''Emmonsaspis'' is a Cambrian

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 ...

, and its fossils were found in the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

-age Parker Slate of

Vermont Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...

in the late 19th century.

Description

''Emmonsaspis'' is a chordate related to '' Metaspriggina'' and '' Nuucichthys''. It grew to roughly in length and probably fed on plankton in the water column. No trace of a

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

is present, although roughly 50 myomeres can be seen in the fossils. It had large eyes and a large organ behind its branchial chamber, probably a liver. There are two species: ''Emmonaspis worthanella'' and ''Emmonaspis cambriensis'' (Walcott(?) 1886(?) 1911(?)). ''E. cambrensis'' has been described as a

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

, a

, an

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

and as a

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

-like organism.

Affinities

It was interpreted by

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

C. D. Walcott in 1911 as a polychaete worm. Although some paleontologists regarded it as an early

allied with ''

Pikaia ''Pikaia gracilens'' is an extinct, primitive chordate marine animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Sim ...

'' et al., Conway Morris suggested in 1993 that it might be a

descendant of the

Vendian The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

form '' Pteridinium'', and a

frondose Frondosity (from Latin ''frondōsus'' meaning 'leafy') is the property of an organism that normally flourishes with fronds or leaf-like structures. Many frondose organisms are thalloid and lack the organization of tissues into organs, with the ...

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

was accepted, until a 2024 study found ''Emmonsaspis'' to be in a polytomy with '' Metaspriggina'' and '' Nuucichthys'' as a stem-group vertebrate.

Notes

Prehistoric jawless fish genera Cambrian chordates Cambrian animals of North America Fossil taxa described in 1886 {{Cambrian-animal-stub