Geobios最新文献

We describe the vertebrate remains found in a Holocene deposit inside the Taiti Cave, Socotra Island (Yemen). The fossils were found in a sand dune occupying almost entirely the main cavity of the Cave, with some bones collected on the surface and the majority of them found under its surface, in particular below a tiny level of hardened sand, the latter probably related to a guano deposit. They were mostly isolated bones, but under the guano layer, some of them were aggregated and recognizable as belonging to owl pellets. The analysis of the vertebrate remains reveals a great prey diversity and, together with the location of the pellet accumulation and the almost perfect preservation of the remains, indicates that the deposit derived from a pellet accumulation made by Tyto alba. This hypothesis is corroborated by a Tyto alba beak fragment found in the Hoq cave, in a deposit of uncertain stratigraphic context. The data presented herein represent the first documented evidence of the presence of Tyto alba on Socotra Island and indicate the probable existence of a now extinct population of Tyto alba on the island during the Holocene, already extinct at the time of the first ornithological surveys during the XIX Century.

Night herons of the genus Nycticorax and Nyctanassa are adept island colonisers, occurring on a number of oceanic islands and island archipelagos. Continental species and those inhabiting large islands are generally not considered threatened, whereas night herons restricted to small, oceanic islands are particularly vulnerable to human interference. As a result, six out of nine described species and one subspecies, all derived from Nycticorax nycticorax, Nycticorax caledonicus or Nyctanassa violacea, are now extinct whereas a further three extinct species await description. The extinct island endemics generally exhibit morphological adaptations to an insular environment and diet, such as an increase or decrease in size, robust jaws and legs, and smaller wings with associated reduced flying ability than founding stock. Here I present an osteological comparison along with historical descriptions of the extinct, oceanic island night herons, with special reference to the Mascarene and Ascension fossil species, and Bonin Island subspecies, and show the degree of morphological changes between the founding and island taxa. I further discuss the reasons why they became extinct.

Linguliformean and craniiformean brachiopods from the Middle and Upper Ordovician of the Brabant Massif (Belgium) are described for the first time and their palaeoecological and palaeobiogeographical implications are discussed. The restricted and generally poorly preserved material was collected from the Abbaye de Villers (Dapingian–Darriwilian) Formation and from the Katian Huet and Fauquez formations. The dark graptolitic mudstones of the latter unit yielded the most diverse assemblage including seven pseudolingulid, obolid, discinid, and craniopsid species while the Abbaye de Villers and Huet formations only yielded one species each. Due to the scarcity of internal morphological details available, comparison of the pseudolingulid and obolid specimens under investigation here was undertaken by running a Principal Component Analysis using a Log-Shape Ratio transformation of linear measurements. The study of valve shape changes at various growth stages helped identify these Belgian specimens at the family and generic levels. Finally, two unusually long (up to 20 mm) shell repair scars are documented in Pseudolingula and reflect predatory attacks at the anterior margin during early growth stages.

A systematic description of the so far unique trilobite fauna and the associated biota from the Arenarie di San Vito Formation, in the outcrops close to the abandoned Tacconis mine (allochthonous nappe zone, Sarrabus, SE Sardinia, Italy), proves the occurrence of Taihungshania shui landayranensis, Ampyx priscus, Asaphellus sp., Merlinia sp., Niobe fourneti?, Geragnostus sp. and Symphysurus sp., accompanied by several taxa of graptolites, ichnofossils and less common bivalves, gastropods, cephalopods and hyolithids. The taphonomical signature, sedimentary structures and “Raphiophorid biofacies” clearly argue for an early Floian age and a median platform (i.e., offshore to shoreface) depositional environment. The occurrence of T. shui landayranensis in Sardinia allows us to determine the age of the Arenarie di San Vito Formation (just below the Sarrabese unconformity) and to discuss the palaeobiogeographical affinities highlighting the value of the “Taihungshania bioprovince”. The Tacconis trilobite fauna displays close affinities with Montagne Noire in France, Taurides in Turkey, Alborz in Iran, and south China, placing the SE Sardinia allochthonous area in a global Ordovician palaeogeographic sketch. A brief discussion on relationships and palaeobiogeographical affinities between the Sardinian nappe zone and the autochthonous “foreland” Sulcis-Iglesiente, which are adjacent today, strongly suggests a separation during the Ordovician, although both areas pertain to the Gondwana margin.

Exceptional fossils preserve non-biomineralized tissues in the geological record and provide crucial information on the evolution of life on Earth. Exceptionally preserved fossils are rarely discovered complete, challenging their morphological description and their palaeontological interpretation. Although decay experiments reconstructing degradation sequences in modern animals are necessary to better understand taphonomic processes involved in exceptional preservation, their applicability to some enigmatic and/or extinct fossil taxa remains limited. Here, based on a representative sample of 423 specimens collected from a single stratigraphic level from the Early Ordovician Fezouata Biota, we reconstruct the degradation sequence of both skeletal remains and soft tissues of stylophorans, an extinct clade of echinoderms. The rare preservation of the water vascular system can be explained by the rapid post-mortem opening of the cover plates resulting from the fast decay of associated muscles and the action of ligaments. In contrast, the proximal aulacophore and associated stylocone formed a particularly decay-resistant closed module, thus favouring the preferential preservation of included soft parts (fore-gut). The non-random location and frequency of pyritised intra-skeletal structures strongly suggest that skeletal elements dictated the preservation of underlying soft parts. As such, taphonomic investigations should not only focus on the environment surrounding a decaying animal, but also on the different environments created within a particular carcass.

Occupation of shallow environments by rhynchonelliform brachiopods is rare during the early late Tremadocian (Tr2). However, in the NW Argentina basin the plectorthoidean Tarfaya purmamarcaensis occupied high-energy environments during this time interval. This species forms up to 15 cm thick monospecific concentrations in shoreface and offshore transition settings, and polytypic pavements in relatively deeper water offshore environments. Generation of such concentrations could be linked to the population dynamics of T. purmamarcaensis. A geometric morphometrics analysis allowed us to recognize four growth stages in the ontogeny of the species. The juvenile phases are absent in high-energy proximal environments and are scarce in the shoreface; in contrast, no representatives of the fourth phase (hypermature adults) have been found in the open platform deposits, and adults are almost absent. Although shell concentrations are usually linked to physical processes (i.e., storm events), the low taphonomic alteration of the shells suggests that transport was not a highly influential factor. Morphological differences (i.e., development of cardinal canals, ribs incurved posterolaterally) in specimens from different environments suggest that the population dynamics could have been the main cause in generating different concentrations. According to the source-sink model, high productivity of brachiopods in the shoreface environment and a passive transport of larvae to the offshore might explain not only the thicker shallow-water concentrations but also the differences in shell growth of populations inhabiting these environments.

A unique, new palaeotaxodont (Protobranchia) genus and species, Yuexiconcha duplicata Zhang, Niu and Johnston, is proposed and described. It is characterized by: a medium-sized, transversely elongated, sub-elliptical shell; heterotaxodont dentition; and posterior tooth row consisting of crowded gradidentate dentition, partially and dorsally overlapped by an additional tooth row that emanates from the beak to form a bitaxodont dentition (new term). Most significantly, a prominent resilifer separates the anterior and posterior tooth rows and shows slight to moderate excavation into the hinge-plate. While a resilifer indicates phylogenetic proximity with Nuculoidea, Yuexiconcha nov. gen. is readily distinguished by its bitaxodont posterior dentition and a more elongate posterior shell lobe and so is provisionally placed in the Family Nuculidae, Order Nuculida. The hinge of Yuexiconcha nov. gen. indicates that a resilifer in palaeotaxodonts first developed in the Ordovician, rather than in the Silurian (Wenlock) as thought previously. Specimens described herein were collected from a fine-grained siliciclastic rock unit in the upper part of the Dongchong Formation in western Guangdong, South China. Other components of the biota occurring with the bivalves are uncommon and include trilobites and brachiopods that indicate a late Middle–early Late Ordovician (late Darriwilian–early Sandbian) age.

The Dapingian (Arenig) siltstones and sandstones of the Tagoat Group, County Wexford, SE Ireland, contain a well-preserved and diverse brachiopod fauna including a new genus of alimbellid, Palaeotagoatia (type species: Orthis Bailyana Davidson) together with the plectorthid Ffynnonia costata (Bates) hibernica nov. subsp. Of the 13 forms documented, at least six are conspecific with brachiopods from the upper Arenig (Dapingian-lowest Darriwilian) Treiorwerth Formation on Anglesey and a further two are identified with species occurring in the older Dapingian Carmel Formation. The faunal province affinities of the fauna are with those assemblages assigned to the peri-insular and marginal Celtic province and which occupied positions within the Middle Ordovician Iapetus Ocean between the Laurentian and Baltic platform provinces. More precise correlation of Middle Ordovician units suggests a significant species richness during the Dapingian-earliest Darriwilian and signalling also an early development of the Celtic province. But the shallow-water siliciclastic facies associated with these islands may also have influenced the distribution of some elements of the Celtic brachiopods and promoted the prevalence of coarse-ribbed orthides, such as Paralenorthis.