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1. chinaXiv:201906.00027 [pdf]

Metatarsal II osteohistology of Xixianykus zhangi (Theropoda: Alvarezsauria) and its implications for the development of the arctometatarsalian pes

QIN Zi-Chuan; ZHAO Qi; XU Xing
Subjects: Biology >> Zoology

The late-branching alvarezsaurian Xixianykus zhangi is among the smallest known non-avialan theropods. With great similarity to its close relatives, it is highly cursorial as indicated by proportionally long lower segments of the hindlimbs and the presence of an arctometatarsalian pes–a highly modified structure that has been suggested to improve cursorial capability in theropods. Here we describe the osteohistology of the metatarsal II of the holotype of X. zhangi (XMDFEC V 0011). Two rarely reported histological features, radial vascular canals and Sharpey’s fibers, are presented in this study. We suggest that both features are related to the development of the arctometatarsalian pes; however, further investigations of metatarsal osteohistology in theropods are required for the validation of our interpretation.

submitted time 2019-06-11 From cooperative journals:《古脊椎动物学报》 Hits156Downloads78 Comment 0

2. chinaXiv:201906.00096 [pdf]

Metatarsal II osteohistology of Xixianykus zhangi (Theropoda: Alvarezsauria) and its implications for the development of the arctometatarsalian pes

QIN Zi-Chuan; ZHAO Qi; XU Xing
Subjects: Biology >> Zoology

The late-branching alvarezsaurian Xixianykus zhangi is among the smallest known non-avialan theropods. With great similarity to its close relatives, it is highly cursorial as indicated by proportionally long lower segments of the hindlimbs and the presence of an arctometatarsalian pes–a highly modified structure that has been suggested to improve cursorial capability in theropods. Here we describe the osteohistology of the metatarsal II of the holotype of X. zhangi (XMDFEC V 0011). Two rarely reported histological features, radial vascular canals and Sharpey’s fibers, are presented in this study. We suggest that both features are related to the development of the arctometatarsalian pes; however, further investigations of metatarsal osteohistology in theropods are required for the validation of our interpretation.

submitted time 2019-06-11 From cooperative journals:《古脊椎动物学报》 Hits39Downloads22 Comment 0

3. chinaXiv:201711.01921 [pdf]

A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids

XU Xing; QIN Zi-Chuan
Subjects: Biology >> Zoology

The Early Cretaceous Jehol dromaeosaurids are taxonomically and morphologically diverse, and one of them, Microraptor zhaoianus, has been suggested to be among the smallest known non-avialan theropods. However, this idea is based on specimens of relatively early ontogenetic stages, and the lower limit of the mature body mass of Jehol dromaeosaurids thus remains unknown. Here we describe a new dromaeosaurid, Zhongjianosaurus yangi gen. et sp. nov., based on a specimen from the Lower Cretaceous Yixian Formation (the middle section of the Jehol Group) from Sihedang, Lingyuan County, Liaoning in Northeast China. While this new taxon is referable to the Microraptorinae, it differs from other microraptorine dromaeosaurids in numerous features, most notably the fusion of proportionally long uncinate processes to dorsal ribs, a humerus with a strongly medially offset proximal end and a large fenestra within the deltopectoral crest, an ulna slightly longer than the humerus, and an arctometatarsalian pes. Most significantly, the estimated 0.31 kg mass of the Z. yangi holotype of an adult individual confirms that some Jehol dromaeosaurids are among the smallest known non-avialan theropods. Our preliminary analysis demonstrates niche differentiation among the Jehol dromaeosaurids, a phenomenon rarely reported among Mesozoic dinosaurian faunas.

submitted time 2017-11-07 From cooperative journals:《古脊椎动物学报》 Hits176Downloads109 Comment 0

4. chinaXiv:201708.00204 [pdf]

A new microraptorine specimen (Theropoda: Dromaeosauridae) with a brief comment on the evolution of compound bones in theropods

XU Xing; LI Feng
Subjects: Geosciences >> Geology

Microraptorinae is a recently discovered subgroup of dromaeosaurid theropods, mostly comprising species from the Lower Cretaceous Jehol Group of western Liaoning, China. Here we describe a new microraptorine specimen from the Jiufotang Formation (the upper section of the Jehol Group) of Dapingfang, Chaoyang, Liaoning, which displays interesting morphological features not previously documented within Microraptorinae. Noteworthy are several osteological features, including dental and ischial ones, which are transitional between the condition of Sinornithosaurus and that of Microraptor. These features highlight the existence of a spectrum of morphological variation between Sinornithosaurus, which is more like a typical dromaeosaurid, and Microraptor, which shares many characteristics with troodontids. However, the taxonomic significance of these variations has not to be fully assessed yet. A feature deserving special mention is the fusion of the pubes to the ilia in this specimen, which has implications for the evolution of compound bones in theropods+. Our preliminary analysis suggests that many compound bones in birds have been formed by sequential fusion of multiple elements in a peramorphic process. 小盗龙亚科是驰龙科兽脚类恐龙中新近发现的一个亚群,多数属种产自中国辽宁西部下白垩统热河群。本文描记一件产自辽宁省朝阳县大平房地区九佛堂组(热河群上段)的小盗龙亚科的新标本,该标本具有一些未曾报道过的有趣形态特征。尤其值得关注的是,一些特征呈现出介于中国鸟龙和小盗龙之间的过渡状态,其中部分来自牙齿和坐骨。这些特征突出显示了在更接近典型驰龙类的中国鸟龙和具有许多伤齿龙科特征的小盗龙之间存在着一系列的形态变异。然而,这些变异特征在分类上的意义尚未得到充分评估。特别值得一提的是该标本中相互愈合的耻骨和肠骨,这一特征有助于阐明复合骨在兽脚类恐龙中的演化模式。初步分析显示许多鸟类的复合骨都是通过在过型形成过程中各组分的顺序愈合形成的。

submitted time 2017-08-11 From cooperative journals:《古脊椎动物学报》 Hits923Downloads291 Comment 0

5. chinaXiv:201708.00181 [pdf]

A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids

XU Xing; QIN Zi-Chuan
Subjects: Geosciences >> Geology

The Early Cretaceous Jehol dromaeosaurids are taxonomically and morphologically diverse, and one of them, Microraptor zhaoianus, has been suggested to be among the smallest known non-avialan theropods. However, this idea is based on specimens of relatively early ontogenetic stages, and the lower limit of the mature body mass of Jehol dromaeosaurids thus remains unknown. Here we describe a new dromaeosaurid, Zhongjianosaurus yangi gen. et sp. nov., based on a specimen from the Lower Cretaceous Yixian Formation (the middle section of the Jehol Group) from Sihedang, Lingyuan County, Liaoning in Northeast China. While this new taxon is referable to the Microraptorinae, it differs from other microraptorine dromaeosaurids in numerous features, most notably the fusion of proportionally long uncinate processes to dorsal ribs, a humerus with a strongly medially offset proximal end and a large fenestra within the deltopectoral crest, an ulna slightly longer than the humerus, and an arctometatarsalian pes. Most significantly, the estimated 0.31 kg mass of the Z. yangi holotype of an adult individual confirms that some Jehol dromaeosaurids are among the smallest known non-avialan theropods. Our preliminary analysis demonstrates niche differentiation among the Jehol dromaeosaurids, a phenomenon rarely reported among Mesozoic dinosaurian faunas. 早白垩世热河生物群的驰龙类恐龙在分类和形态上多样化程度很高,其中的赵氏小盗龙曾被认为是已知体型最小的非鸟兽脚类恐龙之一。然而这个观点依据的标本都处于相对早期的生长发育阶段,因此热河生物群驰龙类恐龙的体型下限仍不明确。本文依据一件产自辽宁省凌源县四合当下白垩统义县组(热河群中部)的标本,描述驰龙类一新种,杨氏钟健龙。这一新种可归入小盗龙类,但它在很多特征上不同于其他小盗龙类,其中最明显的区别是其相对长的钩状突愈合于背肋上,肱骨具有强烈内倾的近端,肱骨三角嵴上有一窗孔,尺骨略长于肱骨,并具有窄跖型的足。最重要的是,已为成年个体的杨氏钟健龙正模估计体重约为0.31 kg, 这证实了热河生物群的一些驰龙类恐龙属于已知体型最小的非鸟恐龙。初步分析显示热河生物群驰龙类恐龙有生态位分化的情况,这一现象在中生代恐龙动物群中报道很少。

submitted time 2017-08-10 From cooperative journals:《古脊椎动物学报》 Hits206Downloads137 Comment 0

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