The legacy of a warm Tertiary survivor: the history of purple clam Amiantis purpurata in South America

BAYER, MARÍA SOL; GORDILLO, SANDRA; MORSAN, ENRIQUE M.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2014 vol. 51 p. 333 - 343

0002-7014

Over Middle-Late Miocene a faunal turnover and the appearance of many unknown taxa in the South Atlantic took place. One of the survivor to this event was the purple clam Amiantis purpurata, which is still alive on Southwest Atlantic coasts. The genus Amiantis has a wide range around the world, but its diagnosis has been confused with Callista?s and Pitaria?s. To reconstruct the South American paleobiogeography of Amiantis´ genus through time and A. purpurata?s paleobiogeography, it has been necessary to rewrite a new diagnosis for this genus. A detailed review of Amiantis´ and A. purpurata?s records around the world through geological time has been carried out. A comparison between shapes (elliptic Fourier analysis) of South American Amiantis? species and a phylogenetic analysis have been performed on museum and own collections. A defined escutcheon and a large pointed pallial sinus are distinctive features of Amiantis over Callista and Pitar. By the resulting cladogram, the origin of Amiantis in South America would be from two lineages, a Pacific origin and an Atlantic origin. With the formation of the cold Malvinas Current, A. purpurata could survive to the fauna turnover of Middle-Late Miocene, because of its location at the confluence of the Brazil and Malvinas currents. In this mixed area, A. purpurata´s larvae would migrate from Uruguay to the south, where they could settle on the coast of the province of Buenos Aires and Golfo San Matías. The characteristics of the Gulf would foster the development and settlement of larvae of the species giving rise to the southernmost population during the Pleistocene. To the Holocene, particularly in the Hypsithermal, environmental conditions would led to migration of A. purpurata´s larvae from Golfo San Matías to Peninsula Valdés. At the end of this event, the water temperature dropped. Then, Golfo San Matías is an isolated, relictual and the southernmost population of A. purpurata species at the present. A. purpurata has been proposed as an indicator of warm temperate waters, quiet calm waters, fine-grained substrate, which lives in shallow coastal environments.