Beibeilong

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Beibeilong
Temporal range:
Ma
Skeleton and line drawing of Baby Louie
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Superfamily: †Caenagnathoidea
Family: †Caenagnathidae
Genus: †Beibeilong
Pu et al., 2017
Type species
†Beibeilong sinensis
Pu et al., 2017

Beibeilong (

Henan Province
) between 1992 and 1993.

Beibeilong was a notably large caenagnathid and among the largest

oviraptorids, another diverse oviraptorosaur family. Within Caenagnathidae it occupies a basal
(primitive) position.

Beibeilong laid one the largest known types of dinosaur eggs,

semi-arid to tropical climates
.

History of discovery

Map locality of HGM 41HIII1219, red star represents the discovery site

During the late 1980s and early 1990s,

oviraptorosaur skeleton with several large eggs—discovered between December 1992 and early 1993 by farmer Zhang Fengchen—became well-known to the public and scientific communities.[1]

In 1993, that block was imported into the

Henan Geological Museum.[1]

Unprepared (left) and prepared (right) block of HGM 41HIII1219

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).[1]

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

generic name, Beibeilong, is derived from the pinyin transliteration for the Chinese 贝贝 (bèibei) and the word 龙 (lóng), 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.[1]

Description

Beibeilong estimated adult size and eggs compared to a 1.8 m (5.9 ft) tall human

Beibeilong was one of the largest oviraptorosaurs. Its body size has been extrapolated from the large Macroelongatoolithus eggs associated with the holotype embryo.[1] It had an estimated adult length of about 7.5 m (25 ft),[3][4] with a body mass around 1.5–2 metric tons (1.7–2.2 short tons).[5][6] The dimensions of Beibeilong were only surpassed or approached by the closely related Gigantoraptor.[7]

Like other caenagnathids, Beibeilong would have been

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.[8][9] It is well-known that many oviraptorosaur species had feathers,[10] including caenagnathids such as Apatoraptor.[11] As for gigantic oviraptorosaurs (like Gigantoraptor), it has been suggested that some of this integument was reduced due to their body dimensions.[7]

Skull

Skull (a, b, c) and pelvic girdle (d) details of embryonic Beibeilong

The

naris (nostril) openings. The nasals also had several nutrient foramina (blood vessel attachments) on their external surface. The lacrimal (straight bone in front of the orbit) had an open-crescentic shape contributing to the anterior border of the orbit (eye socket).[1]

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 frontal was a rather domed bone and formed the upper border of the orbit as well as part of the skull roof. The jugal ("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 postorbital (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 quadratojugal was a tall and nearly triangular bone that was joined by the jugal. Behind the quadratojugal was the quadrate, a squared bone of great importance for the motion of the lower jaw.[1]

The

oviraptorids. Distinctively, the articular bone of Beibeilong extended backwards into a retroarticular process that had a characteristic concave posterior facet.[1]

Postcranial skeleton

Life restoration of embryonic Beibeilong, based on Baby Louie

The

pleurocoels (air-filled hollow depressions) on their 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 sacrum (hip vertebrae fused into a compact structure) of Beibeilong was formed by six sacral vertebrae. The scapula was strap-like and co-joined by the furcula.[1]

Hindlimb details of embryonic Beibeilong

The ilium was a large pelvic bone with a gently convex top border, and its preacetabular process (a recurved anterior ilium expansion, also known as "ala") was longer than the squared off postacetabular process/blade (posterior ilium expansion), another distinct feature of Beibeilong. The acetabulum (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 pubis were united by the pubic peduncle (lower ilium protuberance). The shaft of the ischium was a relatively skinny and rod-like shaft.[1]

The femur (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 lesser trochanter 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 tibia (shinbone) lacked the distinctive boss that is present on the lower end of the cnemial crest in most oviraptorosaurs. Both the fibular crest and its condyle were connected to each other, low, and poorly defined.[1]

Eggs

Eggshell surface (a) and microstructure (b) of a Beibeilong egg

The

Macroelongatoolithus xixiaensis—the largest known type of dinosaur eggs—and, specifically, to giant caenagnathids. They were very elongated with rather rounded poles or ends, and measured between 40–45 cm (16–18 in) 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 1.7 mm (0.17 cm) to 2.56 mm (0.256 cm).[1]

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.[1]

Classification

In 2017, Pu and team considered Beibeilong to have been anatomically similar to, but more

Heyuanninae subfamily).[8] 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.[12][9] Despite their differences, it is known that both groups convergently developed cranial crests.[12]

Skeletal diagrams featuring several members of Caenagnathidae

Below is the obtained cladogram by Pu and team in 2017:[1]

Caenagnathidae

Microvenator celer

unnamed

Beibeilong sinensis

unnamed

Gigantoraptor erlianensis

unnamed

Epichirostenotes aurrier

Anzu wyliei

Hagryphus giganteus

Chirostenotes pergracilis

Apatoraptor pennatus

Elmisaurus rarus

Leptorhynchos elegans

Caenagnathus collinsi

Caenagnathasia martinsoni

Paleobiology

Ontogeny

Embryonic stage of Beibeilong compared to siamese crocodile embryos

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 at their symphysis (i.e., left and right sides cartilaginously fused together at their union) after hatching and retained a consistent size relative to other skull elements during the growth of the individual. Although both genera feature different mandible-to-femur length ratios (approximately 0.87 in Beibeilong vs. 0.45 in Gigantoraptor), indicating differences in relative skull sizes, it is most likely that these result from their respective growth stages.[1]

Shuo Wang and colleagues have concluded that caenagnathids experienced a dietary shift as they aged, based on several features in the dentaries (lateral occlusal grooves and ridges on the occlusal surfaces, interpreted as vestigial tooth sockets). According to the team, juvenile caenagnathids had teeth that were progressively lost during growth. Noting that the perinate Baby Louie specimen of Beibeilong lacks some of these features in the dentary, despite its young age, Wang and team have suggested three scenarios to explain the lack of vestigial alveoli in Beibeilong: (1) that this taxon may have been strictly edentulous; (2) that teeth were indeed present in Beibeilong but were lost before eruption of the null generation of teeth; or (3) that teeth erupted later and were lost at a much higher rate in Beibeilong than other caenagnathids. Thus, the team concluded that vestigial tooth structures should be preserved in more mature specimens.[13]

Speculative life restoration of adult Beibeilong based on other caenagnathids

Gregory F. Funston and colleagues have rejected Wang and colleagues' hypothesis. They have argued that the phylogeny of Caenagnathidae, along with other primitive oviraptorosaurs such as Avimimus, implies that simple dentaries lacking complex structures (such as vestigial alveoli) are the ancestral condition of caenagnathids. They have also rejected the second scenario proposed by Wang and colleagues because it would require a slowdown in the development of the horny beak, which would in turn require caenagnathids to reacquire functional teeth from an edentulous ancestor, and that teeth would offer no adaptive benefit. Lastly, Funston and team have rejected the third scenario given that Gigantoraptor—which is 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.[14]

Reproduction

Beibeilong holotype egg block, showing number of preserved Macroelongatoolithus eggs
Nearly complete Macroelongatoolithus nest (specimen 41HV003-16), showing the complete structure of such nests

Based on comparisons with other Macroelongatoolithus egg clutches, Pu and team have noted that the arrangement and size of the eggs associated with Baby Louie indicates that the original

oviraptorids. Most notably, the team has suggested that the entire Beibeilong nest receoved with Baby Louie 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. They also have noted that Macroelontaoolithus (including eggs associated with Beibeilong) and other elongatoolithid eggs and nests are similarly arranged in clutch configuration and 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).[1]

Kohei Tanaka and team have 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 behavior. Eggshell porosity reflects that eggs of almost all oviraptorosaurs were exposed in the nest without an external covering, such as a substrate. Though most oviraptorosaur nests have eggs arranged in a circular fashion, the morphology of the nest differs in smaller and larger species. Small-bodied oviraptorosaurs (such as oviraptorids with small Elongatoolithus eggs) arranged their nests in a tightened ring-like fashion packed with eggs and a rather small nest center devoid of eggs. Similarly, large-bodied oviraptorosaurs (like Beibeilong or Gigantoraptor with large Macroelongatoolithus eggs) built their nests with a ring-like architectur; however, such nests were not over-packed with eggs and the center was proportionally much larger. 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 have stated that this adaptation would have been beneficial in avoiding egg-crushing because of the body dimensions of nesting adults, and also could have allowed some body contact during incubation in giant oviraptorosaurs.[5]

Although associations of nest-adult oviraptorosaurs (a product of catastrophic live burial events) are generally considered as indicating direct brooding contact incubation, differences in egg numbers and orientation, as well as their overall architecture, suggests that most adult oviraptorosaurs were not necessarily incubating the nest; Tzu-Ruei Yang and colleagues have suggested that these nest-adult associations may represent female oviraptorosaurs in—or after—the process of

oviposition (laying of eggs), or alternatively that female oviraptorosaurs guarded their nests.[15]

Paleoenvironment

Zhang Fengchen, one of the discoverers, at the excavation locality of embryonic Baby Louie

Beibeilong was discovered in the Gaogou Formation, which dates back to the Late Cretaceous epoch,

lacustrine conglomerates, sandstones, and mudstones, indicates a dry subtropical or tropical climate during deposition.[17] The geological horizon in which Baby Louie was found is interpreted as a flat and wide alluvial fan.[16]

The

herbivorous dinosaurs fed mainly on C3 and C4 plants with proportions of 61% and 39%, respectively. The higher ratio of C3 over C4 plants indicates sub-humid or sub-arid climate settings.[18] In addition, numerous scattered amber remains of conifer origin from Gaogou indicate that Araucariaceae were largely present in the Northern Hemisphere of Asia during the Late Cretaceous, including the paleoenvironments in which Beibeilong lived.[19] 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 (well-watered) over xeric (desertic) habitats.[20]

foliage cover and the extinction of the local herbivorous dinosaurs. Many of the fossilized eggs across this formation were possibly unable to hatch due to the paleoenvironmental conditions.[21]

The Gaogou Formation is extremely abundant in fossilized eggs, mostly of dinosaurs and

nanhsiungchelyid turtle Yuchelys.[17]

Taphonomy

Children's Museum of Indianapolis

The preservation state of Baby Louie indicates that the embryo was lying outside its parent egg when it was buried. Its orientation, which is inconsistent with that of the eggs, suggests that an external force pushed it from its underlying egg to the eggs at the top. Elements like the skull have been damaged due to

predators.[1]

See also

References

  1. ^
    PMID 28486442. Supplementary Information Archived 2023-01-20 at the Wayback Machine
    .
  2. ^ Currie, P. J. (1996). "The Great Dinosaur Egg Hunt". National Geographic. Vol. 189, no. 5. pp. 96–111.
  3. ^ Engelhaupt, E. (November 3, 2017). "'Baby Dragon' Dinosaur Found Inside Giant Egg". National Geographic. Archived from the original on January 20, 2023. Retrieved January 20, 2023.
  4. ISSN 0018-165X. Archived
    from the original on November 10, 2022. Retrieved May 14, 2023.
  5. ^
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    S2CID 6649123. Supplementary Information Archived 2022-10-06 at the Wayback Machine
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  16. ^ a b Pan, Z.; Xu, L.; Pu, H.; Jia, S.; Lü, J.; Zhou, S.; Chang, H.; Zhang, H.; Yang, L. (2016). “路易贝贝”产出层位时代及其古环境 [The Geological Age and Paleoenvironment of Baby Louie-Bearing Strata]. Geological Bulletin of China (in Simplified Chinese). 35 (12): 1961–1966.
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  24. ^ Chen, J.; Wang, D.; Feng, J.; Fu, G.; Zhu, S. (2007). "Late Cretaceous Non-Marine Bivalves from the Dinosaur Egg-Bearing Strata of Xixia Basin,Henan,China" 河南西峡盆地晚白垩世含恐龙蛋地层中的双壳类 [Late Cretaceous Non-marine Bivalves from the Dinosaur Egg-Bearing Strata of Xixia Basin, Henan, China]. Acta Palaeontologica Sinica (in Simplified Chinese). 46 (3): 299–313 – via China/Asia On Demand.
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External links
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