| Gaspeaspis Temporal range: Middle Devonian | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | † Placodermi |
| Order: | † Arthrodira |
| Family: | † Phlyctaeniidae |
| Genus: | † Gaspeaspis Pageau, 1969 |
Gaspeaspis is an extinct genus of placoderm fish, which lived during the Middle Devonian period of North America. [1]
Placoderms are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils from the Silurian to the end of the Devonian period. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates, and the rest of the body was scaled or naked depending on the species.
Arthrodira is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches. Arthrodires were the largest and most diverse of all groups of placoderms.
Bothriolepis was a widespread, abundant and diverse genus of antiarch placoderms that lived during the Middle to Late Devonian period of the Paleozoic Era.
Groenlandaspis is an extinct genus of arthrodire from the Late Devonian. Fossils of the different species are found in late Devonian strata in all continents except eastern Asia. The generic name commemorates the fact that the first specimens of the type species were found in Greenland.
Coccosteus is an extinct genus of arthrodire placoderm from the Devonian period. Its fossils have been found throughout Europe and North America. The majority of these have been found in freshwater sediments, though such a large range suggests that they may have been able to enter saltwater. It was a small placoderm, with Coccosteus cuspidatus measuring 29.6–39.4 cm (11.7–15.5 in) long.
Rhenanida is an order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles. The patterns and components of this "mosaic" correspond to the plates of armor in other, more advanced placoderms, suggesting that the ancestral placoderm had armor made of unfused components, as well.
Phyllolepida is an extinct taxon of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. Unlike other flattened placoderms, the phyllolepids were inhabitants of freshwater environments.
Acanthothoraci is an extinct group of chimaera-like placoderms closely related to the rhenanid placoderms. Superficially, the acanthoracids resembled scaly chimaeras and (relatively) heavily armored ptyctodonts. They were distinguished from chimaeras by their large scales and plates, a pair of large spines that emanate from their chests, tooth-like beak plates, and the typical bone-enhanced placoderm eyeball. They were distinguished from other placoderms by differences in skull anatomy and by patterns on the skull plates and thoracic plates that are unique to this order.
The ptyctodontids ("folded-teeth") are placoderms of the order Ptyctodontida, containing the family Ptyctodontidae. With their big heads, big eyes, reduced armor and long bodies, the ptyctodontids bore a superficial resemblance to modern day chimaeras (Holocephali). Their armor was reduced to a pattern of small plates around the head and neck. Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish.
Brindabellaspis stensioi is a placoderm with a flat, platypus-like snout from the Early Devonian of the Taemas-Wee Jasper reef in Australia. When it was first discovered in 1980, it was originally regarded as a Weejasperaspid acanthothoracid due to anatomical similarities with the other species found at the reef.
Phyllolepis is the type genus of Phyllolepida, an extinct taxon of arthrodire placoderm fish from the middle to late Devonian. The species of Phyllolepis, themselves, are restricted to the Famennian-aged freshwater strata of the Late Devonian, around 360 million years ago. Fossils of this genus have been found primarily in Europe and North America. The end of the Devonian saw them disappear in a mass extinction.
Austrophyllolepis is an extinct genus of phyllolepid arthrodire placoderm from Middle to Late Devonian freshwater strata of Australia. The type species, A. ritchiei is found in Givetian to early Frasnian-aged freshwater strata near what is now Mount Howitt. A second species, A. dulciensis, is found from Middle Devonian freshwater strata from the Dulcie Sandstone of Georgina Basin, Central Australia.
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
Homostiidae is a family of flattened arthrodire placoderms from the Early to Middle Devonian. Fossils appear in various strata in Europe, Russia, Morocco, Australia, Canada and Greenland.
Palaeacanthaspis vasta is an extinct acanthothoracid placoderm from the early Devonian of Europe.
Actinolepis is an extinct genus of actinolepid placoderm from the Early Devonian. Four species are known: A. magna from Estonia, A. spinosa from Latvia, the type species A. tuberculata from New Zealand and A. zaikai from Belarus.
Kujdanowiaspis is an extinct genus of arthrodire placoderm fish from the Early Devonian of Podolia (Ukraine), Poland and Spain. Kujdanowiaspis is known from many fragmentary head shields and body armours.
Minjinia turgenensis is a species of placoderm from the Devonian of Mongolia. It is known from a single specimen preserving part of the skull, including remains of endochondral bone, which indicates that a mineralised endoskeleton evolved before the split between bony and cartilaginous fish, and that it was lost in the latter group.
Millerosteus is an extinct genus of coccosteid arthrodire placoderm from the Early Givetian stage of the Middle Devonian period. Fossils are found in the Orkneys and Caithness, Scotland. It was a small placoderm with an body length of 14 cm (5.5 in). Millerosteus is one of the few arthrodires known from specimens preserving the entire skeleton.
Dickosteus is an extinct genus of coccosteid arthrodire placoderm from the Late Eifelian to Early Givetian stages of the Middle Devonian period. Fossils are found in the Orkneys and Caithness, Scotland. It was a small placoderm with a total body length of 43.7 cm (17.2 in). It is one of the few placoderms for which complete bodies are known.
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