Cenozoic

Published on July 15th, 2022 | by David Marshall

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Episode 141: Bolca Fish

Bolca is a site of exceptional preservation of fossils (termed a konservat lagerstätte) located close to Verona, Italy. This 50 million year old limestone was deposited in the Eocene Epoch and contains over 500 species of plants, arthropods terrestrial vertebrates and most notably a lot of fish! The preservation at Bolca is so detailed that even the external colouration of the skin and internal anatomy of many of these fossils can be seen.

Exploring the taphonomy (the processes that occur to a body between death and discovery) and palaeoecology (how fossil organisms lived and interacted with other organisms and their surroundings) of some of the fish from Bolca is Dr Valentina Rossi from University College Cork, Ireland. In this episode, we look at how colour patterns are preserved in a fossil moonfish and look at what that can tell us about how the species lived.

Her open access article can be found here: Rossi et. al. 2022

Additional images and information we also accessed from Friedman and Carnevale 2018, which also makes for excellent background reading.

Location and geology of Pesciaria and Monte Postale, the principal Lagerstätten of Bolca. (a) Location of Bolca in Italy. (b) Topographic map of region immediately NW of the village of Bolca. From Friedman and Carnevale 2018.
The fossils at Bolca have a long history of study with the first reference to them dating back to 1550 in notes written by Mattioli (the ambassador of the Holy Roman Empire to the Venetian Republic). In the 18th century, fossils were being extensively collected and studied. Even Napoleon’s armies confiscated hundreds of fossils, taking them back to Paris. For a full history, see Friedman and Carnevale 2018.
Whilst the fossil fishes are by far the most numerous and impressive, plants and invertebrates are also preserved in stunning quality.
a) Seagrass similar to Phyllospadix or Posidonia; b) Leaf generally assigned to the mallow Sterculia; c) The spiny lobster Justinia desmaresti; d) The medusa (jellyfish) Simplicibranchia bolcensis; e) Hymenopteran insect. From Friedman and Carnevale 2018.
The fossil fish from Bolca are undeniably stunning. They are mostly represented by percomorphs (the most diverse group of fish alive today) but other groups including sharks are also present.
a) The numbfish Titanonarke molini; b) the pycnodont Nursallia veronae; c) the round herring Trollichthys bolcensis; d) the barracudina Holosteus esocinus; e) the surgeonfish Eorandallius elegans; f) the moonfish Mene oblonga; g) the perch-like fish of unclear affinities Ceratoichthys pinnatiformis; h) the cornetfish Urosphen dubia; i) the batfish Eoplatax papilio; j) the mackerel Godsilia lanceolata; k) the monkfish Caruso brachysomus; l) the triggerfish relative Protobalistum imperiale. Scale bars represent 50 mm. From Friedman and Carnevale 2018.
Mene rhombea (left) and schematic reconstruction of the preserved soft tissues (right). By comparing these pictures, you can clearly see the fossil colour patterns and internal anatomy. The colouration was confirmed by the presence of fossil melanosomes (organelles that produce pigment) within the coloured areas and internal organs. Within the stomach there is even evidence for a
From this work, it was possible to reconstruct the appearance of Mene rhombea (right) and compare it to the modern moonfish Mene maculata (left). The modern moonfish, M. maculata, has spotted camouflage and is know to live around coasts feeding on marine invertebrates. The fossil moonfish, M. rhombea, has horizontal stripes, suggesting it was better camouflaged in open waters, or even as part of a school of fish where the stripes would produce a confusing effect for would-be predators. Whilst it’s difficult to fill in the evolutionary gaps between these two fish, some 50 million years apart, it’s still remarkable that we can use this kind of information to compare ecologies over these huge time scales!
Dr Valentina Rossi imaging fossil melanosomes with a scanning electron microscope (SEM).

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