Scientists have described, for the first time, the young of a fish that lived 152 million years ago

The smaller specimens measured just 4–9 centimetres, whilst the adult fish grew to around half a metre. Ultraviolet light helped the scientist to examine the scales, spines and other fine structural details.

This is not a case of new excavations. Many of the fossils were already in museum collections, but under normal lighting conditions, important features were almost imperceptible. The results of the study have been published in the ⁠Swiss Journal of Palaeontology.

Details

Mesturus verrucosus belonged to an extinct group of fish known as the pycnodonts. They had a tall, strongly compressed body, resembling a disc. In shape, these animals resembled some modern coral reef dwellers, although they were not closely related to them.

The fish could grow to a length of approximately 50 centimetres. Its strong teeth were suited to cracking open mollusc shells and sea urchin spines.

Martin Ebert of the Bavarian State Collection of Palaeontology and Geology re-examined the fossils from museum collections. He photographed them under normal and ultraviolet light, and then compared the structure of the head, teeth, fins, scales and spines.

Under ultraviolet light, rows of scales and fine spines covering almost the entire body became visible on the small specimens. These features made it possible to link the small fossils to adult Mesturus verrucosus. The scientist thus established that these were not separate species of small fish, but juvenile specimens of an already known species.

They measured between 4 and 9 centimetres. As they matured, the shape of the body and its individual parts changed noticeably — which is why scientists had previously failed to recognise the connection between the small and large specimens.

The study also helped to correct previous errors in classification. Some fossils that had previously been assigned to the genus Mesturus turned out to be quite dissimilar to it. For these, Ebert established two new genera — Aminiichthys and Goodichthys.

Ultraviolet imaging, however, is not always helpful. Fossils from Eichstätt and Solnhofen show fine details clearly under ultraviolet light, whilst some specimens from Pienten remain dark. It is not yet known why fossils from different locations react differently to light.

Why this is important

Young extinct animals can differ significantly from adults. If palaeontologists do not know how their appearance changed as they grew, juveniles can easily be mistaken for members of a different species.

The new data helps to determine more accurately which fish lived in the ancient seas of Europe and to understand the evolutionary relationships between them. Furthermore, the study shows that important discoveries can be made not only during excavations. Sometimes it is enough to re-examine museum specimens using modern methods.

That said, ultraviolet light cannot be regarded as a universal method for studying fossils: the result depends on the condition of the specimen and, probably, on the composition of the rock.

Background

Fossils of Mesturus verrucosus have been known to scientists since the 19th century. However, the Mesturidae family remains less well studied than many other ancient fish, and its place on the evolutionary tree remains a matter of debate.

Around 152 million years ago, much of what is now Central Europe was covered by a warm sea featuring islands, shallow bays and lagoons. These waters were home to a multitude of fish, sea urchins, molluscs and other animals.

The unique conditions on the seabed of some of these lagoons allowed even the finest details of their bodies to be preserved. Today, the fossils from the Solnhofen area in Bavaria are considered to be among the most intricately preserved finds from the Jurassic period.

In his paper, Ebert also named the new fish species after Gina Mahsa Amini, Renee Good and Alex Pretty. The scientist explained that this was motivated by a desire to honour the memory of those who lost their lives as a result of political violence, reports ⁠Phys.org.

Source

Martin Ebert’s study, “Mesturidae Nursall, 1996 (Actinopterygii, Pycnodontiformes) from the Jurassic of England and Germany”, was published in the Swiss Journal of Palaeontology in 2026.