Porbeagle - Phylogeny and Evolution

Phylogeny and Evolution

Several phylogenetic studies, based on morphological characters and mitochondrial DNA sequences, have established the sister species relationship between the porbeagle and the salmon shark (L. ditropis), which occurs in place of it in the North Pacific. The genus Lamna evolved 65–45 Ma. When its two extant species diverged from each other is uncertain, though the precipitating event was likely the formation of the ice cap over the Arctic Ocean, which would have isolated sharks in the North Pacific from those in the North Atlantic.

Fossilized porbeagle remains are known from Late Miocene epoch (c. 7.2 Ma) deposits in Belgium and the Netherlands, Pliocene epoch (5.3–2.6 Ma) deposits in Belgium, Spain, and Chile, and Pleistocene epoch (2.6 Ma to 12,000 BP) deposits in the Netherlands. However, Lamna teeth that closely resemble those of the porbeagle have been found in the La Meseta Formation on Seymour Island off the Antarctic Peninsula, which date to the middle to late Eocene epoch (50–34 Ma). There is much taxonomic confusion regarding Lamna in the fossil record due to the high degree of variability in adult tooth morphology within species.