Evolution and development of the mammalian jaw joint: Making a novel structure

A jaw joint between the squamosal and dentary is a defining feature of mammals and is referred to as the temporomandibular joint (TMJ) in humans. Driven by changes in dentition and jaw musculature, this new joint evolved early in the mammalian ancestral lineage and permitted the transference of the ancestral jaw joint into the middle ear. The fossil record demonstrates the steps in the cynodont lineage that led to the acquisition of the TMJ, including the expansion of the dentary bone, formation of the coronoid process, and initial contact between the dentary and squamosal. From a developmental perspective, the components of the TMJ form through tissue interactions of muscle and skeletal elements, as well as through interaction between the jaw and the cranial base, with the signals involved in these interactions being both biomechanical and biochemical. In this review, we discuss the development of the TMJ in an evolutionary context. We describe the evolution of the TMJ in the fossil record and the development of the TMJ in embryonic development. We address the formation of key elements of the TMJ and how knowledge from developmental biology can inform our understanding of TMJ evolution.     

The aquatic Lystrosaurus: A palaeontological myth

Evidence previously cited for the aquatic nature of the Triassic mammal‐like reptile Lystrosaurus is reviewed. It is concluded that this evidence does not constitute a convincing case.

General adaptations of aquatic tetrapods are reviewed and applied to the morphology of Lystrosaurus, in order to determine whether aquatic adaptations not previously sought in Lystrosaurus are present It is concluded that few or any such adaptations are present. Such as are, for example a widened knee and flared scapula blade, are as compatible with a digging function, as with swimming.

Nevertheless, the distinctive nature of the skull and to a lesser extent the postcranial skeleton of Lystrosaurus stands out, and several features require functional interpretation. These include: a downwardly‐directed and elongated snout, a short and high temporal region, a pear‐shaped external nasal opening bounded by a rugose ridge, slight dorsal flaring of the scapula, a powerful forelimb and wide knee joint These are dealt with elsewhere (King and Cluver, 1991).     

The external ear morphology and presence of tragi in Australian marsupials

Multiple studies have described the anatomy and function of the external ear (pinna) of bats, and other placental mammals, however, studies of marsupial pinna are largely absent. In bats, the tragus appears to be especially important for locating and capturing insect prey. In this study, we aimed to investigate the pinnae of Australian marsupials, with a focus on the presence/absence of tragi and how they may relate to diet. We investigated 23 Australian marsupial species with varying diets. The pinnae measurements (scapha width, scapha length) and tragi (where present) were measured. The interaural distance and body length were also recorded for each individual. Results indicated that all nectarivorous, carnivorous, and insectivorous species had tragi with the exception of the insectivorous striped possum (Dactylopsila trivirgata), numbat (Myrmecobius fasciatus), and nectarivorous sugar glider (Petaurus breviceps). No herbivorous or omnivorous species had tragi. Based on the findings in this study, and those conducted on placental mammals, we suggest marsupials use tragi in a similar way to placentals to locate and target insectivorous prey. The Tasmanian devil (Sarcophilus harrisii) displayed the largest interaural distance that likely aids in better localization and origin of noise associated with prey detection. In contrast, the smallest interaural distance was exhibited by a macropod. Previous studies have suggested the hearing of macropods is especially adapted to detect warnings of predators made by conspecifics. While the data in this study demonstrate a diversity in pinnae among marsupials, including presence and absence of tragi, it suggests that there is a correlation between pinna structure and diet choice among marsupials. A future study should investigate a larger number of individuals and species and include marsupials from Papua New Guinea, and Central and South America as a comparison.     

Effects of life history variation on vertical transfer of toxicants in marine mammals

Toxicant bioaccumulation poses a risk to many marine mammal populations. Although individual-level toxicology has been the subject of considerable research in several species, we lack a theoretical framework to generalize the results across environments and life histories. Here we formulate a dynamic energy budget model to predict the effects of intra- and interspecific life history variation on toxicant dynamics in marine mammals. Dynamic energy budget theory attempts to describe the most general processes of energy acquisition and utilization in heterotrophs. We tailor the basic model to represent the marine mammal reproductive cycle, and we add a model of toxicant uptake and partitioning to describe vertical transfer of toxicants from mother to offspring during gestation and lactation. We first show that the model predictions are consistent with qualitative patterns reported in empirical studies and previous species-specific modeling studies. Next, we use this model to examine the dependence of offspring toxicant load on birth order, food density, and interspecific life history variation.     

IMMOBILIZATION OF WALRUS WITH ETORPHINE HYDROCHLORIDE AND ZOLETIL®

Abstract: The paper describes the use of the drugs Zoletil® and etorphine for the immobilization of walrus ( Odobenus rosmarus rosmarus ) for attachment of satellite telemetry equipment. Three animals weighing approximately 1,500 kg each were injected intramuscularly with Zoletil® at a dose between 1.4 and 2.2 mg/kg. One walrus died while the two others were adequately restrained. The induction time was between 14 and 29 minutes and the effect lasted for 75-220 min.
Thirty-eight animals of weight 900-1,500 kg were darted intramuscularly with etorphine at a dose between 3.3 and 8 mg/kg. Thirty-six were immobilized although one died later. The induction time for etorphine was two to ten minutes. The action of this drug was terminated with an injection of the antidote di-prenorphine.
The use of etorphine was accompanied by convulsive movements and apnoea while Zoletil® produced a gradual and smooth entry into and withdrawal from immobilization.     

THE ACOUSTIC STRUCTURE OF WOLF HOWLS IN SOME EASTERN TUSCANY (CENTRAL ITALY) FREE RANGING PACKS

ABSTRACT

Italian wolf howls are described for the first time from observations between 2003–2008 of a population living in eastern Tuscany, central Italy. A sample of 37 howls selected among single responses and 128 howls included in the choruses of 7 free ranging packs was recorded and analysed. The mean fundamental frequency of the howls ranged between 274–908 Hz. Two main structures recognised by means of multivariate explorative analysis, in particular Principal Component and Cluster Analysis, were ascribed to breaking and flat howls. Discriminant Function Analysis was applied to the recognised groups with the aim to find a general rule for classification. Howls with different features were correctly assigned to the groups obtained by explorative analysis in 95.8% of cases. The analysis of the variables characterising the structure of the howls suggests that maximum frequency and range of fundamental frequency are the most important parameters for classification, while duration does not appear to play any significant role.