ICHTHYOLITES OF THE OLD RED SANDSTONE

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THE FIRST FISH  

Reproduced with the kind permission of Prof. P. Janvier

The First fish were the Arandaspida and appear at the beginning of the Ordovician about 470 Myn years ago. Probably the best known are Sacabambaspis from Bolivia and Arandaspis from Australia. These jawless fish have a bony fusiform head and a tail covered with rod-like scales. These fish had no paired fins and only had a caudal fin. These Arandaspida are thought to have lived in the shallow coastal waters, surviving by scooping algae-rich mud from the sea floor.

    Sacabambaspis 

Charles Walcott first described the vertebrate fauna of the Harding Sandstone in 1892 and the fauna is now recognized as one of the richest Ordovician vertebrate localities in the world. The fauna is particularly important because it shows that vertebrates began their evolutionary radiation in the early Palaeozoic. The majority of vertebrate fossils from the Harding Sandstone are isolated dermal plates and scales. The only teeth are those that belong to the conodonts

Astraspis desiderata Harding Sandstone, Colorado, USA. Ordovician (M. Caradoc age)

         Fragment and denticles of Astraspis desiderata

       Dermal plates from Eriptychius americanus

       Button and pedestal type denticles

        Shark like denticles

  Conodont tooth of Ptiloconus gracilis

    Conodont tooth of Chirognathus sp.

     Conodont tooth of Stereoconus robustus