FIRST GLIMPSE OF THE SILICIFIED HOT SPRING BIOTA FROM A NEW JURASSIC CHERT DEPOSIT IN THE DESEADO MASSIF, PATAGONIA, ARGENTINA
Authors:
Massini et al
Abstract:
Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discovery of a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved within the geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in-situ and transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns and gymnosperms. Among them, well-preserved in-situ osmundaceous rhizomes in different developmental stages are the dominant component of the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae. The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas, ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropod remains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossil assemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, and exceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantial contribution to the reconstruction of middle Mesozoic terrestrial ecosystems.
Cranial anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China
Authors:
Han et al
Abstract:
Yinlong downsi, from the Upper Jurassic Shishugou Formation, Xinjiang, northwestern China, is the oldest known ceratopsian dinosaur. Here we provide a detailed description of the skull and mandible based on the holotype, three partial skulls, and disarticulated materials from several other specimens. Yinlong can be diagnosed by six autapomorphies: a distinct fossa along the midline of the frontals; a slit-like carotid canal bordered by laminae; premaxillary teeth with a vertical wear facet and a basal shelf; a deep sulcus on the ventral surface of the quadratojugal; large oval nodules concentrated on the lateral surface of the jugal; and a squamosal with an expanded dorsal surface and a long, constricted quadrate process. A detailed comparison with other basal ceratopsians suggests that Yinlong downsi may belong within Chaoyangsauridae. Yinlong also shares many derived characters both with Psittacosaurus and neoceratopsians, suggesting that character evolution in early ceratopsians is complex. Additionally, a caniniform premaxillary tooth is present in one small specimen (IVPP V18636), which may suggest sexual dimorphism or individual variation.
The relationships of Cuspicephalus scarfi Martill and Etches, 2013 and Normannognathus wellnhoferi Buffetaut et al., 1998 to other monofenestratan pterosaurs
Authors:
Witton et al
Abstract:
The evolution of pterodactyloid pterosaurs occurred in a ‘modular’ fashion with ‘pterodactyloid’-type crania and cervical vertebrae evolving in pterodactyloid sister taxa – early monofenestratan pterosaurs – before later postcervical modifications marked the development of the true pterodactyloid condition. This means of evolution creates problems for distinguishing isolated pterodactyloid crania from those of non-pterodactyloid monofenestratans, and has led to uncertainty over the affinities of two Late Jurassic European pterosaurs known only from skulls, Cuspicephalus scarfi Martill and Etches, 2013 and Normannognathus wellnhoferi Buffetaut et al., 1998. Some aspects of their cranial anatomy suggest affinities to early pterodactyloids – specifically the Germanodactylidae – while others indicate a relationship with a group of non-pterodactyloid monofenestratans, the Wukongopteridae. Here, we characterise the skulls of Jurassic monofenestratans to provide greater insight into the identity of these pterosaurs. We find a suite of characters indicating that Cuspicephalus is a wukongopterid, notable for being a particularly large and long snouted member of the group, as well as the youngest, and the first European record of this clade. The affinities of Normannognathus are less clear however. We consider its previous allocation to the Germanodactylidae doubtful, and note some similarities it shares with ctenochasmatoid pterodactyloids, but the only known specimen is probably too fragmentary for confident referral to any specific clade within Monofenestrata.
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A new rhamphorhynchid pterosaur (Pterosauria) from Jurassic deposits of Liaoning Province, China
Authors:
Lü et al
Abstract:
Compared to pterosaurs from the Early Cretaceous from China, Late Jurassic pterosaurs are relatively rare. A new rhamphorhynchid pterosaur, Orientognathus chaoyngensis gen. et sp. nov., is erected based on an incomplete skeleton from the Upper Jurassic Tuchengzi Formation of Chaoyang, Liaoning Province, China. It is identified by the following characters: the toothless tip of the lower jaw is slightly pointed; the length ratio of wing metacarpal to humerus is 0.38, the ulna is shorter than each wing phalanx and the tibia is nearly equal to femur in length. A phylogenetic analysis recovers Orientognathus chaoyngensis as a rhamphorhynchid pterosaur. Orientognathus chaoyngensis is perhaps the youngest Jurassic pterosaur from western Liaoning Province of China.
Upper Jurassic Lagerstätte Shar Teg, southwestern Mongolia
Authors:
Ponomarenko et al
Abstract:
One of the most interesting Mesozoic Lagerstätten, Shar Teg in southwestern Mongolia, is reviewed. The geological structure and oryctocoenoses of Shar Teg are described. Shar Teg is one of the most diverse Jurassic Lagerstätten in terms of fossils represented. Fossils from Shar Teg include aquatic and terrestrial plants, mollusks, crustaceans, insects, fishes, amphibians, reptiles, and mammals. Insects are the most diverse group. To date, a total of 297 species of 161 families and 22 orders have been described or recorded in Shar Teg, making it possible to reconstruct comprehensively the Jurassic biota of the locality. The oryctocoenosis composition is peculiar; it includes only six species described from other localities. The oryctocoenosis appears to link the faunas of eastern Asia, Central Asia, and Europe. A total of 31 new species are described.
A New Upper Jurassic Ophthalmosaurid Ichthyosaur from the Slottsmøya Member, Agardhfjellet Formation of Central Spitsbergen
Authors:
Roberts et al
Abstract:
Abundant new ichthyosaur material has recently been documented in the Slottsmøya Member of the Agardhfjellet Formation from the Svalbard archipelago of Norway. Here we describe a partial skeleton of a new taxon, Janusaurus lundi, that includes much of the skull and representative portions of the postcranium. The new taxon is diagnosed by a suite of cranial character states including a very gracile stapedial shaft, the presence of a dorsal process on the prearticular and autapomorphic postcranial features such as the presence of an interclavicular trough and a conspicuous anterodorsal process of the ilium. The peculiar morphology of the ilia indicates a previously unrecognized degree of morphological variation in the pelvic girdle of ophthalmosaurids. We also present a large species level phylogenetic analysis of ophthalmosaurids including new and undescribed ichthyosaur material from the Upper Jurassic of Svalbard. Our results recover all Svalbard taxa in a single unresolved polytomy nested within Ophthalmosaurinae, which considerably increases the taxonomic composition of this clade. The paleobiogeographical implications of this result suggest the presence of a single clade of Boreal ophthalmosaurid ichthyosaurs that existed during the latest Jurassic, a pattern also reflected in the high degree of endemicity among some Boreal invertebrates, particularly ammonoids. Recent and ongoing descriptions of marine reptiles from the Slottsmøya Member Lagerstätte provide important new data to test hypotheses of marine amniote faunal turnover at the Jurassic-Cretaceous boundary.
Greater palaeobiodiversity in conifer seed cones in the Upper Jurassic Morrison Formation of Utah, USA
Authors:
Gee et al
Abstract:
Although fossil conifer wood, leaves, and pollen have been known from the Upper Jurassic Morrison Formation of the Western Interior of North America for many decades, only a few conifer seed cones have been described as carbonaceous compressions and casts with little internal structure. Recently, however, over 60 silicified seed cones with preserved internal anatomy were amassed by collectors from 11 localities in northeastern and southern Utah and brought to the attention of palaeobotanists. Here we describe the silicified cones from Utah and compare them to one another in size, gross morphology and internal construction. The fossil material is sorted into five new morphotypes of seed cone. Morphotype 1 pertains to Araucariaceae, Morphotype 2 is most likely Pinaceae, and Morphotype 5 is Cheirolepidiaceae. The familial affinity of Morphotypes 3 and 4 cannot be determined at this time. Comparative size analysis based on volume calculations shows that Morphotypes 2, 3, 4 and 5 are extremely small, smaller than any Mesozoic araucarian seed cone, and that Morphotype 1 falls within the range of small fossil araucarian cones. Most cone-bearing localities are situated to the northwest, west, and south of Hanksville in southcentral Utah. With regard to palaeobiodiversity, if Araucaria delevoryasii Gee from Wyoming is included, there are now six morphotypes of seed cones that represent at least three conifer families in Utah and Wyoming. Because many conifers are arborescent and form forests, the new fossil evidence suggests that species-diverse conifer forests or woodlands were a major type of vegetation in the Morrison Formation during the Late Jurassic.
