Jamoytius kerwoodi was a species of primitive, eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

-like jawless fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate 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...

 that lived in the Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 period.

J. kerwoodi is the earliest known anaspid.. It had long, paired fins running along its body - making it a good swimmer. J. kerwoodi resembled a lamprey, especially with its rounded mouth and elongated body. However, as it had no teeth or teeth-like structures in its mouth, it was not carnivorous like its distant modern-day relative, the lamprey

Lamprey

Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...

. It was more likely to have been a filter-feeder or a detrius-feeder, possibly in the manner of larval lampreys.

The fish had a cartilaginous skeleton, and a branchial basket resembling the cyclostomes

Cyclostomata

Cyclostomata is a group of chordates that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have round mouths that lack jaws but have retractable horny teeth...

 - used to suggest that it was a near-ancestor to 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) 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

Chordate

Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...

 synapomorphies

Synapomorphy

In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

.

Further reading

• Long, John A. The Rise of Fishes: 500 Million Years of Evolution Baltimore: The Johns Hopkins University Press, 1996. ISBN 0-8018-5438-5