Beipiaosaurus
Beipiaosaurus | |
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Components of the holotype specimen (prior to the caudal vertebrae re-excavation) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | †Therizinosauria |
Superfamily: | † Therizinosauroidea
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Genus: | †Beipiaosaurus Xu et al. 1999 |
Type species | |
†Beipiaosaurus inexpectus Xu et al. 1999
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Beipiaosaurus
They were relatively small-sized therizinosaurs, measuring 2.2 m (7.2 ft) long and weighing about 27 kg (60 lb) in contrast to the advanced and giant Segnosaurus or Therizinosaurus. The necks of Beipiaosaurus were shorter than in most therizinosaurs, whose are characterized by elongated necks adapted for high-browsing. Also, their feet configuration differs from therizinosaurids, having a generic three-toed pes instead of four as seen in other members.
The exact classification of therizinosaurs had in the past been hotly debated, since their
History of discovery
In 1996, the peasant Li Yinxian discovered a partial skeleton of a theropod dinosaur near the village of Sihetun. On the following year it was confirmed to have come from the lower beds of the Yixian Formation and represent a single individual. On May 27, 1999, the discovery was announced on the famous journal Nature and the type species Beipiaosaurus inexpectus named and described by Xu Xing, Tang Zhilu and Wang Xiaolin. The generic name Beipiaosaurus translates as "Beipiao lizard" after Beipiao, a city in China near the location of its discovery. Beipiaosaurus is known from a single species, B. inexpectus, the specific name, meaning "unexpected" in Latin, referring to the "surprising features in these animals".[1]
The
A second specimen, STM 31-1, a partial skeleton, was described by Xu et al. 2009, which preserves a significant covering of unique, elongated feathers. This specimen consisted of a complete skull, a sclerotic ring, the mandible, the atlas and axis bones, nine additional cervical vertebrae, dorsal vertebrae, seventeen cervical ribs, twelve dorsal ribs, both scapulae and coracoids, one complete humerus and proximal humerus, one complete radius and distal radius, one complete ulna and distal ulna, carpals, and some metacarpals. The rear of the skull of this specimen was badly crushed.[5] Li et al. 2014 mentioned a third specimen labelled under the number BMNHC PH000911. This specimen hails from the Sihetun locality at the Beipiao County in Liaoning Province and compromises a partial individual preserving the skull (badly crushed), most of the vertebral column, both arms and other postcrania. Traces of feather integument were extensively found around the neck area.[6]
Description
Beipiaosaurus was a small therizinosaur, measuring 2.2 m (7.2 ft) in length, and before the discovery of
Distinguishing traits
According to Zanno in 2010, Beipiaosaurus can be distinguished from other therizinosaur taxa based on the following characteristics, which are unique derived traits (
In 2019 Liao and Xu redescribed the holotype skull in detail, noting new unique cranial traits for Beipiaosaurus. These consisted of the large postorbital joint of the frontal and its abrupt transition from the orbital edge, a long and keen anterior joint of the parietal, an elongate bottom branching of the squamosal articulation of the parietal, and the deeply external mandibular fenestra that is located towards the rear.[9]
Cau (2024) suggested that the contemporary
Feathers and color
The first feather impressions were found in the holotype specimen, consisting of short, slender filamentous feathers on the left arm. These impressions indicated that the body was predominately covered by downy feather-like fibers, similar to those of Sinosauropteryx, but longer, and oriented perpendicular to the arm. Xu et al. 1999 suggested that these downy feathers represent an intermediate stage between Sinosauropteryx and more advanced birds (Avialae).[1] The tail was also covered in feathers between four and seven centimeters long, consisting of parallel filaments with a width of 1.5 mm (0.15 cm), without a trace of pennaceous feathers or a tail fan, as indicated by the preserved pygostyle.[4]
Unique among known theropods, Beipiaosaurus also possessed a secondary coat of much longer, simpler feathers that rose out of the down layer. These unique feathers known as EBFFs (elongated broad filamentous feathers) were first described by Xu et al. 2009, based on specimen STM 31-1 consisting of the torso, head and neck. Xu and his team also found EBFFs in the tail of the holotype IVPP V11559, which were revealed by further preparation. Some of these were damaged during preparation though.[5]
The EBFFs differ from other feather types in that they consist of a single, unbranched filament. Most other primitive
In 2009 during an interview at Live Science, Xu stated: "Both are definitely not for flight, inferring the function of some structures of extinct animals would be very difficult, and in this case, we are not quite sure whether these feathers are for display or some other functions." He speculated that the finer feathers served as an insulatory coat and that the larger feathers were ornamental, perhaps for social interactions such as mating or communication.[11]
Li et al. 2014 compared the color and shape of the melanosomes in 181 extant animal specimens, 13 fossil specimens (including Beipiaosaurus) and previous data about the melanosome diversity using
Jianchangosaurus is another primitive therizinosaur taxon known from the same formation that was found with impressions of a series of filamentous and unbranched feathers in its holotype specimen. Only the distal ends of the feather impressions are visible and based on their morphology the feathers are considered to be EBFFs, bearing resemblance to those found along the specimens of Beipiaosaurus. These findings suggest that they might have been used for visual display and were common among early therizinosaurs.[12]
An evo-devo study published in the year 2003 defined what is a feather. It's stated that the integumentary structures of Beipiaosaurus weren't true feathers, those integumentary structures are filaments that are related to feathers.[13]
Classification
The affinities of therizinosaurs were originally obscure and often problematic, giving rise to taxonomic debate since they feature similar adaptations to the unrelated
Beipiaosaurus was first assigned to the
The cladogram below is the result of the performed phylogenetic analysis of the Therizinosauria by Hartman et al. 2019 which is largely based on the data provided by the revision of Zanno in 2010. Beipiaosaurus occupied a more derived position than Falcarius, as previously indicated by Zanno:[15]
Therizinosauria |
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Paleobiology
In 2018, McNamara and colleagues discovered the fossilised remains of skin flakes from numerous feathered dinosaurs from the Jehol Biota and some bird species using scanning electron microscope on the preserved feather impressions. The analyzed fossil taxa consisted of Confuciusornis, Beipiaosaurus, Microraptor and Sinornithosaurus. For Beipiaosaurus, the specimen STM 31-1 was analyzed.[16]
By exposing the skin flakes under an electron microscope they found
In addition, the identified corneocytes structures seem to indicate that non-avian dinosaurs had a similar way of shedding skin to extant birds and mammals. Unlike many reptiles alive today (lizards or snakes) which shed their skin as a single piece or as several large pieces, Beipiaosaurus and other non-avian dinosaurs shed their skin as dandruff, like Confuciusornis, modern birds or mammals.[16]
Paleoecology
Studies suggest that the paleoenvironment of the Yixian Formation involved seasonal climate fluctuations, and was warm and humid, punctuated by dry seasons, in which the environment became more arid.[17] The average yearly temperature during the time of Beipiaosaurus was 10 °C (50 °F), with relatively cold winters for the generally warm Mesozoic era.[18] A study by Wu et al. 2013 concluded that orbital forcing, which is the effect on climate caused by shifts in the tilt of the Earth's axis and by the shape of the Earth's orbit, contributed to the climate fluctuations of this formation.[19]
The Yixian Formation is well known for its great diversity of well-preserved specimens and its dinosaurs, such as the tyrannosauroids
Other contemporaries of Beipiaosaurus included ancient shrimp, snails and slugs, as well as a diverse group of insects, and fish such as
See also
References
- ^ S2CID 204993327.
- ^ doi:10.1002/gj.1045.
- .
- ^ S2CID 128471217.
- ^ PMID 19139401.
- ^ S2CID 4395833.
- PMID 23193135.
- ^ S2CID 53405097.
- .
- .
- ^ Bryner, J. (2009-01-15). "Ancient Dinosaur Wore Primitive Down Coat". Fox News. New York. Archived from the original on 2009-03-04.
- PMID 23734177.
- PMID 12949768.
- .
- PMID 31333906.
- ^ PMID 29802246.
- ^ a b Wang, Y.; Zheng, S.; Yang, W.; Zhang, W.; Ni, Q. (2006). "The biodiversity and palaeoclimate of conifer floras from the Early Cretaceous deposits in western Liaoning, northeast China". International Symposium on Cretaceous Major Geological Events and Earth System: 56A.
- PMID 21393569.
- .
- ^ S2CID 215804994.
External links
- Dinosauria - News of the first Beipiaosaurus discovery.
- Skeletal restoration
- Therizinosauroidea - UCMP, Berkeley
- Detailed skull of STM 31-1 at Sketchfab