DOI: 10.5061/dryad.2019
title: Data from: A phylogenetic and morphologic context for the radiation of an endemic fauna in a long-lived lake: Corbulidae (Bivalvia; Myoida) in the Miocene Pebas Formation of western Amazonia

description: The Corbulidae are one of a handful of a primarily marine bivalve clades
 that exhibit a remarkable radiation, marked by increased species richness
 and divergent morphologies, within a long-lived lake. For corbulids, this
 diversification occurred within the lower to middle Miocene Pebas
 Formation of western Amazonia. Only one taxon associated with this
 radiation (Anticorbula) remains extant. We conducted a series of
 phylogenetic analyses to characterize diversification of Corbulidae within
 the Pebas Formation and relate that diversification to geologically older
 freshwater corbulids from the Paleocene Fort Union Formation of the
 northern Great Plains (United States). We used these results, as well as a
 quantitative examination of morphospace occupation, to infer whether
 Pebasian corbulids represent a true species flock, and whether the
 lacustrine system represented by the Pebas Formation represents a cradle
 of, or reservoir for, freshwater corbulid diversity. We conducted two sets
 of phylogenetic analyses using shell morphology characters. A genus-level
 data set incorporated type species of freshwater corbulid genera, any
 Paleocene representatives of these genera, and selected brackish and
 marine corbulid genera. A species-level analysis added all described
 freshwater corbulid taxa to the genus-level matrix. Our results were
 highly resolved (few most-parsimonious trees), but not particularly robust
 (low branch support). For the genus-level matrix, we used a taxon
 jackknife procedure to explore the effects of taxon sampling on tree
 stability and topology. Jackknife results recover a subclade of freshwater
 taxa (including both Anticorbula and Pachydon species and the Paleocene
 Ostomya sp.) in 92.4% of trees, although placement of this subclade across
 the ingroup varies, as do the topologic positions of other freshwater
 species. Freshwater and marine corbulids also are morphologically distinct
 from each other, a factor that likely reduced the robustness of our
 phylogenetic results. By combining these results with paleoecologic,
 stratigraphic, and morphologic data, we infer that freshwater corbulids
 arose once within the family, prior to the Cenozoic, with three distinct
 freshwater lineages present at their first appearance in the late
 Paleocene of North America. Within the Miocene Pebas system of South
 America, we reconstruct supralimital morphologic evolution within three
 lineages as freshwater taxa became variously adapted to the fluid, dysoxic
 muds characterizing lake-bottom facies representative of the Pebas
 lacustrine system. In addition, corbulids apparently successfully coped
 with high predation pressures from co-occurring shellcrushing predators.
 Finally, we consider that freshwater Corbulidae were primarily fluvial
 taxa throughout their geologic history, with a relatively ephemeral
 radiation within the Pebasian lake system, thus making the Pebasian system
 a cradle of diversity for several corbulid lineages.
description: Char_descripsList of character and character-state descriptions.MatrixCharacter state matrix for phylogenetic analyses and for morphospace analysis.matrix.txtmatrix14speciescopyThis is a simple nexus file, saved as a .txt file with the matrix, taxon labels, and character codes defined. It is stripped down so that the only specifications are for outgroup taxa. See the README file for taxon abbreviations from this file and the taxon names used in the Paleobiology paper that incorporates analyses of this matrix.