热河生物群--探索中生代生命演化的世界级化石宝库

最近十多年来，我国在热河生物群各门类生物研究方面取得了一系列重要的发现和成果。我国辽西地区已经成为世界上研究鸟类起源，恐龙的进化，鸟类、哺乳动物以及被子植物的早期演化和辐射等最重要的地区之一。同位素测年技术的广泛应用，表明热河生物群属于早白垩世，在地球上延续了大约2千万年。热河生物群的繁盛和东亚地区当时特有的温暖的淡水和陆地环境具有密切的联系。而频繁的火山活动又是化石得以大量完美保存的重要因素之一。热河生物群的研究还具有很大的潜力，而对化石的科学发掘和保护的任务还十分艰巨。     

A long-tailed,seed-eating bird from the Early Cretaceous of China

The lacustrine deposits of the Yixian and Jiufotang Formations in the Early Cretaceous Jehol Group in the western Liaoning area of northeast China are well known for preserving feathered dinosaurs, primitive birds and mammals. Here we report a large basal bird, Jeholornis prima gen. et sp. nov., from the Jiufotang Formation. This bird is distinctively different from other known birds of the Early Cretaceous period in retaining a long skeletal tail with unexpected elongated prezygopophyses and chevrons, resembling that of dromaeosaurids, providing a further link between birds and non-avian theropods. Despite its basal position in early avian evolution, the advanced features of the pectoral girdle and the carpal trochlea of the carpometacarpus of Jeholornis indicate the capability of powerful flight. The dozens of beautifully preserved ovules of unknown plant taxa in the stomach represents direct evidence for seed-eating adaptation in birds of the Mesozoic era.     

On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota

Protopteryx, a monotypic fossil bird discovered from the Sichakou basin in Fengning, Hebei, is the most primitive enantiornithine currently known. The bird-bearing strata do not contain the index fossils of the Yixian Formation in western Liaoning; the fish and bird fossils have more primitive features than the related forms found in the Yixian Formation, and the conchostracans are those usually distributed in the Dabeigou and Dadianzi formations in northern Hebei. Besides, the Protopteryx-bearing strata underlie the deposits bearing the index fossils of the Yixian Formation in the neighboring basin. Thus, it could be confirmed that the horizon of Protopteryx should be lower than the Yixian Formation, and is approximately equivalent to the Dadianzi Formation in northern Hebei. This is the lowest horizon of the known fossil birds in China and Mesozoic enantiornithine birds in the world. Accompanying Protop- teryx, there are other birds, acipenseriform fishes, salamanders, and mammals, which compose the Peipiaosteus fengningensis-Protopteryx fengningensis assemblage. This new assemblage traces the vertebrate evolution history of the Jehol Biota back to 130.7 Ma before. It is suggested that the de- marcation of the Jehol Biota should be based on the large-scale tectonic-sedimentary cycles, and Peipiaosteus, instead of Lycoptera, could be taken as the vertebrate representative of the Jehol Biota.     

Pterosaur diversity and faunal turnover in Cretaceous terrestrial ecosystems in China

New specimens and an analysis of the Jehol pterosaur faunae of northeastern China show an unexpected diversity of flying reptile groups in terrestrial Cretaceous ecosystems. Here we report two new pterosaurs that are referred to European groups previously unknown in deposits of northeastern China. Feilongus youngi, from the Yixian Formation, is closely related to the Gallodactylidae and is distinguished by the presence of two independent sagittal crests and a protruding upper jaw. Nurhachius ignaciobritoi, from the Jiufotang Formation, has teeth formed by labiolingually compressed triangular crowns, only previously reported in Istiodactylus latidens from England. With these new discoveries, the Jehol pterosaurs show a wide range of groups including both primitive and derived forms that are not matched by any other deposit in the world. The discoveries also document the turnover of pterosaur faunae, with the primitive Anurognathidae and early archaeopterodactyloids being replaced by derived pterodactyloids. Furthermore, these deposits offer an opportunity to examine the interaction and competition between birds and pterosaurs--it indicates that the avian fauna during the Lower Cretaceous (and possibly most of the Mesozoic) dominated terrestrial, inland regions, whereas pterosaurs were more abundant in coastal areas.     

On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota

Protopteryx, a monotypic fossil bird discovered from the Sichakou basin in Fengning, Hebei, is the most primitive enantiornithine currently known. The bird-bearing strata do not contain the index fossils of the Yixian Formation in western Liaoning; the fish and bird fossils have more primitive features than the related forms found in the Yixian Formation, and the conchostracans are those usually distributed in the Dabeigou and Dadianzi formations in northern Hebei. Besides, the Protopteryx-bearing strata underlie the deposits bearing the index fossils of the Yixian Formation in the neighboring basin. Thus, it could be confirmed that the horizon of Protopteryx should be lower than the Yixian Formation, and Is approximately equivalent to the Dadianzi Formation in northern Hebei. This is the lowest horizon of the known fossil birds in China and Mesozoic enantiornithine birds in the world. Accompanying Protopteryx, there are other birds, acipenseriform fishes, salamanders, and mammals, which compose the Peipiaosteus fengningensis-Protopteryx fengningensis assemblage. This new assemblage traces the vertebrate evolution history of the Jehol Biota back to 130.7 Ma before. It is suggested that the demarcation of the Jehol Biota should be based on the large-scale tectonic-sedimentary cycles, and Peipiaosteus, instead of Lycoptera, could be taken as the vertebrate representative of the Jehol Biota.     

U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues

SHRIMP U-Pb zircon dating was carried out for the Daohugou Biota near Ningcheng of Inner Mongolia and for lavas overlying or underlying sala-mander-bearing strata at Reshuitang in Lingyuan of West Liaoning. The results suggest that the Dao- hugou Biota occurred at an interval from 168 Ma to 164―152 Ma. Both the Daohugou Biota and the salamander-bearing fossil assemblage are the same biota and thus developed from 168 to 152 Ma, i.e. from late Middle Jurassic to the early Late Jurassic. The Daohugou Biota-bearing rocks, resting on the Jiulongshan Formation in disconformity and being overlain in unconformity by Late Jurassic Tuchengzi Formation and Early Cretaceous rocks containing the Jehol Biota, are mainly composed of volcanic-sedi- mentary rocks in a normal sequence. It is recom- mended that the Daohugou Biota and the related stratigraphy should be correlated with the Tiaojishan Formation (Lanqi Formation in West Liaoning) or its synchronous rocks. It is suggested that the Dao- hugou Biota and the Jehol Biota would be neither taken into one biota nor considered as the earliest elements of the Jehol Biota. The Daohugou Biota and the related rocks and the Yixian Formation were respectively formed in different periods of volcanic-sedimentary tectonics.     

A new species from an ornithuromorph（Aves： Ornithothoraces）dominated locality of the Jehol Biota

We report on a new species of ornithuromorph bird, Iteravis huchzermeyeri gen. et sp. nov., from the previously unreported Sihedang locality of the Lower Cretaceous Yixian Formation, the oldest ornithuromorph bearing deposit in the world. Unlike most other Cretaceous localities, specimens from this new quarry are largely referable to Ornithuromorpha, similar to the Lower Cretaceous Aptian Xiagou Formation in Gansu Province. Also similar to the Xiagou avifauna, the fauna at Sihedang is largely dominated by a single taxon（described here）.Differences in faunal dominance may suggest the Sihedang records a unique ecological habitat. This may also explain the dominance of Gansus in the younger Xiagou Formation locality and suggests that previous hypotheses regarding the shift in dominance between Enantiornithes and Ornithuromorpha need to be reassessed in terms of potential ecological biases due to limited sampling. Furthermore, the recognition of an ornithuromorph dominated locality in the Sihedang significantly weakens the signal of such an inferred trend. Compared to most Jehol birds, the new specimen is relatively better preserved in three dimensions revealing morphological details of the skeleton, as well as preserves feather impressions including a rectricial morphology previously unknown among Mesozoic birds.     

Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia

Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and comprise three major parts. The red shales in the lower part were misidentified as belonging to the Tuchengzi Formation. Field excavation has indicated that the shales of upper part of the bed are the major fossil-bearing horizon. Due to strong tectonic activities, sediments were often folded with the sequences inverted in the region. Some newly recognized contacts between the Daohugou Bed and the volcanic rocks showed that the ignimbrite of the Tiaojishan Formation （159-164 Ma） underlies the Daohugou deposits, rather than overlying the latter as previously proposed. Thus, the age of the Daohugou deposits should be younger than the age of the ignimbrite, and thus it was incorrect to correlate the Daohugou Bed with the Middle Jurassic Jiulongshan Formation. Although biostratigraphic studies based on conchostracans and insects support a Middle Jurassic-early Late Jurassic age for the Daohugou deposits, vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota. We propose that the Daohugou fossil assemblage probably represents the earliest evolutionary stage of the Jehol Biota based on both vertebrate biostratigraphy and the sedimentological and volcanic features which suggest the Daohugou deposit belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group.     

A new eutriconodont mammal from the early Cretaceous Jehol Biota of Liaoning,China

A new genus and species of eutriconodont mammal, Chaoyangodens lii gen. et sp. nov., from the Dawangzhangzi bed of Yixian Formation, Lingyuan, Liaoning, is reported. The new species has a tooth formula I5-C1-P1-M3/i4-c1-p1-m4, unique among eutriconodonts in having only one premolar in lower and upper jaws, respectively, and a distinctive diastema between the canine and the premolar. Its simple incisors and reduced premolars show a mosaic combination of primitive and derived features. This new taxon adds to the diverse group of Jehol eutriconodonts. Among the known species from at least three horizons, there seems no evolutionary trend in morphology that is recognizable, except for that larger species are all from the Lujiatun bed of the Yixian Fm. A thorough and systematic analysis involving all the Jehol eutriconodonts is needed to understand their phylogenetic relationships.     

Pyrite framboids associated with the Mesozoic Jehol Biota in northeastern China: Implications for microenvironment during early fossilization

Despite of the recent influx of reports describing important fossil specimens from the Mesozoic Jehol Biota, detailed information on the mechanism of fossilization and paleoenvironment in which these fossils were deposited is scanty. We present an analysis of microenvironment based upon scanning electron microscope observations of in situ pyrite framboids and microcrystallines of plant and vertebrate feather fossils in the Jehol Biota. Pyrite microcrystallines and framboids occur extensively inside and on surface of plant fossils.Framboids found on feathers and in sedimentary matrix were in a lower abundance. These framboids have diameters ranging from 6 μm to 31 μm with an average of 20 μm, indicating a dysoxic aqueous condition with free oxygen level less than 30 μmol/L for the microenvironment where these framboids were formed. The outgrowth of framboids inside plant tissues suggests the presence of water molecules and free oxygen at the cellular level during pyritization; the relative timing between tissue decay and framboid formation implies a rapid tissue degradation occurred during the very early stage of fossilization. This line of reasoning is consistent with the observation that cell level structure of plant fossils from these deposits is rarely preserved. We propose a "fossil envelop" model to accommodate the different geochemical conditions between the microenvironment surrounding the fossil material and the macroenvironment of background lake bottom water.