Gargantuavis

Gargantuavis
Temporal range: Late Cretaceous, 73.5–71.5 Ma
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The holotype of Gargantuavis philoinos, a partial pelvis from Campagne-sur-Aude
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Clade:Euornithes
Genus:†Gargantuavis
Buffetaut & Le Loeuff, 1998
Species: †G. philoinos
Binomial name
Gargantuavis philoinos
Buffetaut & Le Loeuff, 1998

Gargantuavis is a genus of extinct avialan stem-birds containing the single species Gargantuavis philoinos.[1] G. philoinos lived during the late Cretaceous period in what is now southern France and northern Spain. Its fossils were discovered in several formations, which has been dated between 73.5 and 71.5 million years old.[2][3] Gargantuavis is the largest known bird of the Mesozoic. The few known bones suggests a size between the cassowary and the ostrich. A study based on the circumference of the femur gives a mass of 140 kg (310 lb) like modern ostriches.[1] Given its mass Gargantuavis was probably flightless. Its femur shows that it was a graviportal form rather than a cursorial bird.[4] Many aspects of its biology are unknown including its diet (the skull has not yet been found). The ecological niche of Gargantuavis in its ecosystem is also mysterious because it coexisted with large predators like abelisaurids theropods. In any case, and contrary to older assumptions, Gargantuavis shows that the extinction of non-avian dinosaurs was not a necessary condition for the emergence of giant terrestrial birds. It is possible that some of the fossil eggs found in the region, usually attributed to non-avialan dinosaurs, actually belong to this bird.[1][5][2]

Discovery

The first Gargantuavis fossil was found in 1995 in Var, southeastern France. This first specimen, a fragmentary set of pelvic vertebrae (synsacrum), was uncovered near the village of Fox-Amphoux in a paleontological excavation. This specimen has been described in a short note without taxonomic assignation.[6] Several other specimens were later found further west, near the villages of Villespassans, Cruzy, and Campagne-sur-Aude, providing enough fossil material to describe and name the species in 1998. The species name G. philoinos, meaning "wine lover", was chosen because several of these first Gargantuavis bones were found in and around vineyards and wineries.[1] The Genus name refers to Gargantua, the giant main character of a 16th-century French novel by Francois Rabelais.

Gargantuavis specimens are known from five different fossil localities in Europe:

  • The Bastide-Neuve locality, near Fox-Amphoux (Var), yielded the initial specimen reported in 1995, two other partial pelvic fragments (BN 758 and BN 763) described in 2015, and a possible rib fragment found in association with BN 763.[7]
  • The Bellevue locality, near Campagne-sur-Aude (Aude), yielded another partial pelvis (MDE C3-525), which was deemed the holotype in the 1998 description of the genus.[1] This site has been dated to the early Maastrichtian, about 71.5 million years ago.[8]
  • The Combebelle locality, near Villespassans (Hérault), yielded a large femur lacking the distal end (MDE A-08), which was referred to the genus in its initial 1998 description.[1]
  • The Montplo-Nord locality, near Cruzy (Hérault), yielded a single neck vertebra (MC-MN 478) which was referred to the genus in 2013.[9] A synsacrum fragment (MC-MN 1165) and an incomplete left illium (MC-MN 431), both described in 2016, were also found at this locality.[3] More recently, this site has also yielded a complete femur of 23 cm, belonging to an individual of about 50 kg (110 lb).[10]
  • A quarry near the village of Laño in northern Spain (Condado de Treviño) yielded a partial syncranum (MCNA 2538) described in 2017, the only specimen known outside of France.[11] This locality has been dated to the late Campanian age of the late Cretaceous, about 72 to 73.5 million years ago.[12]

Description

MDE A-08, a femur

Though Gargantuavis 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),[6] illia (hip bones), at least one cervical vertebra,[9] 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][10]

Other than its large size, the most unusual feature of Gargantuavis was its pelvis. The pelvis of Gargantuavis was originally reported to be extremely wide, like that of a moa, though a better preserved specimen described in 2015 showed that this interpretation was due to crushing in the original. The hips of Gargantuavis, while still broad, were narrower and more bird-like than originally thought.[7] In addition to their unusual width, which prevented the two ilia from meeting at the front of the pelvis, the acetabulum, or hip socket, of Gargantuavis was set close to the front, rather than closer to the middle of the pelvis.[7]

Some researchers have suggested that Gargantuavis was not a stem-bird at all, but rather a giant pterosaur.[13] However, when this idea was tested by studying the form and internal structure of the bones, its identity as an avialan was supported.[4] The avian nature of Gargantuavis was also confirmed by bone histology showing typical bird features.[14]

Paleoecology

During the time period in which Gargantuavis lived, Europe was an archipelago. the region of southern France and north-western Spain where its fossils are found was part of the large Ibero-Armorican island in the prehistoric Tethys Sea.[15] The rock formations that have yielded Gargantuavis fossils have also produced abundant remains of fish, turtles, crocodylomorphs, pterosaurs, various titanosaurian sauropods (including Ampelosaurus and Lirainosaurus), ankylosaurians, ornithopods, and theropods, including other early avialans, like enantiornithes.[15] The association of abundant fossils of the ornithopod Rhabdodon, and the lack of any hadrosaurid fossils, have been used as index fossils to roughly date these formations to the late Campanian-early Maastrichtian inteval.[15] An age confirmed latter by magnetostratigraphic evidence in two localities. The type locality of Gargantuavis, the Bellevue site in the Marnes Rouges Inferieures Formation, is 71.5 million years old (earliest Maastrichtian).[8] The Spanish site of Laño is slightly older with an age of 72 to 73.5 Ma (latest Campanian).[12]

The anatomy and biology of Gargantuavis are not well known because of the incompleteness of the specimens. The rather broad pelvis shows that Gargantuavis was not a fast runner. No cranial remains have been found. So the shape of the head is unknown and the diet of the animal is uncertain. However, the only known cervical vertebra suggests that Gargantuavis had a rather long and slender neck, which seems to preclude the presence of a massive skull.[9] Contrary to the giant terrestrial Cenozoic birds that lived in ecosystems without predators (or including only small carnivores), Gargantuavis cohabited with abelisaurids and dromaeosaurids 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.[7] Although its fossils are rare, the presence of Gargantuavis from southeastern France to north-western Spain shows that this bird had a wide distribution in the Ibero-Armorican island.[11] It is possible that Gargantuavis lived mainly in a peculiar environment that was not compatible with fossilization. Perhaps this habitat was located far from the rivers and floodplains, which represent most of the fossiliferous deposits in the late Campanian-early Maastrichtian of France and Spain.[5][7][2]

Bone histology showed that Gargantuavis 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 extinct dinornithiformes and in the extant kiwi, which are also insular birds. The titanosaur Ampelosaurus, found together with Gargantuavis in the Bellevue site, shows also a reduction in its growth rate. This growth pattern could be linked to some environmental pressure like periodic food shortages in insular environment. A theory supported by sedimentological and mineralogical studies that indicate episodes of semi-arid and strongly seasonal climate during the Late Cretaceous in Southern France.[14]

Classification

The systematic position of Gargantuavis within Aves is uncertain because of the fragmentary nature of its remains. The shape of its femur suggests that Gargantuavis was not a giant representative of the enanthiornithes, a widespread group of Cretaceous archaic birds. It would be more advanced than these latter because of the higher number of vertebrae in its synsacrum and by the more advanced heterocoelous condition of the only known cervical vertebra. However, its precise position within more derived groups is still unknown. Some features of the pelvis and the cervical vertebra show that Gargantuavis was not closely related to the giant terrestrial birds of the Cenozoic like Gastornithidae, Phorusrhacidae, and Dromornithidae, nor to more recent large flightless birds like moas, elephant birds and extant ratites. Gargantuavis represents probably an endemic evolution on the Late Cretaceous Ibero-Armorican island.[1][9][2]

References

  1. 1 2 3 4 5 6 7 8 Buffetaut, E.; Le Loeuff, J. (1998). "A new giant ground bird from the Upper Cretaceous of southern France". Journal of the Geological Society, London (155): 1–4. doi:10.1144/gsjgs.155.1.0001.
  2. 1 2 3 4 Buffetaut, E.; Angst, D. (2016). "The giant flightless bird Gargantuavis philoinos from the Late Cretaceous of southwestern Europe: a review". In Khosla, A.; Lucas, S.G. Cretaceous Period: Biotic Diversity and Biogeography. Albuquerque: New Mexico Museum of Natural History and Science Bulletin 71. pp. 45–50.
  3. 1 2 Buffetaut, E.; Angst, D. (2016). "Pelvic elements of the giant bird Gargantuavis from the Upper Cretaceous of Cruzy (southern France), with remarks on pneumatisation". Cretaceous Research (66): 171–176. doi:10.1016/j.cretres.2016.06.010.
  4. 1 2 Buffetaut, E.; Le Loeuff, J. (2010). "Gargantuavis philoinos: giant bird or giant pterosaur?". Annales de Paléontologie (96): 135–141. doi:10.1016/j.annpal.2011.05.002.
  5. 1 2 Buffetaut, E. (2012). "Les oiseaux fossiles du Crétacé supérieur de l'Hérault". Bulletin de la Société d’Etude des Sciences Naturelles de Béziers (66): 34–39.
  6. 1 2 Buffetaut, E.; Le Loeuff, J.; Mechin, P.; Mechin-Salessy, A. (1995). "A large French Cretaceous bird". Nature. 377: 110. doi:10.1038/377110a0.
  7. 1 2 3 4 5 Buffetaut, E.; Angst, D.; Mechin, P.; Mechin-Salessy, A. (2015). "New remains of the giant bird Gargantuavis philoinos from the Late Cretaceous of Provence (south-eastern France)". Paleovertebrata. 39 (2)-e3: 1–6. doi:10.18563/pv.39.2.e3.
  8. 1 2 Fondevilla, V., Dinares-Turell, J., Vila, B., Le Loeuff, J., Estrada, R., Oms, O., and Galobart, A. (2016). "Magnetostratigraphy of the Maastrichtian continental record in the Upper Aude Valley (northern Pyrenees, France): Placing age constraints on the succession of dinosaur-bearing sites". Cretaceous Research. 57: 457–472. doi:10.1016/j.cretres.2015.08.009.
  9. 1 2 3 4 Buffetaut, E.; Angst, D. (2013). "New evidence of a giant bird from the Late Cretaceous of France". Geological Magazine (150): 173–176. doi:10.1017/S001675681200043X.
  10. 1 2 Buffetaut, E.; Angst, D. (2017). "New light on the Systematic Position of the Late Cretaceous Giant Bird Gargantuavis". Zitteliana (15th Annual Meeting of the European Association of Vertebrate Palaeontologists) (91): 26.
  11. 1 2 Angst, D.; Buffetaut, E.; Corral, J.-C.; Pereda-Suberbiola, X. (2017). "First record of the Late Cretaceous giant bird Gargantuavis philoinos from the Iberian Peninsula". Annales de Paléontologie. 103 (2): 135–139. doi:10.1016/j.annpal.2017.01.003.
  12. 1 2 Corral, J.C., Pueyo, E.L., Berreteaga, A., Rodriguez-Pinto, A., Sanchez, E., and Pereda-Suberbiola, X. (2016). "Magnetostratigraphy and lithostratigraphy of the Laño vertebrate site: Implications in the uppermost Cretaceous chronostratigraphy of the Basque-Cantabrian Region". Cretaceous Research. 57: 473–489. doi:10.1016/j.cretres.2015.07.015.
  13. ↑ Mayr, G., 2009. Paleogene fossil birds. Berlin, Springer.
  14. 1 2 Chinsamy, A.; Buffetaut, E.; Canoville, A.; Angst, D. (2014). "Insight into the growth dynamics and systematic affinities of the Late Cretaceous Gargantuavis from bone microstructure". Naturwissenschaften (101): 447–552. doi:10.1007/s00114-014-1170-6.
  15. 1 2 3 Csiki-Sava, Z.; Buffetaut, E.; Ősi, A.; Pereda-Suberbiola, X.; Brusatte, S.L. (2015). "Island life in the Cretaceous-faunal composition, biostratigraphy, evolution, and extinction of land-living vertebrates on the Late Cretaceous European archipelago". ZooKeys. 469: 1–161. doi:10.3897/zookeys.469.8439.
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