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Background Guanylate-binding proteins (GBPs) belong to the large guanosine triphosphatases (GTPases) family and have specialised in host defence in vivo against a broad spectrum of invading pathogens. This ancient evolutionary group of genes was first studied in humans and rodents, but its evolution remained largely unknown for nearly 20 years. In recent years, more studies have emerged deepening the knowledge of GBP evolution in specific mammalian groups: Primates, Tupaia , Muroids (Rodents), Bats and Lagomorphs. Results Here, we aimed to present a comprehensive analysis of mammals GBP evolution. Our phylogenetic analysis demonstrates that mammals’ GBPs share a common ancestor and that each major mammalian group has evolved a specific GBP repertoire. Two Monotreme GBP groups, GBP8 and GBP9 , cluster independently in the phylogenetic tree and do not share the synteny of the other mammalian GBP genes. The other two Monotreme GBP groups, GBP1/2/3/5 and GBP4/6/7 , are at the basal position of the main mammalian groups. Marsupials have two GBP groups, Marsupial GBP1/2/3/5 , basal to Placental GBP1/2/3/5 , and Marsupial GBP4/6/7 , basal to Placental GBP4/6/7 . Marsupial GBP1/2/3/5 can be subdivided into three sub-groups, similarly to what is observed in the Placental GBPs, whereas Marsupial GBP4/6/7 underwent several duplication events across species. We also examined the GBP tissue expression pattern in Monodelphis domestica and found that GBPs are ubiquitously expressed in most tissues, with some differences. Noteworthy was the presence of GBP transcripts in late foetal and newborn opossum tissues. Conclusions The GBP genes revealed a distinct evolutionary pattern in each main mammalian group. Phylogenetic analysis shows that Monotremes and Marsupials have specific GBPs. Particularly intriguing is the presence of GBP8 and GBP9 only in Monotremes.

Evidence from the early paleontological record of mammalian evolution has often been interpreted as supporting the idea that mammals were nocturnal for most of their early history. Multiple features of extant mammal sensory systems, such as evolutionary modifications to the light-regulated circadian system, photoreceptor complement, and retinal morphology, support this nocturnal hypothesis for mammalian evolution. Here, we synthesize data on eye shape and orbit orientation in mammals as these data compare to other amniotes. Most mammals differ from other amniotes in retaining an eye design optimized for high visual sensitivity, with the requisite reduction in acuity, which is typically restricted to scotopically (i.e. low light) adapted amniotes. Mammals also possess the more convergent (similarly facing) orbits and, on average, the largest binocular visual fields among amniotes. Based on our analyses, we propose that extant mammals retain a scotopic eye design as well as expanded binocular zones as a result of their nocturnal origin. Only anthropoid primates notably differ from general mammalian patterns, and possibly have evolved an eye shape more typical of the ancestral amniote condition.

The ectotympanic, malleus and incus of the developing mammalian middle ear (ME) are initially attached to the dentary via Meckel's cartilage, betraying their origins from the primary jaw joint of land vertebrates. This recapitulation has prompted mostly unquantified suggestions that several suspected—but similarly unquantified—key evolutionary transformations leading to the mammalian ME are recapitulated in development, through negative allometry and posterior/medial displacement of ME bones relative to the jaw joint. Here we show, using µCT reconstructions, that neither allometric nor topological change is quantifiable in the pre-detachment ME development of six marsupials and two monotremes. Also, differential ME positioning in the two monotreme species is not recapitulated. This challenges the developmental prerequisites of widely cited evolutionary scenarios of definitive mammalian middle ear (DMME) evolution, highlighting the requirement for further fossil evidence to test these hypotheses. Possible association between rear molar eruption, full ME ossification and ME detachment in marsupials suggests functional divergence between dentary and ME as a trigger for developmental, and possibly also evolutionary, ME detachment. The stable positioning of the dentary and ME supports suggestions that a ‘partial mammalian middle ear’ as found in many mammaliaforms—probably with a cartilaginous Meckel's cartilage—represents the only developmentally plausible evolutionary DMME precursor.

Theria represent an extant clade that comprises placental and marsupial mammals. Here we report on the discovery of a new Late Cretaceous mammal from southern Patagonia, Patagomaia chainko gen. et sp. nov., represented by hindlimb and pelvic elements with unambiguous therian features. We estimate Patagomaia chainko attained a body mass of 14 kg, which is considerably greater than the 5 kg maximum body mass of coeval Laurasian therians. This new discovery demonstrates that Gondwanan therian mammals acquired large body size by the Late Cretaceous, preceding their Laurasian relatives, which remained small-bodied until the beginning of the Cenozoic. Patagomaia supports the view that the Southern Hemisphere was a cradle for the evolution of modern mammalian clades, alongside non-therian extinct groups such as meridiolestidans, gondwanatherians and monotremes.

The platypus (Ornithorhynchus anatinus) is one of the world's most evolutionarily distinct mammals, one of five extant species of egg-laying mammals, and the only living species within the family Ornithorhynchidae. Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments. Accumulating knowledge and technological advancements have provided insights into many aspects of its evolutionary history and biology but have also raised concern about significant knowledge gaps surrounding distribution, population sizes, and trends. The platypus' distribution coincides with many of Australia's major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline. In 2016, the IUCN Red Listing for the platypus was elevated to “Near Threatened,” but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally. In this synthesis, we review the evolutionary history, genetics, biology, and ecology of this extraordinary mammal and highlight prevailing threats. We also outline future research directions and challenges that need to be met to help conserve the species.

The function of the skin as a barrier against the environment depends on the differentiation of epidermal keratinocytes into highly resilient corneocytes that form the outermost skin layer. Many genes encoding structural components of corneocytes are clustered in the epidermal differentiation complex (EDC), which has been described in placental and marsupial mammals as well as non-mammalian tetrapods. Here, we analyzed the genomes of the platypus ( Ornithorhynchus anatinus ) and the echidna ( Tachyglossus aculeatus ) to determine the gene composition of the EDC in the basal clade of mammals, the monotremes. We report that mammal-specific subfamilies of EDC genes encoding small proline-rich proteins (SPRRs) and late cornified envelope proteins as well as single-copy EDC genes such as involucrin are conserved in monotremes, suggesting that they have originated in stem mammals. Monotremes have at least one gene homologous to the group of filaggrin ( FLG ), FLG2 and hornerin ( HRNR ) in placental mammals, but no clear one-to-one pairwise ortholog of either FLG , FLG2 or HRNR . Caspase-14, a keratinocyte differentiation-associated protease implicated in the processing of filaggrin, is encoded by at least 3 gene copies in the echidna. Our results reveal evolutionarily conserved and clade-specific features of the genetic regulation of epidermal differentiation in monotremes.

Over many millions of years of independent evolution, placental, marsupial and monotreme mammals have diverged conspicuously in physiology, life history and reproductive ecology. The differences in life histories are particularly striking. Compared with placentals, marsupials exhibit shorter pregnancy, smaller size of offspring at birth and longer period of lactation in the pouch. Monotremes also exhibit short pregnancy, but incubate embryos in eggs, followed by a long period of post-hatching lactation. Using a large sample of mammalian species, we show that, remarkably, despite their very different life histories, the scaling of production rates is statistically indistinguishable across mammalian lineages. Apparently all mammals are subject to the same fundamental metabolic constraints on productivity, because they share similar body designs, vascular systems and costs of producing new tissue.

Vertebrate limb morphology often reflects the environment due to variation in locomotor requirements. However, proximal and distal limb segments may evolve differently from one another, reflecting an anatomical gradient of functional specialization that has been suggested to be impacted by the timing of development. Here, we explore whether the temporal sequence of bone condensation predicts variation in the capacity of evolution to generate morphological diversity in proximal and distal forelimb segments across more than 600 species of mammals. Distal elements not only exhibit greater shape diversity, but also show stronger within-element integration and, on average, faster evolutionary responses than intermediate and upper limb segments. Results are consistent with the hypothesis that late developing distal bones display greater morphological variation than more proximal limb elements. However, the higher integration observed within the autopod deviates from such developmental predictions, suggesting that functional specialization plays an important role in driving within-element covariation. Proximal and distal limb segments also show different macroevolutionary patterns, albeit not showing a perfect proximo-distal gradient. The high disparity of the mammalian autopod, reported here, is consistent with the higher potential of development to generate variation in more distal limb structures, as well as functional specialization of the distal elements.

A dentary of the oldest known monotreme, the Early Cretaceous Teinolophos trusleri, has an internal mandibular trough, which in outgroups to mammals houses accessory jaw bones, and probable contact facets for angular, coronoid, and splenial bones. Certain of these accessory bones were detached from the mandible to become middle ear bones in mammals. Evidence that the angular (homologous with the mammalian ectotympanic) and the articular and prearticular (homologous with the mammalian malleus) bones retained attachment to the lower jaw in a basal monotreme indicates that the definitive mammalian middle ear evolved independently in living monotremes and therians (marsupials and placentals).

This is the first part of a catalogue containing all known types in the mammal collection of Naturalis Biodiversity Center, Leiden, The Netherlands, covering the orders Monotremata to Rodentia in the sequence according to Wilson and Reeder (2005). The remaining orders will be treated in the second part later. The catalogue began in the early 1990s as a basic inventory using historic catalogues. Chris Smeenk, then curator of the mammal collection, researched the types until his death in 2017. The current authors continued his work, resulting in the present publication. We discuss in this first part 427 names. For 341 of these, Naturalis holds name-bearing types. For Sciurus erythrogenys Schlegel, 1863 and Macroxus schlegelii Gray, 1867 we formally designate the lectotypes.