Upper Cretaceous aquatic plants from Northern Mexico

Two aquatic plant genera assignable to Decodon (Lythraceae) and Ceratophyllum (Ceratophyllaceae) are described based on reproductive structures collected from the Cerro del Pueblo Formation (late Campanian [73.5 ma]), Coahuila, Northeast Mexico. Decodon is represented by three small seeds with a pyramidal shape, rounded borders, and a concave ventral surface with a rectangular valve towards the center of the seed ventral surface. The Ceratophyllum spiny fruit has an ellipsoidal central body and two proximal long spines flanking a short pedicel opposite the stylar projection. These new reports confirm the presence of both genera in the Upper Cretaceous sediments of Northeastern Mexico, and add to our recognition of diversity within the widely distributed freshwater communities along the margin of the epicontinental sea.     

Paleoecological patterns in molluscan extinctions and recoveries: comparison of the Cretaceous-Paleogene and Eocene-Oligocene extinctions in North America

Exposures across the Cretaceous-Tertiary (K-T) and Eocene-Oligocene (E-O) boundaries, in Texas and Mississippi, respectively, probably represent the most complete and best-preserved fossil molluscan sequences across these boundary intervals in the world. Outcrops from both boundaries contain pristine aragonitic and calcitic molluscan shells, which were deposited in fine-grained sediments from open marine environments. The K-T and the E-O extinctions exhibit very different recovery patterns, probably reflecting very different causes as well as magnitudes of extinction.The K-T sequence contains a molluscan fossil record that is consistent with an abrupt extinction event at the K-T boundary and a prolonged initial recovery in hostile oceanographic conditions. The uppermost 10 m of Upper Cretaceous sediments contain a diverse (approximately 40 species) molluscan fauna dominated by suspension feeders. The earliest Paleocene sediments immediately above the tsunami bed contain an impoverished fauna dominated by deposit feeders. The Paleocene fauna slowly climbs in diversity but remains relatively impoverished and dominated by deposit feeders for several hundred thousand years after the extinction in conjunction with anomalous δ¹³C values that suggest prolonged suppression of marine primary productivity. Diverse suspension-feeder dominated molluscan assemblages reappear with the resumption of normal conditions of primary production. In the long term, early to middle Paleocene gamma diversity includes evolutionary “bloom taxa,” families that exhibit unusual speciation bursts that subside in the Eocene. Total diversity for the Gulf Coast does not approach Cretaceous levels until the Late Eocene representing a total recovery interval of nearly 25 million years.While the E-O event also reflects a molluscan extinction rate of over 90% in the Gulf of Mexico, there are no signs of hostile environmental conditions in the recovery fauna. Early Oligocene molluscan assemblages are diverse and dominated by suspension feeders characteristic of normal marine conditions. The hiatus at the E-O boundary, however, could have obscured a short-term recovery fauna. There is also no sign of long-term perturbation by the E-O extinction. There are no bloom taxa and gamma diversity approaches pre-extinction levels within a few million years. The overall pattern of the E-O extinction is consistent with extinction (and/or migration) associated with long-term cooling.     

Spider web in Late Cretaceous French amber (Vendée): The contribution of 3D image microscopy

Late Cretaceous amber from La Garnache (France, Vendée) contains filamentous networks that have all the characteristics of spider webs. Using methods of classic and confocal microscopy, the web architecture and the thread structure are described. The geometry of the webs preserved in amber is presented in 3D imaging. Unlike most of the spider webs identified in amber, there are no regular radiating webs growing in two dimensions characteristic of the well-known orb web. A number of the characters would correspond to the apparently irregular organization of cob-type web or sheet web. By using confocal microscopy, we can highlight the preserved autofluorescence of spider silk proteins and new characters are proposed to identify the spider webs or fragments of webs in amber.     

A new tree fern stem,Heilongjiangcaulis keshanensis gen. et sp. nov., from the Cretaceous of the Songliao Basin,Northeast China: a representative of early Cyatheaceae

A new genus and species of Cretaceous Cyatheacean tree fern, Heilongjiangcaulis keshanensis gen. et sp. nov., is erected for several permineralized stems collected at the Keshan County in Songliao Basin, Heilongjiang Province, Northeast China. The new taxon is characterized by a dictyostelic, erect stem with dense multicellular scales and surrounded by persistent petiole bases and adventitious roots. The stem contains a central pith lacking medullary bundles, which is surrounded by a dictyostele, and the cortex externally. Each meristele of the dictyostelic ring is enclosed by a sclerenchyma sheath. The pith and cortex are parenchymatous. The proximal petiole bases present a frond trace composed of numerous meristeles, arranged in 1 abaxial and 2 adaxial arcs, with internally projecting bundles on the upper and lateral sides. The feature combination of the new genus is nearly identical to the anatomical structures of modern scaly genera of the Cyatheaceae apart from the absence of medullary bundles. It is interpreted as a primitive representative of early Cyatheaceae, that closely resembles the modern scaly genera, which suggests that in the Cretaceous, the tree ferns in this family were already in possession of most of the anatomical characteristics observed in extant taxa. The fossil records of the stems, petioles, and spores indicate that during the Jurassic and Cretaceous, the Northeastern region of Asia may have been one of the distribution centers of early Cyatheaceae.     

Enigmatic teeth from the Jurassic–Cretaceous transition of Morocco: The latest known non-mammaliaform cynodonts (Synapsida,Cynodontia) from Africa?

Two tooth morphotypes corresponding to one or two tetrapod species from the Late Jurassic or Earliest Cretaceous locality of Ksar Metlili (KM), Anoual Syncline (eastern Morocco), are reported and described. These teeth cannot be related to any of the identified vertebrate major groups of this site. They are tricusped and uniradiculate, with a high and large main central cusp mesio-distally surrounded by two smaller accessory cusps. Their morphology is reminiscent of several taxa such as pterosaurs, notosuchians and mammals, with which they are compared here. These morphotypes are tentatively referred to cf. Cynodontia indet. They would be the most recent non-mammaliaform cynodonts reported in Africa and among the latest described. The KM specimens display remarkable plesiomorphic dental features with respect to known contemporaneous non-mammaliaform cynodonts. They might indicate the survival of a relict lineage in a North African refugium.     

Latest Miocene Dasyatidae (Neoselachii, Batomorphii) from the Alvalade Basin, Portugal

This paper deals with the only latest Miocene fish fauna so far recognized in Portugal and probably in western Europe through more than 10,000 teeth and many other remnants collected in the Latest Miocene, Esbarrondadoiro Formation (Alvalade basin, southern Portugal). A large number of teeth reported to the family Dasyatidae (ca. 46% among the Myliobatiforms) are described. Several forms were recognized. The concerned deposits are particularly rich in modern type, close to still extant selachian forms. This is confirmed by the presence of different species of Dasyatis. From the thermic point of view, Alvalade basin marine fishes point out to a decrease in the prevailing thermic conditions. The still abundant Dasyatis are in contrast to the rarity of Raja, a genus which suggests temperate or cold, or deeper hence colder waters. Moderately warm water conditions predominated, less than in Tortonian of Lisbon, more than exist today near the Portuguese coasts. The occurrence ratios of the taxa concerned among the exploited sites are quantitatively different. This points out to different paleoenvironmental conditions. The Dasyatis had a litoral/neritic bathymetric distribution and a benthic way of life. However, the Esbarrondadoiro pattern is very different from those from Santa Margarida and Vale de Zebro, which are nearly identical between them as far as Dasyatis gr. gigas and Dasyatis sp. are concerned: Dasyatis gr. gigas may suggest less warm waters, and this is very much compatible with other data that indicate a deeper environment and hence colder waters for Esbarrondadoiro.     

Longevity and growth rate estimates for a polar dinosaur: a Pachyrhinosaurus (Dinosauria: Neoceratopsia) specimen from the North Slope of Alaska showing a complete developmental record

Our knowledge of growth dynamics in large ceratopsian dinosaurs is very poor, in part, due to the paucity of quantifiable age markers such as growth lines in their bones. We sought marker-based, osteohistological evidence for ceratopsid age structure from high Arctic paleolatitudes based on the observations that: (1) extant mammals from high latitudes better express growth lines in their hard tissues than those from lower latitudes, and (2) the occurrence of accentuated growth banding in teeth from Arctic dinosaurs. We examined the long bones in the specimens of Pachyrhinosaurus sp. from the early Maastrichtian of northern Alaska, and found conspicuous osseous banding. Histological analysis of the spacing, structure, pattern and numbers of these bands in the femur of a very large specimen suggests that they are not a taphonomic artefact, rather they appear to reflect annual growth cycling. Counts and measurements of the growth zones suggest that the animal showed rapid linear growth early in ontogeny, sexual maturity in perhaps the 9th year of life, and that it died in the 19th year of life. Our data adds to a growing body of evidence that a genetically distinct northern dinosaurian fauna existed at high paleolatitudes in Alaska during the Late Cretaceous.     

Phylogenetic structure of the extinction and biotic factors explaining differential survival of terrestrial notosuchians at the Cretaceous–Palaeogene crisis

Although the clade Crocodylomorpha is represented by few extant species (Crocodylia), it has a rich fossil record. Hundreds of species, adapted to terrestrial, semi-aquatic and marine environments, have existed over more than 200 million years. Numerous studies have attempted to characterize the factors driving the diversification and extinction events of Crocodylomorpha, resulting in ambiguous and even contradictory conclusions, which points to the need for phylogenetically and temporally smaller-scaled studies. Here, we focus on differential survival at the Cretaceous–Palaeogene (K–Pg) crisis of Notosuchia, a diverse clade of mostly terrestrial Crocodylomorpha that achieved great diversity during the Cretaceous. More precisely, we tested the effect of body size and palaeotemperatures on notosuchian survival probability during the K–Pg crisis as well as the effect of diet on the evolution of their body size. We find that Notosuchia showed an evolutionary trend towards larger body sizes through time, associated with a shift from an omnivorous to a carnivorous diet. This may explain why sebecids were the only notosuchians to survive the K–Pg crisis. We also corroborate the conclusions of previous studies that detected a Lagerstätten effect occurring in the Adamantina Formation (Upper Cretaceous, Brazil, Bauru Group). This work confirms the value of more finely-scaled macroevolutionary studies for understanding the history of a rich and complex group such as Crocodylomorpha.     

Soft–part preservation in heteromorph ammonites from the Cenomanian–Turonian Boundary Event (OAE 2) in north–west Germany

Abstract: From thinly laminated marlstones of the Hesseltal Formation, representing the Late Cenomanian Oceanic Anoxic Event (OAE) 2, at Lengerich in the Teutoburger Wald (Westfalen, north‐west Germany), 17 sediment‐compacted baculitid ammonites with carbonised and partially phosphatised soft parts are recorded. Some preserve remains of the buccal mass, including jaws (occasionally articulated) and radulae, as well as of the cephalic cartilage, such as eye capsules. Such have not yet been recorded previously for the order Ammonoidea. In addition, originally unmineralised parts found preserved in these specimens include extensive portions of the digestive tract, the siphonal tube, false colour patterns (megastriae), as well as traces of what would appear to be the oviduct. At the same levels, patches with numerous isolated horny upper and rarer lower jaws as well as radulae occur; these may represent regurgitates or faeces of larger predators. The cephalopod remains described were deposited in an epicontinental setting, possibly at palaeodepths between 200 and 600 m. In this particular Late Cretaceous fossil Lagerstätte, upper jaws and anaptychi of ammonites rank among the commonest fossils.     

Palaeoecology of the mid‐Cretaceous siphonate bivalve genus Goshoraia (Mollusca,Veneridae) from Japan

Abstract: The mid‐Cretaceous bivalve Goshoraia Tamura, 1977, endemic to Japan, is an early example of shallow‐marine siphonate bivalves of the family Veneridae Rafinesque, 1815. Three species, including one new, are here described: Goshoraia minor Tashiro and Kozai, 1989 (Aptian), G. crenulata (Matsumoto, 1938; Albian–lower Cenomanian) and G. maedai sp. nov. (middle to ?upper Cenomanian). The habitats of Goshoraia have been extensively compared with those of common Cretaceous, nonsiphonate burrowers, such as trigoniids, which range from tidal flat and shoreface to shelf environments. Depth of burial, which can be estimated from the extent of the pallial sinus, increases from the ancestral G. minor to its descendants G. crenulata and G. maedai sp. nov., documenting that the ability to burrow within this genus improved in time. These morphological and palaeoecological changes may be related to the Mesozoic marine revolution during the mid‐Cretaceous.