Phylogenetic Analysis of Pelecaniformes (Aves) Based on Osteological Data: Implications for Waterbird Phylogeny and Fossil Calibration Studies

Abstract

BackgroundDebate regarding the monophyly and relationships of the avian order Pelecaniformes represents a classic example of discord between morphological and molecular estimates of phylogeny. This lack of consensus hampers interpretation of the group's fossil record, which has major implications for understanding patterns of character evolution (e.g., the evolution of wing-propelled diving) and temporal diversification (e.g., the origins of modern families). Relationships of the Pelecaniformes were inferred through parsimony analyses of an osteological dataset encompassing 59 taxa and 464 characters. The relationships of the Plotopteridae, an extinct family of wing-propelled divers, and several other fossil pelecaniforms (Limnofregata, Prophaethon, Lithoptila, ?Borvocarbo stoeffelensis) were also assessed. The antiquity of these taxa and their purported status as stem members of extant families makes them valuable for studies of higher-level avian diversification.Methodology/Principal FindingsPelecaniform monophyly is not recovered, with Phaethontidae recovered as distantly related to all other pelecaniforms, which are supported as a monophyletic Steganopodes. Some anatomical partitions of the dataset possess different phylogenetic signals, and partitioned analyses reveal that these discrepancies are localized outside of Steganopodes, and primarily due to a few labile taxa. The Plotopteridae are recovered as the sister taxon to Phalacrocoracoidea, and the relationships of other fossil pelecaniforms representing key calibration points are well supported, including Limnofregata (sister taxon to Fregatidae), Prophaethon and Lithoptila (successive sister taxa to Phaethontidae), and ?Borvocarbo stoeffelensis (sister taxon to Phalacrocoracidae). These relationships are invariant when ‘backbone’ constraints based on recent avian phylogenies are imposed.Conclusions/SignificanceRelationships of extant pelecaniforms inferred from morphology are more congruent with molecular phylogenies than previously assumed, though notable conflicts remain. The phylogenetic position of the Plotopteridae implies that wing-propelled diving evolved independently in plotopterids and penguins, representing a remarkable case of convergent evolution. Despite robust support for the placement of fossil taxa representing key calibration points, the successive outgroup relationships of several “stem fossil + crown family” clades are variable and poorly supported across recent studies of avian phylogeny. Thus, the impact these fossils have on inferred patterns of temporal diversification depends heavily on the resolution of deep nodes in avian phylogeny.

Reflections on the Phylogenetic Position and Generic Status of Abbott's Booby 'Papasula abbotti' (Aves, Sulidae)

“…I conclude that, from this excerpt, what Warheit means is that Sula and Papasula were sister-taxa to each other, and together they form the sister-group to Morus. My conclusion is supported by Smith [18] who, in his cladistic analysis of Pelecaniformes (lato sensu), recovered those same relationships within Sulidae, and even stated (p: 20) that 'Papasula abbotti is resolved as the sister taxon to Sula in the present analysis identical to the topology recovery by Warheit [1990].' It appears to me that Olson and Warheit [23] viewed a cladogram as a 'ladder of evolutionary progress' wherein the 'species-poor' sister group or branch is referred to as 'basal' or, as they [23] themselves says, 'primitive', and misinterpreted as having characters of the common ancestor.…”

“…abbotti' is the sister-taxon to the clade containing all five species below it; S. sula is the sister-taxon to (S. leucogaster + (S. dactylatra + (S. variegata + S. nebouxi)))); S. leucogaster is the sister taxon to (S. dactylatra + (S. variegata + S. nebouxi))); and S. variegata and S. nebouxi are sister species to each other ( Figure 1A). I should stress that despite differences in style (i.e., diagonal vs. rectangular branches) and position (one is rotated 90 degrees to the other) both the cladogram in Figure 1A and that of Smith [18] show the very same phylogenetic relationships. Figure 1: Clockwise, from top to bottom: Hypotheses of phylogenetic relationships within Sulidae, as recovered in the analyses by (A) Smith [18], (B) Friesen and Anderson [27], and (C) Patterson et al [19].…”

“…Whilst the two first-named taxa respectively comprise six and three species, the latter is monotypic, being represented only by Abbott's Booby [16][17][18][19].…”

“…Nevertheless, I inferred from Smith [18] that such a cladogram was probably taken from the still-unpublished K. I. Warheit's 1990 Ph.D. Dissertation, which was in preparation by the time Olson and Warheit's [23] paper was published. I was unable to obtain a copy of said dissertation, but its abstract reads: 'I established a phylogenetic hypothesis for the relationships within the Sulidae [b] ased on numerical cladistic methods, using 124 discrete skeletal characters.…”

“…Taking that part of Smith's [18] cladogram depicting the relationships among Sulidae (reproduced herein as Figure 1A) and assuming that the most inclusive node (i.e., that comprising the common ancestor of all terminal taxa) is to be ranked at the family level, a cladistic classification by sequencing would appear as follows: Notice that the taxa are arranged in a sequence that reflects their postulated sister-group relationships. Thus, in the classification above, 'S.…”