Balaur (dinosaur)

Balaur Temporal range: Late Cretaceous, 70Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype specimen
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Suborder:	Theropoda
Clade:	Eumaniraptora
Genus:	†Balaur Csiki et al., 2010
Type species
†Balaur bondoc Csiki et al., 2010

Balaur bondoc is a uniquely specialized species of theropod dinosaur which lived in what is now Romania during the latter part of the Late Cretaceous. Balaur was described by scientists in August 2010, and was named after the balaur (Romanian pronunciation: [baˈla.ur]^[1]), a dragon of Romanian folklore. The species name "bondoc" means stocky, so Balaur bondoc means "Stocky dragon" in Romanian. This name refers to the greater musculature that Balaur had compared to its relatives. It is known from a single partial skeleton representing the type specimen.

Seventy million years ago, world sea levels were higher, and the location where its fossils are found was an off-shore part of the European archipelago called Hațeg Island which is also referred to as the "Island of the Dwarf Dinosaurs". Unlike other early members of the group Paraves, which includes Velociraptor, Troodon, and Archaeopteryx, this theropod had not just one but two large, retractable, sickle-shaped claws on each foot, and its limbs were proportionally shorter and heavier than those of its relatives. Given these and nearly twenty other specialized traits, the new genus Balaur was named for this one species. As with other dinosaurs from Hațeg, such as Magyarosaurus, a dwarf sauropod,^[2] its aberrant features are argued to show the effects of its island habitat on its evolution.

Description

Balaur bondoc compared in size to a human

Balaur is a genus of theropod dinosaurs (either an early bird or a member of the more basal paravian lineage Dromaeosauridae) estimated to have lived about 70 million years ago in the late Cretaceous (Maastrichtian), and contains the single species B. bondoc.^[3] The bones of this species were shorter and heavier than those of other 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.^[3] 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.^[3][4]

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.^[3] During the Maastrichtian much of Europe was fragmented into islands, and a number of the animal's bizarre features are thought to be a result of the relatively isolated conditions imposed on many of the populations in this area.^[2] Species which are isolated on islands can be subject to the effects of genetic drift and the founder effect which can magnify the effect of mutations which might be diluted in a larger population. Other island effects such as Foster's rule, which describes how small mainland species become larger and large mainland species become smaller, can take effect. Cretaceous Romania is known, for example, for its dwarf sauropods.^[2]

It is similar in size to Velociraptor, with Balaur's recovered skeletal elements suggesting an overall length of around 1.8–2.1 metres (5.9–6.9 ft).^[3] Hence, in this case, Foster's effect is not evinced.^[3] Yet, when compared to its related species, some 20 unique features were observed, including a re-evolved functional first toe with a large claw that can be hyperextended, 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.^[4][5] Csiki et al. describe this "novel body plan" as "a dramatic example of aberrant morphology developed in island-dwelling taxa."^[3]

Classification

Reconstruction

The position of Balaur relative to other bird-like dinosaurs and early birds has been difficult to determine. The initial phylogenetic analysis placed Balaur closest to the Asiatic mainland dromaeosaurid species Velociraptor mongoliensis, but subsequent analyses found a variety of different possibilities for the classification of Balaur. A study by Brusatte et al. in 2013 found it in an unresolved close relationship with 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.^[6] A large analysis containing a wide variety of coelurosaurs and early birds published in 2013 found that Balaur was not a dromaeosaurid at all, but a basal avialan, more derived than Jeholornithiformes but more basal than Omnivoropterygiformes.^[7] A study published in 2014 found Balaur to be sister to Pygostylia.^[8]

Discovery

Foot of the holotype

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,^[5][9] mistaking them for the remains of an oviraptorosaur.^[10] 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.^[11] The findings were described on August 31, 2010, in the Proceedings of the National Academy of Sciences.^[3] 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.^[12]

Paleobiology

Life restoration, depicted employing a kicking motion as originally proposed

Little is known about the behavior of Balaur, but Csiki speculates that it may have been one of the apex predators in its limited island ecosystem, because no larger teeth have ever been found in Romania. He also believes 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.^[13] 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.^[4][14] 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.^[15] The very short, fused metatarsus of Balaur and enlarged first claw, strange even by dromaeosaur standards, are thought to be consistent with these newer studies, lending further support to the idea that Balaur was a predator.^[16]

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.^[17] 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.^[18]

References

External links

• "'Stocky dragon' dinosaur terrorized Late Cretaceous Europe" article from PhysOrg.com