Polar dinosaurs and the question of dinosaur extinction: a brief review

Although the physiology of dinosaurs is still a matter of controversy, there is no doubt that some of them were able to live in environments that were too cold for ectothermic reptiles, as shown by discoveries of Jurassic and Cretaceous polar vertebrate assemblages which contain dinosaurs but lack turtles and crocodiles. This adaptation of dinosaurs to cool climates invalidates hypotheses according to which dinosaur extinction at the end of the Cretaceous was a result of long-term climatic cooling. The pattern seen at the K/T boundary, with the disappearance of dinosaurs and the survival of ectothermic reptiles, is completely different from that seen in Arctic regions during the Late Cretaceous, where ectotherms disappeared, while dinosaurs subsisted, during cooler periods. The idea of an intense and enduring cold spell at the K/T boundary, caused by the Chicxulub impact, is extremely unlikely in view of the pattern of vertebrate extinction (survival of endotherms, extinction of dinosaurs). Models of environmental events following the impact must take this palaeontological constraint into consideration.     

Polar cyanobacteria versus green algae for tertiary waste-water treatment in cool climates

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened for their potential use in outdoor waste-water treatment systems designed for cold north-temperate climates. The most promising isolate (strain E18, Phormidium sp. from a high Arctic lake) grew well at low temperatures and formed aggregates (flocs) that could be readily harvested by sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean assemblage, denoted Vc) sampled from a tertiary treatment system in Valcartier, Canada. E18 had superior growth rates below 15°C Canada. (μ = 0.20 d-¹ at 10°C under continuous irradiance of 225 μmol photon m-² s-¹) and higher phosphate uptake rates below 10°C (k = 0.050 d-¹ at 5°C) relative to Vc (μ=0.087 d-¹ at 10°C and k = 0.020 d-¹ at 5°C, respectively). The green algal assemblage generally performed better than E18 at high temperatures (at 25°C, μ = 0.39 d-¹ and k = 0.34 d-¹ for Vc; μ = 0.28 d-¹ and k = 0.33 d-¹ for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25°C. Polar cyanobacteria such as strain E18 are appropriate species for waste-water treatment in cold climates during spring and autumn. Under warmer summer conditions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time. This revised version was published online in August 2006 with corrections to the Cover Date.     

被视为恐龙的鸟

尽管于 2 0世纪 2 0年代在亚洲地表层首次发现长有羽毛的恐龙和著名的“龙骨突位点” ,关于鸟类起源的争论仍没有休止。来自化石的证据表明 ,鸟类在进化分支上应归于兽脚类的特殊分支。本文主要阐明完好无损的化石揭示的鸟和非鸟类恐龙的亲密关系和鸟类羽毛及鸟类出现以前的羽毛的起源证据 ,分析体型缩小对飞行进化的重要意义及从新的角度论述鸟类如何飞上了天     

Local climates and growth climates of the sognefjord region

In an agricultural appraisal of a particular region a climatic survey is of great importance. This especially applies to countries like Norway, where climate is marginal for several of the more valuable crops, and where rugged topography induces great contrasts in local climate over short distances. Sognefjord runs nearly due west to east from the Norwegian Sea to the central parts of southern Norway. The regional climate changes from a strongly oceanic type in the western parts to a marked continental type in the innermost parts, some 100 km from the open sea. Over this distance the average length of the growing season, t_d6°C, decreases from about 205 to about 165 days. A three-year survey of the region by means of a network of some 120 climatic stations revealed considerable changes over short distances in irridiation, temperature, precipitation and other climatic elements. The characteristics of the local growth climates are mainly determined by topography (aspect, exposure and height above sea level) and distance from the open sea and fjord. Local variations in warmth-growth climate, here expressed by the length of the growing season and the respiration equivalent, and variations in the water supply, expressed by potential precipitation deficit, are discussed. Practical applications in agricultural planning are considered.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Fossil quality and naming dinosaurs

The intense interest in dinosaurs through the past 30 years might have led to an increase in poor practice in naming new species. A review of the data shows that the reverse is the case. For 130 years, from the 1820s to the 1950s, most new species of dinosaurs were based on scrappy and incomplete material. After 1960, the majority of new species have been based on complete skulls or skeletons, and sometimes on materials from several individuals. This switch in the quality of type specimens corresponds to the recent explosive renaissance of interest in dinosaurs, during which the number of new species named per year has risen, from three or four in the 1950s, to thirty or more today. The pattern of specimen quality varies by continent, with the highest proportion of new species based on good material in North America, then Asia, then South America, then Africa and finally Europe. This ranking reflects a complex pattern of perhaps overstudy in Europe, immensely rich reserves of new dinosaur materials in North America and Asia, and a relative paucity in South America and Africa.     

The cheeks of ornithischian dinosaurs

Except in a couple of very primitive genera the cheek teeth of ornithischians are inset with a lateral space that was roofed by the overhanging maxilla and floored by the massive dentary. This lateral space was delimited by cheeks and the mouth was small. The cheek muscles were not homologous to the Musculus buccinatoris of mammals, but the function was the same, to prevent the loss of food from the sides of the jaws during chewing. The evolution of self-sharpening cheek teeth and of cheeks enabled ornithischians to eat much more resistant plant material and resulted in ornithischians replacing prosauropods as the 'small to medium sized' terrestrial herbivores (up to 10 m).     

Growth dynamics of Australia's polar dinosaurs

Analysis of bone microstructure in ornithopod and theropod dinosaurs from Victoria, Australia, documents ontogenetic changes, providing insight into the dinosaurs' successful habitation of Cretaceous Antarctic environments. Woven-fibered bone tissue in the smallest specimens indicates rapid growth rates during early ontogeny. Later ontogeny is marked by parallel-fibered tissue, suggesting reduced growth rates approaching skeletal maturity. Bone microstructure similarities between the ornithopods and theropods, including the presence of LAGs in each group, suggest there is no osteohistologic evidence supporting the hypothesis that polar theropods hibernated seasonally. Results instead suggest high-latitude dinosaurs had growth trajectories similar to their lower-latitude relatives and thus, rapid early ontogenetic growth and the cyclical suspensions of growth inherent in the theropod and ornithopod lineages enabled them to successfully exploit polar regions.     

Vestigial skeletal structures in dinosaurs

The existence of vestigial structures is one of the main lines of evidence for macroevolution. Here I introduce a phylogenetic bracketing approach to the identification of vestigial structures and apply it to Dinosauria. According to this approach, a structure is considered vestigial if, in comparison with its homolog in at least three successive outgroups, it is reduced to one-third or less its size relative to adjacent structures and if at least distally it has lost the specialized morphology present in the three outgroups. This approach identifies fingers IV and V as vestigial in dinosaurs in general, II–V in sauropods, III in Tyrannosauridae and Caudipteryx , II and III in Shuvuuia and I and III in modern birds. The entire forelimb distal to the elbow is vestigial in Abelisauridae. Vestigial parts of the pelvic girdle and hindlimb include the pubic shaft in Iguanodontia and Ceratopsia, the entire pubis in Ankylosauria, the first metatarsal in derived Iguanodontia, the first metatarsal shaft in Theropoda and the fifth toe in dinosaurs in general. Derived Centrosaurinae and some Chasmosaurus exhibit vestigial supraorbital horns. Some centrosaurines have a vestigial nasal horn. The antorbital cavity is vestigial in Thyreophora, Iguanodontia and Ceratopsidae. I recommend that this information be exploited to increase public awareness of the evidence for macroevolution.     

The phylogenetic relationships of sauropod dinosaurs

A data-matrix of 205 osteological characters for 26 sauropod taxa is subjected to cladistic analysis. Two most parsimonious trees are produced, differing only in the relationships between Euhelopus, Omeisaurus and Mamenchisaurus. The monophyly of the Euhelopodidae (including Shunosaurus) is supported by seven synapomorphies. The Cetiosauridae (Patagosaurus, Cetiosaurus and Haplocanthosaurus) is paraphyletic with respect to the Neosauropoda. The latter clade divides into two major radiations–the ‘Brachiosauria’ (Camarasaurus, brachiosaurids and titanosauroids), and the Diplodocoidea (nemegtosaurids, dicraeosaurids, diplodocids and Rebbachisaurus). Further evidence for the inclusion of Opisthocoelwaudia in the Titanosauroidea is presented. Phuwiangosaurus, a problematic sauropod from Thailand, may represent one of the most plesiomorphic titanosauroids. ‘Peg’-like teeth have evolved at least twice within the Sauropoda. The postspinal lamina, on the neural spines of middle and caudal dorsal vertebrae, represents a neomorph rather than a fusion of pre-existing structures. Forked chevrons may have evolved convergently in the Euhelopodidae and the diplodocid-dicraeosaurid clade, or they may have been acquired early in sauropod evolution and subsequently lost in the ‘Brachiosauria’. The strengths and weaknesses of the data-matrix and tree topologies are explored using bootstrapping, decay analysis and randomization tests. Several nodes are only poorly supported, but this seems to reflect the large proportion of missing data in the matrix (～46%), rather than an abnormally high level of homoplasy. The results of the randomization tests indicate that the ‘data-matrix’ probably contains a strong phylogenetic ‘signal’. The relationships of some forms, such as Haplocanthosaurus, are influenced by the inclusion or exclusion of certain taxa with unusual combinations of character states. Such a result suggests that there are dangers inherent in the view that ‘higher’ level sauropod phylogeny can be accurately reconstructed using only a small number of well-known taxa.     

Climate niches of milkweeds with plesiomorphic traits (Secamonoideae; Apocynaceae) and the milkweed sister group link ancient African climates and floral evolution

? Premise of the study: Climate change that increases mortality of plants and pollinators can create mate-finding Allee effects and thus act as a strong selective force on floral morphology. Milkweeds (Secamonoideae and Asclepiadoideae; Apocynaceae) are typically small plants of seasonally dry habitats, with pollinia and high pollen-transfer efficiency. Their sister group (tribe Baisseeae and Dewevrella) is mostly comprised of giant lianas of African rainforests, with pollen in monads. Comparison of the two groups motivated a new hypothesis: milkweeds evolved in the context of African aridification and the shifting of rainforest to dry forest. Pollinia and high pollen-transfer efficiency may have been adaptations that alleviated mate-finding Allee effects generated by high mortality during droughts. We formally tested whether milkweeds have a drier climate niche by comparing milkweeds with plesiomorphic traits (Secamonoideae) and the milkweed sister group in continental Africa. ? Methods: We georeferenced specimens of the milkweed sister group and Secamonoideae in continental Africa, extracted 19 climatic variables from the Worldclim model, conducted factor analysis to identify correlated suites of variables, and compared the frequency distributions of the two lineages relative to each factor. ? Key results: The distributions of Secamonoideae and the milkweed sister group differed significantly relative to four factors, each correlated with a distinct suite of climate parameters: (1) air temperature (Secamonoideae: cooler), (2) total and (3) summer precipitation (Secamonoideae: drier), and (4) temperature seasonality and isothermality (Secamonoideae: more seasonal and less isothermal). ? Conclusions: Secamonoideae in continental Africa inhabit drier, cooler sites than do the milkweed sister group, consistent with a shift from rainforests to dry forests in a cooling climate.     

Scleromochlus taylori and the origin of dinosaurs and pterosaurs

The phylogenetic position of Scleromochlus taylori has been disputed recently, in terms of whether it is a basal sister group of Pterosauria or of Dinosauromorpha. The seven specimens, all from the Lossiemouth Sandstone Formation (late Carnian, Late Triassic) of Lossiemouth, near Elgin, north-east Scotland, suggest that Scleromochlus shares no unique features with either Pterosauria or Dinosauromorpha, together the Ornithodira, but is a close outgroup. Scleromochlus retains a primitive ankle structure, and it has a slender humerus, femur and fibula. Scleromochlus shows the classic bird-like characters of a tibia that is longer than the femur, and a closely appressed group of four elongate metatarsals. A new group name, Avemetatarsalia (''bird feet''), is established here for the clade consisting of Scleromochlus and Ornithodira, and their descendants. A reanalysis of crown-group archosaur relationships confirms the split into Crurotarsi (crocodile relatives) and Ornithodira (bird relatives), as well as the clear division of Ornithodira into Pterosauria and Dinosauromorpha. Relationships within Crurotarsi are, however, much less clear: Ornithosuchidae probably reside within that clade, and there might be a clade ''Rauisuchia'' consisting of Prestosuchidae and Postosuchus, but support for these relationships is weak. Scleromochlus was probably a bipedal cursor that could adopt a digitigrade stance. However, it is possible that Scleromochlus was also a saltator, capable of leaping long distances.     

Urban climates and the natural environment

The exponential increase in world population accompanied by a growing concentration of these people in towns, create changes in climate not only within but also beyond city margins. Indeed, the modifications may in some cases be world-wide. Cities, because of changes in the heat and water balances and in the chemistry of their air in comparison with rural areas, generate a quite distinctive type of climate, the main features of which are analysed in this paper, more especially in so far as they affect the rural fringes of cities. Air pollution, radiation and sunshine, temperatures, humidities and the patterns of airflow in and around urban areas are considered in turn, particular attention being paid to their effects upon vegetation growth.     

Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition

The timing of sexual maturation in non-avian dinosaurs is not known. In extant squamates and crocodilians it occurs in conjunction with the initial slowing of growth rates as adult size is approached. In birds (living dinosaurs) on the other hand, reproductive activity begins well after somatic maturity. Here we used growth line counts and spacing in all of the known brooding non-avian dinosaurs to determine the stages of development when they perished. It was revealed that sexual maturation occurred well before full adult size was reached-the primitive reptilian condition. In this sense, the life history and physiology of non-avian dinosaurs was not like that of modern birds. Palaeobiological ramifications of these findings include the potential to deduce reproductive lifespan, fecundity and reproductive population sizes in non-avian dinosaurs, as well as aid in the identification of secondary sexual characteristics.     

Deccan volcanism,the KT mass extinction and dinosaurs

Recent advances in Deccan volcanic studies indicate three volcanic phases with the phase-1 at 67.5 Ma followed by a 2 m.y. period of quiescence. Phase-2 marks the main Deccan volcanic eruptions in Chron 29r near the end of the Maastrichtian and accounts for ∼80% of the entire 3500 m thick Deccan lava pile. At least four of the world’s longest lava flows spanning 1000 km across India and out into the Gulf of Bengal mark phase-2. The final phase-3 was smaller, coincided with the early Danian Chron 29n and also witnessed several of the longest lava flows. The KT boundary and mass extinction was first discovered based on planktic foraminifera from shallow marine intertrappean sediments exposed in Rajahmundry quarries between the longest lava flows of the main volcanic phase-2 and smaller phase-3. At this locality early Danian (zone P1a) planktic foraminiferal assemblages directly overlie the top of phase-2 eruptions and indicate that the masse extinction coincided with the end of this volcanic phase. Planktic foraminiferal assemblages also mark the KT boundary in intertrappean sediments at Jhilmili, Chhindwara, where freshwater to estuarine conditions prevailed during the early Danian and indicate the presence of a marine seaway across India at KT time.     

Mechanics of posture and gait of some large dinosaurs

Dimensions of dinosaur bones and of models of dinosaurs have been used as the basis for calculations designed to throw light on the posture and gaits of dinosaurs.
Estimates of the masses of some dinosaurs, obtained from the volumes of models, are compared with previous estimates. The positions of dinosaurs' centres of mass, derived from models, show that some large quadrupedal dinosaurs supported most of their weight on their hind legs and were probably capable of rearing up on their hind legs.
Distributions of bending moments along the backs of large dinosaurs are derived from measurements on models. The tensions required in epaxial muscles to enable Diplodocus to stand are calculated. It is likely that the long neck of this dinosaur was supported by some structure running through the notches in the neural spines of its cervical and dorsal vertebrae. The nature of this hypothetical structure is discussed.
An attempt is made to reconstruct the walking gait of sauropod dinosaurs, from the pattern of footprints in fossil tracks.
The dimensions of dinosaur leg bones are compared to predictions for mammals of equal body mass, obtained by extrapolation of allometric equations. Their dimensions are also used to calculate a quantity which is used as an indicator of strength in bending. Comparisons with values for modern animals lead to speculations about the athletic performance of dinosaurs.
Estimates of pressures exerted on the ground by the feet of dinosaurs are used in a discussion of the ability of dinosaurs to walk over soft ground.     

Avian-like breathing mechanics in maniraptoran dinosaurs

In 1868 Thomas Huxley first proposed that dinosaurs were the direct ancestors of birds and subsequent analyses have identified a suite of 'avian' characteristics in theropod dinosaurs. Ossified uncinate processes are found in most species of extant birds and also occur in extinct non-avian maniraptoran dinosaurs. Their presence in these dinosaurs represents another morphological character linking them to Aves, and further supports the presence of an avian-like air-sac respiratory system in theropod dinosaurs, prior to the evolution of flight. Here we report a phylogenetic analysis of the presence of uncinate processes in Aves and non-avian maniraptoran dinosaurs indicating that these were homologous structures. Furthermore, recent work on Canada geese has demonstrated that uncinate processes are integral to the mechanics of avian ventilation, facilitating both inspiration and expiration. In extant birds, uncinate processes function to increase the mechanical advantage for movements of the ribs and sternum during respiration. Our study presents a mechanism whereby uncinate processes, in conjunction with lateral and ventral movements of the sternum and gastral basket, affected avian-like breathing mechanics in extinct non-avian maniraptoran dinosaurs.     

Triassic environments, climates and reptile evolution

A consideration of all the available data on Triassic vertebrate faunas, and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal-like reptiles and the herbivorous rhynchosaurs in the Norian of the Upper Triassic. This event was apparently quickly followed by the radiation of the dinosaurs, also in the Norian. This conclusion suggests that competition was not the main factor in the initial success of the dinosaurs, but opportunistic radiation following the extinction of major reptile groups. A global review of Triassic sedimentary facies shows that there were climatic and floral changes towards the end of the Triassic. It is envisaged that increasing aridity in the later Triassic, resulting from plate motions and particularly affecting Gondwanaland and southwestern Laurasia, brought about floral changes and then the reptile extinctions. With the rapid evolution of new floras of conifers and bennettitaleans, the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years.     

Evolution of olfaction in non-avian theropod dinosaurs and birds

Little is known about the olfactory capabilities of extinct basal (non-neornithine) birds or the evolutionary changes in olfaction that occurred from non-avian theropods through modern birds. Although modern birds are known to have diverse olfactory capabilities, olfaction is generally considered to have declined during avian evolution as visual and vestibular sensory enhancements occurred in association with flight. To test the hypothesis that olfaction diminished through avian evolution, we assessed relative olfactory bulb size, here used as a neuroanatomical proxy for olfactory capabilities, in 157 species of non-avian theropods, fossil birds and living birds. We show that relative olfactory bulb size increased during non-avian maniraptoriform evolution, remained stable across the non-avian theropod/bird transition, and increased during basal bird and early neornithine evolution. From early neornithines through a major part of neornithine evolution, the relative size of the olfactory bulbs remained stable before decreasing in derived neoavian clades. Our results show that, rather than decreasing, the importance of olfaction actually increased during early bird evolution, representing a previously unrecognized sensory enhancement. The relatively larger olfactory bulbs of earliest neornithines, compared with those of basal birds, may have endowed neornithines with improved olfaction for more effective foraging or navigation skills, which in turn may have been a factor allowing them to survive the end-Cretaceous mass extinction.