PHYLOGENETIC RELATIONSHIPS OF THE SILURIAN AFRO-SOUTH AMERICAN RHYNCHONELLIDE BRACHIOPODS ANABAIA, HARRINGTONINA AND CLARKEIA: INSIGHTS FROM THEIR ONTOGENY

LEONE, F.M.; BENEDETTO, J.L.

Milan

Congreso; 8TH INTERNATIONAL BRACHIOPOD CONGRESS; 2018

8th. IC Brachiopods

8TH INTERNATIONAL BRACHIOPOD CONGRESS ? 11-14 SEPTEMBER 2018SESSION S1PHYLOGENETIC RELATIONSHIPS OF THE SILURIAN AFRO-SOUTH AMERICAN REALM RHYNCHONELLIDE BRACHIOPODS ANABAIA, HARRINGTONINA AND CLARKEIA: NEW INSIGHTS FROM THEIR ONTOGENYM. Florencia Leone1 and Juan L. Benedetto11Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Universidad Nacional de Córdoba, Argentina. flor_l25@hotmail.com; juan.benedetto@unc.edu.arIn recent years the crucial role that changes occurring during ontogeny play in generating intrinsic phenotypic variation within a species, and hence in originating micro and macroevolutionary trends, has been widely accepted (McNamara and McKinney, 2005 and references therein). Processes involving heterochrony, defined as changes over time in the rate and timing of development, are ubiquitous in several taxonomic groups. In the last years significant advances have been made in detecting heterochronic processes in early Paleozoic orthoidean and plectorthoidean brachiopods (Benedetto, 2007, 2008; Benedetto and Muñoz, 2017).Kozlowski (1923), in his original description of the rhynchonellide Clarkeia antisiensis, had already noticed the strong morphological differences between small and large specimens of this species, and Benedetto (1988) described the substantial ontogenetic changes experienced by the related genus Harringtonina affecting even morphologically ?stable? features (e.g. cardinal process, hinge plates) which are considered as having generic and familial diagnostic value (Savage et al., 2000). Interestingly, knowledge of ontogenetic development not only provides additional criteria for taxonomic placement at suprageneric level but also for unraveling evolutionary lineages. This study is based on hundreds of specimens of Clarkeia antisiensis (d?Orbigny) recovered from the Upper Silurian Tarabuco Formation of Bolivia, which form a complete series of growth stages providing a good opportunity for reconstructing its ontogenetic development. On the basis of the ontogeny of Clarkeia antisiensis the case for a close phylogenetic relationship between Harringtonina and Clarkeia is compelling. The fact that juvenile specimens of C. antisiensis are nearly indistinguishable from adult individuals of Harringtonina australis Boucot strongly suggests that Clarkeia evolved from Harringtonina by the heterochronic process of peramorphosis. On the other hand, adult specimens of both the Brazilian Anabaia paraia Clarke and the Precordilleran Anabaia n. sp. never exceed the youngest ontogenetic stage of Harringtonina australis to which share small hinge plates supported by a septalium-like structure and absence of cardinal process.