Form changes inAmiantis purpurata(Bivalvia, Veneridae) shells over the past 100,000 years in North Patagonia (Argentina)

Abstract

Amiantis purpurata shells from the San Matías Gulf (SMG) were analysed in order to compare both morphology and size throughout the late Quaternary in relation to environmental changes. Shells from modern beaches, Holocene marine assemblages (late Holocene, 3630 ± 100 years bp) and interglacial Pleistocene marine assemblages (MIS 5, 100 ka years bp) were studied by measuring the height and length, and using the elliptic Fourier analysis (EFA) to take an outline contour. The Pleistocene shells were smaller, more elliptical and with a deeper lunule than the Holocene and modern ones. No significant differences were recorded in the allometry index throughout the late Quaternary. The variation in size and shape of the A. purpurata shells could be related to the phenotypic plasticity of this species as a response to the environmental changes registered in the SMG during the Quaternary. These changes include variations in sea surface temperatures, salinities and substrates, and also water circulation changes, which would have modified nutrient availability. Morphological changes imply burrowing activity, mechanical stability, nutrient uptake and defence response to predation.

Last interglacial (MIS 5e) sea-level proxies in southeastern South America

“…Gasparini et al (2016) reported a radiocarbon date from the beach-like deposit and, due to the sedimentary environment, considered it to be terrestrial limiting. An OSL date from the beach-like deposit gave a date of 60 ka (Beilinson et al, 2019), which also likely underestimates the true age. If this deposit formed during MIS 5, it gives a terrestrial-limiting elevation of 1.3 ± 3.1 m.…”

“…OSL ages were derived from quartz grains of samples collected at two sites in Uruguay (Rojas and Martínez, 2016) and three sites in Argentina (Martínez et al, 2016;Zárate et al, 2009;Beilinson et al, 2019). Analysis for the Uruguay samples and the site at Ezeiza, Argentina, was completed at the University of Illinois at Chicago (Rojas and Martínez, 2016;Martínez et al, 2016).…”

“…The samples were collected using a PVC pipe with only the inner part of the sample retained for analysis. The OSL sample at Nicolás Vignogna III Quarry was analyzed at Dataçao Labs (Beilinson et al, 2019). The samples were collected using metal tubes and opaque black bags.…”

“…There are extensive surveys of fauna diversity at many MIS 5 sites, including Uruguay (Martínez et al, 2001;Rojas and Martínez, 2016;Rojas and Urteaga, 2011;Rojas et al, 2018b, a), Buenos Aires Province (Aguirre, 1992), Pilar (Fucks et al, 2005), Ezeiza (Martínez et al, 2016), Magdalena , Colorado River delta (Charó et al, 2015), southern Buenos Aires Province (Fucks et al, 2012a), Bahía Blanca (Aliotta et al, 2001), Bahía Anegada (Charó et al, 2013a), San Blas (Charó et al, 2013b(Charó et al, , 2018, San Antonio Oeste (Bayer et al, 2016b, a), Río Negro and Chubut provinces (Pastorino, 2000), Santa Cruz Province (Aguirre et al, 2009), the Camarones area (Aguirre et al, 2006), Bahía Bustamante (Aguirre et al, 2005b), Caleta Olivia (Aguirre, 2003), Puerto Lobos (Aguirre et al, 2005a;Boretto et al, 2013), Tierra del Fuego (Gordillo and Isla, 2011;Gordillo et al, 2010Gordillo et al, , 2013, Patagonia and Tierra del Fuego (Aguirre et al, 2008), and southeastern South America (Aguirre et al, 2011(Aguirre et al, , 2017. Though many of these studies do not add any new sea-level index points, the surveys indicate that environmental conditions in MIS 5 were likely cooler than the Holocene optimum and similar to present conditions in Patagonia.…”

Morphological diversity and discrimination tools of the non-marine ostracod Cypridopsis silvestrii across temporal and spatial scales from Patagonia

“…Specifi cally, they objectively discriminate between close taxa and characterize intraspecific variation and its possible causes (e.g. Monferran et al 2013, Mazzini et al 2014, Aguirre et al 2015, Bayer et al 2016. Ostracods (Class Ostracoda), are small crustaceans with a low-magnesium calcite bivalve carapace ("hard parts") that totally encloses the body and appendages ("soft parts") (Meisch 2000).…”