DOI: 10.5061/dryad.573n5tb57
title: Data from: Evaluation of the ontogeny and sexual dimorphism in a new species of Middle Triassic Darwinulocopina (Crustacea, Ostracoda) from Argentina

description: The Darwinulocopina comprise an interest group of ostracods which where
 among the first invaders of freshwater waters during the late Palaeozoic.
 The Permian–Triassic extinction greatly reduced their diversity, reaching
 present times represented by one family. The darwinulids are regarded as
 “ancient asexuals” since a parthenogenetic mode of reproduction is assumed
 for all the post-Triassic members of the group. However, the high
 diversity achieved during the late Palaeozoic is often associated with
 sexual reproduction. Here we studied a monospecific association of
 ostracods from the Middle Triassic of the Cuyana Basin, Province of
 Mendoza, Argentina, and recognized a new species of Darwinulocopina,
 Prasuchonella? huarpe nov. sp. We discuss the traditional length/height
 and length/width graphical method to recognized ontogeny and/or sexual
 dimorphism in fossil ostracod assemblages, and performed a geometric
 morphometric analysis performed on both lateral and dorsal views of near
 one hundred seventy carapaces. The best results were obtained from the
 analysis in dorsal view, and four ontogenetic stages were discriminated
 (A-3, A-2, A-1 juveniles, adult). This allowed recognizing a main
 ontogenetic trend related to the development of the brooding chamber.
 Although subtle in differences, female carapaces are wider not only at the
 brooding chamber, but also along the whole length, compared to the
 carapaces of the presumptive males. Finally, full systematic descriptions
 and discussions, attempting to unify descriptive criteria for recent and
 fossil darwinulocopin carapaces, are provided. As a result, the need for a
 review of those Mesozoic records of Darwinulocopina, particularly those
 from the Triassic, is noted.
description: Several hundreds of carapaces and a few valves were picked under
 a Nikon SMZ645 stereomicroscope from a single sample. Selected specimens
 were mounted on stubs using carbon conductive adhesive tape, gold coated
 and scanned with a JEOL JSM-6360LV Scanning Electron Microscope (SEM) at
 the Servicio de Microscopía Electrónica del Museo de La Plata, La Plata
 city, Argentina. After examination under SEM, a total of 167 specimens
 were retained for study regarding their preservation, mainly those with
 undeformed dorsal and/or lateral outlines. Length, height, and width for
 carapaces were measured on SEM images. A geometric morphometric analysis,
 following the procedures outlined by Zelditch <i>et al.
 </i>(2004), was performed on the SEM photographs on both dorsal and
 lateral left views of the carapaces. For the dorsal view, two landmarks
 were established: 1) the anterior most and 2) the posterior most points of
 valves contact. The outline for each valve was characterized by a 100
 points curve including both landmarks. The anterior most point of the
 carapace was defined as initial point for the outline on lateral view of
 the carapace, which was characterized by 200 points. Data was standardized
 for position, size and rotational differences by means of a generalized
 least squares Procrustes superposition (Zelditch <i>et al.</i>
 2004, p. 113–119). Logarithm with base 10 of Centroid Size—log(CS)—was
 used as size estimator for all the analyses that required it
 (Zelditch<i> et al.</i> 2004, p. 78). Digitization of the
 landmark configurations was performed on TPSdig2.12 (Rohlf 2008), and a
 Procrustes superposition was done for each data set with CoordGen6h
 (Sheets 2001). Procrustes coordinates were used as data for a Principal
 Component Analysis (PCA) using the software PAST 3.23 (Hammer <i>et
 al.</i> 2001).  HAMMER, Ø., HARPER, D. A. T. and
 RYAN, P. D. 2001. PAST: Paleontological Statistics software package for
 education and data analysis. <i>Palaeontologia
 Electronica</i>, <b>4</b>, 1–9.
 ROHLF, F. J. 2008. tpsDig2. http://life.bio.sunysb.edu/morph/ SHEETS, H. D.2001. IMP: integrated morphometrics package. Department of Physics, Canisius College, Buffalo, N.Y. - http://www3.canisius.edu/~sheets/morphsoft.html - http://www3.canisius.edu/~sheets/moremorph.html ZELDITCH, M. L., SWIDERSKI, D. L., SHEETS, H. D. and FINK, W. L. 2004. <i>Geometric Morphometrics for Biologists: a Primer.</i> Elsevier Academic Press, Amsterdam, 443 pp.