Proposal (976) to South American Classification Committee

Recognize new genus Hesperoburhinus

Černý and Natale (2022) produced the most comprehensive phylogeny of the Charadriiformes to date. Their supermatrix approach included DNA sequence data (27 loci), 69 morphological characters, and 90% of all charadriiform species. They found that the thick-knee genus Burhinus is paraphyletic with respect to Old World Esacus.

Based on those results, Černý et al. (2023) named a new genus, Hesperoburhinus, for the two New World Burhinus species, to maintain the monophyly of Burhinus (restricted to Old World species). They further justified naming a new genus based on the great antiquity of the split between the lineages as postulated in their time-calibrated tree: 30+ mya. A set of plumage characters also supported the distinctiveness of Burhinus.

Their diagnosis is as follows:

“Diagnosis: A clade of exclusively Neotropical thick-knees characterized by the following autapomorphies: (1) crown plumage coloration pattern comprised of three broad, longitudinal stripes, with black lateral stripes bordering a pale, grey median stripe that subdivides the entire pileum (Livezey, 2009: character states 551:b, 552:d, 553:b, 614:d; Figure 3A, cf. Figure 3B, 3C); (2) rectrices subterminally marked with a narrow transverse bar of white (Livezey, 2009: character state 914:c; Figure 3D, cf. Figure 3E, 3F). The genus can be further distinguished from other Burhinidae by superciliary stripes that extend caudally to the side of the neck (Livezey, 2009: character state 566:g; Figure 3G, cf. Figure 3H, 3I). Additionally, we have identified 55 single-nucleotide synapomorphies that unite the members of the genus and distinguish them from all other Burhinidae, as well as from outgroup species Chionis albus, C. minor and Pluvianellus socialis. These are, for COI: C54T, C69T, A81T, C105T, T111C, A126G, A147G, A220G, C222T, C231A, A252T, A255T, C316T, C372G, A375T, A402C, C453A, A486G, A552C, C567T, C576T, A630C, A642C, A669T; and for RAG1: G122A, T134C, G135A, A146G, T171C, T288C, T309C, G554A, T495C, T588C, A629G, T713C, A763G, C765T, C958T, G1137C, C1144T, A1371C, C1434T, A1548C, A1557G, C1677G, A1920T, A2025G, A2292G, T2343C, C2361T, T2434C, G2673A, G2793A, G2862A.

“Type species, by original designation: Charadrius bistriatus Wagler, 1829.

“Referred species: “Oedicnenus” (= Oedicnemus) superciliaris Tschudi, 1843.

“New combinations: Hesperoburhinus bistriatus (Wagler, 1829); Hesperoburhinus superciliaris (Tschudi, 1843).

”ZooBank LSID for genus: A9C859C6-090A-4734-AEEF-E91E5D105F82”

Here is their tree:

Discussion: I personally do not like combining genetic and morphological – I prefer using the genetic data alone to construct the phylogeny and evaluating morphological differences separately. However, in Černý and Natale (2022; Figures 4 and 5 in the paper), analyses of the genetic data alone produced similar results. I favor a YES vote on this proposal even without the issue of paraphyly because the split between Hesperoburhinus is older than that between the sheathbills (Chionidae) and Magellanic Plover (Pluvianellidae) families and certainly much, much older than estimated divergence times in bird genera as a whole. Recognizing Hesperoburhinus emphasizes the comparatively slow morphological evolution in this group. Regardless of one’s views on use of lineage age for defining higher categories, the issue of paraphyly with Esacus requires a change. This solution is preferable to an expanded Burhinus that would merge extralimital Esacus into an expanded Burhinus, especially because we would be meddling with a genus that is not in the SACC area.

As an aside, Černý et al. also noted the problem of homonymy in an expanded Burhinus that would force a change in species names as a reason to maintain those two genera separately; see their paper for details. Looking at the support values in their tree, the minimal if at all divergence between Esacus and Burhinus s.s. (shortest branch by far of any in the tree in Fig. 1 above), and the great similarity between the plumage and morphology of Esacus and Burhinus s.s., I would argue that the former should be merged into the latter, regardless of consequence to nomenclature. All analyses in Černý and Natale (2022), however, showed that Burhinus s.s was indeed monophyletic with respect to Esacus, so assigning generic limits are subjective. Nevertheless, retaining Esacus just to avoid the homonymy seems to me to be a classic case of “tail wagging the dog.” Regardless, it does not affect the recognition of Hesperoburhinus based on the rather amazing antiquity of that lineage (early Oligocene!), which rivals divergence times between many sister families, not just Chionidae and Pluvianellidae. To add some perspective, if the estimated divergence times are even close to being correct, that means that the New World and Old World lineages were already evolving separately when elephants still had not evolved trunks, when the huge pig-like entelodonts were part of the megafauna, when massive pelagornithids were present, when phorusracoid birds were apex predators in South America, and so on.

A YES vote endorses Hesperoburhinus for our taxa. A NO vote means retaining Burhinus but implies merger of Esacus into Burhinus regardless of consequences to nomenclature.

Thanks to David Černý for corrections and input on the first version of this proposal.

Selected references:

ČERNÝ, D., AND R. NATALE. 2022. Comprehensive taxon sampling and vetted fossils help clarify the time tree of shorebirds (Aves, Charadriiformes). Molecular Phylogenetics and Evolution 177: 107620.

ČERNÝ, D., P. VAN ELS, R. NATALE, AND S. M. S. GREGORY. 2023. A new genus-group name for Burhinus bistriatus (Wagler, 1829) and Burhinus superciliaris (Tschudi, 1843). Avian Systematics 1: 31–43.

Van Remsen, June 2023

Vote tabulation: https://www.museum.lsu.edu/~Remsen/SACCPropChart864+.htm

Comments from Stiles: “Definitely YES for recognizing Hesperoburhinus- the evidence seems very solid. The problem regarding Esacus as separate from Burhinus s.s. is for those working with Old World birds to resolve, and does not affect recognition of Hesperoburhinus.”

Comments from Robbins: “I vote YES for erecting a new genus Hesperoburhinus for the two New World Burhinus species based on the Cerny & Natale results. As Gary points out, the Esacus-Old World Burhinus issue is beyond our committee's purview.”

Comments from Areta: “YES. If the impressive age of the node uniting the South American taxa to other Burhinidae is to be trusted, and given the placement of Esacus (which might or might not be worth of recognition), I am fine with recognition of Hesperoburhinus for superciliaris and bistriatus. I tend to look with skepticism at “total evidence” trees, when the signal of the different characters has not been analysed separately.”

Comments from Del-Rio: “YES because of the node date, but I would love to see phylogenetic trees with genomic data.”

Comments from Claramunt: “YES. I think Černý et al. present sufficient arguments for separating the South American species into their own genus. The problem of the paraphyly of the traditional Burhinus, combined with nomenclatorial issues, and levels of divergence, results in a compelling case. Divergence times may be overestimated; my own (unpublished) estimates are around 22Ma, but still old for a genus. But solving the paraphyly plus the fact that Hesperoburhinus is perfectly diagnosable, are more important arguments. My only complaint is the name itself: it’s too long. But we cannot do anything about it. My appeal to people coining new names: take into account that some of us actually use scientific names for oral communication.”

Comments from Zimmer: “YES, for all of the reasons stated in the Proposal. As noted by Santiago, regardless of any questions over the apparent divergence times, this move solves the question of paraphyly of Burhinus with respect to Esacus no matter which course is ultimately adopted by Old World committees (maintain Esacus or merge it into an expanded Old World Burhinus), and Hesperoburhinus is readily diagnosable.”

Comments from Lane: ”YES”