2 = S.572; Figure 2.3 = S.338; Figure 3.1 = S.1926; Figure 4.1 = S.501; Figure 4.2 = S.393; Figure 4.3 = >S.601; Figure 4.4 = S.296; Figure 4.5 = S.137; Figure 4.6 = S.413; Figure 4.7 = S.1822; Figure 4.8 = S.608; Figure 4.9 = S.291; Figure 4.10 = S.92; Figure 4.11 = S.451; Figure 4.12 = S. 596; Figure 4.13 = S.357; Figure 4.14 = S.488; Figure 4.15 = S.726; Figure 6,1 = S.729; Figure 7.1 = S.1706; Figure 7.2 = S.1705; Figure 8.1 = S.440; Figure 8.2 = S.850; Figure 8.4 = I.126; Figure 8.6 = S.2018.

Figure 3. The bauplan of the Nursalliini seems to be much more constant, remaining almost unchanged throughout their stratigraphic distribution, including the species from the beginning of the Upper Cretaceous (1: Nursallia goedeli of the Cenomanian of Haqel, Lebanon; TL = 260 mm), up to those of the Middle Eocene (2: Nursallia veronae from the Ypresian of Monte Bolca, Italy; TL = 277 mm).

Figure 4. The extraordinary morphological variability demonstrated by the 17 genera of Cocodontoidea present at the same time (Cenomanian) in the branch of the eastern Tethys corresponding to present-day Central Lebanon (excluding both Congopycnodus and Cosmodus): 1, Ducrotayichthys; 2, Gladiopycnodus; 3, Hayolperichthys; 4, Ichthyoceros, 5, Joinvillichthys; 6, Monocerichthys; 7, Pankowskichthys; 8, Rostropycnodus; 9, Stenoprotome; 10, Tricerichthys; 11, Gebrayelichthys; 12, Maraldichthys; 13, Coccodus; 14, Corusichthys; 15, Hensodon; 16, Paracoccodus; 17, Trewavasia.

Figure 5. Schematic map of central Lebanon showing the three main fossil sites of this area, En Nammoura, Haqel and Hjoula, which are very close to each other. This is the only area (red circle) where fossils of Coccodontoidea have been found (excluding both Congopycnodus and Cosmodus).

Figure 6. Some examples of specimens of Nursallia tethysensis from Cenomanian-Turonian limestones of different continents: from the Middle East (1: En Nammoura, Lebanon), from Central America (2: Huehuetla, Puebla, Mexico), and from Southern Europe (3: Quero, Italy). 2, courtesy of Professor Jesus Alvarado-Ortega; 3, courtesy of Dr. J. Amalfitano, with permission of the University of Padua (Italy).

Figure 7. Paranursallia gutturosa, Cenomanian, Jebel Tselfat, Morocco: two different morphotypes, putatively corresponding to the two sexes: ‘elongated’ type (1) and ‘shortened’ type (2).

Figure 8. Some examples of specimens of Paranursallia gutturosa from Cenomanian and Turonian limestones of different continents: 1, Jebel Tselfat (Morocco); 2, Gara Sbaa (Morocco); 3, Floresta (Italy); 4, Passo del Furlo (Italy); 5, Cinto Euganeo (Italy); 6, Vallecillo (Mexico). 3, courtesy of Professor Maria Antonietta Rosso, Museo di Geologia dell’Università di Catania, Italy; 5, courtesy of Dr. Paolo Rocca, Dr. Franco Colombara and Dr. Carlotta Fassina, Museo di Cava Bomba, Cinto Euganeo (Padua, Italy).

The following seven specimens are exceptions:

• Nursallia veronae, reproduced in Figure 4.2: Holotype, Museo Civico di Storia Naturale di Verona, No. D-II-173-Vr, picture by Di Ghedoghedo – Opera propria, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=61110703

• Nursallia tethysensis, reproduced in Figure 7.2: Collecciòn Nacional de Paleontologia, housed into the Museo Maria del Carmen Perrilliat at the Instituto de Geologia, Mexico, n. IGM 6618; courtesy of Professor Jesus Alvarado-Ortega.

• Nursallia tethysensis, reproduced in Figure 7.3: Museo di Geologia e Paleontologia dell’Università degli Studi di Padova, n. 32,093; courtesy of Dr Jacopo Amalfitano and Dr Mariagabriella Fornasiero.

• Paranursallia gutturosa, reproduced in Figure 8.5: Museo Geopaleontologico di Cava Bomba di Cinto Euganeo (Padova) n. IG37484; courtesy of Dr Paolo Rocca, Dr Franco Colombara and Dr Carlotta Fassina.

• Paranursallia gutturosa, reproduced in Figure 8.3: of the Museo di Geologia dell’università di Catania, Ex Coll. Leonardi no. 15; courtesy of Prof. Maria Antonietta Rosso.

• Gebrayelichtys vexillarius, reproduced in Figure 4.11: National Science Museum of Tokyo, n. PV-20533; courtesy of Professor Teruya Uyeno.

• Maraldichthys verticalis, reproduced in Figure 4.12: Museo Civico di Storia Naturale di Milano, n. V.3868; courtesy of Dottor Cristiano Dal Sasso.

Acknowledgments

The author thanks Professor Jesus Alvarado-Ortega, of the Instituto de Geologia, Universidad National Autònoma de México, Ciuudad de Mexico, Mexico, for sending images and information about the pycnodonts of the Huehuetla quarry, Puebla, Mexico; Professor Teuya Uyeno, Tokyo, for sending images and information about the Gebrayelichthys from National Science Museum of Tokyo; Doctor Jacopo Amalfitano and Dr Mariagabrella Fornasiero, of University of Padua, for sending images and information about the pycnodonts from the Quero quarry, Italy; Doctor Cristiano Dal Sasso, of the Museo Civico di Storia Naturale di Milano for sending images and information about the Maraldichthys; Professor Maria Antonietta Rosso, professor of Palaeontology at the University of Catania, Italy, for sending me images and information about the Paranursallia gutturosa specimens collected near Floresta (Sicily) and studied by Leonardi (1966); Dr Paolo Rocca, mayor of Cinto Euganeo (Padua, Italy), Dr Francesco Colombara and Dr Carlotta Fassina, respectively, past and extant curators of the Museo di Cava Bomba of Cinto Euganeo (Padua, Italy) for sending me the images and information about the pycnodonts collected in the Cava Bomba quarry (Padua, Italy). Finally, the author thanks Donatella and Luciano Lullo, who took the photographs illustrating this article.

Disclosure statement

No potential conflict of interest was reported by the author.