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’

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.