Revision of the genus Acrochordiceras Hyatt, 1877 (Ammonoidea,Middle Triassic): morphology,biometry, biostratigraphy and intra‐specific variability

Abstract: The family Acrochordiceratidae Arthaber, 1911 ranges in age from latest Spathian to the middle/late Anisian boundary, and it represents a major component of ammonoid faunas during that time. The middle Anisian genus Acrochordiceras Hyatt, 1877 is the most widespread taxon of the family and occurs abundantly worldwide within the low paleolatitude belt. However, there is a profusion of species names available for Acrochordiceras. This excessive diversity at the species level essentially results from the fact that sufficiently large samples were not available, thus leading to a typological approach to its taxonomy. Based on new extensive collections obtained from the Anisian (Middle Triassic) Fossil Hill Member (Star Peak Group, north‐west Nevada) for which a high resolution biostratigraphic frame is available, the taxonomy and biostratigraphy of the genus Acrochordiceras Hyatt, 1877 is herein revised with respect to its intra‐specific variation. Morphological and biometric studies (c. 550 bedrock‐controlled specimens were measured) show that only one species occurs in each stratigraphic level. Continuous ranges of intra‐specific variation of studied specimens enable us to synonymize Haydenites Diener, 1907, Silesiacrochordiceras Diener, 1916 and Epacrochordiceras Spath, 1934 with Acrochordiceras Hyatt, 1877. Three stratigraphically successive species are herein recognized in the low paleolatitude middle Anisian faunas from Nevada: A. hatschekii (Diener, 1907), A. hyatti Meek, 1877 and A. carolinae Mojsisovics, 1882. Moreover, an assessment of intra‐specific variation of the adult size range does not support recognition of a dimorphic pair (Acrochordiceras and Epacrochordiceras) as previously suggested by other workers (Epacrochordiceras is the compressed and weakly ornamented end‐member variant of Acrochordiceras). The successive middle Anisian species of Acrochordiceras form an anagenetic lineage characterized by increasing involution, adult size and intra‐specific variation. This taxonomic revision based on new bedrock‐controlled collections is thus an important prerequisite before studying the evolution of the group.     

Patterns of morphological evolution in the mandible of the house mouse Mus musculus (Rodentia: Muridae)

The worldwide distributed house mouse, Mus musculus, is subdivided into at least three lineages, Mus musculus musculus, Mus musculus domesticus, and Mus musculus castaneus. The subspecies occur parapatrically in a region considered to be the cradle of the species in Southern Asia (‘central region’), as well as in the rest of the world (‘peripheral region’). The morphological evolution of this species in a phylogeographical context is studied using a landmark‐based approach on mandible morphology of different populations of the three lineages. The morphological variation increases from central to peripheral regions at the population and subspecific levels, confirming a centrifugal sub‐speciation within this species. Furthermore, the outgroup comparison with sister species suggests that M. musculus musculus and populations of all subspecies inhabiting the Iranian plateau have retained a more ancestral mandible morphology, suggesting that this region may represent one of the relevant places of the origin of the species. Mus musculus castaneus, both from central and peripheral regions, is morphologically the most variable and divergent subspecies. Finally, the results obtained in the present study suggest that the independent evolution to commensalism in the three lineages is not accompanied by a convergence detectable on jaw morphology. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 635–647.     

Large‐scale evolutionary trends of Acrochordiceratidae Arthaber, 1911 (Ammonoidea,Middle Triassic) and Cope’s rule

Abstract: Directed evolution of life through millions of years, such as increasing adult body size, is one of the most intriguing patterns displayed by fossil lineages. Processes and causes of such evolutionary trends are still poorly understood. Ammonoids (externally shelled marine cephalopods) are well known to have experienced repetitive morphological evolutionary trends of their adult size, shell geometry and ornamentation. This study analyses the evolutionary trends of the family Acrochordiceratidae Arthaber, 1911 from the Early to Middle Triassic (251–228 Ma). Exceptionally large and bed‐rock‐controlled collections of this ammonoid family were obtained from strata of Anisian age (Middle Triassic) in north‐west Nevada and north‐east British Columbia. They enable quantitative and statistical analyses of its morphological evolutionary trends. This study demonstrates that the monophyletic clade Acrochordiceratidae underwent the classical evolute to involute evolutionary trend (i.e. increasing coiling of the shell), an increase in its shell adult size (conch diameter) and an increase in the indentation of its shell suture shape. These evolutionary trends are statistically robust and seem more or less gradual. Furthermore, they are nonrandom with the sustained shift in the mean, the minimum and the maximum of studied shell characters. These results can be classically interpreted as being constrained by the persistence and common selection pressure on this mostly anagenetic lineage characterized by relatively moderate evolutionary rates. Increasing involution of ammonites is traditionally interpreted by increasing adaptation mostly in terms of improved hydrodynamics. However, this trend in ammonoid geometry can also be explained as a case of Cope’s rule (increasing adult body size) instead of functional explanation of coiling, because both shell diameter and shell involution are two possible paths for ammonoids to accommodate size increase.     

Environmental media and shape asymmetry: a case study on turtle shells

Although physical features of the environment are known to influence shape, to date, the effects of many environmental conditions on asymmetry remain unexamined. The present study aimed to examine the relationship between asymmetry and the fluid media (air versus water) that an organism inhabits and, subsequently, to use these findings to test a novel hypothesis that fluid environments can impose selective forces acting to constrain asymmetry to maintain or enhance biomechanical function. We examined carapace asymmetry in 114 species (69 aquatic and 45 terrestrial) from the chelonian superfamily Testudinoidea. The results obtained indicate that environment is correlated with the degree of asymmetry, but in different directions for the two clades that comprise the Testudinoidea. Within the Testuguria, aquatic turtles have lower levels of asymmetry than terrestrial turtles, which is consistent with our proposed biomechanical hypothesis. This pattern was not observed within the Emydidae, possibly due to the much shorter time that terrestrial taxa in this clade have existed. Nevertheless, the present study provides the first evidence for a relationship between fluid media and asymmetry in any taxonomic group.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 483–489.     

Socio-genetic structure of mound-building mice, Mus spicilegus, in autumn and early spring

Mus spicilegus has become a popular biological model species in the last decade because of the evolutionary interest of its behavioural particularities (the building of mounds, bi-parental care and monogamous mating system). The genetic structure of M. spicilegus populations should reflect those life-history traits. Although many studies have reported on mound-building mouse populations in the field or in a semi-natural enclosure, only one used hyper variable genetic markers to assess parentage and social structure. In the present study conducted in Hungary, we analysed individuals from seven highly populous mounds in autumn with the set of loci used in a previous study. Our results confirmed that mounds are inhabited by juveniles from several parental units, but revealed population differences. In a capture–recapture field session in spring, we assessed genetic relationships between individuals after dispersal from the mounds, the other key moment of the life cycle of this species. The results indicate that the social structure at this moment reflects a transition phase between the large over-wintering groups and the monogamous pairs described later in the year. Social bounds forged during the long winter cohabitation may have lasting effects on social and genetic structure of this species. This scenario is discussed in respect of the available literature on this species as well as other species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 689–699.     

Vocal mimicry in wild African Grey Parrots Psittacus erithacus

The ability of captive Grey Parrots Psittacus erithacus to imitate heterospecific sounds is well known. Analysis of a sound recording from Zaire reveals the first evidence of vocal mimicry in the wild of nine species of birds and a bat. Examination of recordings from Gabon and the Ivory Coast indicates that vocal mimicry may be widespread in wild populations. Possible reasons why this phenomenon has not been detected before are discussed.     

Odour-genes eovariance and differential investigation of individual odours in the Mus species complex

Previous research using habituation techniques has demonstrated that greater genetic similarity between two individuals is associated with more similarity in the qualities of their individual odours ('odour-genes eovariance'). We assessed odour similarities across species in two pairs of genetically close species within the Mus species complex (M. musculus and M. domesticus; M. spicilegus and M. macedonicus). Subjects treated odours within each species pair as similar compared with an odour from the other species pair. Subjects also treated odours of M. spicilegus males from the same population as similar compared with the odour of M. spicilegus males from a different population. This confirms odour-genes eovariance across species and within populations and also supports previous findings that odour similarities are more salient than specific odour markers. When adult males were presented with odours of females from two different heterospecific species, subjects spent more time investigating the odour from his own species pair than the other species pair, indicating greater interest in the odour of the closer heterospecific and demonstrating that odour-genes eovariance is reflected in behavioural responses to odours. Implications of odour-genes eovariance as a basis for identifying degrees of genetic relatedness of unfamiliar individuals through similarities in individual odours are discussed.     

Plant palatability and disturbance level in aquatic habitats: an experimental approach using the snail Lymnaea stagnalis (L.)

1. The palatability of aquatic macrophytes to the snail Lymnaea stagnalis was investigated in the laboratory. Eight species of macrophyte were selected from habitats that differed in either flood disturbance regime or nutrient status.
2. In a non-choice test, single macrophyte species were offered to individual snails. The average amount of plant dry mass consumed per Lymnaea dry mass ranged from 3.6 ± 1.4 (±SE) to 63.6 ± 13.9 mg g^–1 day^–1 across plant species. In a choice test, all eight plant species were presented simultaneously to sets of five snails. The average total consumption was 66.1 ± 3.8 mg g^–1 day^–1 and the maximum average consumption for a single plant was 26.2 ± 3.6 mg g^–1 day^–1.
3. In both tests, the amount consumed by snails differed significantly between the plant species. The species growing in undisturbed habitats were the least consumed. Habitat nutrient status was unrelated to plant palatability.
4. These results suggest that macrophyte species growing in habitats that are rarely disturbed by floods allocate a greater proportion of their resources to resisting herbivory.     

NEW JELLYFISH TAXA FROM THE UPPER JURASSIC LITHOGRAPHIC LIMESTONES OF CERIN (FRANCE): TAPHONOMY AND ECOLOGY

Abstract:  Abundant well-preserved jellyfish impressions are described from the Cerin Lagerstätte (Ain, eastern France). The enclosing sediments are lithographic limestones deposited in a Late Kimmeridgian lagoon lying on an emergent reef complex. Two new taxa of Scyphozoa are proposed: Paraurelia cerinensis gen. et sp. nov. (abundant) and Paraurelia sp. A (rare), and two new taxa of Cubozoa: Bipedalia cerinensis gen. et sp. nov. (rare) and Paracarybdea lithographica gen. et sp. nov. (very rare). Rapid covering by a microbial mat helped the preservation of the animals. Many specimens of Paraurelia cerinensis are deformed by slippage down the palaeoslope, which characterizes the margin of the lagoon. Their resultant morphology and their orientation clearly indicate the downslope direction. Tentacles of Bipedalia cerinensis and Paracarybdea lithographica are also orientated according to the palaeoslope. The jellyfish were probably dead individuals occasionally introduced into the Cerin lagoon. However, another hypothesis may be considered with reference to the model of the present-day jellyfish lakes in Palau (Caroline Islands, Western Pacific). Jellyfish could have lived in the more oxygenated upper layer of water of the Cerin lagoon that allowed pelagic life. This situation could have corresponded to short periods of easier communication between the open sea and the lagoon. Jellyfish are only found in the lower beds of the lithographic limestones and their distribution illustrates the supposed evolution of the Cerin lagoon. Initially, it was deep, mainly flooded, with possibly autochthonous jellyfish and allochthonous animals indicating clear marine influence. Later, the lagoon shallowed and its sediments often emerged with marginal marine burrows and plants indicating increasing terrestrial influence.