The oldest acanthomorphs were initially reported by
Louis Agassiz from the
Cenomanian Sannine Formation of Lebanon, and were considered as such for over a century until slightly older remains were identified from the end-
Albian of
Mexico; subsequently an even older member of the group,
Gondwanacanthus decollatus, was reported from the upper
Barremian or lower
Aptian strata of the
Morro do Chaves Formation (
Brazil). Some
otoliths, calcium carbonate structures that form the ears of fishes, have been found from the
Jurassic Period that may belong to acanthomorphs, but the oldest body fossils from this taxon are only known from the early-mid Cretaceous Period, about 120 million years ago. Acanthomorphs from the early Late Cretaceous were small, typically about 4 centimeters long, and fairly rare. However, re-analyses of these scales suggests that they are not true ctenoid scales, and instead resemble those of certain extinct non-teleostean fishes such as the
Macrosemiidae. ==Phylogeny==