On the phylogenetic position of monotremes (Mammalia,Monotremata)

Henosferida from the Middle-Upper Jurassic of Western Gondwana is the most probable sister group for monotremes. They share the derived pretribosphenic structure of lower molars combined with the presumably absent protocone on the upper molars and the plesiomorphic retention of postdentary bones and pseudangular process of the lower jaw. In addition, the two groups share the dental formula with three molars and the position of the Meckel’s groove, which passes ventral to the mandibular foramen. In the course of subsequent evolution, monotremes acquired the mammalian middle ear with three auditory ossicles independently of therian mammals and multituberculates. Jurassic Laurasian Shuotheriidae are probably a sister group of the Gondwanian clade Henosferida + Monotremata. The Jurassic shuotheriid Pseudotribos shows a great plesiomorphic similarity to monotremes in the structure of the pectoral girdle, with a large interclavicle immovably connected to the clavicle. In the lineages leading to therian mammals and multituberculates, the pectoral girdle changed probably independently and in parallel in connection with the establishment of the parasagittal posture of the forelimbs (reduction of the interclavicle, mobile articulation of the interclavicle with clavicle, reduction of the procoracoid, and development of a supraspinous fossa of the scapula) and formation of the mammalian middle ear with three auditory ossicles.     

The systematic position of monotremes reconsidered (Mammalia)

Summary By reinterpretation of the tooth formula ofOrnithorhynchus as dp/P M_1–4 a synapomorphy with Marsupials has been discovered. Monotremes and Marsupials are sister groups, together derived from Theria of the Middle-Crelaceous.     

Seasonal patterns in water, sodium and energy turnover in free-living echidnas, Tachyglossus aculeatus (Mammalia: Monotremata)

The energetics of an egg-laying mammal, the echidna ( Tachyglossus aculeatus ), were studied in the wild by means of isotope turnover techniques. Water and sodium influx rates were highest in summer (47.7±15.3 ml kg^-1 day^-1 and 1.20±0.52 mmol kg^-1 day^-1, respectively) and associated with high metabolic rates (0.509±0.048 ml CO₂ g^-1 h^-1). Water and sodium influxes and metabolic rates were lowest in May and June (7.8±6.4 ml H₂O kg^-1 day^-1, 0.21±0.12 mmol Na kg^-1 day^-1 and 0.205±0.129 ml CO₂ g^-1 h^-1, respectively). These low rates in late autumn/early winter are associated with reduced activity, the animals spending substantial periods of time in torpor. The comparatively low isotope turnover rates of echidnas are a consequence of their diet; ants and termites which have low mass-specific energy contents.     

Terrestrial locomotion in pterosaurs

On the basis of a well‐preserved pelvis of Anhanguera sp. from the Lower Cretaceous (Aptian) of the Chapada do Araripe, Brazil, the problem of terrestrial locomotion in pterosaurs is discussed. A three‐dimensional reconstruction of the pelvis led to a lateral, dorsal and posterior orientation of the acetabula. By use of the preserved proximal ends of the femora of the same individual, the articulation in the hip socket could be tested. The normal articulation of the femur resulted in a horizontal position of the femur shaft, probably during flight. For constructional reasons the femur could not be brought down to a vertical position. Therefore, a parasagittal swing of the femora necessary for a bird‐like stance and gait must have been impossible. It is suggested that in pterosaurs the wing membrane was attached to the upper leg, which helped in stretching, steering and cambering.

Moreover, on the basis of comparisons of the fossil preservation of pterosaurs Compsognathus and Archaeopteryx in the Solnhofen limestone, it is concluded that the femora of pterosaurs were splayed out laterally, and that they had a semi‐erect gait. They were not bipedal animals, but had to use their fore limbs as well on the ground. Nevertheless, as vertebrates extremely adapted to flight, they could not have been able quadrupeds, either.     

Terrestrial locomotion in arachnids

In this review, we assess the current state of knowledge on terrestrial locomotion in Arachnida. Arachnids represent a single diverse (>100,000 species) clade containing well-defined subgroups (at both the order and subordinal levels) that vary morphologically around a basic body plan, yet exhibit highly disparate limb usage, running performance, and tarsal attachment mechanisms. Spiders (Araneae), scorpions (Scorpiones), and harvestmen (Opiliones) have received the most attention in the literature, while some orders have never been subject to rigorous mechanical characterization. Most well-characterized taxa move with gaits analogous to the alternating tripod gaits that characterize fast-moving Insecta - alternating tetrapods or alternating tripods (when one pair of legs is lifted from the ground for some other function). However, between taxa, there is considerable variation in the regularity of phasing between legs. Both large and small spiders appear to show a large amount of variation in the distribution of foot-ground contact, even between consecutive step-cycles of a single run. Mechanisms for attachment to vertical surfaces also vary, and may depend on tufts of adhesive hairs, fluid adhesives, silks, or a combination of these. We conclude that Arachnida, particularly with improvements in microelectronic force sensing technology, can serve as a powerful study system for understanding the kinematics, dynamics, and ecological correlates of sprawled-posture locomotion.     

Postcranial morphology and locomotion of the Eocene raoellid Indohyus (Artiodactyla: Mammalia)

Raoellids are small, raccoon-sized Eocene artiodactyls, closely related to archaic cetaceans (archaeocetes) that have poor representation of postcranial elements in the fossil record. Little is known of the aquatic and terrestrial locomotor affinities of raoellids due to the paucity of their fossil record, leaving a critical gap in our understanding of the earliest portion of the artiodactyl marine invasion. To address this gap, a comparative morphological analysis of the postcranial elements was undertaken based on newly recovered elements of the raoellid Indohyus, archaeocetes and extant artiodactyls. Greater than 200 postcranial elements of Indohyus were described, and some limb element cross-sections were visualised via paleohistological thin sections and CT scans. Results show that during terrestrial locomotion, Indohyus probably had a digitigrade posture and mediolaterally stabilised limbs that functioned mostly in flexion and extension within the parasagittal plane. Quantification of midshaft cross-sectional area for some elements of Indohyus showed an osteosclerotic cortex, a skeletal characteristic associated with aquatic behaviours. Indohyus may represent a critical intermediate in the evolution of the cetacean terrestrial-to-aquatic body plan, as it bears gracile postcranial element proportions similar to a terrestrial artiodactyl but also an incipient form of osteosclerosis compared to pakicetid archaeocetes.     

Terrestrial locomotion in the climbing perch, Anabas testudineus (Bloch) (Anabantidea, Pisces)

Climbing perches use the tail for forward propulsion when on land. The spiny gill covers are used to obtain purchase on the substratum. Unusually amongst teleosts, the opercular and subopercular bone are not bound strongly together into a single operculum. Instead they are joined only by a thin, flexible membrane, so that the fish has two sections of the gill cover hinged separately; the opercular on the suspensorium and the subopercular on the rearmost part of the lower jaw. The gill covers open very widely and the subopercular rotates ventrally as well as laterally. Two modes of locomotion are employed. Usually Anabus adopts a near-upright posture and alternately drives the left and right spiny suboperculars into the substratum, using the tail to vault over the subopercular (which acts in the manner of a short vaulting pole). During vigorous movement the fish may leave the substratum altogether during the vault. Fatigued fish, or fish which have fallen during climbing, move on their sides, using the tail for propulsion and a single spiny opercular which is repeatedly driven into the substratum. Maximum speeds observed on land corresponded to 1.8 body lengths S^?1. No evidence of involvement of the pelvic fins in locomotion was obtained; the pectorals seemed only to help in tilting the head from side to side and did not contribute significantly to forward propulsion. On mud and tree bark the fish were laterally unstable, often resting on their sides. Grassy substrata provided support and permitted a more upright posture. Slope climbing ability was restricted to 25° when climbing tree bark and 30° when climbing grass. Coupled with lateral instability these observations disqualify the species from any tree-climbing capacity. Anabas can climb vertical obstacles of at least half body length in height by pushing the head against the obstacle, using the spiny gill covers for purchase until one or other subopercular hooks over the top of the barrier. The subopercular is then used as a fulcrum for an upwards vault to clear the obstacle.     

Terrestrial locomotion in two species of amphibian larva

Leptopelis hyloides and Chiromantis rufescens, which deposit eggs out of water, are compared with the aquatic breeding Bufo maculatus in terms of the ability of their larvae to move on land. Leptopelis larvae travelled further, faster and in a more consistent direction than Chiromantis larvae; they also survived better on land. Bufo larvae showed no terrestrial locomotion. These facts are related to the breeding behaviour of the three species. Locomotory ability in both Leptopelis and Chiromantis larvae was influenced by relative humidity and in Leptopelis the direction of movement was apparently influenced by topographic gradient and by the position of the closest standing water.     

An X-radiographic and SEM study of the osseous inner ear of multituberculates and monotremes (Mammalia): implications for mammalian phylogeny and evolution of hearing

Multituberculate petrosals with well-preserved, three-dimensional internal anatomy from the Late Cretaceous/early Paleocene Bug Creek Anthills, Montana, U.S.A., are described from X-radiographic and SEM images, as well as from conventional visual observations, and are compared with the anatomy of the osseous inner ear in monotremes and in primitive non-therian and therian mammals. Results of this study indicate that: (1) the cochlea of at least some multituberculates retained a lagena, previously known only in monotremes among mammals; (2) an enlarged vestibule evolved in several lineages of multituberculates independently, and hence is not a synapomorphy of the order; (3) the cochlear canal lacks osseous laminae in support of the short, wide basilar membrane, which was probably inefficient in responding to high-frequency airborne vibrations; and (4) consequently, bone-conducted hearing in some multituberculate species may have been important in interpretation of their surroundings. Comparisons with the inner ear of monotremes and primitive therians indicate that curvature of the cochlea and cribriform plates for passage of vestibulocochlear nerve branches through the petrosal are unlikely homologues between monotremes and therians. From non-therian to therian mammals, there is a distinct morphological gap in the inner ear transition, characterized by acquisition of a number of neomorphs in the therian inner ear; an intermediate stage has yet to be discovered.     

Reproduction in male Pipistrellus pipistrellus (Mammalia: Chiroptera)

The annual reproductive cycle has been investigated in the male pipistrelle bat Pipistrellus pipistrellus. Spermatogenesis occurs during summer and spermatozoa are produced in August and September. The seminiferous tubules then regress rapidly but sperm are stored throughout winter in the cauda epididymidis. Little change is apparent in the morphology of the Leydig cells throughout the year, and histochemical studies have revealed no seasonal differences in the occurrence of enzymes involved in steroidogenesis. The percentage yields of testosterone and androstenedione after incubation of testis and adrenal tissues in vitro with tritiated pregnenolone have been determined and measurements made of the concentration of these hormones in testes and whole blood. Although the highest levels of these androgens are synchronous with spermatogenesis, both continue to be produced by the testes during winter. Studies in castrated bats have confirmed these observations and indicate that the activity of the accessory reproductive organs during winter is dependent on testicular androgens. The testicular cycle of the pipistrelle is not thought to be complicated by adrenal androgenesis, or storage of androgens in the brown fat. The interrelationships between reproduction and hibernation in bats are discussed.     

Body size of Smilodon (Mammalia: Felidae)

The body masses of the three large saber-toothed machairodontines, Smilodon gracilis, S. fatalis, and S. populator, were estimated on the basis of 36 osteological variables from the appendicular skeleton of extant felids. A new model is introduced that takes the reliability of the predictor equations into account, since mass estimates are more reliable when computed from multiple variables per bone. At a body mass range of 55-100 kg, S. gracilis was comparable in size to extant jaguars, and S. fatalis was found to be somewhat lighter than previously assumed, with a body mass range of 160-280 kg, similar to that of the largest extant felid, the Siberian tiger. Smilodon populator was substantially heavier and larger than any extant felid, with a body mass range of 220-360 kg. Particularly large specimens of S. populator almost certainly exceeded 400 kg in body mass. The differences from previous estimates are most likely caused by differences in the databases used for mass estimation.     

Circadian Activity Rhythms in the Australian Platypus, Ornithorhynchus anatinus (Monotremata)

The Australian platypus, Ornithorhynchus anatinus, is one of three extant genera of the order monotremata. Given the divergent evolutionary lineage of monotremes in relation to more commonly studied animals, it was of interest to determine first, whether platypuses possess endogenous biological pacemakers and, second, general parameters of aquatic activity rhythms under artificial and natural light-dark (LD) cycles. Using a novel recording device, aquatic activity rhythms were measured in three platypuses: a paired male and female studied together, and a single female studied in isolation from other platypuses. Under a constant photic environment, some evidence was found for persistent and free-running rhythmicity, indicating the presence of an endogenous circadian pacemaker in the platypus. Under artificial LD cycles the paired animals exhibited a nocturnal pattern of entrainment, although in the single female considerable variability in entrained phase-relations was found under natural LD cycles. Evidence for a circadian pacemaker in the hypothalamic region of platypuses is also discussed.     

A problem in morganucodontid taxonomy (Mammalia)

During the past three decades knowledge of the earliest mammals has greatly increased through study of specimens of morganucodontids of Late Triassic and Early Jurassic age discovered in Africa, Asia and Europe. Communication of the results of diis research has been and continues to be impaired by disputes over the validity or content of the genera Eozostrodon Parrington and Morganucodon Kiihne. On the basis of the limited data available and in the interest of stability of nomenclature, Eozostrodon parvus is the appropriate name for the morganucodontid represented in the fauna preserved in fissure fillings in Holwell Quarry, England. Its diagnostic dental morphology is not duplicated in the extensive samples of the most abundant morganucodontid known from Wales for which the name Morganucodon watsoni is appropriate. Although generic reference of these species is a moot point, recognition of separate species is warranted and, with other data, points to a diverse assemblage of morganucodontids forming part of the base of a prototherian radiation.     

Shape variation in the mole dentary (Talpidae: Mammalia)

The clade Talpidae consists of specialized fossorial forms, shrew‐like moles and semi‐aquatic desmans. As with all higher jawed vertebrates, different functional, phylogenetic and developmental constraints act on different parts of dentary influencing its shape. In order to determine whether morphological variation in the dentary was unified or dispersed into an integrated complex of structural–functional components, a morphometric analysis of the mole dentary was undertaken. The dentary was subdivided into component parts – horizonal ramus; coronoid, condylar, angular processes of the ascending ramus – and outline‐based geometric morphometric methods used to quantify, compare and contrast modes of shape variation within the clade. These were successful in revealing subtle differences and aspects of shape important in distinguishing between mole genera. Closer examination of shape variation within the two fully fossorial mole clades (Talpini and Scalopini) revealed several similarities in ascending ramus shapes between genera from each clade. For example, the broad, truncated appearance of the coronoid process in the talpine genera Talpa and Parascalops was shared with the scalopine genus Scapanus. Also, the more slender, hook‐shaped coronoid process of Euroscaptor and Parascaptor (Talpini) closely resembles that of Scalopus (Scalopini). Interestingly, subspecies (one from each clade) more closely resembled genera other than their own in coronoid process shape. Important distinctions in horizontal ramus shape were found to exist between the two clades, such as the extent of curvature of the ventral margin and relative depth of the horizontal ramus. Results show shape variation in this region is correlated with dental formulae and the relative sizes of the teeth. The taxonomically important dentition differences characteristic of mammals are also reflected in the horizontal ramus results. Moreover, these results suggest size may be affecting shape and the extent of variation in, for example, the coronoid and condylar processes between the semi‐aquatic moles Desmana and Galemys. It is likely that the effects of morphological integration seen at this level of analysis – covariation between shapes of dentary components – may exist because interacting traits are evolving together. Horizontal ramus and coronoid process shape, for example, are similar across Scapanus and Parascalops, but both these shapes have diverged in Scalopus. © 2008 Trustees of the Natural History Museum (London). Journal compilation © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 187–211.