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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.

ch-saca.jpg (12425 bytes)    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)

hh-ord.jpg (115848 bytes)  hard5astraspisdenticle.jpg (99995 bytes)   hard2astraspis.jpg (107367 bytes)  hard3astraspis.jpg (104902 bytes)  Fragment and denticles of Astraspis desiderata

vdHARDIN.jpg (27998 bytes)    harding9eriptychius.jpg (128565 bytes)    Dermal plates from Eriptychius americanus

harding12-button.jpg (134767 bytes)   hard4pedestaldent.jpg (85653 bytes)    Button and pedestal type denticles

hard6shark.jpg (88949 bytes)    hard7shark.jpg (139992 bytes)    Shark like denticles

hard1priloconus.jpg (116176 bytes)  Conodont tooth of Ptiloconus gracilis

 harding10conodont.jpg (89697 bytes)   Conodont tooth of Chirognathus sp.

  harding9stereoconus.jpg (87821 bytes)   Conodont tooth of Stereoconus robustus