Palaeobiogeography of Early Palaeozoic vertebrates
The oldest known Palaeozoic vertebrate record currently is Early Cambrian in age. The first taxa with mineralized exoskeletons are at least Ordovician in age, followed by a sporadic fossil record with Talimaa’s Gap of c. 3 myr in the Rhuddanian (earliest Silurian). Ordovician and Silurian vertebrate faunas are dominated by ‘agnathans’. Early Palaeozoic vertebrates occupied a wide range of environments: nearshore marine to restricted marine in the Ordovician, and on the marine epicontinental shelves of the Silurian. Silurian vertebrates are useful biostratigraphical indicators, as well as good markers of palaeocontinental margins. Two main palaeobiogeographical units are renamed for the Ordovician: a Gondwana Realm and a Laurentia–Siberia–Baltica Realm. Vertebrate fossil localities are more numerous in the Silurian; therefore a series of palaeobiogeographical provinces and realms are defined on Laurentia, Baltica, Avalonia, Siberia, South China and East Gondwana. More discoveries of Silurian vertebrate-bearing localities should certainly help to define additional provinces, in particular along the northern margins of Gondwana and in SE Asia.