Late Triassic (Late Norian) gastropods from the Wallowa Terrane (Idaho,USA)

A diverse Late Triassic (Late Norian) gastropod fauna is described from the Mission Creek Limestone of the Wallowa terrane (Idaho, USA). Sample standardization by rarefaction analysis indicates that the fauna is even more diverse than the Late Triassic gastropod fauna from the Pucara Formation (Peru) which represents the most diverse gastropod fauna from South America. The gastropod fauna consists of 66 species; several genera are reported for the first time from North America. A high percentage of the species are highly ornamented and several have distinct siphonal canals. This suggests that the appearance of truly Mesozoic elements among the gastropods began before the Mesozoic Marine Revolution in other clades. The fauna is dominated by high-spired strongly ornamented procerithiids, a group more characteristic for the Jurassic. Comparison of the present fauna and the Iranian Nayband Formation gastropod fauna show that the procerithiids underwent a first global radiation in the Late Triassic. The high number of new species in this fauna suggests that sampling of Late Triassic gastropod faunas is still incomplete and hinders palaeobiogeographic considerations. Previous suggesions that gastropod faunas from the Wallowa and Wrangellia terranes resemble each other and are distinct from those of Alexander, Chulitna, and Farewell terranes are basically corroborated. The gastropod fauna of the Mission Creek Limestone differs considerably from that of the western and central Tethys but shares several taxa with the Late Triassic gastropod fauna of the Pucara Formation in Peru. Thus, the Hispanic corridor was probably not present in the Norian but opened only in the Early Jurassic. The subfamily Andangulariinae is introduced and placed in the Zygopleuridae. The generaSpiniomphalus, Nodoconus, Gudrunella, Blodgettella, Idahospira, andSiphonilda and the subgenusCryptaulax (Wallowax) are introduced. 27 species are erected. A lectotype is designated forCryptaulax rhabdocolpoides Haas, 1953.      

Sublethal injuries in Middle Jurassic ammonite shells from Poland

Sublethal injuries, the effects of which are seen as regeneration patterns, are described from Late Bajocian and Bathonian (Middle Jurassic) ammonites from Poland (Polish Jura area) for the first time. The total number of ammonite shells bearing signs of sublethal injuries is small (only 11 specimens, which constitute ∼1.2% of all ammonites investigated), and this value is even smaller (∼0.3 to 0.8%) when analysing a large sample of a particular ammonite species. Specimens under consideration represent ten species, belonging to six genera and five families. All the healed injuries are represented by only one type, referred to as the ‘forma verticata’ of Hölder. This type of regeneration, very common in ammonite shells in general, is an effect of a puncture injury of the shell-secreting mantle-epithelia at the apertural margin. Although many different extrinsic (mechanical) factors may be responsible for such healed injuries, here it is most plausible they are an effect of either competitive or predatory activities. Other causes, like collision of the ammonite shells with the substrate in a high-energy environment, are excluded because the sea-bottom was soft and situated below the storm wave-base. From many potential predators inhabiting the Polish Basin during the Bajocian and Bathonian, the most likely to have caused these injuries are other ammonites, belemnites and nautiloids. Crabs, which are cited in the literature as a probable perpetrator of the ‘forma verticata’ injuries, appear unlikely here, as the ammonites under discussion were not purely benthic.     

Ventral bite marks in Mesozoic ammonoids

Reports on the predators of ammonoids are rare, although ammonoids were abundant and diverse invertebrates in many Paleozoic and Mesozoic marine ecosystems. Most previous work on lethal ammonoid predation has focused on (sub)circular tooth marks which resulted from fish and mosasaur attacks. In the present study we discuss a relatively common type of bite mark in ammonoid shells, the ‘ventral bite mark’. This typically occurs in a restricted position on the ventral side of the outer body chamber whorl and does not affect either the aperture or the phragmocone. Ammonoid specimens revealing ventral bite marks used in this study were collected from a wide range of strata which range in age from the Lower Jurassic to the uppermost Cretaceous (close to the Cretaceous–Paleogene boundary). These ventral bite marks are absent in the Paleozoic collections studied. The vast majority of ventral bite marks are situated at the end of the body chamber, close to the phragmocone. This is interpreted as the result of predatory attacks on the back or blind side of ammonoids in their living position. The predators aimed for the vital parts and muscle attachments to obtain the edible soft tissues. The agents for most of the ventral bite marks to ammonoids are probably coleoid cephalopods (especially teuthoids) and predatory fishes to a lesser extent.     

Differential effects of habitat complexity,predators and competitors on abundance of juvenile and adult coral reef fishes

Greater structural complexity is often associated with greater abundance and diversity, perhaps because high complexity habitats reduce predation and competition. Using 16 spatially isolated live-coral reefs in the Bahamas, I examined how abundance of juvenile (recruit) and adult (non-recruit) fishes was affected by two factors: (1) structural habitat complexity and (2) the presence of predators and interference competitors. Manipulating the abundance of low and high complexity corals created two levels of habitat complexity, which was cross-factored with the presence or absence of resident predators (sea basses and moray eels) plus interference competitors (territorial damselfishes). Over 60 days, predators and competitors greatly reduced recruit abundance regardless of habitat complexity, but did not affect adult abundance. In contrast, increased habitat complexity had a strong positive effect on adult abundance and a weak positive effect on recruit abundance. Differential responses of recruits and adults may be related to the differential effects of habitat complexity on their primary predators. Sedentary recruits are likely most preyed upon by small resident predators that ambush prey, while larger adult fishes that forage widely and use reefs primarily for shelter are likely most preyed upon by large transient predators that chase prey. Increased habitat complexity may have inhibited foraging by transient predators but not resident predators. Results demonstrate the importance of habitat complexity to community dynamics, which is of concern given the accelerated degradation of habitats worldwide.     

Specialized shell-breaking crab claws in Cretaceous seas

Here we report on a large brachyuran crab species from the Late Cretaceous of Mexico that has claws indicative of highly specialized shell-breaking behaviour. This crab possessed dimorphic claws (the right larger than the left), armed with several broad teeth, including a curved tooth structure found at the base of the movable finger of the right claw. The curved tooth is similar to the one observed on claws of many living durophagous crabs that use it as a weapon to peel, crush or chip the edges of hard-shelled prey, particularly molluscs. These morphological traits suggest that specialized shell-breaking crab predators had evolved during the Cretaceous, which contradicts previous findings supporting an Early Cenozoic origin for specialized shell crushers within the brachyuran clade.     

A review of selected triassic to Early Cretaceous ferns

After becoming nearly extinct during the Permian, the ferns began a slow recovery during the Triassic as the climate of the earth moderated. As a result, a considerable number and variety were present and widely distributed during the Jurassic and Early Cretaceous. However, with the rapid expansion of the angiosperms during the Late Cretaceous, the ferns once again became reduced in variety and greatly restricted in distribution. Some of the Mesozoic ferns are rather primitive and obviously are closely related descendants of Paleozoic taxa. Such ferns are assigned mostly to the Marattiaceae, Guaireaceae, Osmundaceae, and Gleicheniaceae. The majority of the Mesozoic ferns, however, are distinctive and appear to have originated during that era. These fossil ferns generally fit into modern orders and families such as the Matoniaceae or the Dipteridaceae. In some cases, it is difficult to clearly distinguish some of the Mesozoic ferns from living genera. A portion was presented as an invited paper to the symposium: Evolution of pteridophytes and gymnosperms at the XV International Botanical Congress, Yokohama, Japan (1993).     

The Evolution of Marine Reptiles

Reptiles have repeatedly invaded marine environments despite their physiological constraints as air breathers. Marine reptiles were especially successful in the Mesozoic as major predators in the sea. There were more than a dozen groups of marine reptiles in the Mesozoic, of which four had more than 30 genera, namely sauropterygians (including plesiosaurs), ichthyopterygians, mosasaurs, and sea turtles. Medium-sized groups, such as Thalattosauria and Thalattosuchia, had about ten genera, whereas small groups, such as Hupehsuchia and Pleurosauridae, consisted of only two genera or less. Sauropterygia and Ichthyopterygia were the two longest surviving lineages, with 185 and 160 million years of stratigraphic spans, respectively. Mesozoic marine reptiles explored many different swimming styles and diets. Their diet included fish, cephalopods, other vertebrates, and hard-shelled invertebrates, whereas no herbivore is known at this point. Sauropterygians and ichthyopterygians gave rise to cruising forms that probably invaded outer seas. Intermediate forms that led to the cruising species are known in Ichthyopterygia but not as much in Sauropterygia. Discovery of new fossils should eventually reduce the gap in the fossil record.     

侏罗纪中阶普草蛉的修订及中生代草蛉科的演化*

普草蛉属Mesypochrysa Martynov,1927隶属于脉翅目草蛉科昆虫中的绝灭亚科篱草蛉亚科,是该科中最为古老的属.该属内种间的主要区分特征有前翅亚前缘基横脉0-2支;Rs支脉7-26支;m-cu横脉2、3支;CuA+MP末端4-7栉状分支;1A和2A二分叉或不分叉.该属的中阶普草蛉Mesypochrysa...     

Grazing bioerosion in Jurassic seas: a neglected factor in the Mesozoic marine revolution?

Grazing bioerosion, notably by chitons, gastropods and regular echinoids, is a powerful destructive force in many recent shallow-marine environments and impacts significantly on sessile epibionts through grazing predation and/or unselective dislodgement. Grazing bioerosion was an important component of a major phase of biotic escalation; the Mesozoic marine revolution. Recent investigations of hard substrates in southern British Jurassic marine formations have identified widespread ichnofossils attributable to grazing activity by gastropods and/or chitons, and regular echinoids. The co-occurring benthic macrofaunas include groups that would have been vulnerable to grazing disturbance and dislodgement; notably articulate brachiopods. The emerging ichnological evidence strengthens the argument for grazing bioerosion as a significant contributor to the Mesozoic–Cenozoic decline of the articulate brachiopods, and their retreat to deep-water and/or cryptic refugia.     

First record of a pterosaur landing trackway

The terrestrial progression of pterosaurs, the flying reptiles of the Mesozoic Era, has been debated for over two centuries. The recent discovery of quadrupedal pterodactyloid pterosaur tracks from Late Jurassic sediments near Crayssac, France, shows that the hindlimbs moved parasagittally, as in mammals, birds and other dinosaurs, and the hypertrophied forelimbs could make tracks both close to the body wall and far outside it. Their manus tracks are unique in form, position and kinematics, which would be expected because the forelimbs were used for flight. Here, we report the first record of a pterosaur landing track, which differs substantially from typical walking trackways. The individual landed on both hind feet in parallel fashion, dragged its toes slightly as it left the track, landed again almost immediately and placed the hindfeet parallel again, then placed its forelimbs on the ground, took another short step with both hindlimbs and adjusted its forelimbs, and then began to walk off normally. The trackway shows that pterosaurs stalled to land, a reflection of their highly developed capacity for flight control and manoeuverability.     

Thermal control of hatchling emergence patterns in marine turtles

The emergence patterns of green turtle (Chelonia mydas) hatchlings on two beaches on Ascension Island, South Atlantic were monitored and related to thermal patterns in the sand at 10, 20, 30 and 40 cm depth. A total of 6001 hatchlings were recorded emerging on Long Beach, and 3171 emerged on North East Bay during the study period. No significant difference was observed in the temporal pattern of hatchling emergence among nights, or between the two beaches. Hatchling emergence predominantly occurred at night with over 93% of hatchlings emerging during the hours of darkness. Almost all hatchlings emerging in daylight suffer predation by the Ascension frigatebird (Fregata aquila). Counts of frigatebirds both above the study beaches and offshore were highest just after sunrise, with a smaller peak prior to sunset, when frigatebirds were found to predate hatchlings emerging, crawling down the beach or detected in inshore waters. The likely thermal cues controlling hatchling emergence were investigated (temperature at different depths, thermal gradients in the sand and temperature change). The most plausible thermal factor appears to be the change of temperature at superficial sand depths, with hatchling emergence inhibited when subsurface sand temperatures were increasing. This simple mechanism is likely to ensure predominantly nocturnal hatchling emergence regardless of sand albedo, seasonality or latitude as long as night is relatively cooler than day.