Phylogenetics of modern shorebirds (Charadriiformes) based on phenotypic evidence: analysis and discussion

Abstract

Modern shorebirds (Neornithes: Charadriiformes) are among the most diverse, phylogenetically challenging, and evolutionarily critical of avian orders. Despite several morphological analyses and diverse molecular studies of the order, a consensus regarding relationships within the order, as well as clarity of membership of Turnix, has heretofore remained elusive. This paper describes a cladistic analysis of 1024 phenotypic characters (427 multistate, 209 of which were ordered), which represents an outgrowth of a prior higher-order study. The analysis was performed at species level for all families, exclusive of the highly derived, monophyletic, and intensively studied Alcidae and Lari (the analysis included three out-groups and an in-group, comprising 242 taxa). Characters analysed (excluding 83 poorly known, primarily myological characters) comprised 446 of the skeleton, 558 of the definitive integument, and 20 of natal patterns. Eighty parsimony-uniformative autapomorphies - neutral with respect to summary statistics - were included for descriptive and diagnostic purposes. The analysis found a large set of shortest trees: the majority-rule consensus of these was fully resolved, and most included nodes were unanimously conserved in the solution set. Support was significant for a majority of nodes, both by bootstrap percentages and (for higher-order nodes) support (decay) indices. All families were inferred to be monophyletic in this analysis, although the stability of relationships below intergeneric groups was generally found to be low. Some findings challenge previous morphological results, as well as many groupings variably inferred from molecular data. Close relationships were confirmed between: (1) the Jacanidae and Rostratulidae; (2) the Dromadidae and Haematopodidae; (3) the Ibidorhynchidae and Recurvirostridae; (4) among the Chionididae, Alcidae, Stercorariidae, Rynchopidae, and Laridae; and (5) between the Charadriidae and a clade comprising the Thinocoridae, Phalaropodidae, and Scolopacidae. Pedionomus was inferred to be the sister group of other Charadriiformes, with the Turnicidae arguably considered the sister group of the Charadriiformes or its basalmost member. The Jacanidae and Rostratulidae were strongly supported as sister groups, in agreement with most modern studies. Two points of controversy inferred herein were: Pluvianellus as the sister group of the clade comprising the Alcidae and Lari, and a closer relationship between Thinocoridae and Scolopacidae than between the former and Pedionomus. The topological neighborhood of weakest support involved the position of the Lari-Alcidae (especially relative to the Burhinidae) and the inclusion of Pluvianellus. A lesser point of contention was the rejection of the Glareolinae as closely related to the Laridae and allies, with the Laridae marginally favoured in some molecular studies. The Charadriidae were inferred to comprise four primary subgroups: lapwings (Hoploxypterus and Vanellus), dotterels (nine restricted genera), greater plovers (Pluvialis), and lesser plovers (Anarhynchus and Charadrius). The Scolopacidae comprised four subfamilies, the most speciose of which were the Calidridinae (sandpipers and stints), Tringinae (shanks, curlews, and godwits), and Scolopacinae (snipe and woodcocks). Lesser scolopacid clades included the ‘surfpipers’ (Arenaria and Aphriza) and the ‘meadowpipers’ (Philomachus and Tryngites). Biogeographic and evolutionary implications of the phylogeny are discussed, including the potential of fossils for stratocalibrations, and a revised classification of the order is proposed.