Global vertebrate-based palaeozoogeographical subdivision for the Givetian-Famennian (Middle-Late Devonian): Endemism-cosmopolitanism spectrum as an indicator of interprovincial faunal exchanges

Abstract

The spectrum of proposed endemic-cosmopolitan (E-C) categories is applied to demonstrate faunal interchange between palaeozoogeographic provinces during the Givetian-Famennian, on the assumption that the E-C proportion reflects the isolation rate of the fauna. Mostly endemic groups are useful to establish zoogeographical regionalisation, whereas polydemics and cosmopolitans define the historical trends in the faunal development in various zoogeographical areas. Quantitative and systematic analyses suggest significant isolation of the Laurentian, Baltican, Armorican and East Gondwanan faunas during the Givetian-Frasnian that is possibly due to remoteness of the intracontinental basins from the coastal oceanic areas. North Gondwanan and Siberian faunas, on the contrary, were located close to the coast or in island archipelagos. Laurentian and East Gondwanan faunas were the most isolated during the Givetian. Most often the cosmopolitans include antiarch placoderms, struniiform sarcopterygians, and chondrichthyans; arthrodire and ptyctodont placoderms are more rarely cosmopolitan. These fishes might possess some special eurybiont capabilities. Two realms are recognised for the Givetian: the Ptyctodont and the Phyllolepid-Thelodont Realms. Within the Ptyctodont Realm, the Laurentia and Baltica Provinces form the Psammosteiform-Porolepiform Region. During the Frasnian, the Thelodont Realm including East and North Gondwana, as well as West Yunnan, and the Porolepiform Realm including the Psammosteiform Region (Laurentia + Baltica) are erected. For the Famennian, a single Porolepiform Realm houses the Phyllolepid-Tetrapod Region, including Laurentia, Baltica, and East Gondwana Provinces.