''Jamoytius kerwoodi'' was a species of primitive,
eel
Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
-like jawless
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
that lived in the
Llandovery epoch of the Early
Silurian period.
Long thought of as a "basal anaspid," ''J. kerwoodi'' is now recognized as the best-known member of the
Hyperoartia
Hyperoartia or Petromyzontida is a disputed group of vertebrates that includes the modern lampreys and their fossil relatives. Examples of hyperoartians from early in their fossil record are '' Endeiolepis'' and '' Euphanerops'' (which possessed ...
n
order Jamoytiiformes. It had an elongated body, and is thought to have had, in comparison with relatives known from intact bodies like ''Euphanerops'', a dorsal fin and an anal fin near the rearmost third of its body. Earlier reconstructions depict the creature as having side-fins running the length of its body, starting from behind the branchial openings to the tip of its tail: new research demonstrates that such "fins" are actually deformations of the bodywall as the corpse was being squished post-burial.
In life, ''J. kerwoodi'' resembled a lamprey with a very small mouth. Because the fossil had no teeth, teeth-like structures, nor suggestions of either in its mouth, it was not carnivorous like many modern
lamprey
Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...
s. It was more likely to have been a filter-feeder or a detritus-feeder, possibly in the manner of larval lampreys.
The fish had a cartilaginous skeleton, and a branchial basket resembling the
cyclostomes Cyclostome is a biological term (from the Greek for "round mouth") used in a few different senses:
* for the taxon Cyclostomi, which comprises the extant jawless fishes: the hagfish (Myxini) and the lampreys (Petromyzontidae). This was thought fo ...
- features that suggest that it was a basal member of that clade. It is also the earliest known vertebrate with
camera-type eyes.
It also possessed weakly mineralised scales.
History of research
''Jamoytius'' was originally named by Errol White on the basis of two specimens (the generic name is a reference to
J. A. Moy-Thomas
James Alan Moy-Thomas (12 September 1908 – 29 February 1944) was an English palaeontological ichthyologist.
Son of Alan Moy-Thomas and his wife Gertrude, he was born in London. He had a younger brother Edward and an older sister Joan Carolin ...
[Dawkins, Richard ]The Ancestor's Tale
''The Ancestor's Tale: A Pilgrimage to the Dawn of Life'' is a science book by Richard Dawkins and Yan Wong on the subject of evolution, which follows the path of humans backwards through evolutionary history, describing some of humanity's cou ...
) and, at the time, it was considered to be the most
basal vertebrate known. Since then, it has been reclassified by many workers as having many different affinities, such as an "unspecialized anaspid",
or as a sister taxon to the lampreys,
its difficulty in classification due to difficulties in reconstructing the anatomy;
it does not possess any usual
chordate
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...
synapomorphies. Currently, ''J. kerwoodi'' is now placed in its own order Jamoytiiformes, together with ''
Euphanerops'' and similar agnathans.
Further reading
* Long, John A. ''The Rise of Fishes: 500 Million Years of Evolution'' Baltimore: The Johns Hopkins University Press, 1996.
Links to images
References
Jamoytiiformes
Silurian jawless fish
Silurian animals of Europe
Prehistoric Hyperoartia genera
Fossil taxa described in 1946
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