Beibeilong Holotype Block

''Beibeilong'' (meaning "baby dragon") is a genus of large caenagnathid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 96 million and 88 million years ago. The genus contains a single species, ''Beibeilong sinensis'', named and described in 2017 based on an embryonic skeleton (nicknamed Baby Louie) and partial nest with large eggs that were discovered from the Gaogou Formation of China between 1992 and 1993.

''Beibeilong'' was a notably large caenagnathid and among the largest oviraptorosaurs, estimated at long with a ponderous weight of about , based on comparisons with the closely related ''Gigantoraptor''. The jaws were toothless and developed a horny beak (also known as rhamphotheca), as in most other oviraptorosaurs. Most of the anatomical traits of ''Beibeilong'' are consistent with caenagnathids rather than oviraptorids, which are two of the major oviraptorosaur families. It is classified within this group, Caenagnathidae, where it occupies a basal (primitive) position.

''Beibeilong'' laid one the largest known type of dinosaur eggs, ''Macroelongatoolithus''. Its eggs measured around in length and had a ruggedly ornamented eggshell surface. The typical ''Macroelongatoolithus'' nest was ring-shaped with one or two layers of eggs, and the center was largely devoid of eggs. It is suggested that giant caenagnathids (like ''Beibeilong'') sat directly in the empty-egg center to avoid egg-crushing because of their massive body dimensions.

History of discovery

Baby Louie

During the late 1980s and early 1990s, Chinese farmers excavated and collected a large amount of fossilized dinosaur eggs from Cretaceous rocks and sediments at the Henan Province (China), Gaogou Formation, many of which were embbeded in sediments. Although Chinese authorities tried to regulate the export and eventual illegal sell of the newly discovered dinosaur eggs, many ended up outside the country away from rightful paleontological research, such as rock and gem shows, markets and/or stores during the early 1990s. While they were kept out of China, many of the blocks containing dinosaur eggs were prepared (cleaned) in other countries, which revealed exceptionally preserved embryos in some cases. Among these, a partial specimen block containing a long embryonic oviraptorosaur skeleton with several large eggs became notoriously renowned, discovered between December 1992 and early 1993 by farmer Mr. Zhang Fengchen. Prior to the preparation of the block, this specimen was in 1993 imported into the United States by The Stone Company, which was responsible for the preparation. Some time later, the specimen was in 1996 featured in the cover article for the National Geographic Magazine where the embryonic skeleton was nicknamed as Baby Louie in honor of Louis Psihoyos, who was the photographer for that article. In 2001 the specimen was ultimately acquired by the Indianapolis Children’s Museum, where it was publicly exhibited for as much as 12 years. Even though the original intention of the museum was to repatriate the specimen to China, it was not until 2013 where agreements and documentation became finalized. Nearly 20 years after its initial discovery, in December 2013 the specimen was finally repatriated to China, permanently resting at the Henan Geological Museum with specimen number/catalogue HGM 41HIII1219.Supplementary Information


Despite the return of HGM 41HIII1219 to China, the whereabouts of its exact locality of excavation remained unknown. In 2015 paleotonlogists Hanyong Pu, Philip J. Currie, Junchang Lü, Eva B. Koppelhus, and Songhai Jia in company of Mr. Zhang Fengchen—who participated in the initial discovery of the specimen—, reexamined the purported type locality of excavation, corresponding to the Heimaogou of the Xixia County in outcrops assigned to the Late Cretaceous Gaogou Formation (Xixia Basin). The team found eggshell fragments that are otherwise identical to those observed in HGM 41HIII1219, effectively establishing the locality of provenance. Finally in 2017, the specimen was formally described by Pu and colleagues, naming the new genus and type species ''Beibeilong sinensis''. The holotype, HGM 41HIII1219, consist of a partial semi-articulated embryonic oviraptorosaur skeleton associated in top of a partial nest of 6-8 ''Macroelongatoolithus'' eggs. They noted that preserved eggs are only a small section/block of what would have been the original nest. The generic name, ''Beibeilong'', is derived from the Chinese Pinyin ''beibei'' (baby) and ''long'' (dragon), meaning "baby dragon". The specific name, ''sinensis'', refers to its country of discovery, China (prefix Sino). With the formal naming of ''Beibeilong'' and description of Baby Louie the team reported that remains attributed to a second embryo were found protruding from inside of one of the eggs.

Description

''Beibeilong'' was one of the largest oviraptorosaurs based on the large ''Macroelongatoolithus'' eggs associated with the holotype embryo, measuring as much as long. It has an estimated adult length of about , with a body mass around or . The dimensions of ''Beibeilong'' were only surpassed or approached by the closely related ''Gigantoraptor''.

Skull

The skull of ''Beibeilong'', like most caenagnathids, was edentulous (toothless) as it lacked alveoli (tooth sockets). The had a rugose texture, likely developing a rhamphotheca (horny beak). The 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 unique trait to ''Beibeilong''. The bones of ''Beibeilong'' were fused around the naris (nostril) openings and had several nutrient foramina (blood vessel attachments) on their external surface. The had an open-crescentic shape that contributed to the anterior border of the orbit (eye socket). A small depression on the top border of the posterior process (bony projection or extension) of the lacrimal allowed the frontal bone to overlap, which was unique to ''Beibeilong''. The was rather domed with formed the upper border of the orbit as well as part of the skull roof. The 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 , being the last bone in contribute to the orbit, was a short, slender, and curved element that extended between the frontal and top process of the jugal. The is tall and nearly triangular bone that is joined by the jugal. Behind the quadratojugal was the , a squared bone of great importance for the motion of the lower jaw.

The 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 had a fairly curved top border and formed a relatively low (bony projection that extends upwards from the upper border of the surangular). It was connected to the top border of the dentary through an articular depression. The developed a convex crest-like articulation for the quadrate, which is mostly common in oviraptorids. In particular, the articular bone of ''Beibeilong'' extended backwards into a retroarticular process that had a characteristic concave posterior facet.

Postcranial skeleton

The centra of some had large pleurocoels (air-filled hollow depressions) on their lateral sides. The cervical neural arches (upper, and pointy vertebral region) of ''Beibeilong'' had low neural spines (bony spines developing upward from the top surface of the neural arch) and were X-shaped in top view. The (hip vertebrae) 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 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 ilium and were united by the (lower ilium protuberance). The shaft of the was relatively skinny and rod-like shaft.

The was robust compared to other bones, somewhat bowed, and elongated, slightly larger than the pubis. Unlike most oviraptorosaurs, its femur lacked a ridge-like feature extending along the shaft between the and the lower mid-condyle in most oviraptorosaurs. Both crest and its condyle were low and poorly defined but connected to each other.

Eggs

The eggs of ''Beibeilong'' are identified as belonging to the oospecies '' Macroelongatoolithus xixiaensis''. They were very elongated with rather rounded poles and/or ends, and measured between in length. In its microscopic composition, the eggshell was a two-layered structure with an outer "continuous" layer and inner "mammillary/cone" layer. Although not considered a layer, the boundary separating both outer and inner layers was notably demarcated, undulatory, and wavy. Eggshell thickness varied from to .

The eggshell of ''Beibeilong'' eggs was ornamented on its external surface, characterized by a rugose texture composed by scattered nodes and additional nodes forming ridge-like structures 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

Pu and team in 2017 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; below is the obtained cladogram by Pu and team:

Paleobiology

Ontogeny

In their 2017 description of ''Beibeilong'', Pu and team compared embryonic Baby Louie to ''Gigantoraptor'', which together represent informative stages in the ontogeny (growth) of giant caenagnathids. Elements like the dentary probably fused together after hatching and this element remained with a consistent size (relative to other skull elements) during the growth of the individual. Although both taxa feature different mandible-to-femur length ratios (∼0.87 ''Beibeilong'' vs. 0.45 ''Gigantoraptor'') indicating difference in relative skull sizes, it is most likely that these are product of their respective growth stages.

Shuo Wang and colleagues in 2018 concluded that caenagnathids experienced a dietary shift as they grew up, based on several features in the dentaries of caenagnathids (lateral occlusal grooves and ridges on the occlusal surfaces, interpreted as vestigial tooth sockets). Accordingly, caenagnathids had teeth when young and were progressively lost during their growth. However, the perinate Baby Louie specimen of ''Beibeilong'' lack some these in spite of its young age. Wang and team suggested three scenarios for explaining the lack of vestigial alveoli in ''Beibeilong'', arguing that this taxon was an strictly edentulous; teeth were indeed present in ''Beibeilong'' but were lost before eruption of the null generation of teeth; or, that teeth erupted later and were lost at a much higher rate in ''Beibeilong'' than other caenagnathids, therefore, vestigial tooth structures should be preserved in more mature specimens.

In 2019, Gregory F. Funston with team strongly rejected this interpretation and hypothesis concerning the ontogeny of caenagnathids. They indicated that the phylogeny of Caenagnathidae, along with other primitive oviraptorosaurs such as ''Avimimus'', strongly implies that simple dentaries lacking complex structures (such as vestigial alveoli) are the ancestral condition of caenagnathids. The second point made by Wang and colleagues was also considered unlikely, because it would require a slowdown in the development of a horny beak, which would in turn require caenagnathids to reacquire functional teeth from an edentulous ancestor, and also teeth would offer no adaptive benefit. Lastly, Funston and team rejected the third scenario given that ''Gigantoraptor''—which is mostly similar to ''Beibeilong'', and represents a very mature giant caenagnathid—lacks any occlusal ridges or grooves, hence disproving the hypothesis that ''Beibeilong'' and other caenagnathids had teeth and lost them during ontogeny.

Reproduction

Pu and team in 2017, based on comparisons with other ''Macroelongatoolithus'' egg clutches, noted that the arrangement and size of the eggs associated with ''Beibeilong'' (HGM 41HIII1219) indicates that the original nest would have been large and ring-shaped with a center devoid of eggs. The nest of ''Beibeilong'' was composed of two layers of eggs, despite other ''Macroelongatoolithus'' nests preserving only a single layer of eggs. When brooding the nest, the adult would have sat in the centre of the clutch, as also proposed for the smaller oviraptorids. Most notably, the team suggested that the entire ''Beibeilong'' nest was likely in an advanced stage of incubation when it was buried given that perinate skeletal remains were found in association with 2–3 eggs in the block specimen, including Baby Louie itself. They also noted that ''Macroelontaoolithus'' (including eggs associated with ''Beibeilong'') and other elongatoolithid eggs/nests are very similar in clutch configuration, overall morphology, as well as eggshell texture and histology. These traits indicate that both caenagnathids and oviraptorids probably had fairly comparable nesting behaviours, but also that these features are ancestral for at least the whole Caenagnathoidea (superfamily containing both Caenagnathidae and Oviraptoridae).

In 2018, Kohei Tanaka and team examined several egg clutches of numerous oviraptorosaur specimens, including egg clutches assigned to ''Macroelongatoolithus'', in order to evaluate how the nest configuration correlates to the body size in oviraptorosaur incubation behaviour. Eggshell porosity reflects that eggs of almost certainly all oviraptorosaurs were exposed in the nest without an external covering. Though most oviraptorosaur nests have eggs arranged in a circular fashion, the morphology of the nest is different in smaller and larger species. Small-bodied oviraptorosaurs (such as oviraptorids with small ''Elongatoolithus'' eggs) arranged their nests packed with eggs and a rather small nest center. In contrast, large-bodied oviraptorosaurs (like ''Beibeilong'' or ''Gigantoraptor'' with large ''Macroelongatoolithus'' eggs) built their nests in a ring-like fashion with a considerably large center devoid of eggss. These nest strategies indicate that whereas small-sized oviraptorosaurs sat directly on the eggs, gigantic oviraptorosaurs, such as ''Beibeilong'' or ''Gigantoraptor'', likely sat on the central area devoid of eggs. Tanaka and colleagues pointed out that this adaptation was beneficial to avoid egg-crushing because of the body dimensions of nesting adults, and also could have allowed some body-contact during incubation in these giant oviraptorosaurs.Supplemental Material
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Paleoenvironment

''Beibeilong'' remains have been recovered from the Gaogou Formation located in the Xixia Basin, a unit that dates back to the Late Cretaceous epoch about 96 million and 88 million years ago (Cenomanian-Coniacian stages). This unit is separated into three members: an upper member characterized by alluvial fan and traction current deposits; and the middle and lower members including terrigenous clastic rocks belonging to alluvial fan and braided river sedimentation of intermittent muddy waters. The overall sedimentation across the Gaogou Formation, made up by floodplain and lacustrine conglomerates, sandstones and mudstones, indicate a dry subtropical or tropical climate during deposition. The geological horizon in which Baby Louie was found is interpreted as a flat and wide alluvial fan with subfacies-flowing microfacies.

Examinations made to the δ13C levels in several eggshells from the Gaogou Formation suggest that herbivorous dinosaurs of the Gaogou Formation paleoecosystem feed mainly on C3 plants and C4 plants, which also indicates sub-humid or sub-arid climate settings. Moreover, numerous scattered amber remains of conifer origin indicate that Araucariaceae was largely present in the Northern Hemisphere of Asia during the Late Cretaceous, such as the paleoenvironments in which ''Beibeilong'' lived. The repeated presence of giant caenagnathids (such as the Bayan Shireh caenagnathid or ''Gigantoraptor'') in fluvial-based sedimentation of geological formations suggests that these large oviraptorosaurs preferred mesic habitats (well-watered) habitats over xeric (desertic) ones. Nevertheless, geological evidence from volcanic rocks of the Xionger Mountain found at the Zhaoying Village (where outcrops of the Gaogou Formation are present) indicates that the Gaogou paleoecosystem underwent hostile climate changes, characterized by a drying tendency. Changes in the humidity and precipitation levels negatively altered the paleoflora as well as both river and flood plain paleoenvironments, forcing herbivorous organisms to migrate between the foot of the mountain and flood plains. When the precipitation levels rose, the water bodies and flood plains became repopulated. In addition, carbonate carbon/oxygen isotope analyses indicate that extended periods of climatic changes ultimately deteriorated the Gaogou Formation paleoecosystem as a whole, triggering the loss of foliage cover and by extend the extinction of the local herbivorous dinosaurs. Many of the fossilized eggs across this formation were likely unable to hatch due to the paleoenvironmental conditions.

The Gaogou Formation is extremely abundant in fossilized eggs, mostly those of dinosaurs and turtles. Other remains include multiple invertebrate taxa comprising fresh water non-marine bivalves, gastropods, ostracods, and abundant insect ichnotaxa (fossilized traces left by insect activity). Additional vertebrate taxa found in this unit include the sauropod ''Baotianmansaurus'', and the nanhsiungchelyid turtle '' Yuchelys''.

Taphonomy

The preservation state of Baby Louie indicates that this embryo was lying outside its parent egg when it was buried, and its orientation which is inconsistent with that of the eggs suggests that an external force removed it from its underlying egg to the eggs at the top. Elements like the skull have been damaged due to scavenging and erosion. For instance, the entire skull has collapsed into a horizontal layer, where bones from the right side are best visible, and the premaxillae and dentary tips were partially destroyed after the individual died. There are, however, indications of postmortem scavenging damage left by either osteophagous or boring (borings; tunnel-like holes) insects in skeletal areas, such as the lower portion of the right leg, ilium, upper end of femur, and others. In addition, numerous borings and other elongated burrows left by those organisms are found across Baby Louie. Most skeletal elements are disarticulated, such as the left dentary, overall neck, abdominal region, and limb elements. While not visible, it is suggested that the tail could lie underneath the rest of the body and/or matrix, or alternatively it was ripped off by scavenging predators.

See also

* Timeline of oviraptorosaur research

References

External links

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{{Taxonbar, from=Q29877274

Late Cretaceous dinosaurs of Asia
Oviraptorosaurs
Fossil taxa described in 2017