Pycnodontiformes

Pycnodontiformes
Temporal range: Late Triassic–Eocene
Pycnodontiform diversity
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Subclass: Neopterygii
Order: †Pycnodontiformes
Berg, 1937
Families

Pycnodontiformes is an extinct order of primarily marine bony fish. The group first appeared during the Late Triassic and disappeared during the Eocene. The group has been found in rock formations in Africa, Asia, Europe, North and South America.[1] They were small to middle-sized fish, generally with laterally-compressed deep bodies, some with almost circular outlines,[2] adapted for manuverability in reef-like environments, though the group was morphologically diverse.[3] Most, but not all members of the groups had jaws with round and flattened teeth,[4] well adapted to crush food items (durophagy), such as echinoderms, crustaceans and molluscs.[3] Some pyncodontiformes developed piranha like teeth used for eating flesh.[5][6] Most species inhabited shallow marine reef environments, while a handful of species lived in freshwater or brackish conditions. While rare during the Triassic and Early-Middle Jurassic, Pycnodontiformes became abundant and diverse during the Late Jurassic, exhibiting a high but relatively static diversity during the Early Cretaceous. At the beginning of the Late Cretaceous they reached their apex of morphological and species diversity (much of this due to fossils found in Lebanon, such as Gebrayelichthyidae and Ichthyoceros), after which they began to gradually decline, with a more sudden decline at the end of the Cretaceous due to the collapse of reef ecosystems, finally becoming extinct during the Eocene. They are considered to belong to the Neopterygii, but their relationship to other members of that group is uncertain.[3]

Evolution and diversity[edit]

Macromesodon gibbosus (formerly species of Eomesodon), a species of Brembodontidae from the Jurassic Solnhofen Limestone.

Pycnodontiforms first appeared in the Late Triassic, alongside other successful groups of early neopterygians such as dapediiforms. A contributor for this early radiation of neopterygians was their effectiveness at adapting to different diets. Pycnodonts from the Late Triassic Zorzino Limestone in Italy had short and stout jaws with big crushing teeth for eating hard-shelled prey, while other actinopterygians like saurichthyids and birgeriids mainly occupied top predator piscivorous niches. They originated from marine habitats, specializing for manoeuverability in reef environments, but developed a variety of adaptations during the Mesozoic that enable them to pursue new diets and habitats, such as estuaries and freshwaters. Only a few species adapted for open waters, like those of the family Gyrodontidae.[3] In the Western Tethys, pycnodonts have always had a high species diversity. This stable environment, alongside its favorable climate conditions, supported the dispersal patterns within basal pycnodontids.[7]

They evolved such different jaw structures to avoid potential competition with other groups of durophagous neopterygians, such as the Dapediiformes and the Ginglymodi. Furthermore, their improved jaw performance also differentiated the pycnodonts from these neopterygians in that they allowed them to feed on tougher prey, while their increase in size allowed them to prey on larger items or specialise on a few species. Their families also differentiated amongst themselves in body and jaw shape, implying that they were more diverse in diet and habitat than previously thought.[3]

The fossil record of pycnodonts spans 175 million years, from the Triassic to the Eocene, existing longer than non-avian dinosaurs. Their early record is incomplete, having only three genera from the Late Triassic, all with complete specimens. Whereas from the Early to Mid-Jurassic there are only isolated teeth and jaws, and rarely a few exceptions for better, but still incomplete, fossils. By the Late Jurassic Pycnodontiforms became more common in the fossil record, a fact that relates to the presence of Lagerstätten, providing articulated fossils. This growth continues and, by the Late Cretaceous, they experience a peak in diversity during the Cenomanian. They were severely struck by the K/Pg Extinction and afterwards their diversity shrunk, having never achieved pre-extinction levels of diversity, eventually going extinct by the Late Eocene (Priabonian).[3]

Taxonomy[edit]

Phylogeny[edit]

The phylogenetic relation between pycnodonts and other actinopterygians is uncertain. The difficulty of placing them on a phylogenetic tree arises from the fact that they are a clade defined by a high number of autapomorphies (characteristics shared by a single taxon), which makes them easy to identify, but also makes the study of their relations with other actinopterygians difficult, since characteristics shared by other groups might be obfuscated by the immense amount of features and diversity of pycnodonts.[13]

Previously, Pycnodontiformes where proposed to be a sister group of Teleostei or Teleosteomorpha, but in a 2015 analysis by Poyato-Ariza, they turned up as the most basal Neopterygii among the others of the group included, those being Lepisosteiformes, Semionotiformes, Macrosemiiformes, Halecomorphi and Teleostei.[13]

Actinopterygii

As a means to avoid potential competition, the families of Pycnodontiforms evolved different body and jaw shapes, resulting in a highly diverse group.[3] Pycnodontidae were the most advanced group, being the largest family, comprising 26 known described genera.[14]

Pycnodontiformes

References[edit]

  1. ^ "Pycnodontiformes". Palaeos vertebrates. Archived from the original on 25 October 2008. Retrieved 27 July 2009.
  2. ^ "Pycnodontid fishes from the Kansas Cretaceous". Oceans of Kansas. 16 April 2009. Retrieved 29 July 2009.
  3. ^ a b c d e f g Cawley, John J.; Marramà, Giuseppe; Carnevale, Giorgio; Villafaña, Jaime A.; López‐Romero, Faviel A.; Kriwet, Jürgen (February 2021). "Rise and fall of †Pycnodontiformes: Diversity, competition and extinction of a successful fish clade". Ecology and Evolution. 11 (4): 1769–1796. doi:10.1002/ece3.7168. ISSN 2045-7758. PMC 7882952. PMID 33614003.
  4. ^ McMenamin, M. A. S. (2009). Paleotorus: The Laws of Morphogenetic Evolution. Meanma Press. ISBN 978-1-893882-18-8.
  5. ^ Kölbl-Ebert, Martina; Ebert, Martin; Bellwood, David R.; Schulbert, Christian (2018-11-05). "A Piranha-like Pycnodontiform Fish from the Late Jurassic". Current Biology. 28 (21): 3516–3521.e2. doi:10.1016/j.cub.2018.09.013. ISSN 0960-9822. PMID 30344113. S2CID 53045425.
  6. ^ Vullo, Romain; Cavin, Lionel; Khalloufi, Bouziane; Amaghzaz, Mbarek; Bardet, Nathalie; Jalil, Nour-Eddine; Jourani, Essaid; Khaldoune, Fatima; Gheerbrant, Emmanuel (2017-07-28). "A unique Cretaceous–Paleogene lineage of piranha-jawed pycnodont fishes". Scientific Reports. 7 (1): 6802. doi:10.1038/s41598-017-06792-x. ISSN 2045-2322. PMC 5533729. PMID 28754956.
  7. ^ a b Cawley, John; Lehnmann, Jens; Wiese, Frank; Kriwet, Jürgen (2020). "Njoerdichthys dyckerhoffi gen. et sp. nov. (Pycnodontiformes, lower Turonian) northward migration caused by the Cretaceous Thermal Maximum". Cretaceous Research. 116.
  8. ^ Nelson, Joseph S.; Grande, Terry C.; Wilson, Mark V. H. (2016). Fishes of the World (5th ed.). John Wiley & Sons. ISBN 9781118342336.
  9. ^ van der Laan, Richard (2016). "Family-group names of fossil fishes". {{cite journal}}: Cite journal requires |journal= (help)
  10. ^ a b L. Taverne; L. Capasso (2014). "Ostéologie et phylogénie des Coccodontidae, une famille remarquable de poissons Pycnodontiformes du Crétacé supérieur marin du Liban, avec la description de deux nouveaux genres". Palaeontos. 25. Archived from the original on 2017-07-05. Retrieved 2016-07-05.
  11. ^ Cooper, Samuel L.A.; Martill, David M. (August 2020). "A diverse assemblage of pycnodont fishes (Actinopterygii, Pycnodontiformes) from the mid-Cretaceous, continental Kem Kem Group of south-east Morocco". Cretaceous Research. 112: 104456. doi:10.1016/j.cretres.2020.104456.
  12. ^ Cooper, S.L.A. and Martill, D.M. (2020). "Pycnodont fishes (Actinopterygii: Pycnodontiformes) from the Upper Cretaceous (lower Turonian) Akrabou Formation of Asfla, Morocco" Cretaceous Research 116, 104607
  13. ^ a b Poyato-Ariza, Francisco (2015). "Studies on Pycnodontid fishes (I): Evaluation of their phylogenetic position among actinopterygians". Rivista Italiana di Paleontologia e Stratigrafia. 121 (3): 329–343.
  14. ^ Ebert, Martin (2020). "A new genus of Pycnodontidae (Actinopterygii) from the Upper Jurassic of France and Germany, included in a phylogeny of Pycnodontiformes". Zoological Journal of the Linnean Society. 188 (2): 434–454.
Wikimedia Commons has media related to Pycnodontiformes.
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  • Capasso, Luigi (2021). "Pycnodonts: An overview and new insights in the Pycnodontomorpha Nursall, 2010". Occasional Paper of the University Museum of Chieti, Monographic Publication, 1: 1–223.
  • Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Retrieved 2011-05-17.
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