Review: Gallo V, Cavalcanti MJ, da Silva HMA (2007) Track analysis of the marine palaeofauna from the Turonian (Late Cretaceous). Journal of Biogeography, 34:1167-1172.

Feature Paper: DOWNLOAD Gallo V, Cavalcanti MJ, da Silva HMA (2007) Track analysis of the marine palaeofauna from the Turonian (Late Cretaceous). Journal of Biogeography, 34:1167-1172.

Author Abstract: Aim To analyse the worldwide distribution patterns of Turonian marine biotas using a panbiogeographical approach. 

Location Turonian localities of southern and north-eastern Brazil, Mexico, Canada, central Europe, England and Morocco. 

Method Panbiogeographical track analysis. 

Results Nine generalized tracks and six nodes were found. The generalized tracks comprise two vicariant track patterns (one northern and one mid-southern) across the Atlantic. 

Main conclusions The generalized tracks show clearly two separate marine biotas, which were associated with the proto-South Atlantic and the proto-North Atlantic oceans. These generalized tracks, as well as the two vicariant track clusters between the north and south Atlantic, are identified by vicariant relationships shared by most of the taxa analysed, and illustrate the final break up of the Gondwana and Laurasia supercontinents and the consequences of vicariant events for the biogeography of the Atlantic Ocean.

Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.

Review: This week we start looking at specific examples of applied biogeography now that we have an understanding of several schools of biogeography. The first paper we looked at this week dealt with historical biogeography. This paper uses panbiogeographical track analyses to analyze the global distribution patterns of fossil marine taxa.

The specific fossil group looked at included "marine palaeofauna" from the Turonian (Late Cretaceous, 94 - 89 million years ago) strata. Taxa examined included "foraminifera, ostracods, sponges, brachiopods, molluscs, crustaceans, echinoids, fishes from a variety of taxonomic levels, turtles, crocodiles, lizards, and mosasaurs" though the final analysis involved only those groups with diverse fossil records at all locations examined by the authors worldwide: molluscs, crustaceans, and fishes. 

The panbiogeography analysis used by the authors follows the more rigorous approach of biogeographers today compared to the beginnings of panbiogeography. Locality records are first plotted on a map and then they are connected using mathematical formulas based on minimum spanning trees (minimum distances between points required to connect all points on the plotted map).

To elaborate on our week three seminar series on panbiogeography, the authors sum up their approach to panbiogeography with the following definitions. For further information about panbiogeography, look to the week three papers.

"The panbiogeographical method of track analysis consists of plotting locality records or areas of distribution of various taxa on maps and connecting them using lines following a criterion of minimum distance. These lines are named individual tracks and they correspond to the geographical coordinates of the taxon or the place in the sector of geographical space where the evolution of this taxon occurred. The coincidence of individual tracks of groups not phylogenetically related corresponds to a generalized track, implying a common history (spatial homology). If two or more generalized tracks intersect in an area, the intersection determines a node, which may predict distinct ancestral biotas and geological fragments interrelated in space and time."

Twelve localities worldwide were chosen based on the quality of the fossil record coupled with necessary geographical information: Brazil (2 locations), Morocco, Europe (4), Canada (2), Mexico (4). Data were missing for Asia, so while the study can't really be considered global, it is certainly the largest-scale panbiogeographic survey of the fossil record to date. The result of the authors' track analysis is shown in their figure below.

The authors then go on to explain how each track could have been created from a palaeogeographic standpoint, meaning how various events (such as rising sea levels, plate tectonic rifting of continents, or connection of various seas) resulted in the ability of organisms from one area to expand their ranges into another area.

The authors conclude their interpretations with the observation that "Generalized tracks found in this study illustrate the final break up of the Gondwana and Laurasia supercontinents and the consequences of vicariant events for the biogeography of the Atlantic Ocean. The nodes and main massing correspond to the Mesoamerican gate, identified by Croizat (1958) as one of the main centres of global biological diversity. In this context, it is interesting to note that the world network of generalized tracks for the modern biota illustrated in Croizat (1958, p. 1018, Figure 259) also shows a northern and mid-southern track connection across the Atlantic, and also emphasizes trans-Atlantic connections between the same general localities as included in the present study. This suggests that centres of diversity in the modern world may date at least from Mesozoic times, and that the factors affecting the diversity of past and present terrestrial biotas may also have affected biotas in the marine realm."

We'll finish up next by seeing how track analysis can influence conservation priorities for living taxa today.