中国中生代的鸟类:介绍及综述

最近十来年 ,中国辽宁发现的早白垩世的鸟类化石超过了世界上其它任何一个地区。中国的中生代鸟类化石代表了始祖鸟化石之后鸟类历史上第一次显著的分异。它们不仅包括了带有明显恐龙祖先特征的长尾的鸟类 ,而且还包括了许多进步或特化的种类 ,如早白垩世最大的鸟类 ,最原始的反鸟类 ,以及保存最好的、飞行结构和现生鸟类几乎一样的今鸟类。这些早期鸟类在诸如飞行、大小和食性等所反映的演化、形态和生态学特征等方面出现了重大的分异。具有长尾骨骼的原始基干鸟类热河鸟和驰龙类具有的相似性 ,进一步支持了鸟类起源于恐龙的学说。中国发现的早白垩世的鸟类以及树栖的恐龙化石还为鸟类飞行的树栖起源假说提供了十分重要的证据。“恐龙下树”的假说结合了鸟类起源于恐龙的学说和鸟类飞行的树栖起源学说 ,因此也得到了化石证据的支持。由于多种恐龙带有羽毛 ,因此羽毛不一定代表了恒温。恒温的鸟类可能到了早白垩世的进步鸟类中才开始出现     

辽西化石:凝固了飞翔的秘密

在现生脊椎动物当中,鸟类以其独特的形态区别于其他类群。鸟类具有轻盈的流线型体形,体被羽毛,双翅发达,能够在蓝天中自由翱翔。正是鸟类的独特性使得鸟类起源研究成为进化生物学研究的一个疑难问题。从1996年开始,中国辽西热河生物群陆续产出了一批进步的兽脚类恐龙化石,其中有些化石保存了羽毛或者原始羽毛印痕。这个发现,打破了100多年来始祖鸟在     

鸟类起源研究的进展与现状

近些年来,由于在世界上许多国家相继发现了很多早期鸟类以及与之关系接近的恐龙化石,鸟类起源的研究一时成为国际学术界关注的热点之一。特别是最近几年,我国许多带羽毛恐龙化石的发现,更为这一热点增添了很多色彩。本文旨在简要介绍最近几年国际上关于鸟类起源研究已取得的进展以及尚存在的问题。１带毛的恐龙 自７０年代Ｏｓｔｒｏｍ（１９７３,１９７６）率先复兴了鸟类起源于恐龙的学说以来,鸟类的起源问题便一直成为人们争执的焦点。尽管越来越多的证据表明,鸟类和恐龙的关系最为接近,但持不同观点的学者仍提出了许多疑问。在…     

解惑

听说还有会飞的恐龙,那它得长多大的翅膀啊?恐龙大多是不会飞的,不过现在也有证据表明有一些恐龙会滑翔,比如顾氏小盗龙,它的四肢上长有一些羽毛,我们通常俗称为“四翅恐龙”。有化石证据表明这种体型比较小的恐龙会爬树,并能利用树枝间的落差滑翔。这也涉及了鸟类的飞行起源问题,即鸟类是从快速奔跑中开始学会飞行的,还是首先爬树,利用树间高差滑翔开始飞行的。四翅恐龙的翅膀并不大,化石证据表明它们的翼展大约有1米左右。     

科学家发现鸟类起源于恐龙的最新证据

鸟类的起源一直是国际古生物学界的热点问题之一,自上个世纪60年代末至70年代初,美国耶鲁大学教授约翰·奥斯罗姆复兴了赫胥黎提出的鸟类兽脚类恐龙起源假说后,鸟类起源的研究取得了巨大的进展,来自世界各地不同地史时期的恐龙和早期鸟类的大量化石证据持续不断地出现,有力地支持着这一假说。1986年美国耶鲁大学教授嘉克斯·高斯特首次用分支系统学的方法系统地分析了鸟类与其他初龙类（一个包括恐龙、翼龙、鳄型动物以及一些绝灭支系的爬行动物类群）的关系,     

对于早期鸟类起源与演化过程中一些疑问的个人见解

鸟类起源问题在学术界仍然存在分歧 ,现在大多数古生物学家都支持鸟类起源于恐龙之说。虽然化石证据表明恐龙和早期鸟类之间确实存在很多相似之处 ,但是仍有一些疑问无法得到合理解释 ,那么鸟类是否起源于恐龙呢？很多学者认为霸王龙和驰龙类同鸟类具有较近的亲缘关系 ,但是却无法解释这类进步的恐龙为何出现在比中生代早期化石鸟类更晚的地层之中？笔者认为霸王龙及驰龙类的始祖同鸟类最终始祖之间可能存在较近的亲缘关系 ,可以认为霸王龙及驰龙类在它们的演化过程中除体型以外在其他方面同其始祖之间并无较大区别 ,笔者认为霸王龙可能处于…     

第五届古鸟类与进化国际大会暨辽西热河生物群研讨会将在京召开

生物群研讨会将在京召开 鸟类起源和进化一直是生物学界的重要课题之一。自从 １８６１年发现第一块始祖鸟标本以来,产生了各种有关鸟类起源及进化的学说、假设,同时也留下了许多疑问,其主要原因是化石太少、各种学说都是建立在个别标本之上。 近些年来,在我国北方,特别是辽宁西部,发现了大量的中生代鸟类化石,使我们对生物进化史的这一重要环节有了进一步的认识,极大地开阔了我们的视野,引发了有关鸟类起源、鸟类与恐龙的系统关系等诸多热点问题的争论,推动了世界古鸟类学的发展。我国的鸟类化石材料在时代上稍晚于德国的始祖鸟…     

从新的古生物学及今生物学资料看羽毛的起源与早期演化(英文)

近年来关于羽毛和羽状皮肤衍生物的研究极大促进了我们对羽毛起源与早期演化的理解。结合最新的古生物学与今生物学资料,对一些保存了皮肤衍生物的非鸟恐龙标本进行观察研究,为这个重要的进化问题提供了新见解。推测羽毛的演化在鸟类起源之前就以下列顺序完成了5个主要的形态发生事件:1)丝状和管状结构的出现;2)羽囊及羽枝脊形成;3)羽轴的发生;4)羽平面的形成;5)羽状羽小支的产生。这些演化事件形成了多种曾存在于各类非鸟初龙类中的羽毛形态,但这些形态在鸟类演化过程中可能退化或丢失了;这些演化事件也产生了一些近似现代羽毛或者与现代羽毛完全相同的羽毛形态。非鸟恐龙身上的羽毛有一些现代羽毛具有的独特特征,但也有一些现生鸟羽没有的特征。尽管一些基于发育学资料建立的有关鸟类羽毛起源和早期演化的模型推测羽毛的起源是一个全新的演化事件,与爬行动物的鳞片无关,我们认为用来定义现代鸟羽的特征应该是逐步演化产生的,而不是突然出现。因此,对于羽毛演化而言,一个兼具逐步变化与完全创新的模型较为合理。从目前的证据推断,最早的羽毛既不是用来飞行也不是用来保暖,各种其他假说皆有可能,其中包括展示或者散热假说。展开整合性的研究有望为羽毛的起源问题提供更多思路。     

寻找”飞翔”的恐龙

在我们的一般印象中,恐龙是一种身披鳞片、体形巨大的动物,然而事实也许并不如此,至少有一些种类的恐龙体形小巧、动作灵活,而且长有羽毛。那么,这些长羽毛的恐龙与鸟类起源有什么关系？它们是否就是鸟类的祖先？这些问题一直是进化生物学研究人员关注的焦点,也是争议最多的课题。     

寻找”飞翔”的恐龙

在我们的一般印象中,恐龙是一种身披鳞片、体形巨大的动物,然而事实也许并不如此,至少有一些种类的恐龙体形小巧、动作灵活,而且长有羽毛。那么,这些长羽毛的恐龙与鸟类起源有什么关系？它们是否就是鸟类的祖先？这些问题一直是进化生物学研究人员关注的焦点,也是争议最多的课题。     

Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence

The origin of birds and avian flight from within the archosaurian radiation has been among the most contentious issues in paleobiology. Although there is general agreement that birds are related to theropod dinosaurs at some level, debate centers on whether birds are derived directly from highly derived theropods, the current dogma, or from an earlier common ancestor lacking suites of derived anatomical characters. Recent discoveries from the Early Cretaceous of China have highlighted the debate, with claims of the discovery of all stages of feather evolution and ancestral birds (theropod dinosaurs), although the deposits are at least 25 million years younger than those containing the earliest known bird Archaeopteryx. In the first part of the study we examine the fossil evidence relating to alleged feather progenitors, commonly referred to as protofeathers, in these putative ancestors of birds. Our findings show no evidence for the existence of protofeathers and consequently no evidence in support of the follicular theory of the morphogenesis of the feather. Rather, based on histological studies of the integument of modern reptiles, which show complex patterns of the collagen fibers of the dermis, we conclude that "protofeathers" are probably the remains of collagenous fiber "meshworks" that reinforced the dinosaur integument. These "meshworks" of the skin frequently formed aberrant patterns resembling feathers as a consequence of decomposition. Our findings also draw support from new paleontological evidence. We describe integumental structures, very similar to "protofeathers," preserved within the rib area of a Psittacosaurus specimen from Nanjing, China, an ornithopod dinosaur unconnected with the ancestry of birds. These integumental structures show a strong resemblance to the collagenous fiber systems in the dermis of many animals. We also report the presence of scales in the forearm of the theropod ornithomimid (bird mimic) dinosaur, Pelecanimimus, from Spain. In the second part of the study we examine evidence relating to the most critical character thought to link birds to derived theropods, a tridactyl hand composed of digits 1-2-3. We maintain the evidence supports interpretation of bird wing digit identity as 2,3,4, which appears different from that in theropod dinosaurs. The phylogenetic significance of Chinese microraptors is also discussed, with respect to bird origins and flight origins. We suggest that a possible solution to the disparate data is that Aves plus bird-like maniraptoran theropods (e.g., microraptors and others) may be a separate clade, distinctive from the main lineage of Theropoda, a remnant of the early avian radiation, exhibiting all stages of flight and flightlessness.     

BODY AND LIMB SIZE DISSOCIATION AT THE ORIGIN OF BIRDS: UNCOUPLING ALLOMETRIC CONSTRAINTS ACROSS A MACROEVOLUTIONARY TRANSITION

The origin of birds and powered flight is a classic major evolutionary transition. Research on their origin often focuses on the evolution of the wing with trends of forelimb elongation traced back through many nonavian maniraptoran dinosaurs. We present evidence that the relative forelimb elongation within avian antecedents is primarily due to allometry and is instead driven by a reduction in body size. Once body size is factored out, there is no trend of increasing forelimb length until the origin of birds. We report that early birds and nonavian theropods have significantly different scaling relationships within the forelimb and hindlimb skeleton. Ancestral forelimb and hindlimb allometric scaling to body size is rapidly decoupled at the origin of birds, when wings significantly elongate, by evolving a positive allometric relationship with body size from an ancestrally negative allometric pattern and legs significantly shorten by keeping a similar, near isometric relationship but with a reduced intercept. These results have implications for the evolution of powered flight and early diversification of birds. They suggest that their limb lengths first had to be dissociated from general body size scaling before expanding to the wide range of fore and hindlimb shapes and sizes present in today's birds.     

Gravity-defying Behaviors: Identifying Models for Protoaves

Most current phylogenetic hypotheses based upon cladistic methodologyassert that birds are the direct descendants of derived maniraptorantheropod dinosaurs, and that the origin of avian flight necessarilydeveloped within a terrestrial context (i.e., from the "groundup"). Most theoretical aerodynamic and energetic models or chronologicallyappropriate fossil data do not support these hypotheses forthe evolution of powered flight. The more traditional modelfor the origin of flight derives birds from among small arborealearly Mesozoic archosaurs ("thecodonts"). According to thismodel, protoavian ancestors developed flight in the trees viaa series of intermediate stages, such as leaping, parachuting,gliding, and flapping. This model benefits from the assemblageof living and extinct arboreal vertebrates that engage in analogousnon-powered aerial activities using elevation as a source ofgravitational energy. Recent reports of "feathered theropods"notwithstanding, the evolution of birds from any known groupof maniraptoran theropods remains equivocal.     

Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism

Pterosaurs, enigmatic extinct Mesozoic reptiles, were the first vertebrates to achieve true flapping flight. Various lines of evidence provide strong support for highly efficient wing design, control, and flight capabilities. However, little is known of the pulmonary system that powered flight in pterosaurs. We investigated the structure and function of the pterosaurian breathing apparatus through a broad scale comparative study of respiratory structure and function in living and extinct archosaurs, using computer-assisted tomographic (CT) scanning of pterosaur and bird skeletal remains, cineradiographic (X-ray film) studies of the skeletal breathing pump in extant birds and alligators, and study of skeletal structure in historic fossil specimens. In this report we present various lines of skeletal evidence that indicate that pterosaurs had a highly effective flow-through respiratory system, capable of sustaining powered flight, predating the appearance of an analogous breathing system in birds by approximately seventy million years. Convergent evolution of gigantism in several Cretaceous pterosaur lineages was made possible through body density reduction by expansion of the pulmonary air sac system throughout the trunk and the distal limb girdle skeleton, highlighting the importance of respiratory adaptations in pterosaur evolution, and the dramatic effect of the release of physical constraints on morphological diversification and evolutionary radiation.     

A fossil brain from the Cretaceous of European Russia and avian sensory evolution

Fossils preserving traces of soft anatomy are rare in the fossil record; even rarer is evidence bearing on the size and shape of sense organs that provide us with insights into mode of life. Here, we describe unique fossil preservation of an avian brain from the Volgograd region of European Russia. The brain of this Melovatka bird is similar in shape and morphology to those of known fossil ornithurines (the lineage that includes living birds), such as the marine diving birds Hesperornis and Enaliornis, but documents a new stage in avian sensory evolution: acute nocturnal vision coupled with well-developed hearing and smell, developed by the Late Cretaceous (ca 90Myr ago). This fossil also provides insights into previous 'bird-like' brain reconstructions for the most basal avian Archaeopteryx--reduction of olfactory lobes (sense of smell) and enlargement of the hindbrain (cerebellum) occurred subsequent to Archaeopteryx in avian evolution, closer to the ornithurine lineage that comprises living birds. The Melovatka bird also suggests that brain enlargement in early avians was not correlated with the evolution of powered flight.     

L’origine et l’évolution des oiseaux : 35 années de progrès

The origin and evolution of birds: 35 years of progress. Birds are dinosaurs – specifically, small feathered and flighted theropod dinosaurs that probably originated in Laurasia during the Late Jurassic over 140 million years ago. They are most closely related to other small theropods such as dromaeosaurs and troodontids, terrestrial predators that were fleet-footed hunters. The origin of birds is a classic example of two kinds of macroevolution: the phylogenetic origin of the group, and the sequential assembly of adaptations such as flight that are indelibly associated with birds. These adaptations were not assembled all at once. Rather, a great many characteristics associated with birds and flight first appeared in non-avian dinosaurs, where they were used for many purposes other than flight. These included insulation, brooding, and probably display and species recognition. Birds diversified steadily but gradually after their origin, which is identified with the origin of flight (Archaeopteryx); forelimb and other flight-associated features evolved more rapidly than features associated with the posterior skeleton. The first birds grew more slowly than extant birds do, and more like other small Mesozoic dinosaurs; like them, they probably matured sexually well before they completed their active skeletal growth. The origin of flight is not a problem of “trees down” or “ground up,” but rather an examination of the order in which diagnostic flight characters evolved, and what each stage can reveal about the functions and habits of bird outgroups at those evolutionary junctures.     

Flightless birds are not neuroanatomical analogs of non-avian dinosaurs

Background

In comparative neurobiology, major transitions in behavior are thought to be associated with proportional size changes in brain regions. Bird-line theropod dinosaurs underwent a drastic locomotory shift from terrestrial to volant forms, accompanied by a suite of well-documented postcranial adaptations. To elucidate the potential impact of this locomotor shift on neuroanatomy, we first tested for a correlation between loss of flight in extant birds and whether the brain morphology of these birds resembles that of their flightless, non-avian dinosaurian ancestors. We constructed virtual endocasts of the braincase for 80 individuals of non-avian and avian theropods, including 25 flying and 19 flightless species of crown group birds. The endocasts were analyzed using a three-dimensional (3-D) geometric morphometric approach to assess changes in brain shape along the dinosaur-bird transition and secondary losses of flight in crown-group birds (Aves).

Results

While non-avian dinosaurs and crown-group birds are clearly distinct in endocranial shape, volant and flightless birds overlap considerably in brain morphology. Phylogenetically informed analyses show that locomotory mode does not significantly account for neuroanatomical variation in crown-group birds. Linear discriminant analysis (LDA) also indicates poor predictive power of neuroanatomical shape for inferring locomotory mode. Given current sampling, Archaeopteryx, typically considered the oldest known bird, is inferred to be terrestrial based on its endocranial morphology.

Conclusion

The results demonstrate that loss of flight does not correlate with an appreciable amount of neuroanatomical changes across Aves, but rather is partially constrained due to phylogenetic inertia, evident from sister taxa having similarly shaped endocasts. Although the present study does not explicitly test whether endocranial changes along the dinosaur-bird transition are due to the acquisition of powered flight, the prominent relative expansion of the cerebrum, in areas associated with flight-related cognitive capacity, suggests that the acquisition of flight may have been an important initial driver of brain shape evolution in theropods.

     

Rates of dinosaur limb evolution provide evidence for exceptional radiation in Mesozoic birds

Birds are the most diverse living tetrapod group and are a model of large-scale adaptive radiation. Neontological studies suggest a radiation within the avian crown group, long after the origin of flight. However, deep time patterns of bird evolution remain obscure because only limited fossil data have been considered. We analyse cladogenesis and limb evolution on the entire tree of Mesozoic theropods, documenting the dinosaur–bird transition and immediate origins of powered flight. Mesozoic birds inherited constraints on forelimb evolution from non-flying ancestors, and species diversification rates did not accelerate in the earliest flying taxa. However, Early Cretaceous short-tailed birds exhibit both phenotypic release of the hindlimb and increased diversification rates, unparalleled in magnitude at any other time in the first 155 Myr of theropod evolution. Thus, a Cretaceous adaptive radiation of stem-group birds was enabled by restructuring of the terrestrial locomotor module, which represents a key innovation. Our results suggest two phases of radiation in Avialae: with the Cretaceous diversification overwritten by extinctions of stem-group birds at the Cretaceous–Palaeogene boundary, and subsequent diversification of the crown group. Our findings illustrate the importance of fossil data for understanding the macroevolutionary processes generating modern biodiversity.     

Phylogenetic Context for the Origin of Feathers

A number of hypotheses have been suggested for the origin ofbirds and feathers. Although distributions of functional complexeshave frequently been used to test phylogenetic hypotheses, analysisof the origin of feathers remains hampered by the incompletefossil record of these unmineralized structures. It is alsocomplicated by approaches that confuse the origins of birds,feathers, and flight without first demonstrating that theserelate to the same historical event. Functional speculationregarding the origin of feathers usually focuses on three possiblealternatives: (1) flight; (2) thermal insulation; or (3) display.Recent fossil finds of Late Cretaceous feathered dinosaurs inChina have demonstrated that feathers appear to have originatedin taxa that retained a significant number of primitive nonavianfeatures. Current evidence strongly suggests that birds aretheropod dinosaurs, and that the most primitive known feathersare found on non-flying animals. This further suggests thatfeathers did not evolve as flight structures. Thermoregulatory,display, and biomechanical support functions remain possibleexplanations for the origin of feathers. As the earliest functionof feathers was probably not for aerial locomotion, it may bespeculated that the transitional animals represented by theChinese fossils possessed skin with the tensile properties ofreptiles and combined it with the apomorphic characteristicsof feathers.