Porolepiformes, Jarvik, 1942

Wilk, Olga, 2023, A new look at the Emsian (Early Devonian), sarcopterygian fishes from the Holy Cross Mountains, Poland, with a special reference to porolepiforms, Acta Palaeontologica Polonica 68 (2), pp. 343-357 : 355

Palaeodiversity of Porolepiformes from the Early Devonian of Laurussia

During the Early Devonian, Podłazie Hill in the Holy Cross Mountains was part of the Małopolska block and it belonged to the bigger continent called Laurussia or Euramerica ( Domeier and Torsvik 2014). On the other side of this continent in the area of today’s Canadian Arctic, near the Anderson River, the Bear Rock Formation was formed. Despite the fact that both sites were located on opposite sides of the Euramerican continent, several hundred kilometers apart from each other, the fish assemblages are similar and show close spatial and environmental relations. Among the fauna from the Podłazie Hill, acanthodians, agnathans, chondrichthyans, osteichthyans, and placoderms have been identified (e.g., Tarlo 1957; Kulczycki 1960; Blieck 1980; Szrek and Dupret 2017; Wilk et al. 2022). On the other hand, the Anderson River fauna is represented by common Early Devonian fish remains belonging to acanthodians, placoderms, and osteichthyans ( Schultze and Cumbaa 2017).

In both areas, the amount of the material suggests that conditions during the Emsian were favorable for the development of many fishes. Porolepiforms found in Podłazie belong to the Porolepis and Heimenia , while in the Canadian Arctic remains of Porolepis , Heimenia , Nasogaluakus have been reported. Skull elements, as well as elements of the postcranial skeleton, scales and teeth are common. The presence of at least two genera of porolepiforms (i.e., Porolepis and Heimenia in the Holy Cross Mountains of Poland and the Anderson River in the Canadian Arctic), suggest a viable open-water connection between these two areas during the late Early Devonian, consistent with a wider distribution of Heimenia , Porolepis , and other porolepiforms in the Early Devonian as suggested by Schultze and Cumbaa (2017). This is also confirmed by the fact that outside the area of the Holy Cross Mountains ( Kulczycki 1960; Ørvig 1969) and the Anderson River ( Jarvik 1967; Schultze 1968; Ørvig 1969; Schultze and Cumbaa 2017), the presence of Heimenia was recorded in the Lower Devonian from the Baltic region ( Lyarskaya 1981; Clément 2001a, b), central Europe ( Jessen 1980), China ( Zhu 2000; Zhao and Zhu 2010) and possibly Vietnam ( Thanh and Janvier 1987), while Porolepis is known exclusively from Europe, Spitsbergen, Australia, and Canada ( Gross 1936; Obruchev 1938; Jarvik 1942; Kulczycki 1960; Vorobyeva 1963; Jessen 1980; Schultze 1993, Clément 2004; Johanson et al. 2013; Mondéjar-Fernández 2020).