Morphology of the forelimb of Psilopterus bachmanni (Aves, Cariamiformes) (Early Miocene of Patagonia)

Abstract

Psilopterines are the smallest and most gracile predatory birds belonging to the large terrestrial Phorusrhacidae, which were abundant during the South American Tertiary. Two taxa are recognized from the Santacrucian (late Early Miocene) beds of Argentinian Patagonia: Psilopterus lemoinei and Psilopterus bachmanni. Although the first species was recently redescribed and is well known, in the case of P. bachmanni, the smaller of the two, the forelimb skeleton was virtually unknown until recently. The fossils described herein come from the coast of Santa Cruz Province, and were recovered from the middle levels of the Estancia La Costa Member, Santa Cruz Formation. The specimen includes associated bones of both forelimbs and a fragmentary furcula. The manus of this species, previously unknown, is described here for the first time: the os carpi ulnare and radiale are very stout bones, the carpometacarpus has processi extensorius and alularis very marked and stout and the os metacarpale majus and phalanges digiti majoris are very robust, and the phalanx digiti minoris is flattened. It has been proposed that some species belonging to Psilopterus were able to fly in a clumsy manner. While this work is not intended to certify this condition through complex models, some considerations of the paleobiology of P. bachmanni based on manus movement capabilities and body mass are presented. It seems plausible that P. bachmanni would have had both cursorial and flying capabilities. The information provided here represents an effort to discuss features previously unknown in phorusrhacids and to provide new data that may be useful in future systematic, morpho-functional and evolutionary studies. Keywords Psilopterus Á Santa Cruz Formation Á Forelimb Á Carpometacarpus Á Phorusrhacids Kurzfassung Phorusrhacidae des taxons Psilopterinae sind die kleinsten und grazilsten Raubvögel der großen terrestrisch lebenden Familie Phorusrhacidae, die im Tertiär von Südamerika sehr häufig war. Zwei Taxa aus dem späten Unter-Miozän (Santacrucium) von Patagonien (Argentinien) sind bekannt: Psilopterus lemoinei und Psilopterus bachmanni. Beide wurden ursprünglich sehr oberflächlich beschrieben. Während die erstere Art erst kürzlich neu beschrieben wurde, war das Skelett der Vordergliedmaßen von P. bachmanni bisher praktisch unbekannt. Die Fossilien, die in dieser Arbeit beschrieben werden, stammen aus der Lokalität Puesto Estancia La Costa (=Corriguen Aike), die in der Santa Cruz Provinz liegt. Sie stammen aus den mittleren Schichten der Estancia La Costa Member, Santa Cruz Formation. Das Exemplar besteht aus assoziierten Knochen beider Vordergliedmaßen und einem Fragment der Furcula. Die Hand dieser Art war bisher unbekannt und wird hier im Rahmen dieser Arbeit das erste Mal beschrieben: Ulnare und Radiale sind beide sehr kräftige Knochen, der Carpometacarpus hat kräftige und markante Processi extensorius et alularis. Das Metacarpale majus und die Phalanges digiti majoris sind sehr robust, die Phalanx digiti minoris ist abgeflacht. Frühere Arbeite...

Osteology and phylogenetic affinities of the middle Eocene North AmericanBathornis grallator—one of the best represented, albeit least known Paleogene cariamiform birds (seriemas and allies)

“…Although most of the proximal end of the bone is missing, the processus alularis is preserved and has a ball-shaped facies articularis alularis. The shape of this articulation facet is similar to that of the Cariamidae and phorusrhacids (e.g., Chandler, 1994; Degrange et al, 2015b), and distinguishes Bathornis from non-cariamiform birds. As noted by Wetmore (1944), the sulcus tendineus is very weakly marked, which is also true for the sulcus tendineus of other cariamiform birds.…”

Hind limb morphometry of terror birds (Aves, Cariamiformes, Phorusrhacidae): functional implications for substrate preferences and locomotor lifestyle

“…As previously stated, forelimb reduction in some species, associated with high body mass, indicates that most phorusrhacids were unable to fly ( fling 2003), or that the smaller species were able to fly for very short distances in a clumsy manner (Tonni 1977;Tonni & Tambussi 1988;Tambussi & Noriega 1996;Mourer-Chauviré et al 2011;Degrange 2012;Degrange et al 2015). This indicates that they were obligate terrestrial birds (Degrange 2012).…”

“…As previously stated, forelimb reduction in some species, associated with high body mass, indicates that most phorusrhacids were unable to fly (Ameghino 1895; Andrews 1899; Sinclair & Farr 1932; Alvarenga & Höfling 2003; Chiappe & Bertelli 2006). Several authors have stated that, beyond any doubt, phorusrhacids were cursorial birds (Alvarenga & Höfling 2003; Blanco & Jones 2005; Chiappe & Bertelli 2006) which were unable to fly (Alvarenga & Höfling 2003), or that the smaller species were able to fly for very short distances in a clumsy manner (Tonni 1977; Tonni & Tambussi 1988; Tambussi & Noriega 1996; Mourer-Chauviré et al 2011; Degrange 2012; Degrange et al 2015). This indicates that they were obligate terrestrial birds (Degrange 2012).…”