''Sacabambaspis'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of jawless fish that lived in the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

period. ''Sacabambaspis'' lived in shallow waters on the continental margins of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

. It is the best known arandaspid with many specimens. It is related to '' Arandaspis''.

Description

''Sacabambaspis'' was approximately in length. The body shape of ''Sacabambaspis'' vaguely resembled that of a tadpole with an oversized head, flat body, wriggling tail, and lack of fins. It had characteristic, frontally positioned eyes, like car

head lamp A headlamp is a lamp (electrical component), lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage (language), usage, ''headlamp'' is the term for the ...

Armor

''Sacabambaspis'' had a head shield made from a large upper (dorsal) plate that rose to a slight ridge in the midline, and a deep curved lower (ventral) plate, this headshield is ornamented with characteristic oak-leaf shaped or tear-drop shaped tubercles. Also it had narrow branchial plates which link these two along the sides, and cover the gill area. The eyes were far forward and between them are possibly two small

nostrils A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called tur ...

and they, which are surrounded by what is thought to be endoskeletal bone, and putative nostrils, are found at the extreme anterior of the head, one of the diagnostic features of the arandaspids. The rest of the body was covered by long, strap-like

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

behind the head shield.

Tail

The tail consists of relatively large dorsal and ventral webs and an elongated notochordal lobe, the posterior end of which is bordered by a small fin web. This tail structure clearly differs from that of heterostracans, which are currently grouped with arandaspids and astraspids in the clade

Pteraspidomorphi Pteraspidomorphi 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 ...

(Gagnier 1993, 1995; Donoghue & Smith 2001; Sansom et al. 2005), in which the caudal fin looks diphycercal (i.e. symmetrical) and strengthened by a few large radials (Janvier 1996).

Discovery and species

''Sacabambaspis'' is named after the village of

Sacabamba Sacabamba ( qu, Saqapampa) is a town in the Cochabamba Department in central Bolivia. It is the capital of Sacabamba Municipality Sacabamba Municipality is the fourth municipal section of the Esteban Arce Province in the Cochabamba Department, ...

Cochabamba Department Cochabamba ( ay, Quchapampa Jach'a Suyu, es, Departamento de Cochabamba , qu, Quchapampa Suyu), from Quechua ''qucha'' or ''qhucha'', meaning "lake", ''pampa'' meaning "plain", is one of the nine departments of Bolivia. It is known to be the ...

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

, where the first fossils of the genus were found. ''S. janvieri'' (Gagnier, Blieck & Rodrico, 1986), the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...

of the genus, is known from the Anzaldo Formation of

. There are 30 known specimens of this Bolivian species, all crammed into a very confined area, believed to be the result of a fish kill, probably due a sudden inflow of freshwater from a large storm. They were found associated with a large number of lingulid

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

s, also killed at the same time. Indeterminate specimens (described as ''"Sacabambaspis sp."'') have been found in many countries corresponding to the margin of Gondwana. Young, 1997 described fossils of the genus from the Stokes Siltstone and Carmichael Sandstone of Central Australia. Isolated scales found in the Horn Creek Siltstone from Central Australia have a very similar ornamentation to the Bolivian scales. Specimens have also been reported from

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

. Sansom ''et al.'', 2009 described specimens from the Amdeh Formation of

Oman Oman ( ; ar, عُمَان ' ), officially the Sultanate of Oman ( ar, سلْطنةُ عُمان ), is an Arabian country located in southwestern Asia. It is situated on the southeastern coast of the Arabian Peninsula, and spans the mouth of ...

on the Arabian Peninsula. The Oman discoveries showed that the fish were present all around the periphery of the ancient continent of Gondwana and not just in the southern regions as had previously been shown by the findings from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

and Australia.

Paleobiology

Feeding

Although it had no jaws, the mouth of ''Sacabambaspis janvieri'' was lined with nearly 60 rows of small bony

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or ora ...

plates which were probably movable in order to provide more efficient suction-action through expansion and contraction of the oral cavity and pharynx.

Sensory system

The fossils of ''Sacabambaspis'' show clear evidence of a sensory structure ( lateral line system). This is a line of pores within each of which are open nerve endings that can detect slight movements in the water, produced for example by predators. The arrangement of these organs in regular lines allows the fish to detect the direction and distance from which a disturbance in the water is coming.

References

External links

Pteraspidomorphi
at Palaeos {{Portal bar, Paleontology, Fish Pteraspidomorphi genera Ordovician jawless fish Late Ordovician animals Fossils of Oman Prehistoric fish of Australia Ordovician animals of Oceania Fossils of Australia Ordovician animals of South America Ordovician Argentina Fossils of Argentina Ordovician Bolivia Fossils of Bolivia Fossil taxa described in 1986 Ordovician animals of Asia