Balaur bondoc

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Balaur bondoc
Temporal range: Late Cretaceous, 70  Ma
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Balaur bondoc 1.jpg
Holotype specimen
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Paraves
Genus:† Balaur
Csiki et al., 2010
Species:
†B. bondoc
Binomial name
†Balaur bondoc
Csiki et al., 2010

Balaur is a genus of theropod dinosaur from the late Cretaceous period, in what is now Romania. It is the type species of the monotypic genus Balaur, after the balaur (Romanian pronunciation: [baˈla.ur] [1] ), a dragon of Romanian folklore. The specific name bondoc (Romanian pronunciation: [bonˈdok] [2] ) means "stocky", so Balaur bondoc means "stocky dragon" in Romanian. This name refers to the greater musculature that Balaur had compared to its relatives. The genus, which was first described by scientists in August 2010, is known from two partial skeletons (including the type specimen).

Contents

Fossils of Balaur were found in the Densuș-Ciula and Sebeș Formations of Cretaceous Romania which correspond to Hațeg Island, a subtropical island [3] in the European archipelago of the Tethys sea approximately 70 million years ago. Hațeg Island is commonly referred to as the "Island of the Dwarf Dinosaurs" on account of the extensive fossil evidence that its native dinosaurs exhibited island syndrome, a collection of morphological, ecological, physiological and behavioural differences compared with their continental counterparts. Examples included island gigantism of Hatzegopteryx , island dwarfism of the titanosaur Magyarosaurus dacus , and a reduction in flight capacity in Balaur (Balaur is currently believed to be a basal avialan, a group that includes modern birds, based on phylogenetic analysis, despite being previously grouped within the dromaeosaurid dinosaurs, a group which includes Velociraptor ). This reduction in flight capacity is also seen in extant island birds including the ratites and insular barn owls [4] as well as the extinct moa of New Zealand [5] and the extinct dodo of Mauritius.

Discovery and naming

Skeletal reconstruction showing known remains in white Balaur.png
Skeletal reconstruction showing known remains in white

The first small bones belonging to Balaur bondoc consisted of six elements of the front limbs. Named specimens FGGUB R. 1580–1585, these were discovered in 1997 in Romania by Dan Grigorescu, but the morphology of the arm was so unusual that scientists could not correctly combine them, [6] [7] mistaking them for the remains of an oviraptorosaur. [8] The first partial skeleton was discovered in September 2009 in Romania, approximately 2.5 kilometers north of Sebeș, along the Sebeș river in the Sebeș Formation dating from the early Maastrichtian, and was given the preliminary field number SbG/A-Sk1. Later it received the holotype inventory number EME VP.313. The discovery was made by the geologist and paleontologist Mátyás Vremir of the Transylvanian Museum Society of Cluj Napoca who sent them for analysis to Zoltán Csiki of the University of Bucharest. [9] The findings were described on August 31, 2010, in the Proceedings of the National Academy of Sciences . [10] The 1997 specimens indicate an individual about 45% longer than the holotype; they were also found in a younger stratum.

The generic name Balaur (three syllables, stressed on the second /a/) is from the Romanian word for a dragon of Romanian folklore, while the specific epithet bondoc (pronounced like "boned oak", meaning "a squat, chubby individual") refers to the small, robust shape of the animal. As the balaur is a winged dragon, the name additionally hints at the close relation of Balaur to the birds within Panaves. Bondoc was chosen by the discoverers also because it is derived from the Turkish bunduk, "small ball", thus alluding to the probable Asian origin of the ancestors of Balaur. [11]

Description

Balaur bondoc compared in size to a human Balaur bondoc scalechart 2015.png
Balaur bondoc compared in size to a human

Balaur is a genus of theropod dinosaurs estimated to have lived about 70 million years ago in the late Cretaceous (Maastrichtian), and contains the single species B. bondoc. [10] The bones of this species were shorter and heavier than those of basal paravians. While the feet of most early paravians bore a single, large "sickle claw" on the second toe which was held retracted off the ground, Balaur had large retractable sickle claws on both the first and second toes of each foot. [10] In addition to its strange feet, the type specimen of Balaur is unique for its status of being the most complete theropod fossil from the late Cretaceous of Europe. It also possesses a great number of additional autapomorphies, including a reduced and presumably nonfunctional third finger, consisting of only one rudimentary phalanx. [10] [12]

The partial skeleton was collected from the red floodplain mudstone of the Sebeș Formation of Romania. It consists of a variety of vertebrae, as well as much of pectoral and pelvic girdles, and a large part of the limbs. It is the first reasonably complete and well-preserved theropod from the Late Cretaceous of Europe. [10]

Restoration Balaur by Mark P. Witton.png
Restoration
Balaur reconstructed as an avialan Balaur bondoc as avialan.jpg
Balaur reconstructed as an avialan

It is similar in size to Velociraptor , with Balaur's recovered skeletal elements suggesting an overall length of around 1.8–2.5 m (5.9–8.2 ft) and a body mass of 15 kg (33 lb). [10] [13] Balaur had re-evolved a functional first toe used to support its weight, which bore a large claw that could be hyperextended. It had short and stocky feet and legs, and large muscle attachment areas on the pelvis which indicate that it was adapted for strength rather than speed. [12] [6] Csiki et al. describe this "novel body plan" as "a dramatic example of aberrant morphology developed in island-dwelling taxa." [10] The stocky feet are exemplified by the length of the metatarsus being only two times its width. It is 1.5 times wider than the lower leg. Both traits are unique in the Theropoda. The skeleton of Balaur also shows extensive fusion of limb bones. Wrist bones and the metacarpals are fused into a carpometacarpus. The pelvic bones are fused. The shinbone, calf bone and the upper ankle bones have been fused into a tibiotarsus and the lower ankle bones and the metatarsals into a tarsometatarsus. The degree of fusion is typical for the Avialae, the evolutionary branch of the birds and their direct relatives. [14]

Classification

Left foot and tibia of the holotype Balaur holotype pes and tibia.jpg
Left foot and tibia of the holotype

The position of Balaur relative to other bird-like dinosaurs and early birds has been difficult to determine. The initial phylogenetic analysis placed Balaur bondoc closest to the Asiatic mainland dromaeosaurid species Velociraptor mongoliensis . A 2013 study by Brusatte and colleagues, using a modified version of the same data, found it in an unresolved close relationship with the dromaeosaurids Deinonychus and Adasaurus , with some possible alternative trees suggesting it branched off before the common ancestor of Deinonychus and Velociraptor , while others maintained it as the closest relative of Velociraptor , with Adasaurus as their next closest relative. [14]

More recent analyses using different sets of anatomical data have since cast doubt on a dromaeosaurid classification for Balaur. In 2013, a larger analysis containing a wide variety of coelurosaurs found that Balaur was not a dromaeosaurid at all, but a basal avialan, more closely related to modern birds than to Jeholornithiformes but more basal than Omnivoropterygiformes. [15] A study published in 2014 found Balaur to be sister to Pygostylia. [16] An independent analysis using an expanded version of the original data set (the one that found Balaur to be a dromaeosaurid) drew a similar conclusion in 2014. [17] In 2015, researchers Andrea Cau, Tom Brougham, and Darren Naish published a study which specifically attempted to clarify which theropods were close relatives of Balaur. While their analysis could not completely rule out the possibility that B. bondoc was a dromaeosaurid, they concluded that this result was less likely than the classification of Balaur as a non-pygostylian avialan based on several important bird-like features. Many of the presumed unique traits would in fact have been normal for a member of the Avialae. Typical bird features included the degree of fusion of the limb bones, the functional first toe, the first toe claw not being smaller than the second claw, a long penultimate phalanx of the third toe, a small fourth toe claw and a long fifth metatarsal. [18]

On the other hand, some recent studies continue to place Balaur within the Velociraptorinae. [19] [20]

Paleobiology

Diet and lifestyle

Reconstruction of Balaur as a dromaeosaur, using the originally-proposed kicking motion Balaur bondoc.jpg
Reconstruction of Balaur as a dromaeosaur, using the originally-proposed kicking motion

Little is known about the behavior of Balaur. Because of the lack of skull material, it is impossible to determine by the shape of the teeth whether Balaur was a carnivore or a herbivore. The original description assumed it was carnivorous because it had been found that it was closely related to Velociraptor . Csiki speculated in 2010 that it may have been one of the apex predators in its limited island ecosystem, as neither the skeletons nor teeth of larger theropods have been discovered in Romania. He also believed that it likely used its double sickle claws for slashing prey, and that the atrophied state of its hands indicates that it probably did not use them to hunt. [21] One of the original discoverers indicated that it "was probably more of a kickboxer than a sprinter" compared to Velociraptor , and was probably able to hunt larger animals than itself. [12] [22] However, more recent studies by Denver Fowler and others have shown that the foot anatomy of paravians like Balaur indicate that they used their large claws to grip and pin prey to the ground while flapping with their proto-wings to stay on top of their victim. Once it was worn out, they might have proceeded to feast while it was still alive as some modern birds of prey still do. Due to the shape of the claws, they would not have been effective in slashing attacks. [23] The very short, fused metatarsus of Balaur and enlarged first claw, strange even by true dromaeosaur standards, are thought to be consistent with these newer studies, lending further support to the idea that Balaur was a predator. [24]

Italian paleontologist Andrea Cau has speculated that the aberrant features present in Balaur may have been a result of this theropod being omnivorous or herbivorous rather than carnivorous like most non-avian theropods. The lack of the third finger may be a sign of reduced predatory behavior, and the robust first toe could be interpreted as a weight-supporting adaptation rather than a weapon. These characteristics are consistent with the relatively short, stocky limbs and wide, swept-back pubis, which may indicate enlarged intestines for digesting vegetation as well as reduced speed. Cau referred to this as the "Dodoraptor" model. [25] However, in light of the research done by Fowler et al., Cau has remarked that the anatomy of Balaur may be more congruent with the hypothesis that Balaur was predatory after all. [26]

In 2015, Cau et al. reconsidered the ecology of Balaur again in their reevaluation of its phylogenetic position, arguing that if Balaur was an avialan, it would be phylogenetically bracketed by taxa known to have been herbivorous, such as Sapeornis and Jeholornis . This suggests a non-hypercarnivorous lifestyle to be a more parsimonious conclusion and supports Cau's initial interpretations of its specializations. This is also indicated by the reduced third finger, the lack of a ginglymoid lower articulation of the second metatarsal and the rather small and moderately recurved second toe claw. Balaur had a broad pelvis, a broad foot, a large first toe, and broad lower ends of the metatarsals relative to the articulation surfaces; such a combination can in the remainder of the Theropoda only be found with the herbivorous Therizinosauridae. [18]

Island syndrome

Pair of Balaur bondoc in their native Hateg Island environment of what is now Romania Balaur in Hateg environment.jpg
Pair of Balaur bondoc in their native Hațeg Island environment of what is now Romania

During the Maastrichtian age, much of Europe was fragmented into islands, and a number of the bizarre morphologies of Balaur are thought to be a result of Island syndrome. [27] This describes the differences in the morphology, ecology, physiology and behaviour of island species like Balaur compared to their continental counterparts as a result of the different selection pressures that act on island species. [28] One common effect is Foster's rule which describes how small mainland species become larger and large mainland species become smaller. This is seen in other taxa from Hațeg Island including the pterosaur Hatzegopteryx which exhibited island gigantism and the titanosaur Magyarosaurus dacus which exhibited island dwarfism. [27] However, Balaur appears to have had comparable body size to other basal avialans and closely related dromaeosaurid dinosaurs. Balaur appears to have exhibited other features of island syndrome, most notably a reduced capacity for flight compared to other basal avialans. This reduction in flight capacity is also seen in extant island birds including the ratites and insular barn owls [4] as well as the extinct moa of New Zealand [5] and the extinct dodo of Mauritius.

In addition to island syndrome, species isolated on islands are also affected by genetic drift and the founder effect to a greater degree due to the small effective population size. This can magnify the effects of mutations which may otherwise be diluted in a larger population and may have given rise to some of the neomorphisms seen in Balaur like the retractable claw on its first toe. [10]

In 2010, the increased robustness of Balaur was compared to parallel changes seen in isolated herbivorous mammals. [11] In 2013, it was claimed that Balaur was the only predatory vertebrate known to have become more robust after invading an island niche and it was suggested that its broad feet had evolved to improve postural stability. [14] The 2015 interpretation of Balaur as an omnivorous member of the Avialae, suggested it was the descendant of a flying species that had developed a larger size similar to the development in several other island herbivores. This would then be a rare instance of secondary flightlessness in a paravian to resemble a dromaeosaurid, as predicted by Gregory S. Paul. [18]

Related Research Articles

<i>Velociraptor</i> Dromaeosaurid dinosaur genus from the Late Cretaceous

Velociraptor is a genus of small dromaeosaurid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis, named and described in 1924. Fossils of this species have been discovered in the Djadochta Formation, Mongolia. A second species, V. osmolskae, was named in 2008 for skull material from the Bayan Mandahu Formation, China.

<i>Deinonychus</i> Genus of theropod dinosaur

Deinonychus is a genus of dromaeosaurid theropod dinosaur with one described species, Deinonychus antirrhopus. This species, which could grow up to 3.4 meters (11 ft) long, lived during the early Cretaceous Period, about 115–108 million years ago. Fossils have been recovered from the U.S. states of Montana, Utah, Wyoming, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation, though teeth that may belong to Deinonychus have been found much farther east in Maryland.

<span class="mw-page-title-main">Troodontidae</span> Extinct family of bird-like dinosaurs

Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens, have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.

<span class="mw-page-title-main">Deinonychosauria</span> Extinct clade of dinosaurs

Deinonychosauria is a clade of paravian dinosaurs which lived from the Late Jurassic to the Late Cretaceous periods. Fossils have been found across the globe in North America, Europe, Africa, Asia, South America, and Antarctica, with fossilized teeth giving credence to the possibility that they inhabited Australia as well. This group of dinosaurs are known for their sickle-shaped toe claws and features in the shoulder bones.

<span class="mw-page-title-main">Dromaeosauridae</span> Family of theropod dinosaurs

Dromaeosauridae is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek δρομαῖος (dromaîos), meaning 'running at full speed', 'swift', and σαῦρος (saûros), meaning 'lizard'. In informal usage, they are often called raptors, a term popularized by the film Jurassic Park; several genera include the term "raptor" directly in their name, and popular culture has come to emphasize their bird-like appearance and speculated bird-like behavior.

<i>Adasaurus</i> Extinct genus of dinosaurs

Adasaurus is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago. The genus is known from two partial specimens found in the Nemegt Formation of Mongolia that were partially described in 1983 by the paleontologist Rinchen Barsbold.

<i>Jinfengopteryx</i> Theropod dinosaur genus

Jinfengopteryx is a genus of maniraptoran dinosaur. It was found in the Qiaotou Member of the Huajiying Formation of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.

Kuru is a genus of dromaeosaurid theropod from the Late Cretaceous Barun Goyot Formation of Mongolia. The genus contains only a single species, the type species Kuru kulla, which is known from a fragmentary skeleton including a partial skull.

<span class="mw-page-title-main">Hațeg Island</span> Prehistoric 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 and Eurasian plates towards the end of the Cretaceous. There is no real present-day analog, but overall, the island of Hainan 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.

<i>Hatzegopteryx</i> Genus of large azhdarchid pterosaur from the Late Cretaceous

Hatzegopteryx is a genus of azhdarchid pterosaur found in the late Maastrichtian deposits of the Densuş Ciula Formation, an outcropping in Transylvania, Romania. It is known only from the type species, Hatzegopteryx thambema, named by Buffetaut et al. in 2002 based on parts of the skull and humerus. Additional specimens, including a neck vertebra, were later placed in the genus, representing a range of sizes. The largest of these remains indicate it was among the biggest pterosaurs, with an estimated wingspan of 10 to 12 metres.

<span class="mw-page-title-main">Velociraptorinae</span> Extinct subfamily of dinosaurs

Velociraptorinae is a subfamily of the theropod group Dromaeosauridae. The earliest velociraptorines are probably Nuthetes from the United Kingdom, and possibly Deinonychus from North America. However, several indeterminate velociraptorines have also been discovered, dating to the Kimmeridgian stage, in the Late Jurassic Period. These fossils were discovered in the Langenberg quarry, Oker near Goslar, Germany.

<span class="mw-page-title-main">Paraves</span> Clade of all dinosaurs that are more closely related to birds than to oviraptorosaurs

Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avialans, which include diverse extinct taxa as well as the over 10,000 species of living birds. Basal members of Paraves are well known for the possession of an enlarged claw on the second digit of the foot, which was held off the ground when walking in some species. A number of differing scientific interpretations of the relationships between paravian taxa exist. New fossil discoveries and analyses make the classification of Paraves an active subject of research.

<i>Paludititan</i> Extinct genus of dinosaurs

Paludititan is a genus of titanosaurian sauropod dinosaur which lived in the area of present Romania during the Late Cretaceous. It existed in the island ecosystem known as Hațeg Island.

<span class="mw-page-title-main">Timeline of dromaeosaurid research</span>

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<span class="mw-page-title-main">Anchiornithidae</span> Extinct family of reptiles

Anchiornithidae is a family of eumaniraptorans which could be the basalmost family of birds in the clade Avialae. Anchiornithids have been classified at varying positions in the maniraptoran tree, with some scientists classifying them as a distinct family, a basal subfamily of Troodontidae, members of Archaeopterygidae, or an assemblage of dinosaurs that are an evolutionary grade within Avialae or Paraves.

<i>Imperobator</i> Extinct genus of dinosaurs

Imperobator is a genus of paravian theropod, a group of large, three-toed carnivorous dinosaurs, that lived during the Maastrichtian age of the Late Cretaceous period in what is now James Ross Island in Antarctica. Imperobator is one of only two non-avian theropods known from Antarctica, crossing over to the landmass when it was part of Gondwana. The only described specimen was found in 2003 by an expedition launched by the University of California Museum of Paleontology and initially described as a dromaeosaur in 2007. However, later searches reported more fossils from the site including teeth and skull bones. The fossils were formally described as a new genus of giant paravian in 2019.

The Sebeș Formation is a geological formation in Romania. It is of Maastrichtian age. It is laterally equivalent to the Sard Formation. The base of the formation consists of claystones interbedded with sandstones and conglomerates. It is well known for its fossils which form a component of the Hațeg Island fauna.

Mátyás Vremir was a Romanian geologist and palaeontologist.

<span class="mw-page-title-main">Andrea Cau</span> Italian paleontologist

Andrea Cau is an Italian vertebrate paleontologist. He specializes in the study of dinosaur cladistics. Cau named the unique dromaeosaurid theropod, Halszkaraptor in 2017. He also reanalyzed the theropod Balaur, placing it as a basal avialan rather than a dromaeosaur.

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  24. ↑ Choi, Charles (14 December 2011). "Velociraptors' Killer Claws Helped Them Eat Prey Alive". LiveScience.
  25. ↑ Cau, A (2010). Balaur: More than just a "Double-Sickle-Clawed Raptor" Theropoda, September 1, 2010.
  26. ↑ Cau, A (2011). The Extinction of Dodoraptor (?) Theropoda, December 30, 2011.
  27. 1 2 Stein K; et al. (2010). "Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria)". Proc Natl Acad Sci USA. 107 (20): 9258–9263. Bibcode:2010PNAS..107.9258S. doi: 10.1073/pnas.1000781107 . PMC   2889090 . PMID   20435913.
  28. ↑ Baeckens, Simon; Van Damme, Raoul (20 April 2020). "The island syndrome". Current Biology. 30 (8): R329–R339. doi: 10.1016/j.cub.2020.03.029 . PMID   32315628.

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