Ecomorphological analysis of the graptolite habitats: Preliminary results.

LO VALVO, GERARDO A.; TORO, B.A; BALSEIRO, D.; HERRERA SÁNCHEZ, N.C.

Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

The spatial distribution of Ordovician graptolites has been classically partitioned according to both the lateral and the vertical dimensions of their habitats, and different models can be found in the literature. In this work, we analyze, from an ecomorphological perspective, the composition of the endemic, shallow-water pandemic, and deep-water pandemic habitats proposed in the Scandinavian model, based on the 38 graptolite species identified at Mount Hunneberg. We first quantified the tubaria morphology of 117 graptolite species, certainly classified, to create an empirical morphospace. Twenty two characters of ecomorphological relevance were selected, based on the known interaction between the graptolite tubarium and the environment. These characters included different types of variables, including both continuous and discrete characters, while distances were calculated as the Maximum Observable Rescaled Distance. In the resulting forty-four-dimensional morphospace, created with a Principal Components Analysis, both endemic and pandemic faunas present high morphological diversity, sharing some common strategies. The presence of morphologies with different feeding efficiency in the same habitat suggests some level of niche partitioning. Among the pandemic species, those taxa recognized as deep-water elements are morphologically less diverse than the shallow-water ones, which could be related to a uniform environment. The deep-water elements have a minimum morphological overlap with the endemic faunas, sharing multiramous forms and extensiform tetragraptids. The shallow-water pandemic and endemic faunas share multiramous, reclined four-stiped, and horizontal two-stiped forms. However, within the last morphology, only species belonging to Expansograptus were considered to be pandemic. On the other hand, pendent, declined, and deflexed two-stiped forms are recognized as endemic, as well as the single-stiped species. Scandent species, present in the empirical morphospace, were not used originally to develop the environmental distribution model at Mount Hunneberg due to their absence, probably because a local bias. This group has a high morphological diversity without overlap with the other recognized groups. Scandent morphologies are considered to have high feeding efficiency and most of them are interpreted as shallow-water dwellers, possibly suggesting that the morphological diversity in this environment was much higher than indicated by the Scandinavian model. These preliminary results put forward that this quantitative approach is useful to explore different perspectives about habitat distribution of the Ordovician graptoloids, providing a taxon-free framework based on ecomorphological data and filling gaps of previous models. In the forthcoming future, further taxa will be added to the dataset to compare different models of habitat distribution, the morphological composition and diversity of similar habitats among regions, and temporal differences within and between them.