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Cretaceous Research

Volume 112, August 2020, 104438
Cretaceous Research

Discussion
Gargantuavis is an insular basal ornithurine: a comment on Mayr et al., 2020, ‘A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic’

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Abstract

We agree with Mayr et al., 2020, that a pelvis from the Maastrichtian of Romania closely resembles Garantuavis philoinos, from the Late Cretaceous of the Ibero-Armorican island, showing that gargantuaviids were not restricted to the latter landmass. However, we disagree with many other assertions and interpretations of Mayr et al.: contrary to their claims, lines of arrested growth are known in the bones of many modern birds; not all terrestrial birds have a narrow pelvis; the pubic and ischiadic peduncles are broken on all Gargantuavis pelves from the Ibero-Armorican island; an enlargement of the middle part of the synsacrum (to accommodate the glycogen body) is not present in all Ornithothoraces, since it is absent in Hesperornithiformes (probably because of the low number of preacetabular synsacral vertebrae, as in Gargantuavis); the palaeobiogeographical scenario proposed by Mayr et al. is not supported by palaeogeographical reconstructions of Cretaceous Europe. We conclude that Gargantuavis was a basal ornithurine, at an evolutionay level similar to that of Hesperornithiformes, in all likelihood the result of insular evolution (involving the crossing of sea barriers) on the Late Cretaceous European archipelago.

Introduction

Mayr et al. (2020) describe an interesting pelvis from the Maastrichtian of the Haţeg basin in Romania, which they consider as closely resembling that of Gargantuavis philoinos Buffetaut and Le Loeuff, 1998, from the Late Cretaceous of France and Spain. We agree with this identification, which does indicate that the Gargantuaviidae (as defined by Buffetaut and Angst, 2019) were not restricted to the Ibero-Armorican island, as previously suggested (Buffetaut & Angst, 2016a; Angst & Buffetaut, 2017), but were also present on the Haţeg island of the Late Cretaceous European archipelago. However, we disagree with several of the assertions, interpretations and conclusions of Mayr et al., especially concerning the systematic position and palaeobiogeographical history of Gargantuaviidae, as detailed below.

Institutional abbreviations: MC: Musée de Cruzy; MDE: Musée des Dinosaures, Espéraza; NHMUK: Natural History Museum, London.

Section snippets

Association of other skeletal elements with Gargantuavis pelves

Mayr et al. note that the femora and cervical vertebra that have been referred to Gargantuavis philoinos (Buffetaut and Le Loeuff, 1998, Chinsamy et al., 2014; Buffetaut & Angst, 2013; Angst and Buffetaut, 2017, Buffetaut and Angst, 2019) ‘cannot be assigned to G. philoinos with certainty, since these bones were not found in direct association with pelvic elements’ and therefore limit their discussion of the systematic position of Gargantuavis to the various pelvic elements described from

Lines of arrested growth

In their histological study of the femur from Villespassans, Chinsamy et al. (2014) reported the presence of lines of arrested growth. Apparently implying that these LAGs can be of phylogenetic significance, Mayr et al. comment that lines of arrested growth ‘among crown group birds are only found in the Apterygidae (kiwis) and Dinornithidae (moas), but [...] are present in phylogenetically more basal birds and non-avian dinosaurs’. This is erroneous: LAGs are present in many groups of

Breadth of pelvis

Commenting on the great breadth of the pelvis in Gargantuavis, Mayr et al. state that ‘the pelves of terrestrial flightless neornithine birds, by contrast, are much more elongated and narrower than the pelvis of Gargantuavis’ - a comment already made by Mayr (2009) in connection with his erroneous suggestion that Gargantuavis may have been a pterosaur. As already noted by Buffetaut and Le Loeuff (2010), the pelves of terrestrial flightless neornithines are not necessarily narrow. Among extinct

Systematic position

We (Buffetaut and Angst, 2016a, Buffetaut and Angst, 2019; Angst & Buffetaut, 2017) consider Gargantuavis philoinos as a basal ornithurine, on the basis of the number of synsacral vertebrae (probably 10), the highly heterocoelous character of the cervical vertebrae and the advanced condition of the distal end of the femur. This conclusion is not shared by Mayr et al., who, as noted above, restrict their analysis to the pelvis and conclude that Gargantuavis is not an ornithurine but a

Palaeobiogeographical interpretation

Mayr et al. claim that, contrary to previous interpretations (Buffetaut & Le Loeuff, 1998; Buffetaut & Angst, 2016a; Angst & Buffetaut, 2017), Gargantuavis cannot be considered as the result of insular evolution. In fact, the discovery of a Gargantuavis-like fossil on the Haţeg island only shows that gargantuaviids were not restricted to the Ibero-Armorican island, as previously envisioned on the basis of a fossil record that was restricted to France and Spain. As both the Haţeg area and the

Conclusion

While the discovery of a Gargantuavis-like pelvis in the Maastrichtian of Romania does invalidate the hypothesis that this giant bird was endemic to the Ibero-Armorican island, as correctly noted by Mayr et al., the interpretation of the systematic position and biogeographical history of gargantuaviids put forward by these authors is based on various erroneous or flawed assumptions and must be rejected. We consider that gargantuaviids were large, flightless basal ornithurines, at an

Acknowledgments

Thanks to Sandra Chapman for access to hesperornithiform specimens in the Natural History Museum, London. We thank the editor of Cretaceous Research, Dr Eduardo Koutsoukos, and an anonymous reviewer for their comments.

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