Devonian Fish
A Radiation of Fish
The Devonian interval of the geologic column is known for its radiation of fish groups. Radiation, in this sense, refers to an impressive rise in diversity among and within fish groups compared to the underlying layers. The diversity of fossil fishes, particularly of the jawed varieties, is perhaps the most defining feature of Devonian rocks, leading to the colloquial definition of the Devonian as the “Age of Fishes.”
Several extinct groups of mostly jawless fish are documented in layers below the Devonian, but disparity (differences in phenotypes that exhibit distinct characteristics) and diversity are both much higher in Devonian rocks.
The diversity of jawed fish represented in Devonian sediments includes several types of lobe-finned fishes (the only lobe-finned fishes living today are lungfish and coelacanths), sharks, ray-finned fish, acanthodians, and placoderms (armored fish). The latter two classes are now extinct. GRI hosts a collection of Devonian fossil fish with representatives from five separate groups of jawed fishes.
Abrupt appearance of distinct groups of organisms in the fossil record with limited evidence of transitional forms is a well-known challenge to evolutionary interpretations of biodiversity as resulting from universal common ancestry.
Image based on Long (2003). Stars indicate fish groups that have Devonian specimens represented in the GRI fossil collection. Arrow points to the Devonian interval.
Reference:
Long, J. A., 2003. Rise of Fishes, in Palaeobiology II , eds. D.E.G. Briggs & P.R. Crowther. Blackwell Publishing (Malden, MA), pp. 52-57.
Devonian Fish Fossils at GRI
This predatory fish had short jaws which enabled a powerful bite.
This large predator could grow up to two meters long.
Osteolepis panderi is the smallest osteolepid found among the Orcadian Basin fossils. This is an unusually well-preserved specimen of this species.
This armored fish had a beak-like mouth made of bony dental plates that would grind together and sharpen each other.
Millerosteus minor was a small fish with effective armor plating.
Coccosteus cuspidatus had joints in its bony armor that enabled it to open its jaws widely.
Acanthodian fish like this one are sometimes referred to as “spiny sharks,” because they look somewhat like sharks and have a rigid spine that lines each fin.
Although this specimen is only about 12 cm long, Pterichthyodes could grow over twice this length.
This Middle Devonian fish was similar to some modern fish by having a ray-like bone structure in its fins.
Tristichopterus (top specimen) was similar to Eusthenopteron, but smaller, averaging 35 cm.
Pentlandia (center & bottom) is recognizable for its large posterior dorsal fin.
Glyptolepis has been found in both freshwater and marine desposits, with some fossils measuring up to 75 cm long.
Cheiracanthus is a “spiny shark,” and this specimen comes from Forfarshire, Scotland.
These unusually shaped armored fish were originally thought to be turtles or giant beetles.
This predator was a small, lobe-finned fish. Specimen from Caithness, Scotland.
This lungfish had strong toothplates, suitable for crushing small crustaceans.
The Orcadian Basin and Old Red Sandstone
You may have noticed that most of the GRI specimens of Devonian fish are from Scotland. Most of these come from sediments of the Orcadian Basin. This geological basin appears to have extended from eastern Greenland to Norway, and all the way to northeastern Scotland, but its connections and original extent are not known in detail because of subsequent tectonic disruption. The basin infill contains deposits that have been interpreted as sediments of a mostly freshwater lake (Lake Orcadie). Some beds within these sediments are rich in fossil fish, and have become well-known to paleontologists. For example, the Achanarras Quarry is a famous site in Caithness, Scotland, where more species of Devonian fossil fish have been found than anywhere else in the country (Scottish National Heritage, 2009).
The Orcadian sediments are part of a very extensive geologic unit known as the Old Red Sandstone (ORS). ORS deposits and their equivalents are found across North America and Eurasia. The large-scale distribution of similar sediments indicates that deposition in the Orcadian Basin may have been part of a much larger system, controlled by similar depositional conditions.
Reference:
Scottish National Heritage (ed.) (2009) Achanarras Quarry Nature Reserve, NatureScot [Online]. https://digital.nls.uk/pubs/e-monographs/2020/216588072.23.pdf Available at: https://www.nature.scot/enjoying-outdoors/visit-our-nature-reserves/achanarras-quarry-nature-reserve (Accessed: 03 July 2024).
Hugh Miller
or The Scot, the Church, and the Fossils
Engraving by J. Sartain
One of the earliest and most prolific authorities on Devonian fishes and other fossil vertebrates was Hugh Miller (1802-1856), a stone mason and self-made scientist (Janvier, 1996). His work in the quarries along the northern shores of Scotland inspired a life-long love of geology (Cousin, 1910). Voraciously, he began to collect fossils from the Old Red Sandstone and documented his findings.
Miller was a devout Protestant Christian in the Church of Scotland, and married his wife, Lydia, a school teacher and children’s author whom he had met at his parish church, at the age of 34 (NRS Web Team, 2013).
Three years later, in 1840, Miller became the editor of a new bi-weekly newspaper published by the Church of Scotland: The Witness. As editor, Miller was able to cover significant events in post-Reformation church history, such as the Disruption, a massive protestation in which some 200 clergy left the church (CHDS, 2023) over whether the government should be allowed to appoint ministers (Bayne, 1893). Miller also used The Witness to publish many articles on the Old Red Sandstone which helped popularize interest in the study of natural history and fossil collecting (Janvier, 1996).
As time progressed, Miller grew increasingly reclusive and his writing waxed prolific. John Grant Malcolmson, a fossil enthusiast with a background in geology, was a fan of Miller’s 1835 book, Scenes and Legends of the North of Scotland, and helped share his work among prominent members of the scientific community (Janvier, 1996). One of these scientists was Louis Agassiz, a Swiss paleontologist and geologist, who was the premier authority on vertebrate paleontology. Upon seeing Miller’s detailed drawings of placoderms which carefully pieced together previously misunderstood parts of armored fishes, Agassiz realized these strange creatures were indeed fishes, instead of the previously postulated designation of tortoise or beetle as suggested by other scientists. Agassiz named this newly understood creature Coccosteus (Janvier, 1996).
Miller continued his work as editor of The Witness in spite of his lifestyle of isolation. He referred to himself as the “Robinson Crusoe of geology” (Janvier, 1996). Over the course of several years, he published three successful books which highlighted the synchronicities of geological evidences and the Bible: The Old Red Sandstone, or New Walks in an Old Field (1841), Footprints of the Creator (1850), and Testimony of the Rocks, or Geology in its Bearing on the Two Theologies, Natural and Revealed (1857).
Miller met a tragic end at the age of 54 in 1856 (NRS Web Team, 2013) before the release of Testimony of the Rocks the following year, and several other works that were published posthumously. Despite his short life, Hugh Miller significantly contributed to the growing study of Devonian vertebrates, as well as helped shape Protestant Christianity through the Church of Scotland. He represents an example of a Christian scientist who embraced the notion of the Creator God.
References:
Bayne, P. (1893) The Free Church of Scotland: Her Origin, Founders and Testimony. Edinburgh: T. & T. Clark. Available at: https://archive.org/details/freechurchofsco00bayn (Accessed: August 2024).
CHDS (2023) ‘Digital Witness,’ Cultural Heritage Digitisation Service (CHDS). Edinburgh University Library. Available at: https://libraryblogs.is.ed.ac.uk/diu/2022/12/14/digital-witness/ (Accessed: August 2024).
Cousin, J.W. (1910) A Short Biographical Dictionary of English Literature. London: J.M. Dent & Sons Ltd. eBook Produced by Project Gutenberg, Release Date: August 21, 2004 [EBook #13240] Available at: https://www.gutenberg.org/files/13240/13240-h/13240-h.htm. (Accessed August, 2024).
Janvier, P. (1996) Early Vertebrates. Oxford: Clarendon Press. pp. 308-311.
NRS Web Team (ed.) (2013) National Records of Scotland. Available at: https://www.nrscotland.gov.uk/research/learning/hall-of-fame/hall-of-fame-a-z/miller-hugh (Accessed: August 2024).