''Groenlandaspis'' is an extinct genus of

arthrodire Arthrodira (Greek for "jointed neck") 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 eco ...

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.

Description

As with all other arthrodires, ''Groenlandaspis'' had a joint in the back of its head with its thoracic armor, allowing for its head to be thrown back, increasing its gape. However, as its head is somewhat compressed in comparison with many other arthrodires, and as the dorsal side came to a low, pyramid-like peak, it is believed that ''Groenlandaspis'' could not crane its head back very far. It was a relatively small fish, only in length on average, though one unusually large species, ''G. riniensis'', reached almost a metre in length Gess, Robert W.; Whitfield, Alan K. (August 22, 2020). "Estuarine fish and tetrapod evolution: insights from a Late Devonian (Famennian) Gondwanan estuarine lake and a southern African Holocene equivalent". Biological Reviews. 95 (4): 865–888. doi:10.1111/brv.12590 – via Wiley Online Library. It lived in coastal and fluvial waters, where it is thought to have fed on either very small prey, or detritus; the small dental plates in its mouth strongly suggest that it was incapable of tackling large prey. The possibility that the plates may have been used to, at times, feed on bivalves has also been muted. The body shape of the largest species ''G. riniensis''’ suggests that it was most likely a benthic fish. The presence of crushing tooth plates in the form of flat, noded infragnathals and superagnathals suggest that the species' diet may have included prey with hard external shells such as molluscs, crustaceans or arthropods.Gess, Robert W. and Whitfield Alan K. (2020). "Estuarine fish and tetrapod evolution: Insights from a Late Devonian (Famennian) Gondwanan estuarine lake and a southern African Holocene equivalent". Biological Reviews. doi:10.1111/brv.12590. The armor length of ''G. riniensis'', according to the original description, was approximately , with the head shield having a very broad marginal plate and narrow pineal plate, with the nuchal relatively narrow, being approximately half as broad as it is long. The trunk shield of this species was characterized as having an anterior lateral plate which is almost as broad as long with a relatively straight anterior margin; the median dorsal plate is low with an apex that is posteriorly directed; its posterior dorsolateral plate is very narrow with inflexion of the main lateral line canal situated very close to posterior margin. This species has ornamentation of widely spaced, coarse tubercles.LONG, J.A., ANDERSON, M. E., GESS, R. W. & HILLER, N. (1997). New placoderm fishes from the Late Devonian of South Africa. Journal of Vertebrate Palaeontology 17, 253–268.) ''Groenlandaspis'' is unusual among placoderms in that it is known what color it was; preserved pigment cells in its fossils indicate that its posterior was red and its anterior was silvery-white in a

countershaded Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...

pattern, camouflaging it in the murky, silty waters of the rivers in which it dwelled.

Species

*†''G. mirabilis'' Heintz, 1932 *†''G. antarctica'' Ritchie, 1975 *†''G. riniensis'' Gess and Hiller, 1995 *†''G. disjectus'' Woodward, 1891(originally ''Coccosteus disjectus'') *†''G. pennsylvanica'' Daeschler et al., 2003 *†''G. potyi'' Olive et al., 2015 *†''G. seni'' Janvier and Ritchie, 1977 *†''G. thorezi'' Heintz, 1932 ''Groenlandaspis riniensis'' is one of two arthrodire placoderms described in 1999 from the

Waterloo Farm lagerstätte The Waterloo Farm lagerstätte is a Famennian lagerstätte in South Africa that constitutes the only known record of a near-polar Devonian coastal ecosystem. History and discovery The Waterloo Farm Lagerstätte is an approximately 360 millio ...

in South Africa, with a third species having been subsequently described.GESS, R. W. & TRINAJSTIC, K. M. (2017). New morphological information on, and species of placoderm fish Africanaspis (Arthrodira, Placodermi) from the Late Devonian of South Africa. PLoS One 12(4), e0173169. The species name ‘''riniensis''’ derived from Rini or Rhini, the traditional isiXhosa name for Makhanda/Grahamstown, making it the first ever vertebrate fossil to have an isiXhosa derived scientific name. ''G. riniensis'' appears to have spent its entire life cycle within the Waterloo Farm estuary as it is represented by a full ontogenetic series. Evidence from other Late Devonian localities with similar placoderm taxa which suggest that while many larvae or small juveniles stayed in the littoral zone close to adult habitats, others may have moved upriver to avoid predation. ''G. riniensis'' represents the most frequently preserved fish taxon from the Waterloo Farm site, and may have been the most common vertebrate within the palaeoenvironment, though its frequent preservation may be influenced by preservational bias. ASCATT~1

References

{{Taxonbar, from=Q2200315 Arthrodire genera Placoderms of Antarctica Placoderms of Asia Placoderms of Africa Placoderms of Australia Placoderms of Europe Placoderms of North America Late Devonian animals