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Beipiaosaurus inexpectus
Cretaceous Herbivore

Beipiaosaurus

Beipiaosaurus inexpectus

"Beipiao lizard, unexpected"

Period
Cretaceous · Aptiano
Lived
125–124 Ma
Length
up to 2.2 m
Estimated weight
85 kg
Country of origin
China
Described in
1999 by Xu Xing, Tang Zhi-Lu e Wang Xiao-Lin (IVPP, Beijing)

About this species

Beipiaosaurus inexpectus is a basal therizinosauroid from the Early Cretaceous (early Aptian, around 125 to 124 million years ago) Yixian Formation, Jianshangou Bed, near Sihetun (Beipiao, western Liaoning, China). It reached about 2.2 m in length and preserved two integumentary types: short slender filaments similar to those of Sinosauropteryx, and elongated broad filamentous feathers (EBFFs) 10 to 15 cm long, likely used for display. It was the first therizinosaur shown to bear a feather-like covering, confirming that the group, long interpreted as a late-surviving prosauropod relative, nests among maniraptoran coelurosaurs.

Geological formation & environment

Yixian Formation, Jehol Group, western Liaoning Province, northeastern China. Beipiaosaurus comes from the Jianshangou Bed, near Sihetun, in Beipiao County. Recent 40Ar/39Ar dates (Chang et al. 2017) constrain unit deposition between about 125.8 and 124.1 Ma, corresponding to the early Aptian stage of the Early Cretaceous. It is a volcanosedimentary succession with shallow lakes and tuff layers, producing a world-famous Konservat-Lagerstätte. The same unit yields feathered dinosaurs (Sinosauropteryx, Caudipteryx, Sinornithosaurus), early birds (Confuciusornis), mammals (Eomaia, Repenomamus), pterosaurs, fish, insects and the earliest aquatic angiosperms (Archaefructus).

Image gallery

Ecology and behavior

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Habitat

Margins of volcanic lakes in inland northeastern China, under a cool to cold-temperate climate with recurrent volcanic ash bursts that rapidly buried organisms and generated the Jehol Biota Lagerstätten. Vegetation was dominated by conifers, ginkgoaleans, cycadophytes and the earliest aquatic angiosperms of Archaefructus.

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Feeding

Small to medium-sized herbivore. The small head, long neck and elongated manual claws suggest that it used its hands to pull branches and foliage, probably feeding on leaves, buds and cones of conifers and ginkgos. Small leaf-shaped teeth confirm a plant diet.

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Behavior and senses

Likely bipedal, with upright posture and a tail used as a counterweight; less agile than more gracile maniraptorans. The long EBFFs on neck and back support a role in visual display, perhaps for intraspecific recognition or courtship.

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Physiology and growth

The double filamentous cover (short filaments plus EBFFs) is consistent with at least facultative endothermy and primarily with thermal insulation and display functions. The low-diversity preserved melanosomes indicate a relatively uniform brownish-red colouration.

Paleogeography

Continental configuration

Mapa paleogeográfico do Cretáceous (~90 Ma)

Ron Blakey · CC BY 3.0 · Cretáceous, ~90 Ma

During the Aptiano (~125–124 Ma), Beipiaosaurus inexpectus inhabited Laramidia, the western half of present-day North America, separated from the east by the Western Interior Seaway, a shallow sea dividing the continent. The continents were in very different positions: India was drifting toward Asia, Antarctica was still connected to Australia, and South America was an isolated island.

Bone Inventory

Estimated completeness 55%

Holotype IVPP V11559 is a partial subadult skeleton with an incomplete skull, girdles, partial limbs and vertebrae preserved, plus integumentary filaments. Referred specimens STM 31-1 and BMNHC PH000911 add cranial material and, most importantly, extensive impressions of EBFF feathers on the neck and trunk. Together, the three specimens allow reconstruction of about 55% of the skeleton and most of the animal's filamentous cover.

Found (11)
Inferred (6)
Esqueleto de dinossauro — theropod
Wikimedia Commons (Jaime Headden) CC BY 3.0

Found elements

crânio parcial com mandíbulavértebras cervicaisvértebras dorsaisvértebras sacraisvértebras caudais anteriores e distais coossificadas (estrutura tipo pigostilo)cintura peitoral (escápulas e coracoides)cintura pélvica (ílios, ísquios, púbis)membros anteriores parciais (úmeros, rádios, ulnas, manus com garras)membros posteriores parciais (fêmures, tíbias, fíbulas, metatarsais)filamentos integumentares curtos preservadospenas filamentosas largas e alongadas (EBFFs) no pescoço e tronco em espécimes referidos

Inferred elements

parte do crânio anterior (pré-maxila, porções do maxilar)porções distais da cauda entre os segmentos preservadosautopódio anterior completoautopódio posterior completocostelas completasgastrália

Scientific Literature

15 papers in chronological order — from the original description to recent research.

1993

The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People's Republic of China

Russell, D.A. e Dong, Z.-M. · Canadian Journal of Earth Sciences 30(10), 2107-2127

Description of Alxasaurus elesitaiensis, an Early Cretaceous therizinosauroid from Inner Mongolia. It frames the group before the description of Beipiaosaurus and provides the comparative baseline that eventually places therizinosaurs among theropods.

Size comparison of Alxasaurus elesitaiensis with an adult human, the taxon described by Russell and Dong (1993) that provided the baseline for therizinosauroids before Beipiaosaurus.

Size comparison of Alxasaurus elesitaiensis with an adult human, the taxon described by Russell and Dong (1993) that provided the baseline for therizinosauroids before Beipiaosaurus.

Comparative skeletal reconstructions of several therizinosaurs, a group whose boundaries were first outlined by Russell and Dong (1993) based on Alxasaurus.

Comparative skeletal reconstructions of several therizinosaurs, a group whose boundaries were first outlined by Russell and Dong (1993) based on Alxasaurus.

1999

A therizinosauroid dinosaur with integumentary structures from China

Xu, X., Tang, Z.-L. e Wang, X.-L. · Nature 399, 350-354

Original description of Beipiaosaurus inexpectus based on holotype IVPP V11559 collected at Sihetun (Yixian Formation). The paper documents integumentary filaments similar to those of Sinosauropteryx and provides the first direct evidence that therizinosauroids belong to Coelurosauria, radically repositioning the group.

Holotype IVPP V11559 of Beipiaosaurus inexpectus, the basis of the original description by Xu, Tang and Wang (1999, Nature 399:350). The specimen preserves integumentary filaments alongside postcranial skeletal elements.

Holotype IVPP V11559 of Beipiaosaurus inexpectus, the basis of the original description by Xu, Tang and Wang (1999, Nature 399:350). The specimen preserves integumentary filaments alongside postcranial skeletal elements.

Composite skeletal reconstruction of Beipiaosaurus inexpectus based on IVPP V11559 and STM 31-1. The animal reached about 2.2 m and was described as a basal therizinosauroid in Xu et al. (1999).

Composite skeletal reconstruction of Beipiaosaurus inexpectus based on IVPP V11559 and STM 31-1. The animal reached about 2.2 m and was described as a basal therizinosauroid in Xu et al. (1999).

Figure 1: Beipiaosaurus inexpectus (V11559, holotype).

Figure 1: Beipiaosaurus inexpectus (V11559, holotype).

Figure 2: Beipiaosaurus inexpectus .

Figure 2: Beipiaosaurus inexpectus .

Figure 3: Beipiaosaurus inexpectus .

Figure 3: Beipiaosaurus inexpectus .

Figure 4: Phylogenetic relationships of Beipiaosaurus inexpectus .

Figure 4: Phylogenetic relationships of Beipiaosaurus inexpectus .

2001

First definitive therizinosaurid (Dinosauria; Theropoda) from North America

Kirkland, J.I. e Wolfe, D.G. · Journal of Vertebrate Paleontology 21(3), 410-414

Description of Nothronychus mckinleyi from the Late Cretaceous of New Mexico, the first unequivocal therizinosaurid outside Asia. It extends the group's range to North America and broadens the global context in which Beipiaosaurus, described two years earlier, is framed.

Life reconstruction of Nothronychus, a North American therizinosaurid. Kirkland and Wolfe (2001) established that the clade, to which Beipiaosaurus had already been linked, extended into North America in the Late Cretaceous.

Life reconstruction of Nothronychus, a North American therizinosaurid. Kirkland and Wolfe (2001) established that the clade, to which Beipiaosaurus had already been linked, extended into North America in the Late Cretaceous.

Ilium comparison among therizinosauroids discussed after Kirkland and Wolfe (2001), illustrating the group's morphological diversity and the basal position of Beipiaosaurus.

Ilium comparison among therizinosauroids discussed after Kirkland and Wolfe (2001), illustrating the group's morphological diversity and the basal position of Beipiaosaurus.

2003

Pygostyle-like structure from Beipiaosaurus (Theropoda, Therizinosauroidea) from the Lower Cretaceous Yixian Formation of Liaoning, China

Xu, X., Cheng, Y.-N., Wang, X.-L. e Chang, C.-H. · Acta Geologica Sinica (English Edition) 77(3), 294-298

Reports five co-ossified distal caudals in a Beipiaosaurus specimen, forming a pygostyle-like structure. Documents filaments on the tail but no rectrices, suggesting that the pygostyle's ancestral function was not linked to specialised tail feathers.

Sacral and caudal vertebrae of the Beipiaosaurus holotype IVPP V11559. Xu and colleagues (2003) described a bird-like pygostyle-like structure at the tail tip, but with no associated rectrices.

Sacral and caudal vertebrae of the Beipiaosaurus holotype IVPP V11559. Xu and colleagues (2003) described a bird-like pygostyle-like structure at the tail tip, but with no associated rectrices.

Wrist region of Beipiaosaurus. Early works such as Xu et al. (2003) explored several anatomical blocks of the holotype and referred specimens to underpin inferences about its phylogenetic position.

Wrist region of Beipiaosaurus. Early works such as Xu et al. (2003) explored several anatomical blocks of the holotype and referred specimens to underpin inferences about its phylogenetic position.

2007

A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)

Senter, P. · Journal of Systematic Palaeontology 5(4), 429-463

Phylogenetic review of Coelurosauria that retains Therizinosauroidea as the total-group name for therizinosaurs, with Beipiaosaurus in a basal position. Sets one of the benchmark scenarios for the taxon's placement within Maniraptora in the late 2000s.

Life reconstruction of Beipiaosaurus inexpectus with filamentous integumentary cover, part of comparative iconography used in Coelurosauria phylogenetic reviews such as Senter (2007).

Life reconstruction of Beipiaosaurus inexpectus with filamentous integumentary cover, part of comparative iconography used in Coelurosauria phylogenetic reviews such as Senter (2007).

Comparison of mandibular morphology among therizinosaurians. Senter's (2007) coelurosaur analysis retains Beipiaosaurus as a basal therizinosauroid, consistent with its lightly specialised jaw.

Comparison of mandibular morphology among therizinosaurians. Senter's (2007) coelurosaur analysis retains Beipiaosaurus as a basal therizinosauroid, consistent with its lightly specialised jaw.

2009

A new feather type in a nonavian theropod and the early evolution of feathers

Xu, X., Zheng, X.-T. e You, H.-L. · Proceedings of the National Academy of Sciences (PNAS) 106(3), 832-834

Describes two feather types in Beipiaosaurus: short slender filaments and EBFFs (elongated broad filamentous feathers), 10 to 15 cm long, single-filament structures consistent with stage I of the feather-evolution model. It strengthens a display function rather than a thermoregulatory one for these early structures.

Figure 1 of Xu et al. (2009, PNAS): EBFFs preserved in Beipiaosaurus STM 31-1, showing long broad single filaments distributed along head, neck and trunk.

Figure 1 of Xu et al. (2009, PNAS): EBFFs preserved in Beipiaosaurus STM 31-1, showing long broad single filaments distributed along head, neck and trunk.

Figure 2 of Xu et al. (2009, PNAS): comparison of filaments from Beipiaosaurus and other feathered theropods such as Sinosauropteryx, Dilong and Sinornithosaurus, illustrating early feather diversity.

Figure 2 of Xu et al. (2009, PNAS): comparison of filaments from Beipiaosaurus and other feathered theropods such as Sinosauropteryx, Dilong and Sinornithosaurus, illustrating early feather diversity.

2009

A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution

Zanno, L.E., Gillette, D.D., Albright, L.B. e Titus, A.L. · Proceedings of the Royal Society B 276(1672), 3505-3511

Description of Nothronychus graffami from the Late Cretaceous of Utah and phylogenetic reanalysis of Therizinosauria. The authors discuss herbivory as a recurrent phenomenon among maniraptoran theropods, with Beipiaosaurus representing one of the most basal and earliest records of this dietary shift.

Figure 1 of Zanno et al. (2009, Proc. R. Soc. B): skeletal reconstruction of Nothronychus graffami (UMNH VP 16420) with preserved elements in white, direct context for herbivory in therizinosaurs descended from the Beipiaosaurus lineage.

Figure 1 of Zanno et al. (2009, Proc. R. Soc. B): skeletal reconstruction of Nothronychus graffami (UMNH VP 16420) with preserved elements in white, direct context for herbivory in therizinosaurs descended from the Beipiaosaurus lineage.

Figure 2 of Zanno et al. (2009, Proc. R. Soc. B): time-calibrated phylogeny of 76 coelurosaurs with dietary interpretation, including Therizinosauria as a basal herbivorous clade to which Beipiaosaurus belongs.

Figure 2 of Zanno et al. (2009, Proc. R. Soc. B): time-calibrated phylogeny of 76 coelurosaurs with dietary interpretation, including Therizinosauria as a basal herbivorous clade to which Beipiaosaurus belongs.

2010

A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora)

Zanno, L.E. · Journal of Systematic Palaeontology 8(4), 503-543

Comprehensive alpha-taxonomic and phylogenetic review of Therizinosauria, with formal redefinitions of Therizinosauria, Therizinosauroidea and Therizinosauridae. It confirms Beipiaosaurus as a basal therizinosauroid and a key branch for understanding the origin of the herbivorous lineage within Maniraptora.

Falcarius utahensis, basal therizinosauroid used to reconstruct primitive morphology of the clade.

Falcarius utahensis, basal therizinosauroid used to reconstruct primitive morphology of the clade.

Morphological variation of the pelvic girdle among therizinosaurians, a central character in Zanno's (2010) review and a diagnostic trait used to separate basal therizinosauroids such as Beipiaosaurus.

Morphological variation of the pelvic girdle among therizinosaurians, a central character in Zanno's (2010) review and a diagnostic trait used to separate basal therizinosauroids such as Beipiaosaurus.

2011

Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution

Zanno, L.E. e Makovicky, P.J. · Proceedings of the National Academy of Sciences (PNAS) 108(1), 232-237

Quantitative analysis of herbivorous ecomorphology in theropods, with strong Therizinosauria representation. It demonstrates the independent acquisition of herbivory across multiple coelurosaur lineages and places Beipiaosaurus as a window into the onset of this process in the Early Cretaceous.

Nothronychus mckinleyi, derived North American therizinosauroid, comparative basis for herbivory.

Nothronychus mckinleyi, derived North American therizinosauroid, comparative basis for herbivory.

Manual ungual comparison among therizinosauroids. The elongated claws, compatible with herbivory for pulling branches and foliage, are among the key characters discussed in Zanno and Makovicky (2011).

Manual ungual comparison among therizinosauroids. The elongated claws, compatible with herbivory for pulling branches and foliage, are among the key characters discussed in Zanno and Makovicky (2011).

2013

An unusual basal therizinosaur dinosaur with an ornithischian dental arrangement from northeastern China

Pu, H., Kobayashi, Y., Lü, J., Xu, L., Wu, Y., Chang, H., Zhang, J. e Jia, S. · PLOS ONE 8(5), e63423

Description of Jianchangosaurus yixianensis, a basal therizinosauroid from the Yixian Formation (Liaoning) nearly contemporaneous with Beipiaosaurus. It preserves an articulated skeleton and integumentary filaments, broadening the sample of early therizinosaurs. Some authors discuss whether it is a junior synonym of Beipiaosaurus.

Figure 1 of Pu et al. (2013, PLOS ONE): articulated skeleton (A) and interpretive drawing (B) of Jianchangosaurus yixianensis (41HIII-0308A), a basal therizinosaur from the Yixian Formation coeval with Beipiaosaurus.

Figure 1 of Pu et al. (2013, PLOS ONE): articulated skeleton (A) and interpretive drawing (B) of Jianchangosaurus yixianensis (41HIII-0308A), a basal therizinosaur from the Yixian Formation coeval with Beipiaosaurus.

Figure 11 of Pu et al. (2013, PLOS ONE): filamentous feathers preserved on Jianchangosaurus, directly comparable to the filaments and EBFFs reported in Beipiaosaurus from the same formation.

Figure 11 of Pu et al. (2013, PLOS ONE): filamentous feathers preserved on Jianchangosaurus, directly comparable to the filaments and EBFFs reported in Beipiaosaurus from the same formation.

Figure 1. A photograph of the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. (41HIII-0308A) (A) and line drawing (B).

Figure 1. A photograph of the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. (41HIII-0308A) (A) and line drawing (B).

Figure 2. A, Reconstruction the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. The hip height is approximately 1 meter.

Figure 2. A, Reconstruction the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. The hip height is approximately 1 meter.

Table 1. Measurements in millimeters of selected portions of Jianchangosaurus yixianensis gen. et sp. nov. (41HIII-0308A).

Table 1. Measurements in millimeters of selected portions of Jianchangosaurus yixianensis gen. et sp. nov. (41HIII-0308A).

Figure 3. Photograph of the skull of Jianchangosaurus yixianensis gen. et sp. nov. (A) and line drawing (B).

Figure 3. Photograph of the skull of Jianchangosaurus yixianensis gen. et sp. nov. (A) and line drawing (B).

2014

Melanosome evolution indicates a key physiological shift within feathered dinosaurs

Li, Q., Clarke, J.A., Gao, K.-Q., Zhou, C.-F., Meng, Q., Li, D., D'Alba, L. e Shawkey, M.D. · Nature 507(7492), 350-353

A broad study of melanosomes preserved in fossils shows that Beipiaosaurus had low-diversity melanosomes consistent with uniform brownish-red tones. With the appearance of pennaceous feathers, melanosome diversity increases sharply, suggesting a physiological shift linked to the origin of flight.

Life reconstruction of Beipiaosaurus by Matt Martyniuk. Li et al. (2014) suggest uniform brownish-red tones for the taxon based on preserved melanosomes.

Life reconstruction of Beipiaosaurus by Matt Martyniuk. Li et al. (2014) suggest uniform brownish-red tones for the taxon based on preserved melanosomes.

Soft tissues in maniraptorans including Beipiaosaurus. Melanosome preservation in these tissues underpinned Li et al.'s (2014) comparative analysis of colour evolution in feathered dinosaurs.

Soft tissues in maniraptorans including Beipiaosaurus. Melanosome preservation in these tissues underpinned Li et al.'s (2014) comparative analysis of colour evolution in feathered dinosaurs.

Figure 1: Melanosome length observed in extant feathers, lepidosaur, testudine and archosaur skin, and mammalian hair.

Figure 1: Melanosome length observed in extant feathers, lepidosaur, testudine and archosaur skin, and mammalian hair.

Figure 2: SEM images of melanosomes from extant taxa representing the lowest-aspect-ratio and highest-aspect-ratio forms for each integumentary type.

Figure 2: SEM images of melanosomes from extant taxa representing the lowest-aspect-ratio and highest-aspect-ratio forms for each integumentary type.

Figure 3: Melanosomes from Jehol Group fossils.

Figure 3: Melanosomes from Jehol Group fossils.

Figure 4: Melanosome diversity across Amniota.

Figure 4: Melanosome diversity across Amniota.

2017

Functional niche partitioning in Therizinosauria provides new insights into the evolution of theropod herbivory

Lautenschlager, S. · Palaeontology 60(3), 375-387

Digital reconstruction and biomechanical modelling of therizinosaur mandibles show functional niche partitioning linked to herbivory. Beipiaosaurus occupies one end of the spectrum, with a less specialised jaw compatible with a mixed diet in a young forest environment.

Therizinosaurus cheloniformis, the giant Late Cretaceous therizinosauroid from Mongolia.

Therizinosaurus cheloniformis, the giant Late Cretaceous therizinosauroid from Mongolia.

Erlikosaurus andrewsi, derived therizinosauroid whose skull was functionally modelled by Lautenschlager.

Erlikosaurus andrewsi, derived therizinosauroid whose skull was functionally modelled by Lautenschlager.

2017

New chronostratigraphic constraints on the Yixian Formation with implications for the Jehol Biota

Chang, S.-C., Gao, K.-Q., Zhou, C.-F. e Jourdan, F. · Palaeogeography, Palaeoclimatology, Palaeoecology 487, 399-406

New 40Ar/39Ar radiometric dates on the Yixian Formation constrain deposition to about 125.8 to 124.1 Ma, earliest Aptian. It provides the precise temporal frame in which Beipiaosaurus lived, near the onset of the Jehol volcanosedimentary cycle.

Fauna of the Lujiatun Member of the Yixian Formation. Chang et al.'s (2017) chronostratigraphic refinement places Beipiaosaurus and its contemporaries in the earliest Aptian, around 125 Ma.

Fauna of the Lujiatun Member of the Yixian Formation. Chang et al.'s (2017) chronostratigraphic refinement places Beipiaosaurus and its contemporaries in the earliest Aptian, around 125 Ma.

Fish of the Yixian Formation, members of the Jehol Biota whose chronology was refined by Chang et al. (2017). Beipiaosaurus inhabited the margins of these volcanic lakes.

Fish of the Yixian Formation, members of the Jehol Biota whose chronology was refined by Chang et al. (2017). Beipiaosaurus inhabited the margins of these volcanic lakes.

2019

Cranial osteology of Beipiaosaurus inexpectus (Theropoda: Therizinosauria)

Liao, C.-C. e Xu, X. · Vertebrata PalAsiatica 57(2), 117-132

Detailed redescription of the skull preserved in IVPP V11559. Confirms Beipiaosaurus diagnostic characters, discusses the relatively long mandible compared with other therizinosaurs and provides characters for later phylogenetic analyses.

Cervical vertebrae of holotype IVPP V11559, part of the skull-neck block redescribed by Liao and Xu (2019) in Vertebrata PalAsiatica.

Cervical vertebrae of holotype IVPP V11559, part of the skull-neck block redescribed by Liao and Xu (2019) in Vertebrata PalAsiatica.

Beipiaosaurus display at the Paleozoological Museum of China with feather impressions on the forelimb. The cranial osteology redescribed by Liao and Xu (2019) is grounded in these and related specimens.

Beipiaosaurus display at the Paleozoological Museum of China with feather impressions on the forelimb. The cranial osteology redescribed by Liao and Xu (2019) is grounded in these and related specimens.

2021

Postcranial osteology of Beipiaosaurus inexpectus (Theropoda: Therizinosauria)

Liao, C.-C., Zanno, L.E., Wang, S. e Xu, X. · PLOS ONE 16(9), e0257913

Complete redescription of the postcranium of Beipiaosaurus holotype IVPP V11559, including two previously undescribed dorsal vertebrae. It provides the most robust postcranial character set for the taxon and reaffirms its position as a basal therizinosauroid.

Figure 1 of Liao et al. (2021, PLOS ONE): cervical vertebrae of Beipiaosaurus inexpectus (IVPP V11559) in dorsal view, used for detailed postcranial diagnosis.

Figure 1 of Liao et al. (2021, PLOS ONE): cervical vertebrae of Beipiaosaurus inexpectus (IVPP V11559) in dorsal view, used for detailed postcranial diagnosis.

Figure 6 of Liao et al. (2021, PLOS ONE): right forelimb elements of Beipiaosaurus, showing elongated proportions consistent with a basal therizinosauroid.

Figure 6 of Liao et al. (2021, PLOS ONE): right forelimb elements of Beipiaosaurus, showing elongated proportions consistent with a basal therizinosauroid.

Fig 1.

Fig 1.

Fig 2.

Fig 2.

Fig 3. Photographs of sacral and anterior caudal vertebrae of B . inexpectus (IVPP V 11559).

Fig 3. Photographs of sacral and anterior caudal vertebrae of B . inexpectus (IVPP V 11559).

Table 1. Measurements in millimeters of vertebrae of B . inexpectus (IVPP V 11559).

Table 1. Measurements in millimeters of vertebrae of B . inexpectus (IVPP V 11559).

Famous museum specimens

IVPP V11559 (holótipo) — Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Beijing, China

Wikimedia Commons

IVPP V11559 (holótipo)

Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Beijing, China

Completeness: Esqueleto subadulto parcial com crânio incompleto, vértebras cervicais, dorsais, sacrais e caudais anteriores, cinturas peitoral e pélvica, ambos os membros anteriores e posteriores parciais, filamentos integumentares preservados como impressões escuras no osso e na matriz ao redor
Found in: 1996
By: Li Yinxian (agricultor local, Sihetun)

Holotype IVPP V11559 is the specimen that underpinned the original description by Xu, Tang and Wang in 1999 and the cranial redescription by Liao and Xu (2019) and postcranial redescription by Liao et al. (2021). It was collected in 1996 at Sihetun, Beipiao County, western Liaoning Province, and preserved fossil integumentary filaments that provided the first direct evidence of filamentous covering in a therizinosaur.

STM 31-1 (espécime referido) — Shandong Tianyu Museum of Nature (STM), Pingyi, Shandong, China

Wikimedia Commons

STM 31-1 (espécime referido)

Shandong Tianyu Museum of Nature (STM), Pingyi, Shandong, China

Completeness: Esqueleto parcial com impressões extensas de penas, incluindo EBFFs (elongated broad filamentous feathers) na região do pescoço e tronco
Found in: 2000
By: Equipes de campo da região de Jianshangou, Liaoning

Beipiaosaurus specimen described by Xu, Zheng and You (2009, PNAS) as the basis for defining EBFFs, elongated broad filamentous feathers 10 to 15 cm long consistent with stage I of the feather-evolution model. It is today one of the central pieces of evidence in debates on the non-avian origin of feathers.

BMNHC PH000911 (espécime referido) — Beijing Museum of Natural History (BMNHC), Beijing, China

Wikimedia Commons

BMNHC PH000911 (espécime referido)

Beijing Museum of Natural History (BMNHC), Beijing, China

Completeness: Esqueleto parcial com traços de penas na região do pescoço
Found in: 2001
By: Equipes de campo associadas à Biota de Jehol, oeste de Liaoning

Material referred to Beipiaosaurus inexpectus that complements holotype IVPP V11559 and STM 31-1, particularly on the filamentous cover of the cervical region. It is on display at the Beijing Museum of Natural History.

Classification

Dinosauria
└ Saurischia
└ Theropoda
└ Coelurosauria
└ Maniraptora
└ Therizinosauria

Discovery

First fossil
1996
Discoverer
Li Yinxian, agricultor local de Sihetun
Formal description
1999
Described by
Xu Xing, Tang Zhi-Lu e Wang Xiao-Lin (IVPP, Beijing)
Formation
Formação Yixian, leito de Jianshangou (Grupo Jehol)
Region
Liaoning (oeste; condado de Beipiao)
Country
China
📄 Original description paper

Fun fact

When Beipiaosaurus was described in 1999, it became the unexpected theropod in a very literal way: it bundled three things no one expected to see in the same box, a therizinosaur (a poorly understood group, previously compared to late prosauropod relatives), a herbivore (rare among theropods) and a feathered dinosaur already at 125 million years ago. Ten years later, in 2009, it was back in the headlines (via PNAS) with the discovery of EBFFs (elongated broad filamentous feathers), up to 15 cm long, consistent with stage 1 of the theoretical feather-evolution model, completing in the fossil record all the morphotypes predicted by developmental biologists.