Eocene fossils and the early evolution of frogmouths (Podargiformes): further specimens of Masillapodargus and a comparison with Fluvioviridavis

Abstract

New fossils of the podargiform Masillapodargus longipes are described from the early Eocene German fossil site Messel. Previously unreported skeletal details of this species confirm its assignment to Podargiformes (frogmouths), and especially the wing and pectoral girdle bones exhibit close similarities to crown group Podargiformes. Here, I show that the postcranial skeletal morphology of Masillapodargus is quite different from that of the early Eocene North American taxon Fluvioviridavis, for which podargiform affinities were recently proposed. With regard to the morphologies of the humerus and the coracoid, Fluvioviridavis more closely resembles Steatornithiformes (oilbirds). These may be plesiomorphic similarities, if Steatornithiformes and Podargiformes are sister taxa as recently suggested. Both podargiform affinities of Fluvioviridavis, as well as a sister group relationship between Podargiformes and Steatornithiformes, are, however, only weakly based. A well-founded classification of Fluvioviridavis depends on a better understanding of the basal divergences within extant Strisores, the clade including Bcaprimulgiform^and apodiform birds, which remain controversial.

Total-Evidence Framework Reveals Complex Morphological Evolution in Nightbirds (Strisores)

“…In the case of Masillapodargus and Scaniacypselus, neither of the alternative placements for these taxa indicated by the two total-evidence analyses had obviously superior statistical support. However, the phylogenetic positions for these taxa found under molecular scaffolding were generally more congruent with the conclusions of previous studies [8,36,37,39], and tended to be characterized by greater numbers of unambiguous morphological synapomorphies compared to the results of the simultaneous combined analysis. We are, therefore, hesitant to accept the novel placements recovered for Masillapodargus, Eocypselus, and Scaniacypselus recovered by the combined molecular-morphological analysis.…”

“…Nesbitt et al [36] later described a second specimen of Fluvioviridavis and ran a phylogenetic analysis that recovered it as a stem-podargid, a conclusion also supported by the phylogenetic analysis of Ksepka et al [8]. However, Mayr [37] expressed scepticism of podargiform affinities for Fluvioviridavis, noting that its humerus and coracoid morphology is more similar to that of Steatornis. Mayr instead suggested that Fluvioviridavis was an early-diverging strisorean excluded from a clade including all non-steatornithiform strisoreans (Podargocypseli), a grouping not supported by the present study.…”

“…Most mandibular characters could be scored based on photographs (including an image figured by Mayr [2]), but vertebral characters (chars. [37][38][39][40][41][42] for this taxon were scored as unknown. We were able to score several plumage characters (chars.…”

“…All 13 fossil members of Strisores included by Ksepka et al [8] were retained in our combined matrix. A few character scores for Masillapodargus and Fluvioviridavis were modified based on observations made by Mayr [37] (see Supplementary Text). Hassiavis laticauda, an Eocene strisorean known from complete specimens but not yet included in any formal phylogenetic analysis, was scored into the matrix based on published descriptions [52,53].…”

“…Strisores has a rich Paleogene fossil record [30,31]. Possible representatives of nearly all major strisorean lineages have been identified from Paleogene fossils, including putative stem-oilbirds [32,33], stem-potoos [34], stem-frogmouths [35][36][37], stem-apodiforms [8,38], stem-swifts [39], and stem-hummingbirds [40][41][42][43]. In contrast, no convincing stem-owlet-nightjars from the Paleogene have previously been proposed [30].…”