Coexistence of brachiopod and bivalves in the Late Paleozoic of Western Argentina

BALSEIRO, D.; STERREN, A.F.; CISTERNA, G.A.

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 414 p. 133 - 145

0031-0182

The relationship between brachiopods and bivalves has been widely discussed in previous studies. Based onanalyses at different temporal and spatial scales, several authors have argued either for the indifference or theinteraction between the two clades. In this contribution we evaluate brachiopod and bivalve coexistence attwo different spatial scales in a siliciclastic shelf developed during the Late Paleozoic in Western Argentina. Atregional scale, bivalves were more diverse than brachiopods, although both had a similar total number andcomparable distribution of occurrences. At local scale, however, multivariate analyses indicate that brachiopodsand bivalves were segregated. Null models reinforce this pattern confirming the non-random co-occurrencepattern, and that the coexistence of brachiopods and bivalves was significantly low. In addition, multivariateanalyses indicate that the biotic gradient neither followed the bathymetrical, nor a geographical or temporalgradient. The possibility that such segregation would have been caused by taphonomic (storm) reworking,was also disregarded considering multivariate analyses together with taphonomic evidence. The lack of environmentalsegregation between brachiopods and bivalves, coupled to analyses taking into account ecological guilds,indicates that possible factors controlling the segregation, such as turbidity, substrate or productivity were notrelevant. As a whole, these results suggest a possible competitive interaction between brachiopods and bivalvesat local scales. Interestingly, brachiopod?bivalve coexistence at regional scale did not foster local coexistence,indicating that the processes acting at these two scales are, at least partially, decoupled. Finally, the regionalcoexistence pattern suggests that the major transition between brachiopod and bivalve dominated communitieswas most probably related to processes acting at regional to biogeographic scales rather than to competition.