DOI: 10.5061/dryad.gn5j6
title: Data from: Morphological evolution of the bivalve Ptychomya through the Lower Cretaceous of Argentina

description: The complex morphological evolution of the bivalve Ptychomya throughout
 the well studied Agrio Formation in the Neuquén Basin (west-central
 Argentina, lower/upper Valanginian – lowest Barremian) constitutes an
 ideal opportunity to study evolutionary patterns and processes occurring
 at geological timescales. Ptychomya is represented in this unit by four
 species, the morphological variation of which need to be temporally
 assessed in order to obtain a thorough picture of the evolution of the
 group. Here we use geometric morphometrics to measure variation in shell
 outline, ribbing pattern and shell size in these species. We bracket the
 age of our samples using a combination of ammonoid biostratigraphy and
 absolute ages, and study the anagenetic pattern of evolution of each trait
 by means of paleontological time-series analysis and change tracking. We
 find that evolution in Ptychomya is mostly speciational as the majority of
 traits show stasis, with the exceptions of shell size in P. coihuicoensis
 and shell outline in P. windhauseni, which seem to evolve directionally
 towards larger and higher shells, respectively. Ptychomya displays changes
 in its average morphology and disparity, which are the result of a mixture
 of taxonomic turnover and mosaic evolution of traits. Pulses of speciation
 would have been triggered by ecological opportunity, as they occur during
 the recovery of shallow-burrowing bivalve faunas after dysoxic events
 affecting the basin. On the other hand, the presence of directional
 patterns of evolution in P. coihuicoensis and P. windhauseni seems to be
 the result of a general shallowing-upward trend observed in the basin
 during the upper Hauterivian – lowest Barremian, as opposed to the
 cyclical paleoenvironmental stability inferred for the early/late
 Valanginian – early Hauterivian, which would have prompted stasis in P.
 koeneni and P. esbelta.
description: Ptychomya
 dataThis file contains three
 R objects. These objects are lists with 1) shape (or size) descriptors
 stored as Momocs objects and 2) stratigraphic, geochronologic and
 taxonomic data stored as data frames, for the shell outline, ribbing
 pattern and shell size, respectivelyPtychomya - Agrio
 FmCurvesThis file contains
 isotopic and paleodiversity data, stored as R objects in data frame
 format.isotope and diversity curves -
 Agrio FmSupplementary Figure
 1Supplementary Figure 1.
 Distortion generated by the sliding process on the shape of the ribs of
 Ptychoma, represented with different numbers of coordinates. (A) Original
 curve (1000 coordinates) representing the most complex ribbing pattern in
 our sample. (B) Curve transformed to optimum number of coordinates (416)
 before sliding. (C) Curve transformed to 416 coordinates after sliding.
 (D) Curve transformed to 300 coordinates after sliding. (E) Curve
 transformed to 100 coordinates after sliding. (F) Curve transformed to 30
 coordinates after sliding. For sliding, the first and last coordinates are
 treated as fixed landmarks.Millacarmonaetal_SupplementaryFigure1_2col.eps