Hațeg Island

Hațeg Island was a large offshore island in the Tethys Sea which existed during the Late Cretaceous period, probably from the Cenomanian to the Maastrichtian ages. It was situated in an area corresponding to the region around modern-day Hațeg, Hunedoara County, Romania. Maastrichtian fossils of small-sized dinosaurs have been found in the island's rocks. It was formed mainly by tectonic uplift during the early Alpine orogeny, caused by the collision of the African plate and Eurasian plate towards the end of the Cretaceous. There is no real present-day analog, but overall, the island of Hainan (off the coast of China) is perhaps closest as regards climate, geology and topography, though still not a particularly good match. The vegetation, for example, was of course entirely distinct from today, as was the fauna. Places like Louisiana and Mississippi and other parts of the American Deep South are an even closer climatic and ecological match with a subtropical climate, wet summer season, and coverage by rivers, swamps, and deltas, however they are not islands.

The Hungarian paleontologist Franz Nopcsa theorized that "limited resources" found on the island commonly have an effect of "reducing the size of animals" over the generations, producing a localized form of dwarfism. Nopcsa's theory of insular dwarfism—also known as the island rule—is today widely accepted.

Geography While a variety of estimates regarding the prehistoric island's size have been given over the years, the places it at roughly during the Maastrichtian, or about the size of the modern island of Hispaniola. It was positioned just within the equatorial belt, at about 27°N latitude.Benton, M.J., Csiki, Z., Grigorescu, D., Redelstorff, R., Sander, P.M., Stein, K., and Weishampel, D.B. (2010). "Dinosaurs and the island rule: The dwarfed dinosaurs from Hațeg Island. " Palaeogeography, Palaeoclimatology, Palaeoecology, 293(3-4): 438–454.

Hațeg Island was probably located at least from the nearest land mass. To the northwest was an island corresponding to the Bohemian Massif, to the southeast was an island corresponding to the Balkan–Rhodope Massif (including the modern Rhodope Mountains region), and to the west was a large island corresponding to part of the modern Iberian land mass. The closest continental land mass were portions of the Austro-Alpine region to the west and the Adriatic region to the south.

Hațeg Island itself was surrounded primarily by a deep marine basin, unlike some of the surrounding islands and land masses which were surrounded by shallow seas.

Climate and ecology During the Maastrichtian, the climate of Hațeg Island was subtropical, with an average temperature of . The island experienced marked rainy and dry seasons, but despite this, the plant life on the island was mainly tropical in nature. Carbon isotopes indicate "dry woodland" conditions. This seeming contradiction between the seasonally dry climate and tropical plant species can be explained by the fact that tropical plants can thrive in a seasonally monsoonal environment today as long as they have access to sufficient amounts of water year-round, and the Hațeg environment seems to have been dominated by braided rivers and lakes. Fossils of fruit and angiosperms unearthed in this region are a testament to this. Early rock layers are dominated by volcanic deposits, but these are absent in higher layers, indicating that volcanic activity dropped off during this time.

Paleofauna

About nine species of dinosaurs and several species of pterosaur are thought to have been indigenous to the island. The azhdarchid pterosaurs were rather common predators on this island. These insular reptiles differed from their continental relatives due to island syndrome, which describes the differences in morphology, ecology and physiology seen in insular species compared to their continental relatives. Many of them exhibit island dwarfism, becoming much smaller than their mainland relatives. For example the titanosaur, Magyarosaurus dacus, had a body mass of only while mainland titanosaurs like Patagotitan could reach . Conversely Hatzegopteryx exhibited island gigantism, becoming one of the largest pterosaurs ever to have lived. Similar to how extant bird species exhibit reduced wing size and reduced capacity for flight, Balaur bondoc appears to have secondarily lost its capacity for flight. Balaur is currently believed to be a basal avialan based on recent phylogenetic analyses, however, it was originally proposed to be a member of the avialan sister taxon, Deinonychosauria, based on its limb morphology. Its forelimbs were shorter and stockier than those of Avialae and so visibly incapable of powered flight, which led to this originally incorrect placement within the phylogeny. Mammals are almost exclusively represented by the endemic kogaionid multituberculates, an endemic group that evolved in the island's isolation and developed unique insectivorous habits,Thierry Smith, Codrea Vlad, Red Iron-Pigmented Tooth Enamel in a Multituberculate Mammal from the Late Cretaceous Transylvanian " Hațeg Island ", Article in PLoS ONE 10(7):e0132550-1-16 · July 2015 DOI: 10.1371/journal.pone.0132550 as well as a single eutherian remain.Codrea, Vlad; Smith, Thierry; Dica, Paul; Folie, Annelise; Garcia, Géraldine; Godefroit, Pascal; Van Itterbeeck, Jimmy (2002). "Dinosaur egg nests, mammals and other vertebrates from a new Maastrichtian site of the Hațeg Basin (Romania)". Comptes Rendus Palevol. 1 (3): 173–180. doi:10.1016/S1631-0683(02)00021-0. ISSN 1631-0683. Among the better-known lizards from the formation is Barbatteius, a genus of relatively large lizards with an estimated total length of 80 cm. Its relatively robust morphology suggests that it may have occupied the role of a medium-sized opportunistic predator within the island ecosystem, potentially comparable in ecological role to modern teiids. Barbatteius may also have served as prey for larger predators inhabiting the island, including Balaur bondoc. Remains of an indeterminate dromaeosaurid have also been found. Among these animals are included: Albadraco tharmisensis, an azhdarchid Allodaposuchus precedens, an eusuchian Aprosuchus ghirai, a late surviving atoposaurid crocodyliform Balaur bondoc, originally described as a dromaeosaurid but now believed to be an early example of insular flightless bird, possibly a junior synonym of Elopteryx Barbatodon, a genus of multituberculate represented by at least three species Barbatteiidae, a family of teioid lizards endemic to the island Becklesius nopcsai, a paramacellodid lizard Bicuspidon hatzegiensis, a polyglyphanodontian lizard Bradycneme draculae, an alvarezsaurid Elopteryx nopcsai, an avialan dinosaur Eurazhdarcho langendorfensis, an azhdarchid Ferenceratops shqiperorum, a ceratopsian previously misidentified as a species of the rhabdodontid Zalmoxes Gargantuavis, an avialan dinosaur Heptasteornis andrewsi, a dubious alvarezsaurid Hatzegobatrachus grigorescui, a possible bombinatorid toad Hatzegopteryx thambema, an azhdarchid Kallokibotion bajazidi, a perichelydian testudinatan Kogaionon ungureanui, a multituberculate Kryptohadros kallaiae, a hadrosauromorph Litovoi tholocephalos, a dome-headed multituberculate Magyarosaurus dacus, a titanosaur "Megalosaurus hungaricus", an indeterminate theropod Nidophis insularis, an madtsoiid snake Paludititan nalatzensis, a titanosaur Paralatonia transylvanica, a alytid frog Petrustitan hungaricus, a titanosaur Rhabdodon priscus, a rhabdodontid Sabresuchus sympiestodon, a paralligatorid Struthiosaurus transylvanicus, a struthiosaurin nodosaur Telmatosaurus transylvanicus, a hadrosauromorph Transylvanosaurus platycephalus, a rhabdodontid Uriash kadici, a titanosaur Zalmoxes robustus, a rhabdodontid An unnamed robust-necked azhdarchid pterosaur

Constituent formations The Hațeg Island record is preserved as a number of formations, dating from the late Campanian to the Maastrichtian. These include:

Sânpetru Formation Densus Ciula Formation Sebeș Formation Sard Formation Jibou Formation

Hațeg Island

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