''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% ...
that lived in the
Llandovery epoch of the Early
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...
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
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Jamoytiiformes
Jamoytiiformes is an extinct order of prehistoric jawless fish in the superclass Anaspidomorphi.
Taxonomy
Taxonomy is based on Mikko's Phylogeny Archive
* Family † Achanarellidae Newman 2002
** Genus †'' Achanarella'' Newman 2002 'Achanar ...
. 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 - 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[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
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
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 five ...
synapomorphies
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...
. 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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