''Jamoytius kerwoodi'' is an extinct species of primitive,
eel
Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
-like
jawless fish
Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...
known from the
Patrick Burn Formation in Scotland, dating to the
Llandovery epoch of the Early
Silurian
The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...
period.
Long thought of as a "basal anaspid," ''J. kerwoodi'' is now recognized as the best-known member of the
Hyperoartian
order
Order, ORDER or Orders may refer to:
* A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
...
Jamoytiiformes
''Jamoytius kerwoodi'' is an extinct species of primitive, eel-like jawless fish known from the Patrick Burn Formation in Scotland, dating to the Llandovery epoch of the Early Silurian period.
Long thought of as a "basal anaspid," ''J. kerwoodi' ...
. 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 a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...
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 for ...
- 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 2004 science book by Richard Dawkins and Yan Wong that delves into the topic of evolution. The book adopts a unique approach, retracing the path of humans in reverse chronological ...
) 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 a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...
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 ...
. 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
{{Taxonbar, from=Q46680
Anaspidomorphi
Silurian jawless fish
Silurian animals of Europe
Fossil taxa described in 1946
Anaspidomorphi genera
Monotypic prehistoric fish genera