Comparative analysis of encephalization in mammals reveals relaxed constraints on anthropoid primate and cetacean brain scaling

There is a well-established allometric relationship between brain and body mass in mammals. Deviation of relatively increased brain size from this pattern appears to coincide with enhanced cognitive abilities. To examine whether there is a phylogenetic structure to such episodes of changes in encephalization across mammals, we used phylogenetic techniques to analyse brain mass, body mass and encephalization quotient (EQ) among 630 extant mammalian species. Among all mammals, anthropoid primates and odontocete cetaceans have significantly greater variance in EQ, suggesting that evolutionary constraints that result in a strict correlation between brain and body mass have independently become relaxed. Moreover, ancestral state reconstructions of absolute brain mass, body mass and EQ revealed patterns of increase and decrease in EQ within anthropoid primates and cetaceans. We propose both neutral drift and selective factors may have played a role in the evolution of brain-body allometry.     

Reproductive strategies,body size,and encephalization in primate evolution

In order to understand fully the generally high level of encephalization observed in living primates, we must determine why early primates exhibited moderately large relative brain sizes compared to their early Tertiary contemporaries. The relatively high degree of encephalization in early primates may be related at least in part to the fact that they were highly unusualamong mammals in combining a small body size with a strongly precocial reporductive strategy. Other small, precocial mammals also exhibit moderately high levels of encephalization; but primates appear to have been truly uniquein being the only such small-sized and highly precocial group to give rise to extensive radiations of larger descendants. This is a key element in understanding primate brain evolution, because the initial “head start” of the early primates was translated up to larger sizes in descendants. The possible relationships among encephalization, precociality, small size, and arboreality are discussed, particularly in light of recent debates concerning the validity of the superorder Archonta. This work emphasizes that we need to consider relative brain size as but one element in a complex synergistic network of morphological and life-history features.     

Brain size diversity in adaptation and speciation of subterranean mole rats

We have tested brain size diversity and encephalization in the actively speciating subterranean mole rats of the Spalax ehrenbergi superspecies in Israel. Our sample involved 171 individuals comprising 12 populations and 4 chromosomal species (2n = 52, 54, 58 and 60) distributed parapatrically from the northern Mediterranean region southward (2n = 52, 54→+58→60) into increasingly more arid and unpredictable climatic regimes, approaching the Negev Desert. Our results indicate that relative brain size and encephalization are highest in 2n = 60 as compared with 2n = 52, 54 and 58. We hypothesize that this pattern is adaptive and molded by natural selection. Brain evolution and higher encephalization in the S. ehrenbergi complex appears to be associated with increasing ecological stresses of aridity and climatic unpredictability.     

Comparative genomics analyses of alpha-keratins reveal insights into evolutionary adaptation of marine mammals

Background

Diversity of hair in marine mammals was suggested as an evolutionary innovation to adapt aquatic environment, yet its genetic basis remained poorly explored. We scanned α-keratin genes, one major structural components of hair, in 16 genomes of mammalian species, including seven cetaceans, two pinnipeds, polar bear, manatee and five terrestrial species.

Results

Extensive gene loss and high pseudogenization rate of α-keratin genes were identified in cetaceans when compared to terrestrial artiodactylans (average number of α-keratins 37.29 vs. 58.33; pseudogenization rate 29.89% vs. 8.00%), especially of hair follicle-specific keratin genes (average pseudogenization rate in cetaceans of 43.88% relative to 3.80% artiodactylian average). Compared to toothed whale, the much more number of intact functional α-keratin genes was examined in the baleen whale that had specific keratinized baleen. In contrast, the number of keratin genes in pinnipeds, polar bear and manatee were comparable to those of their respective terrestrial relatives. Additionally, four keratin genes (K39, K9, K42, and K74) were found to be pseudogenes or lost uniquely in cetaceans and manatees.

Conclusions

Species-specific evolution of α-keratin gene family identified in the marine mammals might be responsible for their different hair characteristics. Increased gene loss and pseudogenization rate identified in cetacean lineages was likely to contribute to hair-less phenotype to adaptation for complete aquatic environment. However, the fully aquatic manatee still remained the comparable number of intact genes to its terrestrial relative, probably due to its perioral bristles and bristle-like hairs on the oral disk. By contrast, similar evolution pattern of α-keratin gene repertoire in the pinnipeds, polar bear and their terrestrial relatives was likely due to abundant hair to keep warm when they went ashore. Interestingly, some keratin genes were exclusively lost in cetaceans and manatees, likely as a result of convergent hair-loss phenotype to inhabit completely aquatic environment in both groups.

     

Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)

Calibration of the Brownian diffusion model of Felsenstein indicates that phylogeny may have an influence on body length and other phenotypic measures in Cetacea for as many as 10,000 generations or about 180,000 years, which is negligible in the 35 million year history of extant Cetacea. Observations of phenotypic traits in cetacean species living today are independent of phylogeny and independent statistically. Four methods for estimating body weight in fossil cetaceans are compared: (1) median serial regression involving a set of multiple regressions of log body weight on log centrum length, width, and height for core vertebrae; (2) regression of log whole body weight on log body length for individuals; (3) regression of log whole body weight on log body length for species means; and (4) regression of log lean body weight on log body length for individuals. These yield body weight estimates for the Eocene archaeocete Dorudon atrox of 1126, 1118, 1132, and 847 kg, respectively, with consistency and applicability to partial skeletons favoring the first approach. The whole-body weight expected, P_e (in kg), for a given body length, L_i (in cm), is given by log₁₀ P_e?=?2.784 ? log₁₀ L_i???4.429. Negative allometry of body weight and body length (slope 2.784?<?3.000) means that small cetaceans are shorter and more maneuverable than expected for their weight, while large cetaceans are longer and more efficient energetically than expected for their weight. Encephalization is necessarily quantified relative to a reference sample, most mammals are terrestrial, and terrestrial mammals provide a logical baseline. The encephalization residual for living terrestrial mammals as a class (ER_TC), is the difference between observed log₂ brain weight (E_i in g) and expected log₂ brain weight (E_e in g), where the latter is estimated from body weight (P_i in g), as log₂ E_e?=?0.740 ? log₂ P_i???4.004. ER_TC is positive for brains that are larger than expected for a given body size, and negative for brains that are smaller than expected. Base-2 logarithms make the ER_TC scale intuitive, in uniform units of halving or doubling. Encephalization quotients (EQ) are unsuitable for comparison because they are proportions on a non-uniform scale. Middle Eocene archaeocetes have ER_TC values close to ?2 (two halvings compared to expectation), while late Eocene archaeocetes have ER_TC values close to ?1 (one halving compared to expectation). ER_TC is not known for fossil mysticetes, but living mysticetes have ER_TC values averaging about ?2. Oligocene-Recent odontocetes appear to have ER_TC values averaging about +1 (one doubling compared to expectation) through their temporal range. Definitive interpretation of the evolution of encephalization in Cetacea will require better documentation for Oligocene–Recent mysticetes and odontocetes.     

Virtual brain endocast of Antifer (Mammalia: Cervidae), an extinct large cervid from South America

A diverse fossil record of Cervidae (Mammalia) has been documented in the South American Pleistocene, when these animals arrived during the Great American Biotic Interchange. Using computed tomography-scanning techniques, it is possible to access the endocranial morphology of extinct species. Here, we studied the brain endocast of the extinct late Pleistocene cervid Antifer ensenadensis from southern Brazil, one of the largest forms that lived on this continent, using comparative morphology, geometric morphometrics, and encephalization quotients. The analyzed endocasts demonstrate that A. ensenadensis had a gyrencephalic brain, showing a prominent longitudinal sinus (=sagittal superior sinus), which is also observed in the large South American cervid Blastocerus dichotomus. The encephalization quotient is within the variation of extant cervids, suggesting maintenance of the pattern of encephalization from at least the late Pleistocene. Geometric morphometric analysis suggested a clear and linear allometric trend between brain endocast size and shape, and highlights A. ensenadensis as an extreme form within the analyzed cervids regarding brain morphology.     

Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution

Background

Integration of diverse data (molecules, fossils) provides the most robust test of the phylogeny of cetaceans. Positioning key fossils is critical for reconstructing the character change from life on land to life in the water.

Methodology/Principal Findings

We reexamine relationships of critical extinct taxa that impact our understanding of the origin of Cetacea. We do this in the context of the largest total evidence analysis of morphological and molecular information for Artiodactyla (661 phenotypic characters and 46,587 molecular characters, coded for 33 extant and 48 extinct taxa). We score morphological data for Carnivoramorpha, †Creodonta, Lipotyphla, and the †raoellid artiodactylan †Indohyus and concentrate on determining which fossils are positioned along stem lineages to major artiodactylan crown clades. Shortest trees place Cetacea within Artiodactyla and close to †Indohyus, with †Mesonychia outside of Artiodactyla. The relationships of †Mesonychia and †Indohyus are highly unstable, however - in trees only two steps longer than minimum length, †Mesonychia falls inside Artiodactyla and displaces †Indohyus from a position close to Cetacea. Trees based only on data that fossilize continue to show the classic arrangement of relationships within Artiodactyla with Cetacea grouping outside the clade, a signal incongruent with the molecular data that dominate the total evidence result.

Conclusions/Significance

Integration of new fossil material of †Indohyus impacts placement of another extinct clade †Mesonychia, pushing it much farther down the tree. The phylogenetic position of †Indohyus suggests that the cetacean stem lineage included herbivorous and carnivorous aquatic species. We also conclude that extinct members of Cetancodonta (whales + hippopotamids) shared a derived ability to hear underwater sounds, even though several cetancodontans lack a pachyostotic auditory bulla. We revise the taxonomy of living and extinct artiodactylans and propose explicit node and stem-based definitions for the ingroup.     

Brains of Vespertilionids

Macromorphology and encephalization (EI) of brains were compared in 58 Vespertilionid species, brain composition in 36 species: 46 or 27 species of Vespertilioninae, 8 or 5 species of Miniopterinae, 2 species of Kerivoulinae, and 2 species of Nyctophilinae. Subfamily differences were found in the extent of the cover of the mesencephalon. It is nearly fully covered in Kerivoula papulosa (Kerivoulinae), at least half covered (by the cerebellum) in Miniopterinae, and free (completely or nearly so) in Nyctophilinae and Vespertilioninae. In relative brain size, the Kerivoulinae are highest (average EI = 130), followed by the Miniopterinae (111), Nyctophilinae (102) and Vespertilioninae (95). The higher encephalization of Kerivoulinae and Miniopterinae is accompanied by a marked increase of relative size in cerebellum and striatum, and in Kerivoulinae, in hippocampus and neocortex as well.     

Astragali of Pakicetidae and other early-to-middle Eocene archaeocetes (Mammalia,Cetacea) of Pakistan: locomotion and habitat in the initial stages of whale evolution

Richard Dehm and colleagues of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich made an important collection of early-to-middle Eocene mammals at Ganda Kas in Pakistan during the winter of 1955/56. The genera and species Ichthyolestes pinfoldi and Gandakasia potens were named from this collection. Both are now recognized as early and primitive archaeocete cetaceans. In addition, Dehm’s group collected 16 complete or partial astragali of archaeocetes that were misidentified as artiodactyls. These bring the total number of archaeocete astragali known from Ganda Kas to 28. They separate clearly into four species distinguished by size: from smallest to largest Ichthyolestes pinfoldi Dehm and Oettingen-Spielberg, Pakicetus attocki (West), Gandakasia potens Dehm and Oettingen-Spielberg, and Ambulocetus natans Thewissen et al. Ganda Kas artiodactyls are smaller and rare in comparison. Ichthyolestes and Pakicetus are pakicetid archaeocetes, Gandakasia is presently indeterminate to family, and Ambulocetus is an ambulocetid. Tooth size and astragalus size are highly correlated, corroborating reference of astragali to the first three archaeocete taxa based on teeth. Multivariate morphometric comparison (Auto3Dgm) shows that pakicetid astragali overlap almost completely in shape with those of early artiodactyls. Middle Eocene protocetid astragali are divergent from both. Retention of an astragalus indistinguishable from that of artiodactyls shows that pakicetids are closely related to artiodactyls phylogenetically, but does not make Ichthyolestes and Pakicetus terrestrial or cursorial. Other skeletal elements and bone microstructure indicate that pakicetids were semiaquatic like later protocetids. Tropical riverine and marginal marine facies of the Kuldana Formation are likely habitats for initial stages of the transition from terrestrial artiodactyls to semiaquatic and fully aquatic archaeocetes.     

Nouvelles données sur 'encéphalisation des Reptiles Squamates

New datas on the level of encephalization of Squamate Reptiles This study carried out on 32 species of Lizards, 15 species of Snakes and one Amphisbaenian, the measure of the brain-weight (Brw) and the body-weight (Bdw) of which leads to the determination of the a and k parameters of the SNEL'S formula: Brw =k– Bdw^α. In a first stage we are able to demonstrate with 9 species of Saurians and 2 species of Ophidians, each species being represented by a sample the size of which variing between 30 to 80, that the intrinsic variability of the brain gives a mean value of 6.4% (isoponderal variability) or 7.5% (isometric variability). The intraspecific α coefficients (allometric coefficients of growth or of size) remain between.383 and.500; the mean value of which, .43 will be considered as a characteristic of the order Squamata. The interspecific α. coefficient (filiation coefficient of BAUCHOT and PLATEL) given by the 32 species of Lizards is .669, quite close to those previously calculated from a sample of 23 species (.686). The former values of the indices of encephalization belonging to these 23 species are meanwhile different. Six Lacertidae, selected as referrence Saurians (α= 627) lead to new indices of encephalization, the value of which will not be henceforth altered by the addition of new species to our present sample of Saurians. The various adaptative peculiarities roughly expressed by these indices of encephalization will be shortly studied in detail by the way of the volumetric analysis of the nuclear components of the brain. Amongst the 15 Snakes, the discrimination of 3 Henophidians and 12 Caenophidians leads for the last ones to an a filiation coefficient of .664; the value found for the Henophidians (.750) must be considered with suspicion because it get from only 3 species. We find with Anguis, the Amphisbaenian, some Scincidae and all the Snakes a low level of encephalization linked to the legless condition, which masks perhaps another peculiarities related to the evolutive processus which leads from Lizards to Snakes. The analyses of the K/Bdw relationship leads to results which differ from those found by BAUCHOT with the Insectivores-Primates. Separately Saurians and Ophidians do not show any correlation between the coefficient of encephalization and the body-weight; in compensation the Squamata in a whole show characteristics which express a negative rate of encephalization.     

Trajectories and Constraints in Brain Evolution in Primates and Cetaceans

A negative allometric relationship between body mass (BM) and brain size (BS) can be observed for many vertebrate groups. In the past decades, researchers have proposed several hypotheses to explain this finding, but none is definitive and some are possibly not mutually exclusive. Certain species diverge markedly (positively or negatively) from the mean of the ratio BM/BS expected for a particular taxonomic group. It is possible to define encephalization quotient (EQ) as the ratio between the actual BS and the expected brain size. Several cetacean species show higher EQs compared to all primates, except modern humans. The process that led to big brains in primates and cetaceans produced different trajectories, as shown by the organizational differences observed in every encephalic district (e.g., the cortex). However, these two groups both convergently developed complex cognitive abilities. The comparative study on the trajectories through which the encephalization process has independently evolved in primates and cetaceans allows a critical appraisal of the causes, the time and the mode of quantitative and qualitative development of the brain in our species and in the hominid evolutionary lineage.     

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high‐frequency and ultrasonic sound vibrations and mysticetes to low‐frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a point at which we can explore morphological and physiological changes within the baleen whale inner ear. Traditional comparative anatomy and landmark‐based 3D‐geometric morphometric analyses were performed to investigate the anatomical diversity of the inner ears of extinct and extant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes, but odontocetes are completely separated from mysticetes when semicircular canal landmarks are combined with the cochlear data. The cochlea of the archaeocete Zygorhiza kochii and early diverging extinct mysticetes plot within the morphospace of crown mysticetes, suggesting that mysticetes possess ancestral cochlear morphology and physiology. The PCA results indicate variation among mysticete species, although no major patterns are recovered to suggest separate hearing or locomotor regimes. Phylogenetic signal was detected for several clades, including crown Cetacea and crown Mysticeti, with the most clades expressing phylogenetic signal in the semicircular canal dataset. Brownian motion could not be excluded as an explanation for the signal, except for analyses combining cochlea and semicircular canal datasets for Balaenopteridae. J. Morphol. 277:1599–1615, 2016. © 2016 Wiley Periodicals, Inc.     

Within-species brain-body weight variability: A reexamination of the Danish data and other primate species

A restudy of the Danish brain weight data published by Pakkenberg and Voigt ('64), using partial correlation techniques, confirms and extends their earlier conclusions regarding a much stronger allometric relationship between height and brain weight than between body weight and brain weight. The relationship is particularly strong in males, and not in females, which is hypothesized to be related to higher fat components in the latter. Comparative data for smaller samples of Pan, Gorilla, Pongo, Macaca, Papio, and Saimiri using body weights, suggest that such relationship also hold more strongly in males than females, although more reliable data are greatly needed. In addition to providing within-species ranges of variability for variously derived neural statistics (e.g., encephalization quotients, “extra neurons,” etc.), for “normal” primates, it is suggested that while allometric trends do exist within species, and particularly males, evolutionary pressures leading to larger brain size were probably very diverse, and that any one homogenistic theory is unlikely.     

WHO ARE THE WHALES?

ABSTRACT

Whales, dolphins and porpoises, 80 species of entirely aquatic mammals, constitute the order Cetacea. In the early Eocene, about 55 to 60 million years ago according to paleontologists, distant ancestors of modern cetaceans left land for aquatic life. Cetaceans are diverse; average adult size of cetacean species varies by 1000 to 2000 times. Small and large species occupy all oceans from the equator to the polar seas, some forms inhabit rivers and four species live only in fresh water.

Cetaceans are born in water and spend their entire lives in the aquatic medium. There is a great gap in knowledge about hearing in most cetacean species and especially about how noise and high-intensity sound may affect all cetaceans and other mammals underwater. Studies of temporary threshold shift (TTS) and occupational noise exposure in human divers suggest a cautious approach to cetacean noise exposure until data on cetacean TTS can give us some idea of the dynamic range of cetacean ears.     

Decay of TRPV3 as the genomic trace of epidermal structure changes in the land‐to‐sea transition of mammals

The epidermis plays an indispensable barrier function in animals. Some species have evolved unique epidermal structures to adapt to different environments. Aquatic and semi‐aquatic mammals (cetaceans, manatees, and hippopotamus) are good models to study the evolution of epidermal structures because of their exceptionally thickened stratum spinosum, the lack of stratum granulosum, and the parakeratotic stratum corneum. This study aimed to analyze an upstream regulatory gene transient receptor potential cation channel, subfamily V, member 3 (TRPV3) of epidermal differentiation so as to explore the association between TRPV3 evolution and epidermal changes in mammals. Inactivating mutations were detected in almost all the aquatic cetaceans and several terrestrial mammals. Relaxed selective pressure was examined in the cetacean lineages with inactivated TRPV3, which might contribute to its exceptionally thickened stratum spinosum as the significant thickening of stratum spinosum in TRPV3 knock‐out mouse. However, functional TRPV3 may exist in several terrestrial mammals due to their strong purifying selection, although they have “inactivating mutations.” Further, for intact sequences, relaxed selective constraints on the TRPV3 gene were also detected in aquatic cetaceans, manatees, and semi‐aquatic hippopotamus. However, they had intact TRPV3, suggesting that the accumulation of inactivating mutations might have lagged behind the relaxed selective pressure. The results of this study revealed the decay of TRPV3 being the genomic trace of epidermal development in aquatic and semi‐aquatic mammals. They provided insights into convergently evolutionary changes of epidermal structures during the transition from the terrestrial to the aquatic environment.     

Encephalizations and Cerebral Developments in Genus Homo

As Darwin observed in the second chapter of the The Descent of Man, brain size has the more obvious and direct anatomical correlation with the outstanding cognitive capabilities of our species in comparison with its closest relatives. If we extend the comparison to other mammals, we can observe that cognitive capabilities do not seem to strictly correlate with brain dimension in absolute and in relative terms, and the encephalization quotient (EQ) is not a universal advice of the cognitive capabilities of a particular species, too. Why and how the brain size in our lineage increased dramatically in absolute and in relative way during the last 3 million years? What is the relationship between our outstanding intellective capability and the brain size? The progressive encephalization of our ancestors was the origin or the effect for the development of the intellective capabilities of living humans. Recent advances in the knowledge of intrinsic organization of cerebral cortex and in the patterns of genetic expression are able to better outline the trajectories as the metabolic and structural constraints of the qualitative and quantitative encephalic development. The new scenario led to suggest more accurate explanations of the selective mechanism acting during the evolution of our species.     

An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain

This review examines aspects of cetacean brain structure related to behaviour and evolution. Major considerations include cetacean brain-body allometry, structure of the cerebral cortex, the hippocampal formation, specialisations of the cetacean brain related to vocalisations and sleep phenomenology, paleoneurology, and brain-body allometry during cetacean evolution. These data are assimilated to demonstrate that there is no neural basis for the often-asserted high intellectual abilities of cetaceans. Despite this, the cetaceans do have volumetrically large brains. A novel hypothesis regarding the evolution of large brain size in cetaceans is put forward. It is shown that a combination of an unusually high number of glial cells and unihemispheric sleep phenomenology make the cetacean brain an efficient thermogenetic organ, which is needed to counteract heat loss to the water. It is demonstrated that water temperature is the major selection pressure driving an altered scaling of brain and body size and an increased actual brain size in cetaceans. A point in the evolutionary history of cetaceans is identified as the moment in which water temperature became a significant selection pressure in cetacean brain evolution. This occurred at the Archaeoceti - modern cetacean faunal transition. The size, structure and scaling of the cetacean brain continues to be shaped by water temperature in extant cetaceans. The alterations in cetacean brain structure, function and scaling, combined with the imperative of producing offspring that can withstand the rate of heat loss experienced in water, within the genetic confines of eutherian mammal reproductive constraints, provides an explanation for the evolution of the large size of the cetacean brain. These observations provide an alternative to the widely held belief of a correlation between brain size and intelligence in cetaceans.     

Phylogenetic Relationships of Extinct Cetartiodactyls: Results of Simultaneous Analyses of Molecular, Morphological, and Stratigraphic Data

Although some recent morphological and molecular studies agree that Cetacea is closely related to Hippopotamidae, there is little consensus on the phylogeny within Cetartiodactyla. We addressed this problem by conducting two analyses: (1) a simultaneous cladistic analysis of intrinsic data (morphology and molecules) and (2) a stratocladistic analysis, which included morphological, molecular, and stratigraphic data. Unlike previous simultaneous analyses, we had the opportunity to include data from the recently described hindlimbs of protocetid and pakicetid cetaceans. Our intrinsic dataset includes 73 taxa scored for 8,229 informative characters, of which 208 are morphological and 8,021 molecular. Both analyses supported the exclusion of Mesonychia from Cetartiodactyla and a close phylogenetic relationship between Hippopotamidae and Cetacea. Many polytomies in the strict consensus of the most parsimonious trees for the intrinsic dataset can be attributed to differing positions for Raoellidae, which in some trees is the sister-group to Cetacea. Pruning Raoellidae and 18 other taxa from all most parsimonious produced a fully resolved agreement subtree, which indicates that the Old World taxa Cebochoerus and Mixtotherium are successive stem taxa to Whippomorpha (i.e., Cetacea + Hippopotamidae). The main result of adding stratigraphic information to the intrinsic dataset was that we found fewer most parsimonious trees, which in most respects were congruent with a subset of the shortest trees for the intrinsic dataset. Our stratocladistic analysis supports species of Diacodexis as the most basal cetartiodactyls, a clade of suiform cetartiodactyls, a monophyletic Tylopoda that includes Protoceratidae, and a monophyletic Carnivora. We were unable to identify any pre-Miocene stem taxa to Hippopotamidae, thus its ghost lineage is still 39 million years long. The relatively low Bremer support for many nodes in our trees indicates that our phylogenetic hypotheses should be subjected to further testing.     

Increased brain size in mammals is associated with size variations in gene families with cell signalling,chemotaxis and immune-related functions

Genomic determinants underlying increased encephalization across mammalian lineages are unknown. Whole genome comparisons have revealed large and frequent changes in the size of gene families, and it has been proposed that these variations could play a major role in shaping morphological and physiological differences among species. Using a genome-wide comparative approach, we examined changes in gene family size (GFS) and degree of encephalization in 39 fully sequenced mammalian species and found a significant over-representation of GFS variations in line with increased encephalization in mammals. We found that this relationship is not accounted for by known correlates of brain size such as maximum lifespan or body size and is not explained by phylogenetic relatedness. Genes involved in chemotaxis, immune regulation and cell signalling-related functions are significantly over-represented among those gene families most highly correlated with encephalization. Genes within these families are prominently expressed in the human brain, particularly the cortex, and organized in co-expression modules that display distinct temporal patterns of expression in the developing cortex. Our results suggest that changes in GFS associated with encephalization represent an evolutionary response to the specific functional requirements underlying increased brain size in mammals.     

Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia)

Knowledge about dietary niche is key to understanding hominin evolution, since diet influences body proportions, brain size, cognition, and habitat preference. In this study we provide ecological context for the current debate on modernity (or not) of aquatic resource exploitation by hominins. We use the Homo erectus site of Trinil as a case study to investigate how research questions on possible dietary relevance of aquatic environments can be addressed. Faunal and geochemical analysis of aquatic fossils from Trinil Hauptknochenschicht (HK) fauna demonstrate that Trinil at ∼1.5 Ma contained near-coastal rivers, lakes, swamp forests, lagoons, and marshes with minor marine influence, laterally grading into grasslands. Trinil HK environments yielded at least eleven edible mollusc species and four edible fish species that could be procured with no or minimal technology. We demonstrate that, from an ecological point of view, the default assumption should be that omnivorous hominins in coastal habitats with catchable aquatic fauna could have consumed aquatic resources. The hypothesis of aquatic exploitation can be tested with taphonomic analysis of aquatic fossils associated with hominin fossils. We show that midden-like characteristics of large bivalve shell assemblages containing Pseudodon and Elongaria from Trinil HK indicate deliberate collection by a selective agent, possibly hominin.