Prosimians are a group of primates that includes all living and extinct strepsirrhines, as well as the haplorhine tarsiers and their extinct relatives, the omomyiforms, i.e. all primates excluding the simians. They are considered to have characteristics. Simians emerged within the Prosimians as sister group of the haplorhine tarsiers, therefore cladistically belong to this group. However, simians are traditionally excluded; the term "prosimian" is no longer used in a taxonomic sense, but is still used to illustrate the behavioral ecology of tarsiers relative to the other primates. Prosimians are the only primates native to Madagascar, but are found throughout Africa and in Asia. Being an evolutionary grade rather than a clade, the prosimians are united by being primates with traits otherwise found in non-primate mammals, their diets are less dominated by fruit than those of the simians, many are active arboreal predators, hunting for insects and other small animals in the trees. All prosimians outside Madagascar are nocturnal, meaning that no prosimian competes directly with simian primates.
Related to their nocturnal lifestyle, prosimians lack the colour vision of higher primates. Like most placental mammals, they are in effect red–green colour blind; this allows for more rod cells in the retina. Except in tarsiers, the nocturnal vision is further augmented by a reflective tapetum lucidum behind the retina, similar to that found in other nocturnal mammals; this layer reflects the light that passes through the retina, increasing the photoreceptors exposure to the light. It is however not well developed in diurnal forms like many lemurs. All prosimians possess; these can be found on the second toe in lemurs and lorises, the second and third in tarsiers. Aye-ayes have functional claws on all other digits except the hallux, including a toilet claw on the second toe. Clawlike nails are however found in the small-bodied callitrichids, a group of New World monkeys, though none of them have a toilet claw; the prosimians have retained the primitive mammalian condition of a bicornuate uterus, with two separate uterus chambers.
In the simians, the uterus chambers have fused, an otherwise rare condition among mammals. Prosimians have litters rather than single offspring, the norm in higher primates. While primates are thought of as intelligent animals, the prosimians are not large-brained compared to other placental mammals, their brain-cases are markedly smaller than those of simians of comparable sizes. In the large-eyed tarsiers, the weight of the brain is about the same as that of a single eye. Prosimians show lower cognitive ability and live in simpler social settings than the simians; the prosimians with the most complex social systems are the diurnal lemurs, which may live in social groups of 20 individuals. The nocturnal prosimians are solitary; the prosimians were once a group considered a suborder of the primate order, named in 1811 by Johann Karl Wilhelm Illiger. They have been shown, however, to be paraphyletic - that is, their most recent common ancestor was a prosimian but it has some non-prosimian descendents.
This relationship is shown by the ranks in the list below of the current primate classification between the order and infraorder level. The term "prosimian" is considered taxonomically obsolete, although it is used to emphasize similarities between strepsirrhines and the early primates. Order Primates Suborder Strepsirrhini: non-tarsier prosimians Infraorder †Adapiformes: extinct "lemur-like" primates Infraorder Lemuriformes: lemurs and bushbabies Suborder Haplorrhini: tarsiers and apes Infraorder †Omomyiformes: extinct "tarsier-like" primates Infraorder Tarsiiformes: tarsiers Infraorder Simiiformes: New World monkeys, Old World monkeys and humans Evolution of mammals List of primates Cartmill, M.. "Chapter 2: Primate Classification and Diversity". In Platt, M.. Oxford University Press. Pp. 10–30. ISBN 978-0-19-532659-8. Hartwig, W.. "Chapter 3: Primate evolution". In Campbell, C. J.. Oxford University Press. Pp. 19–31. ISBN 978-0-19-539043-8. Rose, K. D.. The Beginning of the Age of Mammals. Johns Hopkins University Press.
ISBN 978-0-8018-8472-6. Szalay, F. S.. Evolutionary History of the Primates. Academic Press. ISBN 978-0126801507. OCLC 893740473
The Euarchonta are a proposed grandorder of mammals containing four orders: the Scandentia or treeshrews, the Dermoptera or colugos, the extinct Plesiadapiformes, the Primates. The term "Euarchonta" appeared in 1999, when molecular evidence suggested that the morphology-based Archonta should be trimmed down to exclude Chiroptera. Further DNA sequence analyses supported the Euarchonta hypothesis. Despite multiple papers pointing out that some mitochondrial sequences showed unusual properties and were distorting the overall tree, despite Waddell et al. showing near total congruence of mtDNA-based and nuclear-based trees when such sequences were excluded, some authors continued to produce misleading trees. A study investigating retrotransposon presence/absence data has claimed strong support for Euarchonta; some interpretations of the molecular data link Primates and Dermoptera in a clade known as Primatomorpha, the sister of Scandentia. In some, the Dermoptera are a member of the primates rather than a sister group.
Other interpretations link the Dermoptera and Scandentia together in a group called Sundatheria as the sister group of the primates. Euarchonta and Glires together form one of the four Eutherian clades; the current hypothesis, based on molecular clock evidence, suggests that the Euarchonta arose in the Cretaceous period, about 88 million years ago, diverged 86.2 million years ago into the groups of tree shrews and Primatomorpha. The latter diverged prior to 79.6 million years into the orders of Dermoptera. The earliest fossil species ascribed to Euarchonta dates to the early Paleocene, 65 million years ago, but it appears to have been a non-placental eutherian. Although it is known that Scandentia is one of the most basal Euarchontoglire clades, the exact phylogenetic position is not yet considered resolved, it may be a sister of Glires, Primatomorpha or Dermoptera or to all other Euarchontoglires. Waddell, P. J. Y. Cao, M. Hasegawa, D. P. Mindell. 1999a. Assessing the Cretaceous superordinal divergence times within birds and placental mammals using whole mitochondrial protein sequences and an extended statistical framework.
Systematic Biology 48: 119-137. Waddell, P. J. N. Okada, Hasegawa. 1999b. Towards resolving the interordinal relationships of placental mammals. Systematic Biology 48: 1-5. Madsen, O. Scally, M. Douady, C. J. Kao, D. J. DeBry, R. W. Adkins, R. Amrine, H. M. Stanhope, M. J. de Jong, W. W. Springer, M. S. 2001. Parallel adaptive radiations in two major clades of placental mammals. Nature 409, 610–614. Murphy W. J. E. Eizirik, W. E. Johnson, Y. P. Zhang, O. A. Ryder, S. J. O'Brien, 2001a. Molecular phylogenetics and the origins of placental mammals Nature 409:614-618. Waddell, P. J. H. Kishino, R. Ota. 2001. A phylogenetic foundation for comparative mammalian genomics. Genome Informatics Series 12: 141-154. Sullivan, J. and D. L. Swofford. 1997. Are guinea pigs rodents? The importance of adequate models in molecular phylogenetics. J. Mammal. Evol. 4:77–86 Waddell, P. J. Y. Cao, J. Hauf, M. Hasegawa. 1999c. Using novel phylogenetic methods to evaluate mammalian mtDNA, including AA invariant sites-LogDet plus site stripping, to detect internal conflicts in the data, with special reference to the position of hedgehog and elephant.
Systematic Biology 48: 31-53. Ulfur Arnason, et al. 2002. Mammalian mitogenomic relationships and the root of the eutherian tree. Proceedings of the National Academy of Sciences 99: 8151-8156. Jan Ole Kriegs, Gennady Churakov, Jerzy Jurka, Jürgen Brosius, Jürgen Schmitz Evolutionary history of 7SL RNA-derived SINEs in Supraprimates. Trends in Genetics 23: 158-161 doi:10.1016/j.tig.2007.02.002 Nikolaev, S. Montoya-Burgos, J. I. Margulies, E. H. Rougemont, J. Nyffeler, B. Antonarakis, S. E. 2007. Early history of mammals is elucidated with the ENCODE multiple species sequencing data. PLoS Genet. 3:e2, doi:10.1371/journal.pgen.0030002. Gennady Churakov, Jan Ole Kriegs, Robert Baertsch, Anja Zemann, Jürgen Brosius, Jürgen Schmitz. 2008. Mosaic retroposon insertion patterns in placental mammals
The Eocene Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch; the start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. The end is set at a major extinction event called the Grande Coupure or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay; as with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are uncertain. The name Eocene comes from the Ancient Greek ἠώς and καινός and refers to the "dawn" of modern fauna that appeared during the epoch; the Eocene epoch is conventionally divided into early and late subdivisions.
The corresponding rocks are referred to as lower and upper Eocene. The Ypresian stage constitutes the lower, the Priabonian stage the upper; the Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Palaeocene–Eocene Thermal Maximum at 56 million years ago to a maximum during the Eocene Optimum at around 49 million years ago. During this period of time, little to no ice was present on Earth with a smaller difference in temperature from the equator to the poles. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene-Oligocene transition at 34 million years ago. During this decrease ice began to reappear at the poles, the Eocene-Oligocene transition is the period of time where the Antarctic ice sheet began to expand. Greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature.
The end of the PETM was met with a large sequestration of carbon dioxide in the form of methane clathrate and crude oil at the bottom of the Arctic Ocean, that reduced the atmospheric carbon dioxide. This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, it is hypothesized that the sequestration was due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion; this is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm while other proxies such as pedogenic carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years. Sources for this large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from the PETM event in the sea floor or wetland environments.
For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. At about the beginning of the Eocene Epoch the amount of oxygen in the earth's atmosphere more or less doubled. During the early Eocene, methane was another greenhouse gas that had a drastic effect on the climate. In comparison to carbon dioxide, methane has much greater effect on temperature as methane is around 34 times more effective per molecule than carbon dioxide on a 100-year scale. Most of the methane released to the atmosphere during this period of time would have been from wetlands and forests; the atmospheric methane concentration today is 0.000179% or 1.79 ppmv. Due to the warmer climate and sea level rise associated with the early Eocene, more wetlands, more forests, more coal deposits would be available for methane release. Comparing the early Eocene production of methane to current levels of atmospheric methane, the early Eocene would be able to produce triple the amount of current methane production; the warm temperatures during the early Eocene could have increased methane production rates, methane, released into the atmosphere would in turn warm the troposphere, cool the stratosphere, produce water vapor and carbon dioxide through oxidation.
Biogenic production of methane produces carbon dioxide and water vapor along with the methane, as well as yielding infrared radiation. The breakdown of methane in an oxygen atmosphere produces carbon monoxide, water vapor and infrared radiation; the carbon monoxide is not stable so it becomes carbon dioxide and in doing so releases yet more infrared radiation. Water vapor traps more infrared than does carbon dioxide; the middle to late Eocene marks not only the switch from warming to cooling, but the change in carbon dioxide from increasing to decreasing. At the end of the Eocene Optimum, carbon dioxide began decreasing due to increased siliceous plankton productivity and marine carbon burial. At the beginning of the middle Eocene an event that may have triggered or helped with the draw down of carbon dioxide was the Azolla event at around 49 million years ago. With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, a floating aquatic fern, on the Arctic Ocean.
Compared to current carb
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement and number of teeth in a given species at a given age; that is, the number and morpho-physiology of the teeth of an animal. Animals whose teeth are all of the same type, such as most non-mammalian vertebrates, are said to have homodont dentition, whereas those whose teeth differ morphologically are said to have heterodont dentition; the dentition of animals with two successions of teeth is referred to as diphyodont, while the dentition of animals with only one set of teeth throughout life is monophyodont. The dentition of animals in which the teeth are continuously discarded and replaced throughout life is termed polyphyodont; the dentition of animals in which the teeth are set in sockets in the jawbones is termed thecodont. The evolutionary origin of the vertebrate dentition remains contentious. Current theories suggest either an "outside-in" or "inside-out" evolutionary origin to teeth, with the dentition arising from odontodes on the skin surface moving into the mouth, or vice versa.
Despite this debate, it is accepted that vertebrate teeth are homologous to the dermal denticles found on the skin of basal Gnathostomes. Since the origin of teeth some 450mya, the vertebrate dentition has diversified within the reptiles and fish: however most of these groups continue to possess a long row of pointed or sharp-sided, undifferentiated teeth that are replaceable; the mammalian pattern is different. The teeth in the upper and lower jaws in mammals have evolved a close-fitting relationship such that they operate together as a unit. "They'occlude'", that is, the chewing surfaces of the teeth are so constructed that the upper and lower teeth are able to fit together, crushing, grinding or tearing the food caught between."All mammals except the monotremes, the xenarthrans, the pangolins, the cetaceans have up to four distinct types of teeth, with a maximum number for each. These are the incisor, the canine, the premolar, the molar; the incisors occupy the front of the tooth row in lower jaws.
They are flat, chisel-shaped teeth that meet in an edge-to-edge bite. Their function is cutting, slicing, or gnawing food into manageable pieces that fit into the mouth for further chewing; the canines are behind the incisors. In many mammals, the canines are pointed, tusk-shaped teeth, projecting beyond the level of the other teeth. In carnivores, they are offensive weapons for bringing down prey. In other mammals such as some primates, they are used to split open hard surfaced food; the premolars and molars are at the back of the mouth. Depending on the particular mammal and its diet, these two kinds of teeth prepare pieces of food to be swallowed by grinding, shearing, or crushing; the specialised teeth—incisors, canines and molars—are found in the same order in every mammal. In many mammals the infants have a set of teeth that are replaced by adult teeth; these are called primary teeth, baby teeth or milk teeth. Animals that have two sets of teeth, one followed by the other, are said to be diphyodont.
The dental formula for milk teeth is the same as for adult teeth except that the molars are missing. Because every mammal's teeth are specialised for different functions, many mammal groups have lost teeth not needed in their adaptation. Tooth form has undergone evolutionary modification as a result of natural selection for specialised feeding or other adaptations. Over time, different mammal groups have evolved distinct dental features, both in the number and type of teeth, in the shape and size of the chewing surface; the number of teeth of each type is written as a dental formula for one side of the mouth, or quadrant, with the upper and lower teeth shown on separate rows. The number of teeth in a mouth is twice that listed. In each set, incisors are indicated first, canines second, premolars third, molars, giving I:C:P:M. So for example, the formula 18.104.22.168 for upper teeth indicates 2 incisors, 1 canine, 2 premolars, 3 molars on one side of the upper mouth. The deciduous dental formula is notated in lowercase lettering preceded by the letter d: for example: di:dc:dp.
An animal's dentition for either deciduous or permanent teeth can thus be expressed as a dental formula, written in the form of a fraction, which can be written as I. C. P. MI. C. P. M, or I. C. P. M / I. C. P. M. For example, the following formulae show the deciduous and usual permanent dentition of all catarrhine primates, including humans: Deciduous: / × 2 = 20; this can be written as di2.dc1.dm2di2.dc1.dm2. Superscript and subscript denote upper and lower jaw, i.e. do not indicate mathematical operations. The dashes in the formula are not mathematical operators, but spacers.'d' denotes deciduous teeth. Another annotation is 22.214.171.124.1.0.2, if the fact that it pertains to deciduous teeth is stated, per examples found in some texts such as The Ca
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head close to the sensory organs for senses such as vision; the brain is the most complex organ in a vertebrate's body. In a human, the cerebral cortex contains 14–16 billion neurons, the estimated number of neurons in the cerebellum is 55–70 billion; each neuron is connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. Physiologically, the function of the brain is to exert centralized control over the other organs of the body; the brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows coordinated responses to changes in the environment.
Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain. The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. Recent models in modern neuroscience treat the brain as a biological computer different in mechanism from an electronic computer, but similar in the sense that it acquires information from the surrounding world, stores it, processes it in a variety of ways; this article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates. It deals with the human brain insofar; the ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context.
The most important is brain disease and the effects of brain damage, that are covered in the human brain article. The shape and size of the brain varies between species, identifying common features is difficult. There are a number of principles of brain architecture that apply across a wide range of species; some aspects of brain structure are common to the entire range of animal species. The simplest way to gain information about brain anatomy is by visual inspection, but many more sophisticated techniques have been developed. Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, sliced apart for examination of the interior. Visually, the interior of the brain consists of areas of so-called grey matter, with a dark color, separated by areas of white matter, with a lighter color. Further information can be gained by staining slices of brain tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations.
It is possible to examine the microstructure of brain tissue using a microscope, to trace the pattern of connections from one brain area to another. The brains of all species are composed of two broad classes of cells: neurons and glial cells. Glial cells come in several types, perform a number of critical functions, including structural support, metabolic support and guidance of development. Neurons, are considered the most important cells in the brain; the property that makes neurons unique is their ability to send signals to specific target cells over long distances. They send these signals by means of an axon, a thin protoplasmic fiber that extends from the cell body and projects with numerous branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body; the length of an axon can be extraordinary: for example, if a pyramidal cell of the cerebral cortex were magnified so that its cell body became the size of a human body, its axon magnified, would become a cable a few centimeters in diameter, extending more than a kilometer.
These axons transmit signals in the form of electrochemical pulses called action potentials, which last less than a thousandth of a second and travel along the axon at speeds of 1–100 meters per second. Some neurons emit action potentials at rates of 10–100 per second in irregular patterns. Axons transmit signals to other neurons by means of specialized junctions called synapses. A single axon may make as many as several thousand synaptic connections with other cells; when an action potential, traveling along an axon, arrives at a synapse, it causes a chemical called a neurotransmitter to be released. The neurotransmitter binds to receptor molecules in the membrane of the target cell. Synapses are the key functional elements of the brain; the essential function of the brain is cell-to-cell communication, synapses are the points at which communication occurs. The human brain has been estimated to contain 100 trillion synapses; the functions of these synapses are diverse: some are excitatory.
The pen-tailed treeshrew is a treeshrew native to southern Thailand, the Malay Peninsula and some Indonesian islands. It is the only species in the genus Ptilocercus. All other treeshrew species are grouped in the family Tupaiidae, it is considered the closest relative of extant primates. Pen-tailed treeshrews are the only known mammals that consume alcohol every night, other than humans. According to a study of treeshrews in Malaysia, they spend several hours per night consuming the equivalent of 10 to 12 glasses of wine with an alcohol content up to 3.8% drinking fermented nectar of the bertam palm. This nectar contains one of the highest alcohol concentrations of all natural foods. Pen-tailed treeshrews consume large amounts of this nectar while showing no signs of intoxication. Measurements of a biomarker of ethanol breakdown suggest that they may be metabolizing it by a pathway, not used as by humans, their ability to ingest high amounts of alcohol is hypothesized to have been an evolutionary adaptation in the phylogenic tree.
However, how pen-tailed treeshrews benefit from this alcohol ingestion or what consequences of consistent high blood alcohol content might factor into their physiology is unclear. The Ptilocercidae are a family within the order Scandentia. Numerous morphological and genetic differences support the classification of the Ptilocercidae as a separate family from the rest of the treeshrews which diverged around 63 million years ago. Treeshrews were considered a close relative of primates, but recent genetic data have concluded that the Dermoptera, not the Ptilocercidae, are the appropriate out-group for study of primates. Moskowitz, C. 2008. Tiny Tree Shrew Is World's Heaviest Drinker