• Negligible effect of tooth reduction on body mass in Mesozoic birds

    分类: 地球科学 >> 地质学 提交时间: 2018-04-04 合作期刊: 《古脊椎动物学报》

    摘要:Tooth reduction and loss was an important evolutionary process in Mesozoic birds. Analysis of evolutionary trends in the total mass of the dentition, a function of tooth size and tooth number, has the potential to shed light on the evolutionary pattern of tooth reduction and loss, and on the causes of this pattern. Because modern birds lack teeth, however, they cannot provide the basis for a model that would allow estimation of tooth masses in their Mesozoic counterparts. We selected the teeth of crocodilians as analogues of those in Mesozoic birds because the former are the closest living relatives of the latter, and the two groups are similar in tooth morphology, tooth implantation, and tooth replacement pattern. To estimate tooth masses in Mesozoic birds, we formulated four regression equations relating tooth mass to various linear dimensions, which were measured in 31 intact isolated teeth from eight individual crocodiles (Crocodylus siamensis). The results for Mesozoic birds show that dental mass as a proportion of body mass was negligible, at least from the perspective of flight performance, suggesting that selection pressure favoring body mass reduction was probably not the primary driver of tooth reduction or loss. Variations in dental mass among Mesozoic birds may reflect the different foods they ate, and the different types of feeding behavior they displayed.

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

    分类: 地球科学 >> 地质学 提交时间: 2017-08-11 合作期刊: 《古脊椎动物学报》

    摘要: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。

  • Therocephalian (Therapsida) and chroniosuchian (Reptiliomorpha) from the Permo-Triassic transitional Guodikeng Formation of the Dalongkou Section, Jimsar, Xinjiang, China

    分类: 地球科学 >> 地质学 提交时间: 2017-08-10 合作期刊: 《古脊椎动物学报》

    摘要:The Guodikeng Formation encompasses the terrestrial Permo-Triassic transition sequence in China. This formation crops out in the Dalongkou section, Jimsar, Xinjiang where remains of the dicynodonts Jimusaria and Lystrosaurus were found. We are describing here a therocephalian and a chroniosuchian from the Dalongkou section, which are the first records of these groups for the Guodikeng Formation. Diagnostic characters of the new therocephalian, Dalongkoua fuae gen. and sp. nov., include maxillary ventral margin strongly concave in lateral view; incisors spatulated and rounded; incisors and canines with faint serrations; coronoid process of the dentary with a marked external adductor fossa; triangular reflected lamina of the angular with two smooth concavities. Chroniosuchians are represented by several postcranial elements and the vertebral morphology is similar to Bystrowiana and Bystrowiella. These remains are interpreted as representing a Bystrowianidae indeterminate. The new findings increase the diversity of the Guodikeng Formation that is now represented by three or four dicynodonts, one therocephalian and one chroniosuchian. All these groups survived the massive P-T extinction but disappear from the fossil record in the Middle to Upper Triassic. 锅底坑组是重要的二叠—三叠系过渡序列,本组在新疆吉木萨尔大龙口出露广泛,产出吉木萨尔兽以及水龙兽两类二齿兽类。本文报道了在大龙口剖面首次发现的兽头类和迟滞鳄类,这也是此二类群在锅底坑组的首次报道。新发现的兽头类被命名为付氏大龙口兽(Dalongkoua fuae)。其鉴定特征包括上颌骨犬后齿齿槽外边缘向背向凹入;切齿有圆形和匙形;切齿和犬齿有微弱的锯齿;齿骨冠状突有显著的收肌窝;反折翼近三角形,有两个平滑的凹陷。锅底坑组目前有3~4属二齿兽类、1属兽头类和1属迟滞鳄类,这一发现增加了其多样性。这些类群都在二叠纪末的大灭绝中幸存下来,直到中晚三叠世才消失。

  • Review of historical and current research on the Late Cretaceous dinosaurs and dinosaur eggs from Laiyang, Shandong

    分类: 地球科学 >> 地质学 提交时间: 2017-08-10 合作期刊: 《古脊椎动物学报》

    摘要:Here we briefly review the history of research on the Laiyang dinosaur and dinosaur egg faunas, summarize the contributions of C. C. Young and other elder paleontologists to the discoveries of the Late Cretaceous dinosaurs and dinosaur eggs from Laiyang, and introduce the new discoveries and the advances in the research on the Laiyang faunas. The new investigations in Laiyang from 2008 have found a series of valley developed in plain and more than ten new dinosaur or dinosaur egg fossil beds. In 2010, we began the massive excavations at two localities in Jingangkou and collected abundant dinosaurs and other vertebrate fossils, such as a new saurolophine, some theropod material and a new taxon of turtle egg. The bone beds in Locality 2 with the typical sedimentary and burial patterns of mudflow, and these fossil deposits are interpreted as having been carried and deposited by mudflow. The re-observation and the CT scanning data of the crest of Tsintaosaurus spinorhinus (IVPP V 725) show that the crest is fractured and solid. However, based on the re-observations of its cranial and postcranial specimens, we consider that Tsintaosaurus spinorhinus is a valid taxon of lambeosaurines, which have the hollow crest. Therefore, the crest of Tsintaosaurus might not belong to the skull of this individual, and the true form of the crest needs to be confirmed in the future work. We reassess the three species of Tanius, and obtain several results. 1) Tanius sinensis and Tanius chingkankouensis are the valid species of Tanius; 2) Tanius laiyangensis is invalid.; 3) the sacrum and ilium of Tanius chingkankouensis with typical hadrosaurid features should not be referred to Tanius. 简要回顾了莱阳恐龙和恐龙蛋化石群的研究历史和以杨钟健为代表的老一代地质古生物学者对莱阳恐龙和恐龙蛋研究和发现的杰出贡献,并介绍了莱阳恐龙和恐龙蛋的最新发现和若干研究进展。在近年来对莱阳周边地层进行的大规模考察中,发现了一系列发育在平原上的恐龙峡谷群;以及其中蕴含的十几个恐龙和恐龙蛋新地点和新层位。2010年开始,在对莱阳金岗口村附近的2个化石地点的发掘中,发现了以鸭嘴龙科为主的大量脊椎动物化石和蛋化石,包括一类新的栉龙亚科成员,一些大型兽脚类恐龙化石,以及一新的龟鳖类蛋化石等。2号地点化石富集层具有典型的泥石流沉积特征和骨骼埋藏特征。对棘鼻青岛龙的特殊头饰进行了CT扫描和三维重建,发现其头饰是实心结构,但其他骨骼特征证明棘鼻青岛龙属于具有头饰的赖氏龙亚科是确定无疑的,所以目前发现的头饰应不是其真实状态或根本不属于其头部骨骼。此外,对谭氏龙1属3种的重新观察研究得出以下结论:中国谭氏龙和金刚口谭氏龙应是有效属种,但部分骨骼还有疑问,还需要进一步研究,而莱阳谭氏龙为无效属种。

  • A new ionoscopiform fsh (Holostei: Halecomorphi) from the Middle Triassic (Anisian) of Yunnan, China

    分类: 地球科学 >> 地质学 提交时间: 2017-08-10 合作期刊: 《古脊椎动物学报》

    摘要:Ionoscopiformes, sister to Amiiformes, are an extinct group of halecomorph fishes previously known mainly from the late Middle Triassic (Ladinian) and Late Jurassic of Europe and the Early Cretaceous of the New World. They have not been known in China until recently two ionoscopiforms (Robustichthys and Panxianichthys) were found from the early Middle Triassic (Anisian) of Yunnan and Guizhou, respectively. Here, a new ionoscopiform, Subortichthys triassicus gen. et sp. nov., is described on the basis of six well-preserved specimens from the early Middle Triassic (Pelsonian, Anisian, ~244 Ma) marine deposits exposed in Luoping, eastern Yunnan, China. The discovery documents the second ionoscopiform from the Luoping fossil beds and one of the oldest ionoscopiforms in the world, providing important information for understanding the origin and early diversifcation of this group. Subortichthys is an unambiguous halecomorph as it possesses two synapomorphies of this clade: a symplectic articulating with the lower jaw and a notched posterior margin of the maxilla. Within the phylogenetic framework of the Halecomorphi, results of the phylogenetic analysis place Subortichthys at the base of the Ionoscopiformes because it bears a sensory canal in the maxilla (an ionoscopiform synapomorphy), but lacks derived features of other ionoscopiforms. Notably, Subortichthys is distinguished from other members of this order with a unique combination of features, such as presence of three or four pairs of extrascapulars and a much expanded third infraorbital posteriorly contacting the preopercle. The new material reveals that the earliest diversifcation of ionoscopiforms was well undertaken in South China (a part of east Paleotethys Ocean then) by the early Middle Triassic (Anisian). 预言鱼目是近鲱形类的一个绝灭支系,被认为是弓鳍鱼目的姐妹群。预言鱼目化石过去主要发现于欧洲的中三叠世拉丁期和晚侏罗世地层以及新大陆的早白垩世地层。近年来,在云南和贵州的中三叠世安尼期地层中分别发现了一种预言鱼目鱼类化石(强壮鱼和盘县鱼), 代表了该目在中国的首次发现。根据产于云南罗平中三叠世安尼期(~244 Ma)海相地层中的6块保存良好的鱼化石,命名了预言鱼目一个新的属种,三叠复兴鱼(Subortichthys triassicus gen. et sp. nov.)。三叠复兴鱼是罗平生物群中发现的第二种预言鱼目鱼类,代表了预言鱼目最古老的化石记录之一,为研究该目的起源和早期分异提供了重要信息。复兴鱼无疑可以归入近鲱形类,因为它具有近鲱形类两个共近裔性状,续骨与下颌关节以及上颌骨后缘具有凹缺。分支分析结果表明,复兴鱼位于预言鱼目的基部,因为它具有该目的重要鉴定特征,上颌骨具有感觉管,但它不具有其他预言鱼目鱼类的进步特征。特别的是,复兴鱼具有一些独特的性状,如额外肩胛骨3或4对、第三眶下骨特别宽大并与前鳃盖骨前缘相接等。复兴鱼的发现表明预言鱼目鱼类在华南地区(三叠纪时期位于古特提斯洋的东部)的早期分异至少发生在中三叠世早期(安尼期)。

  • Early Mammut from the Upper Miocene of northern China, and its implications for the evolution and differentiation of Mammutidae

    分类: 地球科学 >> 地质学 提交时间: 2017-08-08 合作期刊: 《古脊椎动物学报》

    摘要:Mammut is the terminal taxon of the proboscidean group Mammutidae, which survived to the Late Pleistocene. Although this genus was widely distributed in the Pliocene of Eurasia and the Pleistocene of North America, little is known about its early evolution. Here, we report on Mammut cf. M. obliquelophus from the Upper Miocene of northern China based on new fossil material, including an almost complete juvenile cranium and other remains, which show many primitive features within Mammutidae and clearly demonstrate the morphological evolution of Mammut. The strongly laterally expanded lateral wing of the occiput and the presence of basal constriction of the incisive fossa display cranial similarity between Mammut cf. M. obliquelophus and both Eozygodon morotoensis and Choerolophodon guangheensis, early representatives of the Mammutidae and Choerolophodontidae, respectively, indicating the close relationship between these two groups: both of them are located at the basal phylogenetic positions in Elephantimorpha.This result is further confrmed by a cladistic analysis.