Chondrosteus

{{Short description|Extinct genus of fishes}}

{{Speciesbox

| fossil_range = {{fossilrange|201.4|185|Hettangian to Sinemurian}}

| image = Chondrosteus acipenseroides - Lyme Regis.jpg

| image_caption = Chondrosteus acipenseroides fossil from Teylers Museum, Haarlem

| taxon = Chondrosteus acipenseroides

| parent_authority = Egerton, 1858 (ex Agassiz, 1834)

| authority = Egerton, 1858 (ex Agassiz, 1834)

| synonyms = * {{extinct}}C. crassior Egerton, 1858

• {{extinct}}C. pachyurus Egerton, 1858

}}

Chondrosteus ("cartilage bone" in Greek) is a genus of extinct marine actinopterygian (ray-finned fish) belonging to the family Chondrosteidae. It lived during the Hettangian and Sinemurian (early Early Jurassic) in what is now England.{{cite web|url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=34988|title=Chondrosteus|publisher=Paleobiology Database|access-date=March 16, 2012}} Chondrosteus is related to sturgeons and paddlefishes as part of the clade Acipenseriformes, and is one of the earliest known definitive members of the group.{{cite journal |last1=Hilton |first1=Eric J. |last2=Forey |first2=Peter L. |title=Redescription of †Chondrosteus acipenseroides Egerton, 1858 (Acipenseriformes, †Chondrosteidae) from the lower Lias of Lyme Regis (Dorset, England), with comments on the early evolution of sturgeons and paddlefishes |journal=Journal of Systematic Palaeontology |date=2009 |volume=7 |issue=4 |pages=427–453 |doi= 10.1017/S1477201909002740|bibcode=2009JSPal...7..427H |s2cid=86821521 }} Similar to sturgeons, the jaws of Chondrosteus were free from the rest of the skull (projectile jaw system). Its scale cover was reduced to the upper lobe of the caudal fin like in paddlefish.{{cite journal |last1=Bemis |first1=William E. |last2=Findeis |first2=Eric K. |last3=Grande |first3=Lance |title=An overview of Acipenseriformes |journal=Environmental Biology of Fishes |date=1997 |volume=48 |issue=1–4 |pages=25–71|doi=10.1023/A:1007370213924 |bibcode=1997EnvBF..48...25B |s2cid=24961905 }}

It is represented by a single species, C. acipenseroides, from the Blue Lias of Lyme Regis. This species was first mentioned by Louis Agassiz in 1834, but was not officially described until 24 years later by Philip Grey Egerton, who used Agassiz's original name for the taxon.{{Cite book |last=Agassiz |first=Louis |url=https://books.google.com/books?id=-lw-W5lrLFYC&pg=PR5 |title=Recherches sur les poissons fossiles |date=1833 |publisher=Imprimerie de Petitpierre |language=fr}}{{Cite journal |last1=Hornung |first1=Jahn J. |last2=Sachs |first2=Sven |date=2020-01-22 |title=First record of Gyrosteus mirabilis (Actinopterygii, Chondrosteidae) from the Toarcian (Lower Jurassic) of the Baltic region |journal=PeerJ |language=en |volume=8 |pages=e8400 |doi=10.7717/peerj.8400 |doi-access=free |issn=2167-8359 |pmc=6982408 |pmid=32002331}} The species C. crassior Egerton, 1858 and C. pachyurus Egerton, 1858 differ from C. acipenseroides only in size and ossification of plates, and likely only represent ontogenic growth stages of C. acipenseroides. The only known Chondrosteus specimens outside of Lyme Regis are a poorly-preserved specimen from Barrow-on-Soar and a Hettangian-aged post-cranial skeleton from Watchet in a private collection, which represents the oldest record of the genus.

The species Chondrosteus hindenburgi from the Toarcian (late Early Jurassic) of Germany was reallocated to the genus Strongylosteus. Although some authors have suggested that the latter might be a junior synonym of Chondrosteus, there are no recent comparative studies on these two genera.{{cite journal |last1=Bemis |first1=William E. |last2=Findeis |first2=Eric K. |last3=Grande |first3=Lance |title=An overview of Acipenseriformes |journal=Environmental Biology of Fishes |date=1997 |volume=48 |issue=1–4 |pages=25–71|doi=10.1023/A:1007370213924 |bibcode=1997EnvBF..48...25B |s2cid=24961905 }}

File:Catalogue of the fossil fishes in the British Museum (Natural History) (1889) (20393616949).jpg