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Characterised by the presence of large ornamented bony spines in front of all the fins except the caudal and tiny scales that have a bulbous base. First described by Agassiz in 1844 they are often called the ‘spiny sharks’ although there is much debate as to whether they are closer to the bony fish than elasmobranches. They lasted almost 200 Myn years from the Early Silurian to the Early Permian. The three major acanthodian clades are the Climatiiformes, Ischnacanthiformes and Acanthodiformes. The climatiiforms are the oldest, having elaborate bony shoulder girdle armour and many spines. The ischnacanthiformes were predators with teeth and the acanthodiformes filter feeders that were the longest surviving group. The acanthodians are mostly marine but given their presence in the Old Red Sandstone these had to be living freshwater.


Acanthodian from 'Catalogue of Fossil Fishes' AS Woodward 1891


Acanthodii in my collection


Climatius reticulatus, Lower Devonian,  Tillywhandland, Scotland

This early climatiiform had numerous, heavily ornamented, broad based fin spines. The two large dorsal, single anal, paired pelvic, four paired intermediate and large paired pectoral fin spines would have made it a very nasty mouthful. It has an advanced shoulder girdle made up of a three paired pinnal plates and a single anterior and posterior lorical bony plate. Articulated examples are incredibly rare.

jj-clim1.jpg (130075 bytes)   ventero-lateral presentations

clim6.jpg (254455 bytes)

p-climatspine.jpg (50398 bytes)  Ventral animal 

climatius.jpg (222527 bytes) Very large skull


Vernicomacanthus uncinatus Lower Devonian,  Tillywhandland, Scotland



Brachyacanthus scutiger Lower Devonian,  , Scotland




Euthacanthus macnicolli Lower Devonian,  Tillywhandland, Scotland

Another classic early climatiiform, with a much less advanced shoulder girdle than Climatius, made up of only single paired pinnal plates. It also had five intermediate spines and is toothless.

hh-euth.jpg (137299 bytes) 




Parexus recurvus, Lower Devonian,  Tillywhandland, Scotland

Notable for its very large anterior dorsal fin spine. The shoulder girdle of Parexus is intermediate between those of Climatius and Euthacanthus, being formed of a single lorical and paired pinnal plates. 


climatius2.jpg (300477 bytes) 

  climatitoothwl.jpg (173703 bytes)  



Mesacanthus mitchelli (Egerton) Lower Devonian, Tillywhandland, Scotland

Mesacanthus means 'middle spine' because as well as being the basal acanthodiform, it is the only one to have intermediate spines between the pectoral and pelvics. As with all acanthodians it was a filter feeder, with well developed rakers.  

IMG_1482.jpg (297798 bytes)  p-mesacanthus.jpg (67410 bytes)

gg-isch2.jpg (46535 bytes) Multi slab with 20 plus fish


Ischnacanthus gracilis   Lower Devonian,  Tillywhandland, Scotland

As can be seen below, this basal Ischnacanthiform has robust upper and lower jaw bones, the biting surface of which contains gnathal bones looking rather like fused rows of teeth. The name means 'thin spine' and as can be seen again below, they lacked the boney plates seen in the shoulder girdle of the climatiiformes.

gg-ischbig1.jpg (95000 bytes)  gg-ischbig2.jpg (107996 bytes)   Skull detail of a large individual. Very fine dentary structures

p-icanthus.jpg (83294 bytes)    large, but slightly smaller

IMG_1478.jpg (142590 bytes)


Unknown Welsh Borders Acanthodian (Part of the wonder-block - see osteostracans)

199.JPG (376949 bytes)  St Maughans Formation, LORS, Brecon, Wales



Cheiracanthus sp.    Mid Devonian     

First described by Agassiz in Poissons fossiles, this is a common Middle Devonian Acanthodiform.

r-bigacan.jpg (72795 bytes)   Cheiracanthus latus, Tynet burn, Scotland

CHEIR.jpg (109692 bytes)  Cheiracanthus latus, Tynet burn, Scotland

che2.jpg (146568 bytes)   IMG_1488.jpg (385610 bytes)   hh-euthventspiall.jpg (110593 bytes)   Achanarras, Scotland


 Diplacanthus sp.   Mid Devonian    Tynet burn, Scotland

Again, this common Middle Devonian Climatiiform was first described by Agassiz. Meaning 'paired-spines', it was a deep bodied fish that retained its ancestors intermediate spines (2 pairs) but lacked the heavily armored shoulder girdle. It lacks ancillary gill covers, is toothless and had particularly short jaws.

DIPLA.jpg (123858 bytes)  Tynet burn, Scotland

IMG_1486.jpg (241086 bytes)  Achanarras, Scotland



Acanthodes sulcatus.    Carboniferous,  Peel Glen, Scotland

One of the most specialised of all acanthodians with the anal and dorsal fins in the same posterior position and loss of the pelvic fins

beardenacanthod.jpg (105544 bytes)   beardenacanthodhead.jpg (164374 bytes)   beardenacanthodhead2.jpg (147347 bytes)  


Other Acanthodes sp

russian1.jpg (32346 bytes)  Acanthodes sp, Mazon creek USA

IMG_1475.jpg (524526 bytes)  Acanthodes bronni, Lebach, Germany

IMG_1485.jpg (309482 bytes)   Acanthodes lundiBear Gulch, USA




hh-homala.jpg (83097 bytes)   Homalacanthus concinnus    U.Devonian    Miguasha   Canada

fishspine2.jpg (35418 bytes)  Triazeugacanthus    U.Devonian    Miguasha   Canada

fishspine.jpg (22539 bytes)   Gyracanthus sp.   Carboniferous(Namurian)    Cowdenbeath, Scotland