Beibeilong (Chinese: , ) is a genus of large caenagnathid dinosaurs that lived in China during the Late Cretaceous epoch, about 96 million to 88 million years ago. The genus contains a single species, Beibeilong sinensis. The species was named and described in 2017 through analysis of an embryonic skeleton (nicknamed Baby Louie) and partial nest with large eggs that were discovered in the Gaogou Formation of China (Henan Province) between 1992 and 1993.
Beibeilong was a notably large caenagnathid and among the largest oviraptorosaurs, estimated at long (extrapolated from the large embryo and eggs) with a ponderous weight of about , based on comparisons with the closely related Gigantoraptor. Its jaws—in a similar fashion to most other oviraptorosaurs—were toothless and developed a horny beak (also known as rhamphotheca). Most of the anatomical traits of Beibeilong are consistent with caenagnathids rather than oviraptorids, another diverse oviraptorosaur family. Within Caenagnathidae it occupies a basal (primitive) position.
Beibeilong laid one of the largest known types of dinosaur eggs, Macroelongatoolithus. Its eggs measured around in length and had ruggedly ornamented eggshell surfaces. The typical Macroelongatoolithus nest was ring-shaped with one or two layers of eggs, and the center was largely devoid of eggs. Giant caenagnathids (like Beibeilong) may have sat directly in the empty center to avoid egg-crushing because of their massive body dimensions. The paleoenvironments in which Beibeilong lived consisted of relatively mesic (humid, well-watered) floodplains crossed by rivers with semi-arid to tropical climates.
History of discovery
During the late 1980s and early 1990s, Chinese farmers excavated and collected a large amount of fossilized dinosaur eggs from Cretaceous strata of the Gaogou Formation in Henan Province, China, many of which were directly embbeded in sediments (in situ). Although Chinese authorities tried to regulate the export and illegal sales of newly discovered dinosaur eggs during the early 1990s, many ended up outside the country where they were displayed at rock and gem shows, markets, and stores, instead of being used for paleontological research. While they were kept abroad, many of the blocks containing dinosaur eggs were prepared (cleaned), revealing well preserved embryos in some cases. Among these, a partial specimen block containing a long embryonic oviraptorosaur skeleton with several large eggsdiscovered between December 1992 and early 1993 by farmer Zhang Fengchenbecame well-known to the public and scientific communities. Supplementary Information .
In 1993, that block was imported into the United States by The Stone Company, which was responsible for its preparation. In 1996, the specimen was featured on the cover of National Geographic Magazine, which nicknamed the embryonic skeleton Baby Louie in honor of its photographer, Louis Psihoyos. In 2001, the specimen was acquired by the Indianapolis Children's Museum, where it was publicly exhibited for about 12 years until a repatriation agreement was finalized in 2013. In December 2013, the specimen was repatriated to China, where it was housed at the Henan Geological Museum.
In 2015, paleontologists Hanyong Pu, Philip J. Currie, Junchang Lü, Eva B. Koppelhus, and Songhai Jia traveled to the site where Zhang Fengchen purportedly discovered the specimen and found eggshell fragments identical to those observed on the eggs associated with Baby Louie, confirming that Baby Louie was excavated in the Heimaogou locality (Xixia County) in outcrops assigned to the Late Cretaceous Gaogou Formation (Xixia Basin).
In 2017, the entire specimen was formally described by Pu and colleagues, naming the new genus and species Beibeilong sinensis. Baby Louie was assigned the specimen number HGM 41HIII1219 and designated as the holotype specimen of the species. The specimen consists of a partial embryonic oviraptorosaur skeleton on top of an associated partial nest of 6–8 Macroelongatoolithus eggs. Pu and colleagues noted that the preserved eggs represent only a small area of what would have been the original nest. The generic name, Beibeilong, is derived from the pinyin transliteration for the Chinese () and the word (), meaning "baby dragon". The specific name, sinensis, refers to its country of discovery, China (prefix Sino). The team also reported that remains attributed to a second embryo were found protruding from inside one of the eggs.
Description
Beibeilong was one of the largest oviraptorosaurs. Its body size has been extrapolated from the large Macroelongatoolithus eggs associated with the holotype embryo. It had an estimated adult length of about , with a body mass around . The dimensions of Beibeilong were only surpassed or approached by the closely related Gigantoraptor. Supplementary Information
Like other caenagnathids, Beibeilong would have been bipedal with well-developed legs. The head would have been small with a rhamphotheca (horny beak) at the tip of the jaws, supported by a long neck. The hands would have developed long fingers that bore large curved unguals (claw bones). The trunk would have ended in a moderate-sized tail. It is well-known that many oviraptorosaur species had feathers, including caenagnathids such as Apatoraptor. As for gigantic oviraptorosaurs (like Gigantoraptor), it has been suggested that some of this integument was reduced due to their body dimensions.
Skull
The skull of Beibeilong, like most caenagnathids, was edentulous (toothless) as it lacked (tooth sockets). The (front bone of the upper jaw) had a rugose texture, likely developing a rhamphotheca. The (bone following the premaxilla) was rather short and low, giving form to the (hole in the skull behind the nostril opening), and had a pronounced antorbital fossa (depression), which was strongly demarcated by two long ridge-like structures on the external surface of the maxilla, a trait unique to Beibeilong. The bones of Beibeilong were coossified together (bone fusion), and were major bones contributing to the naris (nostril) openings. The nasals also had several nutrient (blood vessel attachments) on their external surface. The (straight bone in front of the orbit) had an open-crescentic shape contributing to the anterior border of the orbit (eye socket).
A small depression on the top border of the posterior process (bony projection pointing backwards) of the lacrimal allowed the frontal bone to overlap, which was unique to Beibeilong. The was a rather domed bone and formed the upper border of the orbit as well as part of the skull roof. The ("cheek" bone) was a long and rather thin bone making contact with the maxilla and lacrimal, as in most oviraptorosaurs, and gave shape to the lower border of the orbit. The (small bony bar below the frontal), the last bone involved in forming the orbit, was a short, slender, and curved element that extended between the anterior end of the frontal and top process of the jugal. The was a tall and nearly triangular bone that was joined by the jugal. Behind the quadratojugal was the , a squared bone of great importance for the motion of the lower jaw.
The (front bone of the lower jaw) of Beibeilong was relatively short and deep with proportions similar to that of other caenagnathids (such as Gigantoraptor or Microvenator), and had an overall plate/shovel-like tip with a downturned sharp edge. The posterior end of the dentary formed the external (circular hole in the lower jaw). The (bone that joined the dentary at its upper edge) had a fairly curved top border and formed a relatively low (bony projection that extended upwards from the upper border of the surangular). It was connected to the top border of the dentary through an articular depression. The (bone located just below the surangular) developed a convex crest-like articulation for the quadrate, which is mostly common in the distantly related oviraptorids. Distinctively, the articular bone of Beibeilong extended backwards into a retroarticular process that had a characteristic concave posterior facet.
Postcranial skeleton
The (vertebral main body) of some (neck vertebrae) had large pleurocoels (air-filled hollow depressions) on their sides. The cervical (upper, and pointy vertebral region) of Beibeilong had low (bony spines developing upward from the top surface of the neural arch) and were X-shaped in top view. The (hip vertebrae fused into a compact structure) of Beibeilong was formed by six sacral vertebrae. The was strap-like and co-joined by the furcula.
The was a large pelvic bone with a gently convex top border, and its (a recurved anterior ilium expansion, also known as "ala") was longer than the squared off (posterior ilium expansion), another distinct feature of Beibeilong. The (hole in the pelvic girdle formed by the ilium, ischium, and pubis) had its top border formed by the ilium with a broad gentle arch. Both the ilium and were united by the (lower ilium protuberance). The shaft of the was a relatively skinny and rod-like shaft.
The (thigh bone) was robust compared to other bones, somewhat bowed, elongated, and slightly larger than the pubis. Unlike most oviraptorosaurs, Beibeilong femora lacked a ridge-like feature extending along the shaft between the and the lower mid-condyle (rounded region for articulation). Furthermore, the accessory trochanter of the femur was poorly developed, a unique trait of Beibeilong. The (shinbone) lacked the distinctive boss that is present on the lower end of the in most oviraptorosaurs. Both the crest and its condyle were connected to each other, low, and poorly defined.
Eggs
The eggs of Beibeilong belong to the oospecies Macroelongatoolithus xixiaensisthe largest known type of dinosaur eggsand, specifically, to giant caenagnathids. They were very elongated with rather rounded poles or ends, and measured between in length. In its microscopic composition, the eggshell was a two-layered structure with an outer continuous layer (non-interrupted orientation of the microstructure) and an inner mammillary/cone layer (rounded and interrupted orientation of the microstructure). Although not considered a layer, the boundary separating both the outer and inner layers was demarcated, undulatory, and wavy. Total eggshell thickness varied from to .
The eggshell of Beibeilong eggs was ornamented on its external surface, characterized by a rugose texture composed of nodes that were both scattered and that formed ridge-like and irregular chain-like structures. Like other Macroelongatoolithus nests, a complete Beibeilong nest would have been ring-shaped with a center devoid of eggs.
Classification In 2017, Pu and team considered Beibeilong to have been anatomically similar to, but more basal (primitive) than Gigantoraptor. This conclusion was consistently recovered in their phylogenetic analyses incorporating ontogenetically (growth) variable characteristics. Beibeilong was recovered within the oviraptorosaur family Caenagnathidae in a relatively basal position. Members of this family are distinguished from other oviraptorosaurs in their skeletal proportions, most notably in their skull anatomy. For instance, members of Oviraptoridae have deep and robust jaws, highly positioned nasal cavities, as well as different hand morphologies (such as the Heyuanninae subfamily). Caenagnathids, on the other hand, have more elongated, pointy, and flat skulls with low nasal cavities, and in turn their manual ungual anatomy is rather generic/simple. Despite their differences, it is known that both groups convergently developed cranial crests.
Below is the obtained cladogram by Pu and team in 2017:
Paleobiology Ontogeny