Developmental process of the modern house shrew's molars: implications for the evolution of the tribosphenic molar in Mesozoic mammals.

Phylogenetically, the tribosphenic molars-prototypes of multi-cusped cheek teeth in marsupial and placental mammals-are derived from the single-cusped conical teeth of reptiles through the addition of cusps. Ontogenetically, mammalian molars are formed through the interface between the dental epithelium and mesenchyme (future enamel-dentin junction), becoming geometrically complex by adding epithelial signaling centers, called enamel knots, which determine future cusp positions. To reevaluate cusp homologies in Mesozoic mammals from an ontogenetic perspective, this study tracked molar development in a living placental mammal species, the house shrew (Suncus murinus), whose molars are morphologically the least derived from tribosphenic prototypes. The development of shrew molars proceeded as if it replayed the evolutionary process of tribosphenic molars. The first formed enamel knots gave rise to the evolutionarily oldest cusps-upper paracone and lower protoconid. The order of formation of other enamel knots and their location in development seemed to trace the order of cusp appearance in evolution. The parallel relationship between ontogeny and phylogeny of mammalian molars, if any, suggests that a change in the timing between developmental events rather than a change in the morphogenetic mechanism itself, should have been a major causal factor for the evolutionary transformation of tooth morphology.

Diphyodont tooth replacement of Brasilodon-A Late Triassic eucynodont that challenges the time of origin of mammals.

Two sets of teeth (diphyodonty) characterise extant mammals but not reptiles, as they generate many replacement sets (polyphyodonty). The transition in long-extinct species from many sets to only two has to date only been reported in Jurassic eucynodonts. Specimens of the Late Triassic brasilodontid eucynodont Brasilodon have provided anatomical and histological data from three lower jaws of different growth stages. These reveal ordered and timed replacement of deciduous by adult teeth. Therefore, this diphyodont dentition, as contemporary of the oldest known dinosaurs, shows that Brasilodon falls within a range of wide variations of typically mammalian, diphyodont dental patterns. Importantly, these three lower jaws represent distinct ontogenetic stages that reveal classic features for timed control of replacement, by the generation of only one replacement set of teeth. This data shows that the primary premolars reveal a temporal replacement pattern, importantly from directly below each tooth, by controlled regulation of tooth resorption and regeneration. The complexity of the adult prismatic enamel structure with a conspicuous intra-structural Schmelzmuster array suggests that, as in the case of extant mammals, this extinct species would have probably sustained higher metabolic rates than reptiles. Furthermore, in modern mammals, diphyodonty and prismatic enamel are inextricably linked, anatomically and physiologically, to a set of other traits including placentation, endothermy, fur, lactation and even parental care. Our analysis of the osteodental anatomy of Brasilodon pushes back the origin of diphyodonty and consequently, its related biological traits to the Norian (225.42 ± 0.37 myr), and around 25 myr after the End-Permian mass extinction event.

Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals.

Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species.1-7 The Cenozoic radiation of placental mammals, the foundational example of this concept,8,9 gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs.10-13 However, study of this and other radiations has focused on variation in evolutionary rates,4,5,7,14 leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized.15-17 We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.

End-of-Life Decisions: Palliative Care, Hospice, and Euthanasia for Exotic Animals.

A great deal of attention has been directed toward developing better options for palliative care and hospice, and improving euthanasia techniques in all species. Euthanasia of exotic pets is technically more difficult because of anatomic differences and small patient size. Traditional intravenous euthanasia techniques in conscious patients are stressful and should generally be avoided in exotic pets; simple intramuscular administration of high dosages of anesthetics followed by delivery of euthanasia solutions is preferred. Options for mammals, birds, and reptiles are presented.

Reawakening of Ancestral Dental Potential as a Mechanism to Explain Dental Pathologies.

During evolution, there has been a trend to reduce both the number of teeth and the location where they are found within the oral cavity. In mammals, the formation of teeth is restricted to a horseshoe band of odontogenic tissue, creating a single dental arch on the top and bottom of the jaw. Additional teeth and structures containing dental tissue, such as odontogenic tumors or cysts, can appear as pathologies. These tooth-like structures can be associated with the normal dentition, appearing within the dental arch, or in nondental areas. The etiology of these pathologies is not well elucidated. Reawakening of the potential to form teeth in different parts of the oral cavity could explain the origin of dental pathologies outside the dental arch, thus such pathologies are a consequence of our evolutionary history. In this review, we look at the changing pattern of tooth formation within the oral cavity during vertebrate evolution, the potential to form additional tooth-like structures in mammals, and discuss how this knowledge shapes our understanding of dental pathologies in humans.

Non-volant mammals of the Ibura National Forest, northeastern Brazil

Less than 10% of the original Atlantic Forest cover now remains standing in the Brazilian state of Sergipe, although few scientific studies have focused on its mammalian diversity. The present study describes the diversity of non-volant mammals found in the Ibura National Forest (INF), based on live trapping, and direct and indirect observations. We sampled the IBF on six days per month between June 2012 and August 2013, using live-traps (Sherman-type) positioned in pairs (ground and understory). We equally sampled semideciduous forest and an abandoned Eucalyptusplantation with dense understory (over 30 years). We also used non-systematics methods (direct observations, vestiges, camera-trap, and opportunistic captures). We recorded 18 species, from 12 families and 7 orders considering all the applied methods. Among recorded species, Bradypus torquatusand Lontra longicaudisare considered threatened of extinction. Considering only the live-trapping (totaling 3,240 trapping nights), we captured 125 individuals (3.85% success) from four species, Marmosa demerarae(52%), Didelphis albiventris(19.2%), Cerradomys vivoi(15.2%), and M. murina(13.6%). Estimated and observed richness was the same, suggesting a satisfactory effort. Didelphis albiventrisand M. demeraraeshowed significantly higher captures in the dry seasons. Didelphis albiventrisand C.vivoishowed significantly higher captures in the substratum, and M. demeraraehigher in the understory. Cerradomysvivoishowed significantly higher captures in the Eucalyptusphytophysiognomy. Non-Metric Multidimensional Scaling and the ANOSIM showed a significant difference in the captured species among semidecidual forest and Eucalyptus. Despite the small area (144 ha), the INF still houses a relatively high mammalian diversity. Further investigations may help to understand the role of habitat reduction in the diversity and habitat partitioning among mammal species in the Atlantic Forest of Northeastern Brazil.

Complex mammalian-like haematopoietic system found in a colonial chordate.

Haematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are haematopoietic stem cells (HSCs), which are multipotent and self-renewing, and generate the entire repertoire of blood and immune cells throughout an animal's life1. Although there have been comprehensive studies on self-renewal, differentiation, physiological regulation and niche occupation in vertebrate HSCs, relatively little is known about the evolutionary origin and niches of these cells. Here we describe the haematopoietic system of Botryllus schlosseri, a colonial tunicate that has a vasculature and circulating blood cells, and interesting stem-cell biology and immunity characteristics2-8. Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other3,4,7. Using flow cytometry, whole-transcriptome sequencing of defined cell populations and diverse functional assays, we identify HSCs, progenitors, immune effector cells and an HSC niche, and demonstrate that self-recognition inhibits allospecific cytotoxic reactions. Our results show that HSC and myeloid lineage immune cells emerged in a common ancestor of tunicates and vertebrates, and also suggest that haematopoietic bone marrow and the B. schlosseri endostyle niche evolved from a common origin.

RUNX2 repeat variation does not drive craniofacial diversity in marsupials.

BACKGROUND: Runt-related transcription factor 2 (RUNX2) is a transcription factor essential for skeletal development. Variation within the RUNX2 polyglutamine / polyalanine (QA) repeat is correlated with facial length within orders of placental mammals and is suggested to be a major driver of craniofacial diversity. However, it is not known if this correlation exists outside of the placental mammals. RESULTS: Here we examined the correlation between the RUNX2 QA repeat ratio and facial length in the naturally evolving sister group to the placental mammals, the marsupials. Marsupials have a diverse range of facial lengths similar to that seen in placental mammals. Despite their diversity there was almost no variation seen in the RUNX2 QA repeat across individuals spanning the entire marsupial infraclass. The extreme conservation of the marsupial RUNX2 QA repeat indicates it is under strong purifying selection. Despite this, we observed an unexpectedly high level of repeat purity. CONCLUSIONS: Unlike within orders of placental mammals, RUNX2 repeat variation cannot drive craniofacial diversity in marsupials. We propose conservation of the marsupial RUNX2 QA repeat is driven by the constraint of accelerated ossification of the anterior skeleton to facilitate life in the pouch. Thus, marsupials must utilize alternate pathways to placental mammals to drive craniofacial evolution.

Anatomy and Disorders of the Oral Cavity of Miscellaneous Exotic Companion Mammals.

Unusual mammalian species such as the hedgehog, sugar glider, and miniature pig are encountered with increasing frequency in exotic companion medicine. Disease of the oral cavity can occur in any species; although occasionally encountered in exotic mammalian species, it is rarely described in the literature. Anatomy and dentition vary significantly; diagnosis and treatment are often extrapolated from that known in other species. The best-documented disease of the oral cavity in this group of species is oral neoplasia in the hedgehog.

Mass-Specific Metabolic Rate Influences Sperm Performance through Energy Production in Mammals.

Mass-specific metabolic rate, the rate at which organisms consume energy per gram of body weight, is negatively associated with body size in metazoans. As a consequence, small species have higher cellular metabolic rates and are able to process resources at a faster rate than large species. Since mass-specific metabolic rate has been shown to constrain evolution of sperm traits, and most of the metabolic activity of sperm cells relates to ATP production for sperm motility, we hypothesized that mass-specific metabolic rate could influence sperm energetic metabolism at the cellular level if sperm cells maintain the metabolic rate of organisms that generate them. We compared data on sperm straight-line velocity, mass-specific metabolic rate, and sperm ATP content from 40 mammalian species and found that the mass-specific metabolic rate positively influences sperm swimming velocity by (a) an indirect effect of sperm as the result of an increased sperm length, and (b) a direct effect independent of sperm length. In addition, our analyses show that species with higher mass-specific metabolic rate have higher ATP content per sperm and higher concentration of ATP per µm of sperm length, which are positively associated with sperm velocity. In conclusion, our results suggest that species with high mass-specific metabolic rate have been able to evolve both long and fast sperm. Moreover, independently of its effect on the production of larger sperm, the mass-specific metabolic rate is able to influence sperm velocity by increasing sperm ATP content in mammals.

Red Iron-Pigmented Tooth Enamel in a Multituberculate Mammal from the Late Cretaceous Transylvanian "Hateg Island".

Mammals that inhabit islands are characterized by peculiar morphologies in comparison to their mainland relatives. Here we report the discovery of a partial skull associated with the lower jaws of a Late Cretaceous (≈70 Ma) multituberculate mammal from the Carpathian "Hateg Island" of Transylvania, Romania. The mammal belongs to the Kogaionidae, one of the rare families that survived the Cretaceous-Paleogene mass extinction in Europe. The excellent preservation of this specimen allows for the first time description of the complete dentition of a kogaionid and demonstration that the enigmatic Barbatodon transylvanicus presents a mosaic of primitive and derived characters, and that it is phylogenetically basal among the Cimolodonta. Another peculiarity is the presence of red pigmentation in its tooth enamel. The red coloration is present on the anterior side of the incisors and on the cusps of most of the teeth. Energy-dispersive X-ray spectrometry (EDS) analysis reveals that the pigmented enamel contains iron, as in living placentals. Such a red pigmentation is known in living soricine shrews and many families of rodents, where it is thought to increase the resistance of the enamel to the abrasion that occurs during "grinding" mastication. The extended pattern of red pigment distribution in Barbatodon is more similar to that in eulipotyplan insectivores than to that in rodents and suggests a very hard diet and, importantly, demonstrates that its grasping incisors were not ever-growing. As inferred for other endemic Transylvanian vertebrates such as dwarf herbivorous dinosaurs and unusual theropod dinosaurs, insularity was probably the main factor of survival of such a primitive mammalian lineage relative to other mainland contemporaries of the Northern hemisphere.

Diversidad, abundancia relativa y patrones de actividad de mamíferos medianos y grandes en una selva seca del Istmo de Tehuantepec, Oaxaca, México / Diversity, relative abundance and activity patterns of medium and large mammals in a tropical deciduous forest in the Isthmus of Tehuantepec, Oaxaca, Mexico

The use of camera traps and mammal track search are complementary methods to monitoring species of which is not well documented their natural history, as in the case of medium and large mammals. To ensure its conservation and good management, it is necessary to generate information about the structure of the community and their populations. The objective of the present study was to estimate the diversity, relative abundance and activity patterns of medium and large mammals in a tropical deciduous forest located in the Isthmus of Tehuantepec, Oaxaca, Mexico. Samplings were conducted in three month intervals, from September 2011 to May 2013. We used photographic-sampling and track search, two complementary sampling methods. For photographic-sampling, 12 camera traps were placed covering an area of 60km², while for the tracks search a monthly tour of four line-transect surveys of three kilometers length each was undertaken. We obtained a total of 344 pictures with 5 292 trap-days total sampling effort; in addition, 187 track records in a total of 144km. With both methods we registered 21 species of mammals, in 13 families and seven orders, and five species resulted in new records to the area. The diversity index of Shannon-Wiener obtained with the method of tracks was H´=2.41, while the most abundant species were Urocyon cinereoargenteus (IAR=0.23) and Pecari tajacu (IAR=0.20). By the method of trap the most abundant species were P. tajacu (IAR=2.62) and Nasua narica (IAR=1.28). In terms of patterns of activity P. tajacu, N. narica and Odocoileus virginianus were primarily diurnal species; Canis latrans and Leopardus pardalis did not show preference for any schedule in particular, and Didelphis virginiana and Dasypus novemcinctus preferred to have nocturnal activity. This information can be of help to the creation of programs of management and conservation of mammals of medium and large in the Isthmus of Tehuantepec, Oaxaca, México. Rev. Biol. Trop. 62 (4): 1433-1448. Epub 2014 December 01.

Para asegurar la conservación y buen manejo de mamíferos medianos y grandes, es necesario generar información sobre la estructura de la comunidad y de sus poblaciones. El objetivo del presente estudio fue estimar la diversidad, abundancia relativa y patrones de actividad de mamíferos medianos y grandes en una selva baja caducifolia en el Istmo de Tehuantepec, Oaxaca, México. El muestreo se llevó a cabo a intervalos de tres meses de septiembre 2011 a mayo 2013. Se utilizaron dos métodos complementarios: se colocaron 12 cámaras trampa cubriendo un área de 60km² y se realizó la búsqueda de rastros en transectos lineales de tres kilómetros de longitud. Se obtuvieron un total de 344 fotografías con un esfuerzo de muestreo de 5 292 días-trampa; además, 187 rastros en un total de 144km recorridos. En total se registraron 21 especies de mamíferos, de 13 familias y siete órdenes. El índice de diversidad de Shannon-Wiener fue más alto con el método de rastros (H´=2.41). Las especies más abundantes por medio de rastros fueron: Urocyon cinereoargenteus (IAR=0.23) y Pecari tajacu (IAR=0.20). Por medio del fototrampeo las especies más abundantes fueron: P. tajacu (IAR=2.62) y Nasua narica (IAR=1.28). Los patrones de actividad de P. tajacu, N. narica y Odocoileus virginianus fueron diurnos; Canis latrans y Leopardus pardalis no presentaron preferencia hacia algún horario en particular y Didelphis virginiana y Dasypus novemcinctus tuvieron actividad nocturna. Esta información puede ser de ayuda para la creación de programas de manejo y conservación de mamíferos medianos y grandes en el Istmo de Tehuantepec, Oaxaca, México.

Patterning and post-patterning modes of evolutionary digit loss in mammals.

A reduction in the number of digits has evolved many times in tetrapods, particularly in cursorial mammals that travel over deserts and plains, yet the underlying developmental mechanisms have remained elusive. Here we show that digit loss can occur both during early limb patterning and at later post-patterning stages of chondrogenesis. In the 'odd-toed' jerboa (Dipus sagitta) and horse and the 'even-toed' camel, extensive cell death sculpts the tissue around the remaining toes. In contrast, digit loss in the pig is orchestrated by earlier limb patterning mechanisms including downregulation of Ptch1 expression but no increase in cell death. Together these data demonstrate remarkable plasticity in the mechanisms of vertebrate limb evolution and shed light on the complexity of morphological convergence, particularly within the artiodactyl lineage.

Pathology of the exotic companion mammal gastrointestinal system.

A variety of disease agents can affect the gastrointestinal tract of the exotic companion mammal, some of which can pose zoonotic health concerns. Many conditions present with nonspecific clinical signs (lethargy, variable degrees of diarrhea, and for most sick rodents, presenting hunched with spiky fur), necessitating additional laboratory testing to reach a diagnosis. Primary tumors of the digestive tract are also presented as well as miscellaneous conditions ranging from toxins to trauma.

Bronchial tree architecture in mammals of diverse body mass / Arquitectura del árbol bronquial en mamíferos de diferentes masas corporales

The anatomy of mammal's lung air space constitutes the bronchial tree which disposition is associated to air flux dynamics. Casts obtained from human, pig and rat lungs were studied to analyze possible differences of the bronchial tree architecture in mammals with diverse dimensions and posture. Air spaces were filled with polymers through trachea followed by acid corrosion. Tracheal and main bronchial division's diameters were measured to relate with body mass using allometry. The results revealed a dichotomic bronchial branching pattern in the human casts and a monopodial pattern in animals. In allometric relationship trachea was larger in rats, then pigs and lastly in humans, differences were statistically significant, the same occurs in right bronchus, as in the left bronchus there was no difference between rat and pig. The linear relationship between the human tracheal diameters was 1.2 times larger than the pig and 6.7 times larger than the rat; the pig tracheal diameter was 5.6 times larger than the rat. Quadruped position of the pig and rat is linked to a horizontal air way while the erect position, biped in human, correspond to a vertical air way. A big mammal shows less respiratory frequency than small mammals. Mammals with small, medium and high body mass allied to diverse posture and habits was compared revealing morphological differences in the bronchial trees as different allometric correlations between quadruped animals and human biped.

La anatomía de los espacios aéreos en los pulmones de mamíferos constituyen el árbol bronquial cuya disposición es asociada a la dinámica del flujo aéreo. Moldes obtenidos de los pulmones de humanos, cerdos y ratones fueron estudiados para analizar las posibles diferencias de las arquitecturas de los árboles bronquiales en mamíferos de diferentes dimensiones y posturas. Los espacios aéreos fueran llenados con polímeros por la tráquea y posterior corrosión con ácido. Los diámetros de la tráquea y de las principales divisiones de los bronquios fueron medidos y relacionados con las masas corporales por medio de alometría. Los resultados revelaron uno patrón dicotómico en los moldes de humanos y un patrón monopodial en los animales. La relación alométrica determinço que la tráquea es mayor en los ratones, seguidos de los cerdos y por último en los humanos, las diferencias fueran estadísticamente significativas. Lo mismo ocurrió en el bronquio derecho en cambio en el bronquio izquierdo no hubo diferencia entre el cerdo y el ratón. La relación linear entre los diámetros de la tráquea fue 1,2 mayor en el humano comparada con el cerdo y 6,7 mayor que el ratón, el diámetro de la tráquea del cerdo fue 5,6 mayor que el ratón. La posición cuadrúpede del cerdo y del ratón es vinculada a una vía aérea horizontal en cuanto a que la posición erecta en humanos corresponde a una vía aérea vertical. Los grandes mamíferos muestran menor frecuencia respiratoria que los pequeños mamíferos. Mamíferos con masas corporales pequeñas, medias y grandes con diversas posturas y hábitos fueron comparados mostrando diferencias morfológicas en los árboles bronquiales así como diferentes correlaciones alométricas entre animales cuadrúpedos y humanos bípedos.

Surgical castration of the male common hippopotamus (Hippopotamus amphibius).

In a prospective, clinical, surgery study we report here for the first time, in detail, on the surgical castration of 10 captive adult male common hippopotami (Hippopotamus amphibius). The successful procedures, a species-specific modification of standard equine castration techniques, provide valuable insight into the spatially dynamic nature of the common hippopotamus testis. The use of ultrasonography to locate the testis before and during the procedures and species-specific positioning during surgery greatly facilitated this distinctive procedure. Additionally, this surgical method provides an important additional tool for captive management of the common hippopotamus. Castration of individual males not only facilitates population control but can potentially also be employed to limit intermale aggression.

Comparative study of hair follicle morphology in eight mammalian species and humans.

BACKGROUND: The objective of the present study was the investigation of hair follicle morphology in eight mammalian species in order to evaluate the species-specific contribution of hair follicles to skin penetration particularly with regard to the utilization of the different animal species as skin models for human skin. METHODS: Cyanoacrylate skin surface biopsy method (CSSB), light microscopy and also digital photography were used for the measurements of hair follicle morphology. RESULTS: The results revealed species-specific differences regarding the pattern of hair follicle distribution and also differences with regard to hair follicle parameters and characteristics. The results also showed that hair follicles generally possess enormous reservoir capacities, regarding the follicular volume. In all examined species, hair follicles reached at least one-fifth of stratum corneum storage capacity. The results were compared with human data obtained in a previous study. CONCLUSION: With regard to hair follicle morphology and skin structure, the porcine skin seems to be the most appropriate skin model for human skin analog to previous investigations, whereas the skin of dog, cat, and rabbit showed the most significant differences.

Mammal disparity decreases during the Cretaceous angiosperm radiation.

Fossil discoveries over the past 30 years have radically transformed traditional views of Mesozoic mammal evolution. In addition, recent research provides a more detailed account of the Cretaceous diversification of flowering plants. Here, we examine patterns of morphological disparity and functional morphology associated with diet in early mammals. Two analyses were performed: (i) an examination of diversity based on functional dental type rather than higher-level taxonomy, and (ii) a morphometric analysis of jaws, which made use of modern analogues, to assess changes in mammalian morphological and dietary disparity. Results demonstrate a decline in diversity of molar types during the mid-Cretaceous as abundances of triconodonts, symmetrodonts, docodonts and eupantotherians diminished. Multituberculates experience a turnover in functional molar types during the mid-Cretaceous and a shift towards plant-dominated diets during the late Late Cretaceous. Although therians undergo a taxonomic expansion coinciding with the angiosperm radiation, they display small body sizes and a low level of morphological disparity, suggesting an evolutionary shift favouring small insectivores. It is concluded that during the mid-Cretaceous, the period of rapid angiosperm radiation, mammals experienced both a decrease in morphological disparity and a functional shift in dietary morphology that were probably related to changing ecosystems.

Exploring the mammalian sensory space: co-operations and trade-offs among senses.

The evolution of a particular sensory organ is often discussed with no consideration of the roles played by other senses. Here, we treat mammalian vision, olfaction and hearing as an interconnected whole, a three-dimensional sensory space, evolving in response to ecological challenges. Until now, there has been no quantitative method for estimating how much a particular animal invests in its different senses. We propose an anatomical measure based on sensory organ sizes. Dimensions of functional importance are defined and measured, and normalized in relation to animal mass. For 119 taxonomically and ecologically diverse species, we can define the position of the species in a three-dimensional sensory space. Thus, we can ask questions related to possible trade-off vs. co-operation among senses. More generally, our method allows morphologists to identify sensory organ combinations that are characteristic of particular ecological niches. After normalization for animal size, we note that arboreal mammals tend to have larger eyes and smaller noses than terrestrial mammals. On the other hand, we observe a strong correlation between eyes and ears, indicating that co-operation between vision and hearing is a general mammalian feature. For some groups of mammals we note a correlation, and possible co-operation between olfaction and whiskers.

The radiation of cynodonts and the ground plan of mammalian morphological diversity.

Cynodont therapsids diversified extensively after the Permo-Triassic mass extinction event, and gave rise to mammals in the Jurassic. We use an enlarged and revised dataset of discrete skeletal characters to build a new phylogeny for all main cynodont clades from the Late Permian to the Early Jurassic, and we analyse models of morphological diversification in the group. Basal taxa and epicynodonts are paraphyletic relative to eucynodonts, and the latter are divided into cynognathians and probainognathians, with tritylodonts and mammals forming sister groups. Disparity analyses reveal a heterogeneous distribution of cynodonts in a morphospace derived from cladistic characters. Pairwise morphological distances are weakly correlated with phylogenetic distances. Comparisons of disparity by groups and through time are non-significant, especially after the data are rarefied. A disparity peak occurs in the Early/Middle Triassic, after which period the mean disparity fluctuates little. Cynognathians were characterized by high evolutionary rates and high diversity early in their history, whereas probainognathian rates were low. Community structure may have been instrumental in imposing different rates on the two clades.