Sublethal punctures in body chambers of Mesozoic ammonites (forma aegrafenestra n. f.), a tool to interpret synecological relationships, particularly predator-prey interactions

The new forma aegrafenestra n. f. sensuHölder (1956) is introduced to describe healed injuries to the body Chambers of Jurassic/Cretaceous ammonites, primarily behind the peristome but normally excluding the peristome itself. The different outlines and positions of these window-like sublethal injuries indicate two different Subtypes of injury inflicted by two different types of predator. Some of the large-scale ventral injuries occurring since the Late Devonian were presumably due to attacks by durophagous vertebrates, whereas the smaller, more or less rounded and mainly lateral puncture marks in Liassic to Cretaceous ammonite Shells can be traced back to unsuccessful attacks by stomatopod crustaceans. Identification of the specific predators responsible for characteristic injuries will give information about synecological relationships and life-modes of the attacked ammonites.     

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.     

Toarcian and Aalenian (Jurassic) ammonites from the Shemshak Formation of the Jajarm area (eastern Alborz, Iran)

In the Jajarm area (eastern Alborz Mountains, NE Iran) the ?Upper Triassic — Lower Bajocian siliciclastic Shemshak Formation is up to 2000 m thick. Whereas the lower third of the formation is nearly exclusively non-marine, the upper two-thirds are fully marine. The middle part is characterized by several levels containing a relatively diverse and well preserved assemblage of ammonites of the Toarcian to Aalenian stages. Two sections of the ammonite-bearing strata, spaced 20 km, are presented and correlated by means of ammonite biostratigraphy. The ammonite fauna consists of 27 taxa, some of which are recorded for the first time from the Alborz Mountains. The ammonites are briefly described and their palaeobiogeographic context is reviewed. The ammonite fauna of the Shemshak Formation at Jajarm, as elsewhere in North and Central Iran, is exclusively Northwestern Tethyan in character and is closely related to the faunas of Northwestern and Central Europe.     

The ammonitella: a model of formation with the aid of the embryonic shell of archaeogastropods

Recent archaeogastropoda secrete their first conch (primary shell) without producing increments of growth. This conch remains attached to the epithelium responsible for its production until completed. Only afterwards does tissue detach from the edge of the shell and the conch begins to function as a protective exoskeleton. After a potential swimming phase by the veliger larva, the organic primary shell is deformed by mechanical means through muscular tension from the inside and the outside of the conch. It then becomes mineralized by aragonitic crystallites and, thus, functional for the use of a benthic animal. The embryonic conch of ammonites (ammonitella) is devoid of increments of growth. The inner lip (dorsal side) of the aperture became flattened after the evenly rounded primary conch had been secreted. The primary organic shell was mineralized by aragonitic crystallites from within. All these features of the formation of the ammonitella can be interpreted in the light of early shell formation of recent archaeogastropods.     

Critical‐weight‐range marsupials in northern Australia are declining: a commentary on Fisher et al. (2014) ‘The current decline of tropical marsupials in Australia: is history repeating?’

Many mammal species are declining in parts of Australia's tropical savannas, for reasons that are not yet well defined. A recent paper (Fisher et al., 2014, Global Ecology and Biogeography, 23 , 181–190) suggested that the primary cause is predation by feral cats, with the main evidence presented being a purported over‐representation of small species amongst the marsupials that have contracted in range (‘small body size signifies high current extinction risk’). However, a review here of the information presented in that paper shows that no marsupial species smaller than 100 g has shown range contraction in northern Australia, and that most (15 of 17) declines are of species in the ‘critical weight range’ (35 g to 5.5 kg).     

鲍鱼壳蛋白组分研究进展

鲍鱼壳是一种研究生物矿化机制的理想矿物材料,其贝壳蛋白在矿物形成过程中发挥着重要的调控作用。目前分离获得的鲍鱼贝壳基质蛋白组分多为水溶性蛋白,研究的重点多集中在序列分析,结构解析和功能鉴定及三者之间的关联方面。本文在此简要介绍鲍鱼壳蛋白组分近年的研究进展,希望能对进一步阐释贝壳矿化机理相关问题提供帮助。     

Functional interpretation of inner shell layers in Triassic ceratid ammonites

The wrinkle layer the inner prismatic layer are described in three Triassic ceratid genera: Phyllocludiscites. Megaphyllites Proarcestes. Both layers have their counterparts in the shell wall of the recent Nautilus: the wrinkle layer corresponds to the mantle-adhesive layer the inner prismatic layer to the myostracal layer in Nautilus. A detailed structural functional comparison between these layers is given. The wrinkle layer is also compared with the oblique prismatic layer in recent gastropods.     

Further fossil cephalopods from Jamaica

Fossil cephalopods are rare in the Antillean region. A deformed conch of a kossmaticeratid ammonite,Pseudokossmaticerasl sp., from the Maastrichtian of the Blue Mountain Inlier is the first ammonite from southeastern Jamaica. This tentative systematic assignment is in agreement with the age otherwise assigned to these rocks.Cimomia sp. cf.C. vaughani (Gardner) is a hercoglossid nautiloid from the Lower-Middle Eocene Chapelton Formation of western central Jamaica. This is only the fourth nautiloid from this unit; all previous records were ofHercoglossa sp. The specimen is unusual amongst Antillean fossil cephalopods in including the sponge boringEntobia isp., probably indicating a period of post-mortem residence on the sea floor.      

Chromosomal abnormalities as a cause of recurrent abortions in Egypt

BACKGROUND:

In 4%-8% of couples with recurrent abortion, at least one of the partners has chromosomal abnormality. Most spontaneous miscarriages which happen in the first and second trimesters are caused by chromosomal abnormalities. These chromosomal abnormalities may be either numerical or structural.

MATERIAL AND METHODS:

Cytogenetic study was done for 73 Egyptian couples who presented with recurrent abortion at Genetic Unit of Children Hospital, Mansoura University.

RESULTS:

We found that the frequency of chromosomal abnormalities was not significantly different from that reported worldwide. Chromosomal abnormalities were detected in 9 (6.1%) of 73 couples. Seven of chromosomal abnormalities were structural and two of them were numerical.

CONCLUSION:

Our results showed that 6.1% of the couples with recurrent abortion had chromosomal abnormalities, with no other abnormalities. We suggest that it is necessary to perform cytogenetic in vestigation for couples who have recurrent abortion.     

Unexpected resilience of species with temperature-dependent sex determination at the Cretaceous-Palaeogene boundary

It has been suggested that climate change at the Cretaceous-Palaeogene (K-Pg) boundary, initiated by a bolide impact or volcanic eruptions, caused species with temperature-dependent sex determination (TSD), including dinosaurs, to go extinct because of a skewed sex ratio towards all males. To test this hypothesis, the sex-determining mechanisms (SDMs) of Cretaceous tetrapods of the Hell Creek Formation (Montana, USA) were inferred using parsimony optimizations of SDMs on a tree, including Hell Creek species and their extant relatives. Although the SDMs of non-avian dinosaurs could not be inferred, we were able to determine the SDMs of 62 species; 46 had genotypic sex determination (GSD) and 16 had TSD. The TSD hypothesis for extinctions performed poorly, predicting between 32 and 34 per cent of survivals and extinctions. Most surprisingly, of the 16 species with TSD, 14 of them survived into the Early Palaeocene. In contrast, 61 per cent of species with GSD went extinct. Possible explanations include minimal climate change at the K-Pg, or if climate change did occur, TSD species that survived had egg-laying behaviour that prevented the skewing of sex ratios, or had a sex ratio skewed towards female rather than male preponderance. Application of molecular clocks may allow the SDMs of non-avian dinosaurs to be inferred, which would be an important test of the pattern discovered here.     

Chromosomal abnormalities associated with mental retardation in female subjects

Chromosomal abnormalities are thought to be the most common cause of mental retardation (MR). However, apart from a few selected types with typical aneuploidy, like Downs syndrome, Klinefelter syndrome, Turner syndrome, etc., the frequency of detectable chromosomal abnormalities in association with idiopathic MR is very low. In this study, we have investigated chromosomal abnormalities in female MR subjects (n = 150) by high-resolution GTG banding. Of them, 30 cases were diagnosed as Downs syndrome. Among the remaining (n = 120), chromosomal abnormalities/marked polymorphisms were detectable in only three MR cases (0.025).