Arandaspida is a taxon of very early, jawless

prehistoric fish __NOTOC__ Prehistoric fish are early fish that are known only from fossil records. They are the earliest known vertebrates, and include the first and extinct fish that lived through the Cambrian to the Quaternary. The study of prehistoric fish is ...

which lived during the

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. Arandaspids represent some of the oldest known

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

. The group represents a subclass within the class

Pteraspidomorphi Pteraspidomorpha is an extinct class of early jawless fish. They have long been regarded as closely related or even ancestral to jawed vertebrates, but the few characteristics they share with the latter are now considered as basal traits for al ...

, and contains only one order, the Arandaspidiformes. The oldest known genus of this group is '' Sacabambaspis'' found in

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Characteristics

The head armor of arandaspids is elongated, fusiform, with a rather flat dorsal shield, and a bulging ventral shield. In the anterior part of the dorsal shield are two closely set holes, which have been thought to be a paired pineal opening, but which are more likely the external openings of the endolymphatic ducts. The eyes, surrounded by a sclerotic ring, are housed in a notch at the anterior end of the dorsal shield. The nostrils are not clearly located, but may have been situated between the eyes. Ventrally, the ventral lip of the mouth is armed with long series of small oral plates which recall those of heterostracans. The gill openings are probably numerous (more than 15) and minute. They opened between the diamond-shaped platelets which separate the dorsal from the ventral shield. The body is covered with rod-shaped scales arranged in chevrons, and the tail is probably pad-shaped and diphycercal. The dermal bones of arandaspids consist of aspidine (acellular bone) and are ornamented with oakleaf-shaped tubercles which seem to contain no dentine. The sensory-lines were housed in narrow grooves between the tubercles.

Taxonomy

Taxonomy based on the work of Mikko's Phylogeny Archive, Nelson, Grande and Wilson 2016 and van der Laan 2018. * Order †Arandaspidiformes Ritchie & Gilbert-Tomlinson, 1977 ** Family †Astraspididae Halstead 1993 *** Genus †'' Astraspis'' Dineley & Loeffler 1976 ** Family †Arandaspididae Ritchie & Gilbert-Tomlinson, 1977 orophoraspididae Halstead 1993; Sacabambaspidae*** Genus †'' Andinaspis'' Gagnier, 1991 non Ritchie & Gilbert-Tomlinson, 1977 *** Genus †'' Apedolepis'' Young, 1997 *** Genus †'' Arandaspis'' Ritchie & Gilbert-Tomlinson, 1977 *** Genus †'' Areyongalepis'' Young, 2000 *** Genus †'' Pircanchaspis'' Erdtmann ''et al.'', 2000 *** Genus †'' Porophoraspis'' Ritchie & Gilbert-Tomlinson, 1977 *** Genus †'' Ritchieichthys'' Sansom ''et al.'', 2013 *** Genus †'' Sacabambaspis'' Gagnier, Blieck & Rodrico, 1986

References

{{Taxonbar, from1=Q3621278, from2=Q25398124, from3=Q19890834 Pteraspidomorphi Ordovician jawless fish Vertebrate subclasses Early Ordovician first appearances Late Ordovician extinctions de:Pteraspidomorphi#Arandaspida

Characteristics

Taxonomy

See also

References