[Paleontology • 2024] Body Size and Evolutionary Rate Analyses reveal Complex Evolutionary History of Alvarezsauria

 

1, Bonapartenykus; 2, Patagonykus; 3, Alvarezsaurus;
4, Alnashetri; 5, Albertonykus; 6, Heptasteornis;
7, Dzharaonyx; 8, Linhenykus; 12, Bannykus. 

in Meso, Pol, Chiappe, Qin, Díaz-Martínez, ... et Pittman. 2024. 

DOI: doi.org/10.1111/cla.12600

Artwork by Abel G. Montes.

Abstract

Some of the smallest examples of dinosaurian body size are from alvarezsaurians, an enigmatic group of maniraptoran coelurosaurians with a peculiar combination of anatomical features unique among theropods. Despite the large number of alvarezsaurian species described worldwide and the increased understanding this has provided, the body-size macroevolution of alvarezsaurians has received little attention. Here we reconstruct and analyse directional trends of alvarezsaurian body-size evolution through an integrated analysis of body mass, ontogenetic age, and morphological rate data enabled by a comprehensively revised phylogeny. Our analyses identify four periods of high morphological rate evolution (Bathonian–Callovian, Hauterivian–early Berriasian, early Cenomanian, and late Cenomanian–Turonian) that we link to the key effects of animal body-size changes for the first time, including morphological novelty, structural reduction and simplification, elevated homoplasy, and behavioral changes associated with miniaturization. In doing so, this study provides a holistic example of miniaturization in a Mesozoic vertebrate group that offers a framework for other detailed studies of animal body-size evolution, including in more disparate groups.

Relative body sizes of Alvarezsauria calibrated with the geological age of known alvarezsaurian taxa and showing their continental distribution. Silhouettes calibrated with body mass. The range of blues represents the forms of the Upper Jurassic, the range of pink represents the forms of the Lower Cretaceous, the range of reds represents the forms of the Upper Cretaceous of Patagonia, and the range of greens represents the Parvicursorinae.

Life reconstruction of 12 alvarezsaurians that illustrate body-size change in the clade.
1, Bonapartenykus; 2, Patagonykus; 3, Alvarezsaurus; 4, Alnashetri; 5, Albertonykus; 6, Heptasteornis; 7, Dzharaonyx; 8, Linhenykus; 9, Haplocheirus; 10, Shishugounykus; 11, Kol; 12, Bannykus.

 Artwork by Abel G. Montes.

Jorge Gustavo Meso, Diego Pol, Luis Chiappe, Zichuan Qin, Ignacio Díaz-Martínez, Federico Gianechini, Sebastián Apesteguía, Peter J. Makovicky and Michael Pittman. 2024. Body Size and Evolutionary Rate Analyses reveal Complex Evolutionary History of Alvarezsauria. Cladistics. Early View. DOI: doi.org/10.1111/cla.12600

[Paleontology • 2023] Jaculinykus yaruui • A New alvarezsaurid Dinosaur (Theropoda: Alvarezsauria) from the Upper Cretaceous Baruungoyot Formation of Mongolia provides insights for Bird-like Sleeping behavior in Non-avian Dinosaurs

Jaculinykus yaruui

Kubo, Kobayashi, Chinzorig & Tsogtbaatar, 2023

 

DOI: 10.1371/journal.pone.0293801

Artwork courtesy of Seiji Yamamoto

 

Abstract

Alvarezsauria is a group of early-branching maniraptoran theropods that are distributed globally from the Late Jurassic to the latest Cretaceous. Despite recent increases in the fossil record of this group, the scarcity of complete specimens still restricts interpreting their detailed anatomy, ecology, and evolution. Here, we report a new taxon of derived alvarezsaur, Jaculinykus yaruui gen. et sp. nov., from the Late Cretaceous of Mongolia, which represents a nearly complete and articulated skeleton. Our phylogenetic analysis reveals that Jaculinykus belongs to the sub-clade of Alvarezsauridae, Parvicursorinae, and forms a mononphyletic group with Mononykus and Shuvuuia. Its well-preserved manus has only two fingers, composed of a hypertrophied digit I and greatly reduced digit II, which implies an intermediate condition between the tridactyl manus of Shuvuuia and monodactyl manus of Linhenykus. This highlights a previously unrecognized variation in specialization of alvarezsaurid manus. Notably, the preserved posture of the specimen exhibits a stereotypical avian-like sleeping position seen in the troodontids Mei and Sinornithoides. Evidence of this behavior in the alvarezsaur Jaculinykus suggests that stereotypically avian sleeping postures are a maniraptoran synapomorphy, providing more evidence of bird-like traits being distributed broadly among avian ancestors.

Geographic and stratigraphic occurrence of the Mongolian alvarezsaurids.
(C) The stratigraphic horizon of  Jaculinykus yaruui gen. et sp. nov. and other alvarezsaurids in the Nemegt, Baruungoyot, and Djadokhta formations. The composite stratigraphy was modified from Eberth [2018] and Jerzykiewicz and Russell [1991].

Geographic and stratigraphic occurrence of the Mongolian alvarezsaurids.
(A) Plan view of Mongolia. (B) Location of Jaculinykus yaruui gen. et sp. nov. (MPC-D 100/209) and alvarezsaurid occurrences in the Nemegt Basin. The map was generated using Simplemappr (www.simplemappr.net) before modification and modified from Jerzykiewicz et al. [2021]. 

Holotype of Jaculinykus yaruui gen. et sp. nov. (MPC-D 100/209).
(A) Photograph of the specimen. (B) Explanatory drawing of (A). Highlighted areas refer to the indication of the skeletal elements; skull in green, tail in grey, pectoral girdle and forelimbs in red, pelvis and hind limbs in purple.
(C) Reconstruction of Jaculinykus yaruui gen. et sp. nov. Grey areas are missing parts.

Life restoration of sleeping posture of Jaculinykus yaruui

 (Artwork courtesy of Seiji Yamamoto)

Systematic paleontology

Dinosauria Owen, 1842  

Theropoda Marsh, 1882 

Maniraptora sensu Gauthier, 1986  

Alvarezsauria Bonaparte, 1991  

Alvarezsauridae Bonaparte, 1991  

Parvicursorinae Karhu and Rautian, 1996  

Jaculinykus yaruui gen. et sp. nov.

 

Etymology: Jaculinykus is from “Jaculus,” a tiny dragon from the Greek myth, and “onykus,” claw; yaruui, derived from Mongolian word, yaruu (яаруу): speedy (= hasty).

Holotype: The type specimen (MPC-D 100/209) is a nearly complete skeleton with a skull, missing some cranial elements (vomers, nasals, postorbitals, and supraoccipitals), eighth or ninth cervical vertebra, posterior dorsal vertebrae, seven anterior caudal vertebrae, sternum, furcula, right manual phalanx (II-2), right manual ungual and left fibula (Fig 2). It is housed in the Institute of Paleontology of Mongolian Academy of Sciences (IP-MAS), Ulaanbaatar, Mongolia.

Type locality and horizon: Nemegt locality, Ömnögovi Province, Mongolia (Fig 1). The specimen was collected from the upper section of the Baruungoyot (or Barun Goyot) Formation, suggested as the Campanian in age, (Fig 1). The stratigraphic horizon of Jaculinykus belongs to a part of “Big Red” in the transitional stratigraphic interval (Zone 4).

Diagnosis: Jaculinykus differs from all other alvarezsaurs in having a dorsoventrally high narial opening of the premaxilla, medially curved parasagittal crest on the parietal, slender and nearly straight dentaries, triangular-shaped deltopectoral crest being separated from the humeral head by a notch, strong medial tab of metacarpal I, weakly developed proximodorsal process of phalanx I-1, robust medial condyle of the tibia relative to the fibular condyle, and sharply indented base of the ascending process of astragalus. Jaculinykus is also distinguished from other alvarezsaurs by the unique combination of the following characters: slender ischial shaft relative to the pubic shaft, an open popliteal fossa of the femur, and prominent external projection of the ectocondylar tuber of the femur. It differs from the hypothesized sister taxon Shuvuuia deserti in possessing the following additional features: the deltopectoral crest being separated from the humeral head by a notch; the absence of the third manual digit. It also differs from stratigraphically same or older (the Baruungoyot Formation) alvarezsaurid, Ondogurvel alifanovi, from the same locality (the Nemegt locality) in possessing the following features ....

Evolution of avian-like sleeping posture in theropod dinosaurs. Skeletal disposition of Jaculinykus yaruui gen. et sp. nov. (MPC-D 100/209) in dorsal (photograph courtesy of Tomonori Tanaka) (A) and ventral (reversed) (B) views. (C), Interpretive line drawing of skeletal disposition.
 (D), Life restoration of sleeping posture of Jaculinykus yaruui (Artwork courtesy of Seiji Yamamoto).
(E), Simplified coelurosaurian phylogeny represents presence for evidence of avian ‘tuck-in’ posture.

 Kohta Kubo, Yoshitsugu Kobayashi, Tsogtbaatar Chinzorig and Khishigjav Tsogtbaatar. 2023. A New alvarezsaurid Dinosaur (Theropoda, Alvarezsauria) from the Upper Cretaceous Baruungoyot Formation of Mongolia provides insights for Bird-like Sleeping behavior in Non-avian Dinosaurs. PLoS ONE. 18(11): e0293801. DOI: 10.1371/journal.pone.0293801

[Paleontology • 2021] Growth and Miniaturization among Alvarezsauroid Dinosaurs

representative alvarezsauroids, Haplocheirus sollers (left), Patagonykus puertai (upper middle), Linhenykus monodactylus (lower middle), 
illustrating the body size and dieting change in alvarezsauroid dinosaurs.

in Qin, Zhao, ... et Xu, 2021.

 DOI: 10.1016/j.cub.2021.06.013

Reconstruction: Zhixin Han/ artstation.com/xinyanjun

 

Highlights

• How and why the bizarre alvarezsauroid dinosaurs miniaturized is poorly known

• We reveal a rapid Late Cretaceous alvarezsauroid miniaturization and radiation

• Osteohistological data show highly variable growth strategies among alvarezsauroids

• Alvarezsauroid miniaturization is possibly associated with adaptations to digging

Summary

Sustained miniaturization, here defined as a drop in body size of at least two orders of magnitude from ancestors to descendants, is a widespread and important phenomenon in animals but among dinosaurs, miniaturization occurred only rarely, once in the lineage leading to birds and once in the Alvarezsauroidea, one of the most bizarre theropod groups. Miniaturization and powered flight are intimately linked in avialan theropods but the causes and patterns of body size reduction are less clear in the non-volant Alvarezsauroidea. Here, we present results from analyses on a comprehensive dataset, which not only includes new data from early-branching alvarezsauroids but also considers the ontogenetic effect based on histological data. Our analyses show that alvarezsauroid body mass underwent rapid miniaturization from around 110 to 85 mya and that there was a phylogenetic radiation of small-sized alvarezsauroids in the Late Cretaceous. Our analyses also indicate that growth strategies were highly variable among alvarezsauroids, with significant differences among extremely small taxa. The suggested alvarezsauroid miniaturization and associated phylogenetic radiation are coincident with the emergence of ants and termites, and combining previous functional morphological data, our study suggests that alvarezsauroid miniaturization might have been driven by ecological changes during the Cretaceous Terrestrial Revolution, more specifically by a shift to the myrmecophagous ecological niche.

 

Keywords: growth strategy, growth rate, body size evolution, miniaturization, alvarezsauroid dinosaurs, ontogenetic effect, osteohistology, phylogenetic radiation, Cretaceous Terrestrial Revolution, ecological niche

four representative alvarezsauroids, Haplocheirus sollers (left), Patagonykus puertai (upper middle), Linhenykus monodactylus (lower middle) and Bannykus wulatensis (lower right), illustrating the body size and dieting change in alvarezsauroid dinosaurs.

Reconstruction: Zhixin Han/ artstation.com/xinyanjun

 Zichuan Qin, Qi Zhao, Jonah N. Choiniere, James M. Clark, Michael J. Benton and Xing Xu. 2021. Growth and Miniaturization among Alvarezsauroid Dinosaurs. Current Biology. 31(16); 3687-3693.e5. DOI: 10.1016/j.cub.2021.06.013

[Paleontology • 2021] Shuvuuia deserti • Evolution of Vision and Hearing Modalities in Theropod Dinosaurs

Shuvuuia deserti  Chiappe, Norell, & Clark, 1998

in Choiniere, Neenan, Schmitz, ... et Benson, 2021. 

DOI: 10.1126/science.abe7941

  twitter.com/Kimi_Chap 

 

Abstract

Owls and nightbirds are nocturnal hunters of active prey that combine visual and hearing adaptations to overcome limits on sensory performance in low light. Such sensory innovations are unknown in nonavialan theropod dinosaurs and are poorly characterized on the line that leads to birds. We investigate morphofunctional proxies of vision and hearing in living and extinct theropods and demonstrate deep evolutionary divergences of sensory modalities. Nocturnal predation evolved early in the nonavialan lineage Alvarezsauroidea, signaled by extreme low-light vision and increases in hearing sensitivity. The Late Cretaceous alvarezsauroid Shuvuuia deserti had even further specialized hearing acuity, rivaling that of today’s barn owl. This combination of sensory adaptations evolved independently in dinosaurs long before the modern bird radiation and provides a notable example of convergence between dinosaurs and mammals.

 Jonah N. Choiniere, James M. Neenan, Lars Schmitz, David P. Ford, Kimberley E. J. Chapelle, Amy M. Balanoff, Justin S. Sipla, Justin A. Georgi, Stig A. Walsh, Mark A. Norell, Xing Xu, James M. Clark and Roger B. J. Benson. 2021. Evolution of Vision and Hearing Modalities in Theropod Dinosaurs. Science. 372, 6542; 610-613. DOI: 10.1126/science.abe7941

  twitter.com/Kimi_Chap/status/1390411550071132167

 

 Michael Hanson, Eva A. Hoffman, Mark A. Norell and Bhart-Anjan S. Bhullar. 2021. The Early Origin of A Birdlike Inner Ear and the Evolution of Dinosaurian Movement and Vocalization. Science. 372, 6542. 601-609. DOI: 10.1126/science.abb4305

  twitter.com/AnjanBhullar/status/1390465252672823297

 

Revealing behavioral secrets in extinct species

Extinct species had complex behaviors, just like modern species, but fossils generally reveal little of these details. New approaches that allow for the study of structures that relate directly to behavior are greatly improving our understanding of the lifestyles of extinct animals (see the Perspective by Witmer). Hanson et al. looked at three-dimensional scans of archosauromorph inner ears and found clear patterns relating these bones to complex movement, including flight. Choiniere et al. looked at inner ears and scleral eye rings and found a clear emergence of patterns relating to nocturnality in early theropod evolution. Together, these papers reveal behavioral complexity and evolutionary patterns in these groups.

[Paleontology • 2020] Trierarchuncus prairiensis • the Last Alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana

 Trierarchuncus prairiensis

Fowler, Wilson, Freedman Fowler, Noto, Anduza & Horner, 2020

 DOI: 10.1016/j.cretres.2020.104560 

 DickinsonMuseumCenter.com

Highlights

• A growth series of hand claws and other fossil material from a new taxon, Trierarchuncus prairiensis, of the unusual theropod family Alvarezsauridae is described.

• One claw is the most complete known for Alvarezsauridae and challenges assumptions about the lack of curvature in derived members of the group and demonstrates that alvarezsaurid claws could be of higher curvature than typically reconstructed.

• The possible growth series suggests that alvarezsaurid manual unguals may have changed morphology through ontogeny, with younger individuals retaining more basal characteristics. This has implications for taxonomy and phylogeny of the group as some taxa are described based on probable juvenile remains.

• Trierarchuncus derives from the uppermost Maastrichtian Hell Creek Formation of Montana, and is therefore the youngest known alvarezsaurid and was one of the very last dinosaurs, which went extinct at the K–Pg boundary mass extinction.

Abstract

The enigmatic Alvarezsauria (Dinosauria: Theropoda) are characterized by extremely short forelimbs with a single functional digit bearing a large, robust ungual. Alvarezsauria are first recorded from the Jurassic of China, but are otherwise mostly known from the Cretaceous of South America and Asia, including a number of relatively complete skeletons. North America has yielded only a fragmentary skeleton from the lower Maastrichtian Horseshoe Canyon Formation, Alberta, and a pubis, partial ischium, and metatarsal from the upper Maastrichtian Hell Creek Formation, Montana, and Lance Formation, Wyoming. Here we describe new alvarezsaurid material from the Hell Creek Formation, Montana, comprising a metatarsal III, distal end of a radius, and three manual digit (MD)-I unguals, which form a progressive size series. One MD-I ungual is the most complete yet described, and is much more curved than typically depicted for Alvarezsauridae. Manual D-I unguals are of particular interest as they undergo a number of changes within the clade, including enclosure of the ventral blood vessel groove, development of a ventral sulcus, and increased robusticity and rugosity. Comparison among the new specimens suggests that these features also develop ontogenetically, which may have taxonomic implications. Stratigraphic data shows that alvarezsaurids occur through most of the ∼85 m thick Hell Creek Formation, with the uppermost specimen occurring ∼10 m below the upper contact with the Fort Union Formation. As such these are the youngest known alvarezsaurid remains and demonstrate that the clade survived at least until ∼1–200 kyrs before the Cretaceous–Paleogene mass extinction.

Keywords: Dinosaur, Theropoda, Alvarezsauridae, Mononykus, Hell Creek Formation, Late Cretaceous

 Systematic Paleontology 

Dinosauria Owen, 1842 

Saurischia Seeley, 1888 

Theropoda Marsh, 1881 

Maniraptora Gauthier, 1986 

Alvarezsauridae Bonaparte, 1991 

Trierarchuncus prairiensis gen. et sp. nov. 

Derivation of name. The genus name refers to the 'trierarch', specifically a seafaring ship's captain (trirēmē ships of ancient Greece), and 'uncus' meaning hook (Latin). Species name means 'of the prairie', referring to the gentle plains of eastern Montana (in particular the American Prairie Reserve) where the new material was discovered.

  

Denver W. Fowler, John P. Wilson, Elizabeth A. Freedman Fowler, Christopher R. Noto, Daniel Anduza and John R.Horner. 2020. Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research. In Press. DOI: 10.1016/j.cretres.2020.104560

twitter.com/df9465/status/1281788167842979841

Trierarchuncus prairiensis (“Captain Hook of the prairie”): a new species of bizarre hook-handed alvarezsaurid dinosaur.

DickinsonMuseumCenter.com/badlands_research-2020newalvarezsaurid

[Paleontology • 2019] Shishugounykus inexpectus • A New Alvarezsaurian Theropod from the Upper Jurassic Shishugou Formation of western China

Shishugounykus inexpectus

Qin, Clark, Choiniere & Xu,  2019

nature.com/articles/s41598-019-48148-7 

Abstract

Alvarezsaurian dinosaurs, a group of bizarre theropods with greatly shortened and modified forelimbs, are known mostly from the Cretaceous of Asia and South America. Here we report a new alvarezsaurian, Shishugounykus inexpectus gen. et sp. nov., based on a specimen recovered from the Middle–Upper Jurassic Shishugou Formation of the Junggar Basin, western China. Together with two other alvarezsaurians from this formation, i.e., Haplocheirus sollers and Aorun zhaoi, these Shishugou forms represent the only known Jurassic alvarezsaurians worldwide. Similar to the two other Shishugou alvarezsaurians, this new alvarezsaurian displays early stages in the development of the highly modified alvarezsaurian forelimb, but it possesses a number of manual features closer to the typical coelurosaurian theropod condition. Combining morphological and histological features, our analysis indicates that the earliest known alvarezsaurians are variable in size and other important morphological features, and in particular display a mosaic distribution of forelimb features.

Figure 1: Skeletal anatomy of Shishugounykus inexpectus (IVPP V23567). 
Skeletal reconstruction showing preserved elements. (A), Skeletal silhouette showing preserved bones (missing portions shown in gray; Scale bar, 200 mm); (B), Partial left frontal in dorsal and ventral view; (C), Partial right frontal and parietal in dorsal and ventral view; (D), Partial right angular in lateral view; (E), Right articular in dorsal view; (F), An anterior dorsal in lateral view; (G), A posterior dorsal in lateral view; (H), Two most anterior sacrals in lateral view; (I), An anterior caudal in lateral view; (J), A posterior caudal in lateral view; (K), Right scapula in lateral view; (L), Partial left humerus in anterior, posterior, lateral and medial view; (M), Proximal end of right ulna; (N), Proximal end of right radius; (O), Right manus in lateral, dorsal and ventral view; (P), Partial left ilium in lateral and medial view; pubis (Q) and ischium (R) in lateral view; (S), Right femur in posterior, lateral, anterior and medial view; (T), Left tibia in anterior, posterior, lateral and medial view; (U), Left and right fibulae in lateral view; (V), Partial left metatarsals II and III, left pedal phalanges III-1 and 2, IV-1, 2, and 4 in dorsal view.

 (Figure abbreviations see supplementary materials; Scale bar, 20 mm; The skeletal silhouettes are created by Aijuan Shi using Adobe Illustrator, www.adobe.com/products/illustrator.html).

Systematic palaeontology

Theropoda Marsh, 1881

Maniraptora Gauthier, 1986

Alvarezsauria Bonaparte, 1991

Shishugounykus inexpectus gen. et sp. nov

Etymology: The generic name is a combination of Shishugou (Chinese Mandarin for the formation which produced the holotype specimen of the new animal; translates as “rock” “tree” “wash” for the abundant petrified wood in the formation) and onyx (Greek, “claw); the specific name refers to the unexpected discovery of a new alvarezsaurian species from the Middle-Late Jurassic Shishugou Formation, which has produced fossils of two other Jurassic alvarezsaurians, i.e., Haplocheirus sollers and Aorun zhaoi.

Holotype: IVPP V23567, a partial skeleton (Fig. 1) including several cranial elements (possible partial right frontal and partial right parietal, partial left frontal, partial right angular, and right articular), three dorsal vertebrae, four sacral vertebrae, three caudal vertebrae, partial right scapula, partial left humerus, partial right ulna and radius, nearly complete right manus, partial left ilium, ischium, and pubis, complete right femur, partial left femur, nearly complete left and right tibiae, partial left and right fibula, a distal tarsal, partial left metatarsals II and III, left pedal phalanges III-1 and 2, IV-1, 2, and 4, and a few rib fragments and unidentifiable pieces. All recovered bones are clearly from one individual given that they are preserved in a small area (about 0.2 square meters), without any other bone nearby.

    

Diagnosis: Shishugounykus inexpectus differs from all other alvarezsaurians in having the following unique combination of features (* marks the autapomorphies; we use the II-III-IV identity of manual digits in tetanurans): supratemporal fossa occupying large portion of frontal and with indistinct anterior border (sharp anterior border in early-branching alvarezsaurians such as Haplocheirus sollers and supratemporal fossa occupying a small portion of frontal in late-branching alvarezsaurians); scapula with hollow acromial process but without lateral concavities*; humeral internal tuberosity mediolaterally constricted distally*, giving it a “pinched” appearance; metacarpal III straight in dorsal view (laterally bowed in most other alvarezsaurians including Haplocheirus sollers); ungual III-3 subequal in size to ungual II-2 (considerably smaller in most other alvarezsaurians including Haplocheirus sollers); iliac medial surface with step-wise transition from ischial peduncle to pubic peduncle*; distal end of metatarsal II asymmetrically ginglymoid*.

Locality and Horizon: Wucaiwan, Junggar Basin, Xinjiang, People’s Republic of China, Middle-Upper Jurassic Shishugou Formation34,35,36,37. The holotype-fossil-bearing bed is located between two volcanic tuff layers with radiometric (40Ar/39Ar) ages of 161.2 ± 0.2 and 158.7 ± 0.3 Ma, respectively35,36,37,38. The two tuff layers are separated by a section of fluvial sediments that is 90 meters thick, and assuming constant sedimentation rates this means that each meter of sediment is around 0.0278 million years36, if the sedimentation rate was relatively constant. Based on a section thickness of 36 meters between the holotype-fossil-bearing bed and the lower tuff layer, we infer that the holotype-bearing bed is ∼160.2 Ma. Using a similar method, previous studies estimate the geological ages of the fossil-bearing beds for Aorun zhaoi (about 13 m below the lower tuff) and Haplocheirus sollers (about 40 m above the lower tuff) fossils are ∼161.6 Ma and ~160.1 Ma37, respectively.

Figure 4: Time-calibrated alvarezsaurian phylogeny showing alvarezsaurian hand evolution (Scale bar, 10 mm); silhouettes show the size variation both in early-branching and late-branching alvarezsaurians.

    

Zichuan Qin, James Clark, Jonah Choiniere and Xing Xu. 2019. A New Alvarezsaurian Theropod from the Upper Jurassic Shishugou Formation of western China. Scientific Reports. volume 9, Article number: 11727. nature.com/articles/s41598-019-48148-7 

     

[Paleontology • 2018] Qiupanykus zhangi • A New Alvarezsaurid Dinosaur from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province, central China

Qiupanykus zhangi  

Lü, Xu, Chang, Jia, Zhang, Gao, Zhang, Zhang & Ding, 2018

 DOI:  10.31035/cg2018005 

Illustration: Zhao Chuang. 

An alvarezsaurid dinosaur skeleton was discovered from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province of centtral China. It represents a new alvarezsaurid dinosaur Qiupanykus zhangi gen. et sp. nov. A phylogenetic analysis recovers Qiupanykus nested within the unresolved clade, which includes Asian and north American taxa. The skeleton of the new specimen is preserved in association with eggshells. The eggshell morphologies show that these eggs belong to oviraptorid eggs, skeletal remains of which were discovered from the same area. The alvarezsaurid skeleton associated with eggshell fragments may indicate that these eggs were broken by the strong thumb-claws of the former and that alvarezsaurid dinosaurs may be egg-eaters.

Keywords: Vertebrate paleontology, alvarezsaurid dinosaur, Qiupanykus, Late Cretaceous, central China

Figure 2. The photograph (a) and outline drawings (b) of Qiupanykus zhangi.

 Abbreviations: cd: caudal vertebrae; f: femur; hc: haemal arch; il: ilium; mt(II-IV): metatarsls II-IV; ti: tibia; p: pubis; pp: pedal phalanx; sv: sacral vertebrae.

Systematic paleontology

Maniraptora (Gauthier, 1986)

Alvarezsauridae (Bonaparte JF, 1991)

Qiupanykus zhangi gen. et sp. nov.

Etymology: The generic name refers to the Qiupa town, Luanchuan County, where the specimen was discovered. The specific name is in honor of Shuancheng Zhang for his logistic support with fossil searching and excavations in the field.

Holotype: Incomplete skeleton comprising most posterior axial elements and most of hindlimb elements. The specimen 41HIII-0101 is housed in the collections of the Henan Geological Museum, Zhengzhou, China.

Holotype locality and horizon: The specimen (41HIII-0101) was found in Guanping, Qiupa Town, Luanchuan County of Henan Province; Qiupa Formation (Bureau of Geology and Mineral Resources of Henan Province, 1989; Lü JC et al., 2007)

Diagnosis: A small-sized alvarezsaurid dinosaur with the following combination of characters: posterior sacral vertebrae bearing a strong ventral keel; proximal caudals with transverse processes centrally positioned on centrum; pubic articular surface of the pubic peduncle of ilium is reduced and knob-like; fibular crest of tibia large and quadrangular; functional sacrum made up of eight vertebral elements (two anterior caudal plus six sacral vertebrae); a small pneumatic foramen is present in caudal vertebrae.

....

Figure 4. Life scene of Qiupanykus zhangi. 

(drawn by Zhao Chuang)

Behaviour of alvarezsaurid dinosaurs

The skeleton of Qiupanykus is associated with an eggshell fragment near its tail. The thickness of the eggshell fragment is 1.8 mm. Some features, such as linearituberculate ornamentation type, including nodes and short ridges, two structural layers (non-prismatic), and relatively thick shell, are all identical to the Luanchuan oviraptorosaur eggshells (Tanaka K et al., 2011). Using the formula (Elongatoolithidae) by Tanaka K et al. (2016), the estimated egg mass of the eggshell is: Log10 egg mass = 1.569×log10 (1.8)+2.655, the thickness of the egg shell is 1.8 mm, then the Egg mass is 1136.377 g (95% CI: 715 g to 1809 g). The femur circumference of Qiupanykus is 17.09 mm. Based on the formula (log10 BM = 2.754×log10(femur circumference－0.683) by Campione NE et al. (2014), the estimated body mass for Qiupanykus: is 515 g (log10 BM = 2.754×log10 17.09－0.683). The estimated egg mass is much heavier than the estimated body mass of Qiupanykus. Thus, the egg could not be laid by Qiupanykus.

Alvarezsaurid dinosaurs bear highly specialized arms, whose purpose is still a mystery. They are regarded that the special arms were used to burrow (Perle A et al., 1993) or break open termite mounds (like modern anteaters), and possible to feed on insects (Senter P, 2005). However, the skeleton is associated with eggshell fragments from Luanchuan area, and the eggshell fragment morphologies indicate that those eggs belong to oviraptorid eggs (Tanaka K, personal communication, 2017). There is another case found from north-western Patagonia of Argentina, where an alvarezsaurid skeleton is preserved with eggs (Agnolin FL et al., 2012). Although Agnolin et al. thought the eggs associated with the alvarezsaurid Bonapartenykus ultimus were laid by an alvarezsaurid dinosaur, they pointed out that the external ornamentation patterns of Arriagadoolithus expressed on the outer shell surface is similar to elongathoolithid eggs. Arriagadoolithus was possibly laid by oviraptorosaurid dinosaurs. Thus, there are three possibilities about the relationship between the alvarezsaurid skeletons and eggs (egg fragments) associated with them: (1) Eggshell fragments were buried with alvarezsaurid skeleton by coincidence, and the eggshell is nothing to do with the skeleton. (2) The eggs were laid by alvarezsaurid dinosaurs and (3) The eggshell fragments were from eggs broken by alvarezsaurid dinosaurs and the eggs were not laid by them. However, considering the strong thumb claw of alvarezsaurid dinosaurs, we prefer to the third interpretation. Alvarezsaurid dinosaurs perhaps use their special claw to break eggs, and they are perhaps egg-eaters (Fig. 4).

Conclusion: 

The skeleton of Qiupanykus is associated with oviraptorid egg shell fragments suggesting that at least the derived alvarezsaurid dinosaurs may be an egg-eaters, which use their special arms (the strong thumb claws) to pierce the hard eggshell. Qiupanykus is a relatively small sized alvarezsaurid and it represents the youngest alvarezsaurid dinosaur from China so far.

Jun-Chang Lü, Li Xu, Hua-Li Chang, Song-Hai Jia, Ji-Ming Zhang, Dian-Song Gao, Yi-Yang Zhang, Cheng-Jun Zhang and Fang Ding. 2018. A New Alvarezsaurid Dinosaur from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province, central China. China Geology. 1(1): 28–35. DOI:  10.31035/cg2018005