Biogeographical links of the South American-Antarctic bryozoan biota in Cenozoic (Early Paleocene-Miocene)

Moyano strongly pointed out that the origins and evolutionary history of the Bryozoa both Antarctica and magellanic South America could not be understood without reference to the still  poorly known but very  extensive Paleocene and Lower Miocene  faunas of Patagonia (see Moyano, 1983.

The taxonomic studies with the extensive use of SEM of more than 110 bryozoan specimens of the Early Paleocene (Danian) and the Lower Miocene of the southern South America  (Patagonia) from the Canu’s collections (1908-1911) at the Bernardino Rivadavia Museum have revealed that cyclostomes and cheilostomes  have their taxonomical  counterparts among the late Early Eocene fauna of Seymour Island, Antarctic Peninsula (Hara, 2008). One of the example is the  anascan  microporoidean  represented by austral Aspidostoma Hincks, 1881 genus, known from the Paleogene and the Neogene strata of the triangle Antarctica-South America-Australia-New Zealand. It shows their  earliest  fossil record in the Lower Danian of Patagonia, therefore Patagonia should be  consider as an important place of origin and migration route of this genus. A rich occurrence of Aspidostoma  has been also described from the late Early Eocene, clastic sediments of the La Meseta Fm. on Seymour Island  (Hara 2001).  Other bryozoans such as umbonulomorph (lepraliellids) represented by  multilaminar, massive Celleporaria  Lamouroux, 1821  occur also in the shallow-water Roca Fm. of Patagonia and predated  the rich  occurrence of this genus from the late Early Eocene of the La Meseta Fm. (Seymour Island). Particularly important for taxonomy and closest biogeographical connection of South America-Antarctic during the Early Paleocene up to the Lower Miocene has the  common occurrence of several  globular, multilaminar cyclostomes of Ceriopora,  Reptomulticava, as well as reticulate colonies of Reticresis, branched microporidean Aspidostoma, and nodular multilaminar umbonulomorphs of Celleporaria and  Osthimosia.

Biogeographical  comparision of the southern South America  bryozan fauna  of the Early Paleocene age is interesting because  the Canu’s collections contains important  information  that some of the taxa have the earliest  fossil records in the Patagonian  shallow-water  Roca Fm., which predated  the younger New Zealand and Antarctic  bryozans ranging from the latest Paleocene- Early Eocene.

The Southern Ocean  bryozoans seems to be a product of the long period of evolution in situ, possibly streaching back to late Cretaceous, therefore the reconstruction of the Cenozoic ecosystem,  possible migration routes and  paleobiogeography  of the Weddellian Province of the southern hemisphere should be refer to the Antarctic fauna, possibly of the Createous age. 

Hara U., 2001 – Bryozoa from the Eocene of Seymour Island, Antarctic Peninsula. Palaeontologia Polonica. In: Palaeontological Results of the Polish Antarctic Expeditions, Part III, 60: 33–156.

Hara U., 2008. Biogeographical relationship of the Cenozoic South America -Antarctic  bryozoan biota: an example  of austral Aspidostoma genus in Antarctica: a Keystone in Changing  World – Online Proceedings of the 10th ISEAS, edited  by A. K. Cooper and C.R.Raymond et al. USGS open File Report 2007-xxx, Extended Abstract yyy, 1-5.

Moyano, G.H.,I., 1983. Southern Pacific  Bryozoa : a general view with emphasis on Chilian species. Gayana, Zoologia, 46, 1-45.