Pycnodontiformes Temporal range: | |
---|---|
Pycnodontiform diversity | |
Scientific 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 the Sannine Formation of 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]
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]
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. [16]
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. [16]
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. [17]
Pycnodontiformes | |
The Gonorynchiformes are an order of ray-finned fish that includes the important food source, the milkfish, and a number of lesser-known types, both marine and freshwater.
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Semionotiformes is an order of ray-finned fish known from the Middle Triassic (Anisian) to the Late Cretaceous (Maastrichtian). Their closest living relatives are gars (Lepisosteidae), with both groups belonging to the clade Ginglymodi within the Holostei. The group includes both freshwater (Semionotidae) and marine adapted forms. Many members of the family Macrosemiidae, had elongated dorsal fins, often associated with an adjacent area of skin which was free of scales. These fins were likely undulated for use in precision swimming. The body morphology of macrosemiids suggests that they were slow swimmers who were capable of maneuvering around complex topography, such as reef environments.
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Pycnodus is an extinct genus of ray-finned fish from the Eocene period. It is wastebasket taxon, although many fossils from Jurassic or Cretaceous are assigned to this genus, only Eocene species, P. apodus is valid. As its name suggests, it is the type genus of Pycnodontiformes.
Anomoeodus is an extinct genus of prehistoric marine ray-finned fish belonging to the family Pycnodontidae. This genus primarily lived during the mid-to-late Cretaceous period, ranging from the Albian to the very end of the Maastrichtian age, and possibly into the Danian. The first fossils of Anomoeodus were described by Louis Agassiz in 1833, although they were described under Pycnodus. Some studies have recovered it as a wastebasket taxon.
Coelodus is an extinct genus of marine and possibly freshwater pycnodont fish. It contains only one definitive species, C. saturnusHeckel, 1854, from the Late Cretaceous of Slovenia. Other species from the Late Jurassic to the Eocene have also been attributed to this genus based on isolated dental elements, but their assignment to Coelodus is uncertain, and this genus likely represents a non-monophyletic wastebasket taxon. A potential diagnostic trait is a prearticular tooth row with three regular highly elongated teeth.
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Pycnodontidae is an extinct family of ray-finned fishes, ranging from the Jurassic period until the Eocene. It was the largest and most derived family of the successful Mesozoic fish order Pycnodontiformes, and one of only two families to survive into the Cenozoic.
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Dapediidae is an extinct family of neopterygian ray-finned fish that lived from the Middle Triassic to Late Jurassic. It is the only family of the order Dapediiformes. Its members were historically placed within the ginglymodian family Semionotidae, but were moved to their own family in 1966.
Coccolepididae is an extinct family of ray-finned fish, known from the Early Jurassic to Early Cretaceous, most of which were originally referred to the type genus Coccolepis. They had a widespread distribution, being found in North and South America, Australia, Asia and Europe. They are mostly known from freshwater environments, though several species have been found in marine environments. They are morphologically conservative, and have poorly ossified endo and exoskeletons, which usually results in poor preservation. This makes it difficult to distinguish species. They are generally small fish, with the largest known specimens reaching a length of 210 mm. Historically, they have been classified as members of “Palaeonisciformes”, a paraphyletic grouping of non-neopterygian fish, due to their plesiomorphic conservative morphology closely resembling those of many other groups of primitive fish. Some recent authors have suggested that they may belong to the order Chondrostei as relatives of the Acipenseriformes.
Lepidotidae is an extinct family of fish, known from the Jurassic and Cretaceous periods. Most species were originally assigned to the genus Lepidotes which was long considered a wastebasket taxon. Cladistic analysis has indicated that they are close relatives of gars, with both being members of the order Lepisosteiformes. Members of the family are known from both marine and freshwater environments. Their bulky body morphology and small median fins suggests that they were slow-moving fish that were capable of performing fine movements in order to grasp prey. Lepidotes sensu stricto had peg-like grasping marginal teeth and crushing palatal teeth, and is known to have consumed small crustaceans, while Scheenstia had low rounded crushing marginal teeth, indicating a durophagous diet.
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Neoproscinetes is a genus of extinct pycnodontid fish from the Cretaceous Santana Formation of Brazil. Fossils of this species have also been discovered in the Riachuelo Formation.
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(help)Capasso, Luigi (2023). "Atlas of Pycnodonts: A pictorial guide to the Pycnodontomorpha (Pisces, Actinopterygii)". èDicola Publisher, Castellana, Italy; pp. 1-240.