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 Catalogue of Fossil Fishes AS Woodward 1891 Cephalaspis murchisoni - Ledbury

The Osteostraci or Cephalaspids as they were once known are the most ‘famous’ of all fossil agnathans. The first forms are seen in the Wenlockian of Scotland (Ateleaspis) and the last (Escuminaspis) in the Frasian of Miguasha, Canada. They are thought to have lived in shallow marine/deltaic environments, but there is some suggestion that rivers may have played a part in their life-cycle. It is thought they were mostly suspension-feeders and may have been made extinct by the massive expansion of the antiarch placoderms which occupied the same niche in the mid-Devonian

They are identified by a large bony headshield containing the eyes, nasal apparatus, pineal opening and the characteristic cephalic sensory fields at the sides of the shield. Most Osteostraci have a horseshoe-shaped headshield with sharp posterolateral cornual processes, to the inner margins of which the pectoral fins are attached.

Osteostraci Classification


        Ateleaspis - Early Silurian (Wenlockian), Generalised form







It has been suggested that most of the osteostracan diversication occurred before the Wenlockian because this period sees both Ateleaspis the most generalised primitive form and derived cornuates such as Tremataspis.

They are widely distributed across the Old Red Sandstone of Europe and North America. The UK has some spectacular sites.

Osteostraci in my collection (click on thumbnails to see larger images)

Ateleaspis tessellata traquair           Silurian (Wenlockian)    Lesmahagow/Hagshaw inlier, Scotland

Ateleaspis is earliest vertebrate to have paired appendages. As with all Osteostraci, they also have a network of sensory fields made up of loose platelets of bone  (not differentiated in ateleaspis) located along the mid-line and the lateral edges of the headshield. These sensory areas are  connected to a complex of nerve channels and ducts which eventually connect with the labyrinth of the brain. It is thought that these area function as follows; when the animal moves up in the water the platelets are pushed down on the channels below them sending a signal to the portion of the brain associated with orientation and movement 

In Ateleaspis, the sensory fields  extend into the fins which are an extension of the headshield. Thus it has been suggested that the fins and fields developed together as means of stabilizing swimming along with the sense organs to provide feed-back control for it. 

atel3.jpg (160497 bytes)   atelhea.jpg (121607 bytes)   atel6.jpg (168053 bytes)   atel5.jpg (193726 bytes)  An extraordinary complete dorsal fish with the head and body preserved in a nodule and with the tail preserved in  fish-bed. A true masterpiece of fossil preparation.

atela.jpg (116853 bytes)   atelab.jpg (120970 bytes)   atelac.jpg (130937 bytes)  An almost complete animal ventrally preserved in a nodule.

ss-atel2.jpg (71791 bytes)   ss-atel1.jpg (81684 bytes) Pos/Neg of an Ateleaspis head preserved in fishbed

atel2.jpg (203059 bytes)    atel1.jpg (240701 bytes)   Pos/Neg of 3D Ateleaspis found in nodule

   atel1pos.jpg (130579 bytes)       atel1negative.jpg (223764 bytes)    Pos/neg of 3D preserved oralobranchial chamber


Hirella gracilis    Upper Silurian    Ringerike, Norway

Hirella is a basal osteostracan only marginally more complex than Ateleaspis. It has narrow paired fins and an oralobranchial chamber closed ventrally by large dermal platelets

hirel2.jpg (72182 bytes)   From Heintz 1939

ss-hirella.jpg (116719 bytes)   ss-hirella2.jpg (116762 bytes)    Mass-mortality plate

 ss-hirellaventral.jpg (98686 bytes)    hirel.jpg (118879 bytes)  Ventral presentation     

  ss-hirellatail.jpg (64328 bytes)  Tail



The Zenaspids are usually large osteostracans with tuberculated ornamentation and a large hypophyseal foramen. They are found in the Lower Devonian of Britain and Podolia  They have a massive headshield with posteriorly enlarged sensory fields and thick, narrow cornual processes.

     pagei3.jpg (144366 bytes)   homepagecephstage1.jpg (42729 bytes)        Zenaspis pagei  Lower Devonian,   Turin Hill, Scotland 


 powr1.jpg (204151 bytes)            Zenaspis powriei   Lower Devonian, Scotland


Cephalaspis sp. x 2  Welsh borders (part of the Wonderblock...see also acanthodian)

ceph4.jpg (136338 bytes)   ce5.jpg (79858 bytes)     St Maughans Formation, LORS, Brecon, Wales


Yvonaspis campbelltonesis    New Brunswick, Canada

p-ccambelton.jpg (107792 bytes)     fishyvon.jpg (55924 bytes)         


Osteostracan fauna from the Lower Devonian of Podolia, Ukraine

For the last 150 years, the Lower Devonian  outcrops along the banks of the Dniester river in Podolia have been yielding wonderful fish remains. Despite the first descriptions of cephalaspids from the region being in 1874, little work has been done on the 19 species known, although recent papers by Janvier and Voichyshyn go a long way to addressing this lack of information.

   gg-ukr1.jpg (117311 bytes)    Zychaspis siemiradzkii  gg-ukr2.jpg (167919 bytes)   Stensiopelta pustulata  gg-ukr3.jpg (148508 bytes)   

Z. siemiradzkii

  stm-ceph2.jpg (127670 bytes)     uk-ceph.jpg (225575 bytes)  

ceph2.jpg (54483 bytes)      ceph1.jpg (105035 bytes)    The ventral covering of the oralobranchial chamber, and one of the pectoral

 ceph3.jpg (87785 bytes)  horizontal ventral caudal lobe, a unique character of osteostracans that is rarely observed

ss-cephukr1.jpg (79990 bytes)     ss-cephukr2.jpg (95718 bytes)   Z. siemiradzkii headshields

stm-ceph1.jpg (112331 bytes)   Hevaspis kozlowskii

  ss-cephukr3.jpg (49992 bytes)     Stensiopelta pustulata



Osteostracan fauna from the Silurian (Wenlock-Ludlow) Saaremaa Island, Estonia

The Osteostracans of Saarema island in Estonia, while being very early in the fossil record are a highly specialised group of small thyestiida. While most of this group show the classic cornuate morphology (Thyestes) others such as Witaaspis and Tremataspis are non-cornuate.


   thystes.jpg (74718 bytes)   Thyestes

thys.jpg (100975 bytes)   thysa.jpg (86175 bytes)  thysb.jpg (79779 bytes)   


gg-protceph1.jpg (89589 bytes)   Witaaspis schrencki   


  ss-trem.jpg (56210 bytes)      trem.jpg (50521 bytes)      Tremataspis mammillata     


gg-trem.jpg (42729 bytes)   Tremataspis schmidti  



Osteostraci images from literature

 ss-ostimage2.jpg (93479 bytes)  Poissons fossiles  Agassiz  Cephalaspis Lyelli  

ss-ostimage3.jpg (70606 bytes) ss-ostimage9.jpg (95058 bytes) Cephalaspids of Great Britain  Stensio1932  Cephalaspis powriei Lankester  

ss-ostimage4.jpg (118943 bytes)    Stensio 1932 Cephalaspis whitei  showing canals of sub-aponeurotic vascular plexus

ss-ostimage8.jpg (70999 bytes)   Cephalaspids of Great Britain  Stensio 1932 Cephalaspi pagei 


ss-ostimage5.jpg (72374 bytes) Cephalaspids of Great Britain  Stensio 1932 Sclerodus pustuliferous agassiz 

ss-ostimage6.jpg (86870 bytes)  Fishes of the Old Red Sandstone of Britain Powrie and Lankester 1868 (C.powrie pagei asper)