Spatial and stratigraphic distribution of the rhynchonelliformean brachiopod Productorthis Kozlowski: fast migrations or parallel evolution?

BENEDETTO, J.L.

Fossils & Strata

Taylor and Francis

Lugar: London; Año: 2008 vol. 54 p. 21 - 29

0300-9491

Productorthis angulensis Benedetto, the oldest presently known species of Productorthis, is a conspicuous element of the volcano-sedimentary Molles Formation (Arenig, Oepikodus evae Zone) of the Famatina Range, western Argentina. Its origin by heterochrony from Panderina ambigua Benedetto – which comes from the underlying Suri Formation – is well supported by ontogenetic data, suggesting that Productorthis may has originated in the volcanic-arc settings developed along the proto-Andean margin of Gondwana. Outside of Famatina, its lowest occurrence is from the Volkhov Stage (B. navis Zone) of Baltica. There, like in the Famatina Range, the first appearance of Productorthis almost immediately postdates the occurrence of Panderina. Two different explanations can be proposed to account for such stratigraphic and paleogeographic distribution: (1) the Baltic species of Productorthis evolved from the Famatinan P. angulensis and subsequently migrated rapidly to Baltica, (2) the Baltic species of Productorthis evolved from the local species Panderina abscissus (Pander), lacking direct phylogenetic relationships with the Famatinan lineage. The second hypothesis implies that Productorthis originated independently in Gondwana and Baltica. The parallel evolution of Baltic and Famatinan lineages may have been the result of heterochronic processes operating on morphologically close, but geographically segregated, species of Panderina. By the late Arenig-early Llanvirn, Productorthis dispersed into volcanic islands and microcontinents within the Iapetus Ocean, and by the Caradoc it becomes largely confined to Laurentia. Benedetto, the oldest presently known species of Productorthis, is a conspicuous element of the volcano-sedimentary Molles Formation (Arenig, Oepikodus evae Zone) of the Famatina Range, western Argentina. Its origin by heterochrony from Panderina ambigua Benedetto – which comes from the underlying Suri Formation – is well supported by ontogenetic data, suggesting that Productorthis may has originated in the volcanic-arc settings developed along the proto-Andean margin of Gondwana. Outside of Famatina, its lowest occurrence is from the Volkhov Stage (B. navis Zone) of Baltica. There, like in the Famatina Range, the first appearance of Productorthis almost immediately postdates the occurrence of Panderina. Two different explanations can be proposed to account for such stratigraphic and paleogeographic distribution: (1) the Baltic species of Productorthis evolved from the Famatinan P. angulensis and subsequently migrated rapidly to Baltica, (2) the Baltic species of Productorthis evolved from the local species Panderina abscissus (Pander), lacking direct phylogenetic relationships with the Famatinan lineage. The second hypothesis implies that Productorthis originated independently in Gondwana and Baltica. The parallel evolution of Baltic and Famatinan lineages may have been the result of heterochronic processes operating on morphologically close, but geographically segregated, species of Panderina. By the late Arenig-early Llanvirn, Productorthis dispersed into volcanic islands and microcontinents within the Iapetus Ocean, and by the Caradoc it becomes largely confined to Laurentia.