| Gargantuavis | |
|---|---|
 | |
| Theholotype ofGargantuavis philoinos, a partial pelvis fromCampagne-sur-Aude | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Family: | †Gargantuaviidae Buffetaut and Angst, 2019 |
| Genus: | †Gargantuavis Buffetaut & Le Loeuff, 1998 |
| Species: | †G. philoinos |
| Binomial name | |
| †Gargantuavis philoinos Buffetaut & Le Loeuff, 1998 | |
Gargantuavis (meaning 'gargantuan bird') is anextinctgenus of large, primitive bird containing the single speciesGargantuavis philoinos.[1] It is the only member of themonotypicfamilyGargantuaviidae. Its fossils were discovered in several formations dating to 73.5 and 71.5 million years ago in what is now northern Spain,Southern France, and Romania.[2][3]Gargantuavis isthe largest known bird of theMesozoic, a size ranging between thecassowary and theostrich, and a mass of 141 kg (311 lb) like modern ostriches, exemplifying the extinction ofnon-avian dinosaurs was not a necessary condition for the emergence of giant terrestrial birds.[1] It was once thought to be closely related to modern birds, but the 2019 discovery of a pelvis identified as cf.Elopteryx nopcsai from what wasHațeg Island (present-day Romania) shows several primitive features.[4]
Its femur shows that it was agraviportal form rather thancursorial, not adapted for running.[5] Due to fragmentary remains, many aspects of its biology and ecology are unknown, such as its diet. It coexisted with large predators likeabelisauridtheropods, herbivores such asankylosaurians andtitanosauriansauropods, as well aspterosaurs,crocodylomorphs, turtles, fish, and various archaic birds.[1][6][2]
The firstGargantuavis fossil was found in 1995 inVar, southeastern France. This first specimen, a fragmentary set of pelvic vertebrae (synsacrum), was uncovered near the village ofFox-Amphoux in a paleontological excavation and described by French paleontologists Eric Buffetaut and Jean Le Loeuff, who noted the synsacrum's similarity to that of modern birds.[7] Several other specimens were later found further west, near the villages ofVillespassans,Cruzy, andCampagne-sur-Aude, providing enough fossil material to describe and name the species in 1998. Thegenus name refers to Gargantua, thegiant and protagonist of the 16th-century French novelThe Life of Gargantua and of Pantagruel byFrancois Rabelais, and theLatinavis. Thespecies namephiloinos, meaning "one who likes wine", was chosen because several of the firstGargantuavis bones were found in and around vineyards and wineries.[1]
Gargantuavis specimens are known from six localities in Europe:
ThoughGargantuavis is only known from a few isolated fossil bones, some information about its life appearance and ecology have been inferred by studying their details.Gargantuavis is known from several specimens representing a few limited parts of the skeleton: synsacra (the fused vertebrae above the hip),[7] ilia (hip bones), at least one cervical vertebra,[10] and two femora (upper leg bone), which was referred to the species based on the fact that it seems to fit well with the hip.[1][11] No cranial remains have been found, so the shape of the head is unknown. However, the only known cervical vertebra suggests thatGargantuavis had a rather long and slender neck, which seems to preclude the presence of a massive skull.[10]
Other than its large size, the most unusual feature ofGargantuavis was its pelvis. It was originally reported to be extremely wide, like that of amoa, though a better preserved specimen described in 2015 showed that this interpretation was due to crushing in the original. The hips ofGargantuavis, while still broad, were narrower and more bird-like than originally thought.[8] In addition to their unusual width, which prevented the two ilia from meeting at the front of the pelvis, thehip socket was set close to the front rather than to the middle of the pelvis.[8] The rather broad pelvis shows thatGargantuavis was not a fast runner.[10]
During the Late Cretaceous, Europe was anarchipelago. Southern France and north-western Spain where its fossils are found was part of the large Ibero-Armorican island in the prehistoricTethys Sea.[14] The rock formations that have yieldedGargantuavis fossils have also produced abundant remains of fish, turtles,crocodylomorphs, pterosaurs, various titanosauriansauropods (includingAmpelosaurus andLirainosaurus),ankylosaurians,ornithopods, andtheropods, including other early avialans, likeenantiornithes.[14] The association of abundant fossils of the ornithopodRhabdodon, and the lack of anyhadrosaurid fossils, have been used asindex fossils to roughly date these formations to the lateCampanian-earlyMaastrichtian interval,[14] an age confirmed later bymagnetostratigraphic evidence in two localities. The type locality ofGargantuavis, the Bellevue site in theMarnes Rouges Inferieures Formation, is 71.5 million years old (earliest Maastrichtian).[9] The Spanish site of Laño is slightly older with an age of 72 to 73.5 Ma (latest Campanian).[13]
Since no skull remains have been found, the diet of the animal is uncertain.[10] Contrary to the giant terrestrialCenozoic birds that lived in ecosystems without predators (or including only small carnivores),Gargantuavis cohabited with abelisaurid anddromaeosaurid theropods, so the place of this giant terrestrial bird in the Late Cretaceous ecosystems of the Ibero-Armorican island is unclear.Gargantuavis seems to have been an uncommon part of the fauna in its region. Despite numerous digs at sites where its bones have been found since its discovery, most have yielded only single specimens.[8] Although its fossils are rare, the presence ofGargantuavis from southeastern France to north-western Spain shows that this bird had a wide distribution in the Ibero-Armorican island.[12] It is possible thatGargantuavis lived mainly in an environment that was not compatible with fossilization, such as areas far from the rivers andfloodplains, which represent most of the fossiliferous deposits in the late Campanian-early Maastrichtian of France and Spain.[6][8][2]
Bonehistology showed thatGargantuavis had a rapid early growth followed by an extended period (of at least 10 years) of slow cyclical growth before to attain skeletal maturity. A similar pattern is known in extinctdinornithiformes and in the extantkiwi, which are also insular birds. The titanosaurAmpelosaurus, found together withGargantuavis in the Bellevue site, shows also a reduction in its growth rate, possibly linked to some environmental pressure like periodic food shortages. This is supported bysedimentological andmineralogical studies which indicate episodes ofsemi-arid and strongly seasonal climate during the Late Cretaceous in Southern France.[15]
The systematic position ofGargantuavis with other birds is uncertain because of the fragmentary nature of its remains.[16] Some researchers suggested thatGargantuavis was not a stem-bird at all, but rather a giantpterosaur,[17] but this was rejected based on the presence of more bird-like conditions.[5][15] The shape of its femur suggested thatGargantuavis was not a giant representative of the enantiornithes, a group of archaic birds, rather more advanced because of the higher number of vertebrae in the synsacrum and the more advancedheterocoelous condition (saddle-shaped joint) of the only known cervical vertebra. It was once thought to be closely related to the archaicPatagopteryx, but a study of the complete femur suggested that the species belongs toOrnithuromorpha, and probablyOrnithurae, being more closely related to moderns birds than to, belonging to its own monotypic family Gargantuaviidae.[16][1][10][2]
However, the discovery of a pelvis from what was Hațeg Island showssupratrochanteric processes on the femora, a lack of aglycogen body, and a lack of fusion of the pelvic bones around the hip socket, meaning it was not closely related to Ornithurae, and likely not even a member ofOrnithothoraces which includes modern birds and their closest ancestors. The archaic Hațeg avian theropodsElopteryx andBalaur bear some similarity toGargantuavis remains, which may indicate the three form someclade native to the Late Cretaceous European archipelago, though they have ambiguousaffinities.[4] This was questioned by other authors, and it is claimed that it was a basal ornithurine, at an evolutionary level similar to that ofHesperornithies,[18] but the authors of the original study stood by their 'cautious' conclusion.[19]
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