Nové abstrakty k 22.3.2010

   Nových abstraktů je tentokrát skutečně velké množství, a to jsou z tohoto přehledu ještě vynechány výhradně paleoklimatologické práce bez užšího vztahu k pan-avianům. Sérii výtahů opět (až na jedinou výjimku, kterým je popis juvenilního jedince lufengosaura z Acta Geologica Sinica) shromáždil Jerry Harris - tak tomu bylo i v prvním případě a totéž lze pravidelně očekávat i v budoucnosti. Abstrakty ve většině případů pocházejí z aktuálních vydání žurnálů Palaeogeography, Palaeoclimatology, Palaeoecology a Journal of Systematic Palaeontology.

    Jedním z nejzajímavějších je podle mého práce Rogera Bensona, který pokračuje ve své už několik let trvající sérii sólových prací o britských střednějurských primitivních tetanurách. Dočkali jsme se nového popisu nejstaršího známého dinosaura, megalosaura, stejně jako obsáhlé kladistické analýzy potvrzující megalosauroidní příslušnost některých problematický taxonů typu piveteausaura. Nyní přišel na řadu Magnosaurus nethercombensis, jeho revize však, zdá se, nebyla jediným předmětem práce. Autor se v ní také zabývá veškerým materiálem, který byl prohlašován za tetanuří a který svým stářím magnosaura převyšuje. Tato škála je relativně pestrá a zahrnuje jak anonymní materiál, který už někdy ani nelze podrobit osobnímu přezkoumání (ztracený materiál ze syntypové série druhu 'Streptospondylus cuvieri'), tak i celkem slušně známé druhy (Cryolophosaurus ellioti). Svým stářím se tyto fosilie pohybují od ještě relativně rozumného toarku, posledního stupně spodní jury, až po svrchnotriasový nor, ve kterém by přítomnost tetanury dnešní časovou kalibraci fylogenetických hypotéz skutečně "rozhodila". To, že mezi tetanury těžko patří Protoavis, by nikoho nemělo překvapit; jakmile opustíme Chatterjeeho velmi kontroverzní "ptačí interpretaci" a přijmeme současný konsenzus, podle kterého se jedná o chiméru složenou z pozůstatků celkem primitivních diapsidů a těžko zařaditelného teropodního materiálu, stane se podpora pro tuto hypotézu velmi slabou. Stejně tak Cryolophosaurus byl již dříve odhalen jako zástupce kladu blízkého dilofosaurovi, který dosud nemá formálně definované jméno a který je výrazně primitivnější než tetanury (Smith et al. 2007). Celkem zajímavé ale je, že ani spodnojurský čínský therizinosaur Eshanosaurus podle Bensona nemůže být bezpečně identifikován jako tetanura; Barrett (2009) přitom nenašel proti tomuto výkladu, založenému na celkem typické stavbě čelistí a chrupu, vážný protiargument.

    Stejně zajímavá je i fylogenetická studie archosaurů od Brusatteho a kolektivu, přestože se soustředí hlavně na strukturu druhého hlavního sub-kladu archosaurů, pan-krokodylianů. Autoři tvrdí, že jejich výsledky dobře odpovídají stratigrafickým datům. Naznačené vztahy vyžadují relativně dlouhé chybějící linie ve spodním triasu, a podporují existenci velkého vymírání mezi karnem a norem, které mohlo být přímo zodpovědné za první velký evoluční úspěch dinosaurů. Bylo by jistě zajímavé vědět, jaký pterosauří taxon Brusattemu a ostatním vyšel jako nejbazálnější nebo jaká je pozice skleromochla (byl-li vůbec zahrnut), ale o tom už abstrakt neinformuje. Z dalších prací lze zmínit ty, které se tak či onak týkají ontogeneze - již zmíněný juvenilní jedinec sauropodomorfa druhu Lufengosaurus huenei ukazuje na rozdíly, které panovaly mláďaty a dospělci této skupiny pan-avianů a v souvislosti s dalšími podobnými objevy dokazuje, že i velmi konkrétní anatomické změny lze zobecnit. Rumunští paleontologové mezitím dokazují, že jistý specifický typ fosilizovaných vajec mohl patřit nejen titanosaurům, jak se obecně soudí, ale i bazálním hadrosauridům. A přestože už nejsem daleko od toho, abych vyjmenoval rovnou všechny zde přetištěné abstrakty, zmínku si určitě zaslouží i práce Honeho a kolektivu popisující objev, jenž výmluvným způsobem - byť ne tak dramatickým, jako známá fosilie "zmrazená v boji" - dokládá a rozvíjí potravní vztahy mezi dravým dromaeosauridem velociraptorem a býložravým protoceratopsem.

Benson, R. B. J. 2010. The osteology of Magnosaurus nethercombensis (Dinosauria, Theropoda) from the Bajocian (Middle Jurassic) of the United Kingdom and a re-examination of the oldest records of tetanurans. Journal of Systematic Palaeontology 8 (1):131-146.

Magnosaurus nethercombensis from the Lower Bajocian (Middle Jurassic) of Dorset, UK is a valid species, possessing a single autapomorphy: the presence of anteroposteriorly elongate foramina, inclined anterodorsally and located ventrally on the lateral surface of the dentary. It is the oldest known definite tetanuran dinosaur and shows two tetanuran features: a reduced ischial peduncle of the ilium and the presence of a marked femoral extensor groove. Other records of putative early tetanurans are reviewed: 'Zanclodon cambrensis' from the Rhaetian of Wales; remains from the Norian-Hettangian of Switzerland; Shuvosaurus and Protoavis from the Norian of Texas; Eshanosaurus from the Hettangian of China; theropod remains originally included in the syntype series of Scelidosaurus from the Hettangian-Sinemurian of England; a fragmentary skeleton from the Sinemurian of Italy; Cryolophosaurus from the Sinemurian-Pliensbachian of Antarctica; the partial skeleton of a small theropod from the Toarcian of Morocco; and the lost syntype material of 'Streptospondylus cuvieri' from the Toarcian of Whitby. None of these records can be confidently considered to be the earliest tetanuran record. An early Middle Jurassic age for the earliest-known tetanuran is more consistent with a restricted content of Ceratosauria, comprising Ceratosaurus, Elaphrosaurus, and abelisauroids, than with a wider content including coelophysoids, due to reduction in the length of phylogenetic ghost lineages. 

Brusatte, S.L., Benton, M.J., Desojo, J.B., and Langer, M.C. 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida). Journal of Systematic Palaeontology 8 (1):3-47.

Crown group Archosauria, which includes birds, dinosaurs, crocodylomorphs, and several extinct Mesozoic groups, is a primary division of the vertebrate tree of life. However, the higher-level phylogenetic relationships within Archosauria are poorly resolved and controversial, despite years of study. The phylogeny of crocodile-line archosaurs (Crurotarsi) is particularly contentious, and has been plagued by problematic taxon and character sampling. Recent discoveries and renewed focus on archosaur anatomy enable the compilation of a new dataset, which assimilates and standardizes character data pertinent to higher-level archosaur phylogeny, and is scored across the largest group of taxa yet analysed. This dataset includes 47 new characters (25% of total) and eight taxa that have yet to be included in an analysis, and total taxonomic sampling is more than twice that of any previous study. This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosauria and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades. Support values are low, suggesting rampant homoplasy and missing data within Archosauria, but the phylogeny is highly congruent with stratigraphy. Comparison with alternative analyses identifies numerous scoring differences, but indicates that character sampling is the main source of incongruence. The phylogeny implies major missing lineages in the Early Triassic and may support a Carnian-Norian extinction event. 

Dumont, E. R. 2010. Bone density and the lightweight skeletons of birds. Proceedings of the Royal Society B: Biological Sciences. doi: 10.1098/rspb.2010.0117.

The skeletons of birds are universally described as lightweight as a result of selection for minimizing the energy required for flight. From a functional perspective, the weight (mass) of an animal relative to its lift-generating surfaces is a key determinant of the metabolic cost of flight. The evolution of birds has been characterized by many weight-saving adaptations that are reflected in bone shape, many of which strengthen and stiffen the skeleton. Although largely unstudied in birds, the material properties of bone tissue can also contribute to bone strength and stiffness. In this study, I calculated the density of the cranium, humerus and femur in passerine birds, rodents and bats by measuring bone mass and volume using helium displacement. I found that, on average, these bones are densest in birds, followed closely by bats. As bone density increases, so do bone stiffness and strength. Both of these optimization criteria are used in the design of strong and stiff, but lightweight, manmade airframes. By analogy, increased bone density in birds and bats may reflect adaptations for maximizing bone strength and stiffness while minimizing bone mass and volume. These data suggest that both bone shape and the material properties of bone tissue have played important roles in the evolution of flight. They also reconcile the conundrum of how bird skeletons can appear to be thin and delicate, yet contribute just as much to total body mass as do the skeletons of terrestrial mammals.

Grigorescu, D., Garcia, G., Csiki, Z., Codrea, V. & Bojar, A.-V. 2010. Uppermost Cretaceous megaloolithid eggs from the Haţeg Basin, Romania, associated with hadrosaur hatchlings: search for explanation. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.031.

Four localities in the Upper Cretaceous (Maastrichtian) of the Haţeg Basin (in order of discovery, Tuştea, Toteşti-baraj, Nălaţ-Vad and Livezi) have yielded clutches of megaloolithid eggs. Egg morphology and size, eggshell thickness, external ornamentation and internal microstructure, pore density and geometry, as well as morphology of the clutches (where this could be observed) are all similar among the four localities, allowing the assignment of the eggs to Megaloolithus cf. siruguei. Most egg occurrences are related to paleosols of variable chemical composition and maturity, developed within different parts of the floodplain.
The nesting horizon from Tuştea was partially reconstructed on a 160 m2 surface, allowing a thorough analysis of the taphonomy of the eggs and clutches. It has also yielded hatchling remains at different ontogenetic developmental stages, and even, more rarely, embryo remains as well. The bones occur in the vicinity of or even within the clutches; in a single case, incompletely ossified embryonic skeletal remains, including a dentary tooth, were found inside an incomplete egg. Without exception, the neonate remains belong to the basal hadrosaurid Telmatosaurus transsylvanicus, one of the common dinosaur species in the faunal assemblage. No sauropod neonate remains were found in the nesting horizon from Tuştea; only a fragmentary pelvic girdle and caudal vertebrae of an adult titanosaurian were unearthed recently 20 cm above the nesting horizon. None of the other three megaloolithid localities in the Haţeg Basin provided neonatal remains of any dinosaur species.
Despite the general consensus that the Megaloolithus oogenus belongs exclusively to titanosaurian sauropods, the co-occurrence of megaloolithid eggs and hadrosaurid neonatal remains at Tuştea seems to contradict this view. Previous cladistic analyses of dinosauroid ootaxa might offer an explanation of this controversial issue. These analyses have revealed that Megaloolithidae appears to be the sister-group of Spheroolithidae, usually regarded as a hadrosaurid egg family. Perhaps a significant amount of homoplasy is present in the evolution of dinosaurian eggs, whose structure depends on incubation environment as well as biology and physiology of the reproductive system itself, and that the oospecies of Megaloolithus might have been laid by different higher-level taxa, including both titanosaurian sauropods and (basal) hadrosaurids. Understanding the significance of this paraphyletic distribution requires further study.

Hone, D. W. E., Choiniere, J., Sullivan, C., Xu, X., Pittman, M. & Tan, Q. 2010. New evidence for a trophic relationship between the dinosaurs Velociraptor and Protoceratops. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.028.

Reconstructing the palaeoecology of extinct tetrapods is fraught with difficulties. Fossilized evidence of direct trophic interactions between tetrapods is rare, whether the interactions involve predation or scavenging. Typically this evidence is limited to preserved stomach contents or bite marks on bones (when they can be confidently attributed to specific taxa) that make it possible to begin to piece together the trophic webs that existed in ancient ecosystems. The dramatic ‘fighting dinosaurs’ fossil of a Velociraptor preserved in combat with a Protoceratops provides an outstanding, but still lone, example of the two taxa interacting. Here new evidence of a Velociraptor feeding on the carcass of a Protoceratops is presented, based on tooth-marked bones of the latter that were found in association with shed teeth of the former in Upper Cretaceous deposits at Bayan Mandahu, Inner Mongolia, China. In contrast to the case of the fighting dinosaurs, which seems to represent active predation by a Velociraptor, the tooth marks on the Bayan Mandahu material are inferred to have been produced during late-stage carcass consumption either during scavenging or following a group kill. Feeding by Velociraptor upon Protoceratops was probably a relatively common occurrence. 

Marsicano, C. A., Mancuso, A. C., Palma, R. M. & Krapovickas, V. 2010. Tetrapod tracks in a marginal lacustrine setting (Middle Triassic, Argentina): taphonomy and significance. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.009.

Fossil tetrapod footprints not only provide valuable information about trackmaker paleobiology but also to give insight into details of the depositional conditions of the substrate at the time of imprinting. Therefore, in the present study the mode of formation and taphonomy of footprints in different substrates was used to investigate the gait and walking dynamics of the trackmakers as well as a source of additional information on the environmental conditions of the track-bearing beds during imprinting.
  The analyzed section corresponds to thick Middle Triassic lacustrine/deltaic deposits of the Ischichuca/Los Rastros Formation (Ischigualasto-Villa Unión Basin) that crops out at the Quebrada de Ischichuca in northwestern Argentina. Part of the track-bearing surfaces correspond to the top of sandy distributary channel mouth bars in a distal delta front setting that were exposed along the lake margin during a lake level fall. Cross-cutting relationships observed among ripple-marks, the footprints, and invertebrate traces of a softground suite of the Scoyenia ichnofacies suggest an omission surface. Measured trackway orientations in the sandstones are perpendicular to the paleo-shoreline, with the animals coming and going along the exposed top of the bars, probably for drinking. Laterally, the distal delta front deposits interfinger with track-bearing wackestone beds of palustrine origin deposited in a restricted local embayment lateral to the delta influenced environment. Trackway orientations in the wackestones are, in contrast, consistent with the animals moving nearly parallel to the lake border, probably along a preferred route. Evidences of a relative high groundwater table at the time of imprinting in the track-bearing surfaces are revealed by the well developed rims of extruded sediment and collapsed digits in the studied tracks and the nearly absence of associated desiccation cracks on the same surfaces. Nevertheless, temporary emergence cannot be ruled out when paleosoil formation was probably promoted as can be observed in the microstructure of both sandstones and wackestones. Moreover, footprint preservation in the wackestones might have been enhanced by partial hardening of the trampled surface during subaerial exposure. Combining ichnofossil content and taphonomy with facies analysis we identified in the lower part of the Ischichuca/Los Rastros succession a relatively rapid withdrawal of the water basinward that was probably due to a forced regression during early rifting of basin evolution.
  Footprints can also provide valuable information about locomotion dynamics and trackmaker behavior. Thus, the sideways deformation observed in the studied footprints, attributed to basal archosaurs and putative basal dinosaurs, can be related to an outward rotation of the foot during the step cycle, a condition that might allied to the development of the parasagittal posture in Archosauria. Besides, the densely trampled surface described herein constitutes the first documented evidence of putative social behavior among therapsid dicynodonts, the most important group of herviborous animals in the early Mesozoic terrestrial ecosystems throughout Gondwana. 

Sekiya, T. & Dong, A., 2010. A new juvenile specimen of Lufengosaurus huenei Young, 1941 (Dinosauria: Prosauropoda) from the Lower Jurassic Lower Lufeng Formation of Yunnan, Southwest China. Acta Geologica Sinica - English Edition, 84 (1):11-21.

A skull and a series of associated cervical vertebrae (ZLJ0112) discovered from the Lower Lufeng Formation (Lower Jurassic) are determined as a juvenile specimen of Lufengosaurus huenei Young 1941 based on amended autapomorphies. Differences between ZLJ0112 and the holotype (sub-adult specimen) are considered as ontogenetic characteristic changes of L. huenei. Since some of these differences are present in other prosauropod dinosaurs (i.e., forms of the maxillary vascular foramen are irregular; the frontal contribution to the dorsal margin of the orbit is substantial; the frontal contribution to the supratemporal fossa is absent; the supratemporal fenestra is visible in lateral view; the supraoccipital inclined at 75 degrees; the parasphenoid rostrum lies level with the occipital condyle; the retroarticular process is short; the axial postzygapophysis project caudally beyond the end of the centrum) they may be common ontogenetic changes in prosauropod dinosaurs.

Weishampel, D. B., Csiki, Z., Benton, M. J., Grigorescu, D. & Codrea, V. 2010. Palaeobiogeographic relationships of the Haţeg biota – between isolation and innovation. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.024.

The biogeographic significance of the Late Cretaceous Haţeg fauna is assessed using both faunal and phylogenetic analyses. Although extremely endemic at the species level, the Haţeg fauna is part of a larger European palaeobioprovince compared to roughly contemporary (Campanian-Maastrichtian) terrestrial faunas elsewhere in Europe. Phylogenetic analyses of five Haţeg taxa, calibrated by biostratigraphic occurrences provide evidence of long ghost lineages. The geographic distributions of kogaionids, Kallokibotion, Allodaposuchus, and Zalmoxes (together with their European sister taxa) may have arisen from vicariant events between western Europe and North America, while the distribution of Telmatosaurus is an example of European endemism of Asiamerican origin.
While Haţeg seems to have acted as a dead-end refugium for Kallokibotion and Telmatosaurus, other faunal members (and their immediate sister taxa) are not restricted to Transylvania, but known otherwise from localities across southern Europe. In addition, Transylvania may have acted as an evolutionary cradle for kogaionids.
Transylvania and the other southern faunas of Europe may represent a distinct division of the Late Cretaceous European palaeobioprovince. A boundary between this Tethyan Europe and the more western and northern cratonic Europe suggests something like the Wallace Line in the Malay Archipelago, in which two distinct faunal provinces with separate histories within a much larger, seemingly uniform geographic region are separated by a narrow boundary.

Zdroje:

• Barrett, P. M. 2009. The affinities of the enigmatic dinosaur Eshanosaurus deguchiianus from the Early Jurassic of Yunnan Province, People's Republic of China. Palaeontology 52 (4):681-688. 
• Smith, N. D., Makovicky, P. J., Hammer, W. R. & Currie, P. J. 2007. Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society 151:377–421.