Ordovician paleobiogeography of the Suborder Cheirurina (Trilobita)

The Suborder Cheirurina is a diverse trilobite clade, ranging from the latest Cambrian to the Devonian. The Ordovician paleobiogeography of the group is explored based on the distribution of genera. Major tectonostratigraphic units and Ordovician ages (Tremadocian, Floian, Dapingian, Darriwilian, Sandbian and Katian) were recorded for each genus . Cluster analysis (agglomerative hierarchical clustering) and non - metric multidimensional scaling (NMDS) were performed independently for each Ordovician age. The results characteri ze the Ordovician distribution of Cheirurina as two main general patterns. First, there was a marked decrease in endemicity through the Ordovician. Second, latitude seems to play a significant role in the distribution of Cheirurina, at both genus and family levels. Pliomerids and encrinurids occur overwhelmingly at low latitudes. The two main exceptions are Placoparia (Pliomeridae) and Dindymene (Encrinuridae), which are distributed in high latitude terranes. Within Cheiruridae, members of Eccoptochilinae are typical of high latitude Gondwana. Conversely, acanthoparyphines, cheirurines, deiphonines, heliomerines and sphaerexochines are mainly distributed in low or intermediate latitudes.