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Cephalaspis sp.
Cephalaspis #1
Cephalaspis is an extinct genus of the major clade Osteostaci 4), and a armored fish group of so called ‘Ostracoderms’. Osteostraci are one of the most diverse groups of extinct agnathans, which lived from the Early 4) or Late 2) Silurian to the Late Devonian 2), 4), and are considered the sister group gnathostomes (jawed vertebrates) 2).
Cephalaspis #4
The specimen of the representative species (type species) Cephalaspis lyelli Agassiz was given to the British Museum by Sir Charles Lyell 7) known as the author of "Priciples of Geology". C. lyelli was named after him.
Cephalaspis has a characteristic horseshoe-shaped head with extending processes called "cornuata" 2), 4). C. lyelli is about 25cm in length and its head shield is about one-third of total length 6), 7).
Cephalaspis #2
On the dorsal surface of the headshield, there are eyes in the center, depressions of braincase which have regarded as sense organ or electric organ, unpaired dorsal electric field in the median and paired lateral electric fields 2), 4), 6). These fields have been interpreted as homologous to the lateral line system in bony fishes 2).
Cephalaspis #5
On the ventral side of the cephalic shiled, there are an mouth opening 1), 2), 4), 6) and several pairs of gills openings 2), 4).
Cephalaspis #3
There is a median crest on top of trunk 2), 6), which may include an anterior dorsal fin 2), and posterior dorsal fin lies far backwards 6).
The caudal fin is epicercal, that is, like that of a shark with large upper lobe 2),6). There are well developed pectral fins which are large and paddle-shaped 6), 7). A ventral fin and an anal fin are not found 6).
Cephalaspis
Cephalaspis probably lived on sucking organic debris from the bottom, or preying on small benthic animals 2), 3).
As their eyes are on dorsal surface and their mouth is on ventral side, they would not reply on their eyes for feeding but use them for defence. They might have been prey for the predators of the time 5). Actually, the partialy digested headshields of small Cephalaspis have found from the body cavity of large Acanthodians, which suggests that small Osteostraci may have formed part of the diet of them 3).
They have inhabited fresh-water, marginal brackish or edges of the continents, such as rivers, lakes, lagoons, deltas 2), 3).
created in March 2017.
References:
  1. Allis Jr EP (1931) Concerning the mouthopening and certain features of the visceral endoskelton of Cephalaspis. J Anat. 65(Pt 4): 509–527.
  2. Carlsson A (2006) Description of a new osteostracan species from Ukrainewith a brief analysis of the interrelationships of Scolenaspida. Uppsala University.
  3. Denison RH (1956) A review of the habitat of the earliest vertebrates. In Fieldiana: Geology; Vol.11 No.8. Chicago Natural History Museum. Chicago.
  4. Janvier P (1997) Osteostraci. Version 01 January 1997 (under construction). in The Tree of Life Web Project
  5. Prehistoric Wildlife
  6. Stensiö EA (1932) The cephalaspids of Great Britain. British Museum (Natural History). London
  7. White EI (1958) On Cephalaspis lyelli Agassiz. Palaeontology 1(2): 99-105.