Friday, January 13, 2017

[PaleoOrnithology • 2017] The Extreme Insular Adaptation of Garganornis ballmanni Meijer, 2014: A Giant Anseriformes of the Neogene of the Mediterranean Basin


Figure 4. Reconstruction of Garganornis ballmanni Meijer, 2014 based on the newly described fossil remains. This reconstruction is based on a generic Western Palaearctic Goose with short and robust tarsometatarsus, short toes and very short wings according to the known elements of Garganornis ballmanni.

Illustration made by Stefano Maugeri. 
DOI: 10.1098/rsos.160722 

Abstract

New skeletal elements of the recently described endemic giant anseriform Garganornis ballmanni Meijer, 2014 are presented, coming from the type-area of the Gargano and from Scontrone, southern and central Italy, respectively. The new remains represent the first bird remains found at Scontrone so far, and another shared element between these two localities, both part of the Apulia-Abruzzi Palaeobioprovince. The presence of a very reduced carpometacarpus confirms its flightlessness, only previously supposed on the basis of the very large size, while the morphologies of tarsometatarsus and posterior phalanges clearly indicate the adaptation of G. ballmanni to a terrestrial, non-aquatic, lifestyle. Its very large body size is similar to that observed in different, heavily modified, insular waterfowl and has been normally interpreted as the response to the absence of terrestrial predators and a protection from the aerial ones. The presence of a carpal knob in the proximal carpometacarpus also indicates a fighting behaviour for this large terrestrial bird species.

KEYWORDS: fossil bird, Anseriformes, flightlessness, insular gigantism, Miocene, Italy



Systematic Palaeontology

Class AVES Linnaeus, 1758
Order ANSERIFORMES Wagler, 1831

Family Insertae sedis

GARGANORNIS n. gen.
Meijer, 2014. DOI:  10.1016/j.crpv.2013.08.001 

Type species. Garganornis ballmanni n. sp.

Derivation of name. Masculine, after the Italian region Gargano where the quarries are located, and ‘ornis’, Greek for bird.; ‘ballmanni’ refers to Peter Ballmann who was the first to describe the fossil avifauna of Gargano.

Holotype. Distal left tibiotarsus (RGM 443307), Fig. 2.

Diagnosis. A very large representative of the order Anseriformes characterized by the following unique combination of characters; central placement of the canalis extensorius, medially displaced condylus medialis, fossa intercondylaris very wide and shallow, distal opening of canalis extensorius circular, a less pronounced difference in width of the condylus lateralis and condylus medialis, condylus medialis projecting further cranially than condylus lateralis, a reduced epicondylus lateralis and a modestly developed epicondylus medialis, a reduced sulcus m. fibularis, a deep sulcus extensorius and the lateral half of pons supratendineus sunken.

Type locality. Posticchia 5 fissure filling, Gargano pedemountain belt (41.8° N, 15.4° E), Province of Foggia, Italy.



Conclusion

The data presented here confirm the taxonomic validity of G. ballmanni as a strongly modified species of crown-group Anatidae endemic to the Late Miocene Apulia-Abruzzi Palaeobioprovince of central-southern Italy, on the basis of fossil remains found in the Gargano area and at Scontrone.

The newly described material, although not perfectly preserved, gives new osteological details of the morphology of G. ballmanni, which confirms its flightlessness and its extreme adaptation to a terrestrial, non-aquatic, lifestyle. Furthermore, we observed evidence for wing fighting behaviour.

Garganornis ballmanni also demonstrates the strong endemic character of the Late Miocene Apulia-Abruzzi Palaeobioprovince, already suggested by the highly modified mammals and birds. The Mediterranean Sea thus confirms its role as centre of speciation and its islands can also be confirmed to be an intermediate type of island, with faunal composition halfway between oceanic and continental ones, characterized by a very impoverished mammal fauna with high degree of endemism and no terrestrial carnivores, and by a diversified bird fauna with highly modified taxa.


Marco Pavia, Hanneke J. M. Meijer, Maria Adelaide Rossi and Ursula B. Göhlich. 2017. The Extreme Insular Adaptation of Garganornis ballmanni Meijer, 2014: A Giant Anseriformes of the Neogene of the Mediterranean Basin.  Royal Society Open Science.  DOI: 10.1098/rsos.160722 

Hanneke J. M. Meijer. 2014 A Peculiar Anseriform (Aves: Anseriformes) from the Miocene of Gargano (Italy) [Un ansériforme particulier (Aves : Ansériformes) en provenance du Miocène du Gargano, Italie]. C. R. Palevol. 13(1); 19–26. DOI:  10.1016/j.crpv.2013.08.001 


Abstract
A new large representative of the Anseriformes, Garganornis ballmanni n. gen. et n. sp., from the Miocene of Gargano, Italy, is described from the distal end of a left tibiotarsus. G. ballmanni displays morphological features that are characteristic of the Anseriformes, but differs from all extant and fossil Anseriformes, as well as from taxa closely related to Anseriformes. G. ballmanni is characterized by a very wide and shallow fossa intercondylaris, a less pronounced difference in width of the lateral and medial condyle, reduced epicondyli, and a circular opening of the distal canal. G. ballmanni is larger than any living member of Anseriformes, and with an estimated body mass between 15.3 and 22.3 kg, it was most likely flightless. Although the observed similarities between G. ballmanni and basal taxa might indicate that G. ballmanni represents an insular relict of a stem lineage, it is considered more likely that G. ballmanni was a species of waterfowl highly adapted to a terrestrial lifestyle in an insular environment where mammalian carnivores are rare.
Keywords: Anseriformes; Gargano; Italy; Miocene; Insular evolution

Conclusion: Garganornis ballmanni n. gen. et n. sp. displays morphological features that are characteristic for Anseriformes, but differs from all extant and fossil Anseriformes, as well as from taxa closely related to Anseriformes. Given the marked differences between G. ballmanni and related taxa, as well as the fact that important diagnostic features of the condyles are not preserved, I consider an “incertae sedis” position most appropriate. It should be noted however, that insular evolution can result in morphologies that deviate from the ancestral state, and make it difficult to trace a taxon's ancestry. The observed similarities between G. ballmanni and basal taxa might indicate that G. ballmanni represents an insular relict of one of these basal lineages. Although insular environments can serve as refugia and preserve stem lineages, an alternative hypothesis considers G. ballmanni a species of waterfowl highly adapted to an insular environment, with a morphology that is interpreted as adaptations to a terrestrial lifestyle in an environment where mammalian carnivores are rare. Given similar adaptations in waterfowl from other islands and the highly insular nature of the Gargano fauna, I consider the latter scenario most likely. G. ballmanni thus represents an example of convergent evolution of waterfowl in island ecosystems.

Résumé: Un nouveau grand représentant des ansériformes, Garganornis ballmanni n. gen. et n. sp., est décrit sur la base de l’extrémité distale d’un tibiotarse gauche dans le Gargano (Miocène, Italie). G. ballmanni présente des traits morphologiques qui sont caractéristiques des ansériformes, mais diffèrent de tous les ansériformes actuels et fossiles, ainsi que des taxons étroitement liés aux ansériformes. G. ballmanni est caractérisé par une fosse antérieure intercondylienne large et peu profonde, une différence peu prononcée dans la largeur des condyles latéral et médial, des épicondyli réduits, et une ouverture circulaire du canal distal. G. ballmanni est plus grand que tous les ansériformes actuels, et, avec une masse estimée entre 15,3 et 22,3 kg, il était probablement incapable de voler. Bien que les similitudes observées entre G. ballmanni et les taxons de base puissent indiquer que G. ballmanni représente une relique insulaire d’une lignée primitive, il est considéré comme plus probable que G. ballmanni ait été une espèce d’oiseau aquatique très adaptée à un mode de vie terrestre, dans un environnement insulaire où les mammifères carnivores étaient rares.
Mots clés: Ansériformes; Gargano; Italie; Miocène; Évolution insulaire

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