Beipiaosaurus

***Beipiaosaurus*** (meaning "Beipiao Lizard") is a genus of therizinosauroid theropod dinosaurs that lived in Asia during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the discovery of *Yutyrannus*, *Beipiaosaurus* were among the heaviest dinosaurs known from direct evidence to be feathered. *Beipiaosaurus* is known from three reported specimens. Numerous impressions of feather structures were preserved that allowed researchers to determine the feathering color which turned out to be brownish.

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 prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical theropods. *Beipiaosaurus*, being considered to be a primitive therizinosauroid, has features which suggest that all therizinosauroids, including the more derived Therizinosauridae, to be coelurosaurian theropods, not sauropodomorph or ornithischian relatives as once believed.

## Description

*Beipiaosaurus* was a small therizinosaur, measuring 2.2 m (7.2 ft) in length, and before the discovery of *Yutyrannus* they were the largest dinosaurs known from direct evidence to be feathered. It is estimated to have weighed about 27 kg (60 lb) based on femur length. More advanced therizinosaurids have four functional toes, but the feet of *Beipiaosaurus* still have reduced inner toes, showing that the derived therizinosaurid condition may have evolved from a three-toed therizinosauroid ancestor. The head was large relative to other therizinosaurs, with the lower jaw measuring about same length as the femur. The neck appears to be shorter compared to other therizinosaurs. In 2003 the pygostyle, consisting of the fused five last vertebrae of the tail, was described in greater detail, suggesting that the original function of the pygostyle was not linked with pennaceous feathers.

### 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 (autapomorphies): a low ridge is present on the front of the thighbone shaft which extends upwards from the inner condyle; the last four dorsal vertebrae are fused; from at least the seventh vertebra onwards the tail vertebrae are fused into a pygostyle; a prominent triangular flange extends outwards, away from the body, from the underside of the first metacarpal; the skull is large, about as long as the thighbone; the first phalanx of the first digit has a joint surface with the claw, that is elongated in the direction of the finger tip on the outer side of its lower part; on the front edge of the ischium a projection, the obturator process, has a wavy profile with a tip that is curved downwards; the "boot" at the lower end of the ischium has twice the width, measured from the front to the rear, of the lower shaft of the ischium.

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.

### 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). 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.

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.

The EBFFs differ from other feather types in that they consist of a single, unbranched filament. Most other primitive feathered dinosaurs have down-like feathers made up of two or more filaments branching out from a common base or along a central shaft. The EBFFs of *Beipiaosaurus* are also much longer than other primitive feather types, measuring about 100–150 mm (10–15 cm) long, roughly half the length of the neck. In *Sinosauropteryx*, the longest feathers are only about 15% of the neck length. The EBFFs of *Beipiaosaurus* are also unusually broad, up to 3 mm (0.30 cm) wide in the holotype. The broadest feathers of *Sinosauropteryx* are only 0.2 mm (0.020 cm) wide, and only slightly wider in larger forms such as *Dilong*. Additionally, where most primitive feather types are circular in cross section, EBFFs appear to be oval-shaped. None of the preserved EBFFs were curved or bent beyond a broad arc in either specimen, indicating that they were fairly stiff. They were probably hollow, at least at the base.

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.

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 scanning electron microscopes. They found that color in dinosaurs seem to be slightly connected with their physiology. While some species of living reptiles (lizards or crocodiles, which are ectothermic) have less diversity in the shape of melanosomes and darker color ranges, some maniraptorans, birds and mammals (which are endothermic) have an increased diversity of melanosome shapes and more vivid colors. The examined specimen of *Beipaosaurus*, BMNHC PH000911, preserves feather impressions which are located in the neck area. These are filamentous/sparse in structure and the sampled melanosomes were sphere-shaped and inferred to had a brownish colouration like those in modern reptiles which fall within the range of dark brownish colourations.

*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.

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.

## *Beipiaosaurus* in The Amazing Dinosaur Adventure

Mason the *Beipiaosaurus*Presley the *Beipiaosaurus*Justin the *Beipiaosaurus*