''Ferruaspis'' (from Latin ''ferrum'', meaning "iron", referencing its preservation in

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

, and Greek ''aspis'', meaning "shield", a common suffix for fossil fish genera) is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of freshwater osmeriform

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

from the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

of Australia. It contains a single species, ''F. brocksi'', and is the only member of the family Ferruaspidae. It was closely related to the extant Southern Hemisphere smelts in the family

Retropinnidae The Retropinnidae are a family of bony fishes that contains the Southern Hemisphere smelts and graylings. They are the only members of the suborder Retropinnoidei. They are closely related to the northern smelts ( Osmeroidei), which they greatly ...

. It is named after professor Jochen Brocks of the

Australian National University The Australian National University (ANU) is a public university, public research university and member of the Group of Eight (Australian universities), Group of Eight, located in Canberra, the capital of Australia. Its main campus in Acton, A ...

.'''' ''Ferruaspis'' is known from extraordinarily well-preserved specimens recovered from the McGraths Flat

lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

. These specimens provide a highly detailed glimpse into its life history, ecology, and physical appearance. Aside from an indeterminate

percomorph Percomorpha () is an extremely large and diverse clade of ray-finned fish. With more than 17,000 known species (including Scombroidei, tuna, Syngnathiformes, seahorses, gobies, Cichlidae, cichlids, flatfish, Labridae, wrasse, Perciformes, perches ...

fish, it is the only fish known from this site.

Description

''Ferruaspis'' specimens are unique for having poorly-preserved hard tissues (with the

otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...

s missing), but extremely well-preserved soft tissues down to the microscopic level. These include

melanophores Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast ...

, which allows for the coloration of the fish to be reconstructed. Based on the melanophores, ''Ferruaspis'' was

countershaded Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, an ...

with two light stripes running horizontally across its side. ''Ferruaspis'' is one of only three prehistoric animals known to have preserved melanophores (most prehistoric animals for which color can be reconstructed have preserved

melanosome A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotectio ...

s instead), alongside an indeterminate

colubrid Colubridae (, commonly known as colubrids , from , 'snake') is a family of snakes. With 249 genera, it is the largest snake family. The earliest fossil species of the family date back to the Late Eocene epoch, with earlier origins suspected. Colu ...

snake from the

of Spain and a specimen of the

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

Stenopterygius ''Stenopterygius'' is an extinct genus of thunnosaur ichthyosaur known from Europe (England, France, Germany, Luxembourg and Switzerland). History ''Stenopterygius'' was originally named by Quenstedt in 1856 as a species of ''Ichthyosaurus'', '' ...

''.

Ecology

The stomach contents of ''Ferruaspis'' primarily consist of the larvae of the phantom midge '' Chaoborus abundans'', whose fossils are common in the McGraths Flat deposits. Aside from a small

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

recovered in the stomach of one specimen, these suggest that ''Ferruaspis'' inhabited the

pelagic zone The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

of the lake and fed near the surface. In addition, one specimen of ''Ferruaspis'' shows infection by a

glochidium The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels. These larvae are t ...

, a larva of a river mussel that parasitizes fish early in its life. This suggests that the freshwater mussels relied on ''Ferruaspis'' as a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

for part of their life cycle. ''Ferruaspis'' inhabited an

oxbow lake An oxbow lake is a U-shaped lake or stream pool, pool that forms when a wide meander of a river is meander cutoff, cut off, creating a free-standing body of water. The word "oxbow" can also refer to a U-shaped bend in a river or stream, whether ...

ecosystem surrounded by

temperate rainforest Temperate rainforests are rainforests with coniferous or Broad-leaved tree, broadleaf forests that occur in the temperate zone and receive heavy rain. Temperate rainforests occur in oceanic moist regions around the world: the Pacific temperate ...

. This lake was located significantly inland from any marine ecosystem, and west of the

Great Dividing Range The Great Dividing Range, also known as the East Australian Cordillera or the Eastern Highlands, is a cordillera system in eastern Australia consisting of an expansive collection of mountain ranges, plateaus and rolling hills. It runs roughl ...

. This suggests that unlike most extant retropinnids, which have an

amphidromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

lifestyle, ''Ferruaspis'' lived in a freshwater habitat for its entire life. However, it is possible that ''Ferruaspis'' was a species with both amphidromous and land-locked populations that spent their entire lives in freshwater, with the McGraths Flat fossils representing the latter.

References

{{Taxonbar, from=Q133539056

† A dagger, obelisk, or obelus is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death (of people) or extinction (of species or languages). It is one of the mo ...

Monotypic prehistoric ray-finned fish genera Langhian genera Cenozoic fish of Oceania Prehistoric fish of Australia Miocene fish Fossils of Australia Fossil taxa described in 2025