''Lepidaspis serrata'' ("serrated scaly shield") is an extinct heterostracan

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 ...

from Early

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. Its scientific name refers to the fact that the armor is composed of hundreds of tiny scales with serrated edges. Although it is regarded as a heterostracan, its exact placement within Heterostraci is regarded as ''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'', as the fact that it is currently impossible to discern where its dorsal and ventral plates (which are made up of a mosaic of the aforementioned tiny scales) end or begin. Some experts regard it as being descended from the basal heterostracans of the

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 ...

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Enigmatic Heterostraci taxa Heterostraci genera Devonian fish of North America {{Devonian-jawless-fish-stub