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''Asteracanthus'' (from , 'star' and , 'spine') is an extinct genus of hybodont, known from the
''Asteracanthus'' was among the largest known hybodontiforms, reaching a length of . The dentition of ''Astercanthus'' is high crowned and multicusped. The low-rounded teeth previously attributed to the genus actually belong to '' Strophodus''. Like ''Strophodus'', the fin spines are covered in
Middle Jurassic
The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...
(Bathonian
In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...
) to the Early Cretaceous
The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...
(Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...
).
Description
''Asteracanthus'' was among the largest known hybodontiforms, reaching a length of . The dentition of ''Astercanthus'' is high crowned and multicusped. The low-rounded teeth previously attributed to the genus actually belong to '' Strophodus''. Like ''Strophodus'', the fin spines are covered in tubercle
In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal.
In plants
A tubercle is generally a wart-like projectio ...
s, rather than the ribbing typical of other hybodont fin spines.
Fossil records
The genus as currently circumscribed dates from the Middle Jurassic (Bathonian
In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...
) to Early Cretaceous (Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...
) of Europe, including Germany, Switzerland, England and France. A complete skeleton was described in 2021 from the Late Jurassic (Tithonian
In the geological timescale, the Tithonian is the latest age (geology), age of the Late Jurassic Epoch and the uppermost stage (stratigraphy), stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 annum, Ma and 143.1 ±0.6 (mi ...
) aged Solnhofen Limestone
The Solnhofen Limestone or Solnhofen Plattenkalk, formally known as the Altmühltal Formation, is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organi ...
. Previously considered synonymous, the genus '' Strophodus'' (Middle Triassic-Late Cretaceous) is now considered distinct, with the teeth of ''Asteracanthus'' having more in common with '' Hybodus'' and '' Egertonodus.''
Ecology
The genus seems to have been adapted for open marine conditions and likely had an epibenthic habit (swimming just above the seafloor). It was likely a slow swimmer. The teeth are suggested to have been adapted for grasping, with the teeth at the sides of the mouth serving a crushing function. ''Asteracanthus'' was probably adapted for feeding on a wide range of prey, ranging from moderately hard shelled to soft-bodied, likely including fish, crustaceans, echinoderms, hard shelledmolluscs
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
and cephalopods like belemnites. Teeth of ''Asteracanthus'' found with the remains of marine reptiles suggest that it may have also engaged in scavenging.
Taxonomy
Many of the species previously assigned to this genus are now placed in '' Strophodus,'' with a 2021 study considering ''Asteracanthus ornatissimus'' the only certain species in the genus. The study considered the genus ''incertae sedis
or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
'' within Hybodontiformes.
References
Further reading
*L. Agassiz. 1837. Recherches Sur Les Poissons Fossiles. Tome III (livr. 8–9). Imprimérie de Petitpierre, Neuchatel viii-72 {{Taxonbar, from=Q22286593 Hybodontiformes Cretaceous extinctions Jurassic cartilaginous fish Cretaceous cartilaginous fish Prehistoric cartilaginous fish genera Fossil taxa described in 1837 Taxa named by Louis Agassiz