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Paleogeography reconstruction of the Early Triassic world (left panel), showing that fishes and ichthyosaurs vacated the equator during the Smithian, with tetrapods exclusively occurring in the northern and southern middle to high latitudes…

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from article Ancient lethal hothouse

A scanning electron microscope image of the Early Triassic conodont Neospathodus, which is used for temperature reconstruction in this study.

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from article Tetrapod origins

Paleogeographical map showing the distribution of continents and seas during the Late Devonian, and the position of the localities that have produced tetrapod remains. 1, Pennsylvanian Red Hill (U.S.); 2, Scat Craig (Scotland); 3, East Greenland; 4,…

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from article Stress and depression

Diagram of the hypothalamic-pituitary-adrenal axis. ACTH, adrenocorticotropin; CRH, corticotropin-releasing hormone.

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from article Phylogenetics: predicting rarity and endangerment

Phylogenetic tree of the family Hominidae [consisting of humans (Homo sapiens) and the great apes—orangutan (Pongo pygmaeus), common chimpanzee (Pan troglodytes), pygmy chimpanzee (Pan paniscus), and gorilla (Gorilla gorilla)], with branch lengths…

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from article Phylogenetics: predicting rarity and endangerment

(Top) Number of mammal species within various IUCN Red List categories. (Bottom) Percent of threatened (critically endangered + endangered + vulnerable) species within each major mammalian order; primates, including the great apes, contain the…

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from article Bdelloid rotifers

Bdelloid rotifer Adineta vaga and its egg.

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from article Bdelloid rotifers

Evidence for HGT in bdelloid rotifers. The phylogenetic trees are shown for two genes coding for the enzymes galacturonidase (a) and UDP-glycosyltransferase (b). The corresponding genes from the bdelloid rotifer Adineta vaga do not cluster with…

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from article Bdelloid rotifers

A possible pathway for desiccation-induced transformation of bdelloid oocyte nuclei. Semidegraded foreign DNA (in blue) from ingested food particles may enter the bdelloid body cavity during a period of desiccation and, upon recovery, become…

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from article Elephant phylogeny

Molars of Loxodonta africana (left) and Elephas maximus (right) showing multiple ridges, or lamellae, on the surface of the molar teeth, instead of cusps as in other mammals.

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from article Elephant phylogeny

A composite phylogeny of the Proboscidea based on published phylogenetic trees. An approximate timescale is shown, although the phylogeny is not drawn to scale. However, the majority of the recognized genera are included. MYA = million years ago.

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from article Responses to acute sun exposure in large whales

Sun exposure and whales. (a) Differences in skin color (SC) and time spent at the surface (ST) among blue whales (Balaenoptera musculus, Bm), sperm whales (Physeter macrocephalus, Pm), and fin whales (Balaenoptera physalus, Bp). (b) Melanocyte…

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from article Responses to acute sun exposure in large whales

Prevalence of gross blisters and microscopic epidermal abnormalities in blue whales (light gray bars), sperm whales (dark gray bars), and fin whales (black bars). Sample sizes are indicated in the figure. Bars: ±SE (standard error).

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from article Post-Paleozoic ecological complexity

Two contrasting relative abundance distributions from Ordovician and Pleistocene assemblages of skeletonized bottom-dwelling marine animals, representing early Paleozoic and late post-Paleozoic time intervals, respectively. Abundances are shown on a…

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from article Post-Paleozoic ecological complexity

(a) Simple and (b) complex model relative abundance distributions (RADs) are shown as the proportions of individuals belonging to each species in a community, with species ordered from most to least abundant. Distributions were calculated with the…

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from article Post-Paleozoic ecological complexity

(a) Percentages of complex RADs for fossil assemblages in the Paleozoic and post-Paleozoic are shown. All statistically significant RADs are summarized within successive geologic time periods as mean values (circles) and error bars indicating one…

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from article Sensory structures in crocodilians

Crocodilians take advantage of the air-water interface. This alligator is bellowing, creating what is called a “water dance” with his body. He is also vocalizing low-frequency sounds.

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from article Sensory structures in crocodilians

Note the ears of the alligator above the surface of the water. There are slits behind the large eyes that create the ear flap.

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from article Sensory structures in crocodilians

Dome pressure receptors (DPRs) on the skin of crocodilians.

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from article Humboldt squid beak biomimetics

The biomimetic approach. Interrelations in biological materials between the function of the tissues, their properties, their structure at multiple length scales (from the macroscopic scale to the nanoscale), and the biochemistry of the building…

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from article Humboldt squid beak biomimetics

Biomolecular and mechanical gradients in squid beak.

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from article Humboldt squid beak biomimetics

Molecular cross-links formed in tanned (hard) portions of the beak. Current research aims at elucidating whether dominant cross-link mechanisms involve (a) unbound catechols or (b) peptide-bound catechols (dopa).

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from article Bubble-rafting snails

(a) Live bubble-rafting violet snail (Janthina exigua) with float and egg capsules (labeled “e”) [photo courtesy of Denis Riek; www.roboastra.com]. (b) Live female wentletrap (Epifungium ulu) with egg mass (labeled “e”) and dwarf male (indicated by…

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from article Bubble-rafting snails

Evolutionary relationships of janthinids and epitoniids. (Left) Reduced evolutionary tree showing the results of a multigene DNA analysis of violet snails (top four species), wentletraps, and other putative benthic sister lineages. Violet snails are…

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from article Phthalates in western Aleutian Island seabirds

Map of islands from which samples have been collected (2009–2014).

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from article Indohyus: the origin of whales

A block of sediment showing several disarticulated bones of Indohyus. At least 25 individuals of various ages were preserved in this death assemblage.

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from article Indohyus: the origin of whales

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from article Indohyus: the origin of whales

The skull of Indohyus (RR 208) has a middle ear cavity that was filled with air in life. This cavity has been filled in with sediment during the fossilization process. The ear is broken in this specimen, showing the thickness of the medial wall.…

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from article Indohyus: the origin of whales

Diagram showing that Indohyus is the closest fossil relative to cetaceans, with Hippopotamus being the closest living relative.

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from article Oxytocin and autism

Oxytocin increases eye contact. (a, b) Gaze time spent on the face under oxytocin and placebo. (c, d) Gaze time spent on different regions of interest under oxytocin and placebo. (Reprinted with permission from E. Andari et al., Promoting social…

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from article Oxytocin and autism

Oxytocin improves social comprehension. (a) Computer ball game showing the amount of reciprocation of each partner toward the participant P (indicated by the tinted arrows). Gray arrows indicate a healthy subject's performance. (b) Number of balls…

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from article Oxytocin and autism

Time course of ball tosses during the computer ball game. Cumulative number of balls sent by participants (vertical axis) after each trial played by the good partner (horizontal axis). (Reprinted with permission from E. Andari et al., Promoting…

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from article Factors related to risk of autism

Rising prevalence rates of autism in the United States (1997–2008). PDD: pervasive developmental disorder. (Left panel: C. A. Boyle et al., Trends in the prevalence of developmental disabilities in US children, 1997–2008, Pediatrics, 127:1034–1042,…

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from article Pulsar navigation

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from article Pulsar navigation

Crab Nebula and pulsar in the x-ray band, imaged by NASA's Chandra X-ray Observatory. (NASA, CXC, SAO)

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from article Pulsar navigation

ARGOS satellite with the USA experiment.

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from article Venomous crustacean

Head and front end of the trunk of the remipede Speleonectes tulumensis. (Copyright and courtesy of Bjoern von Reumont)

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from article Venomous crustacean

Three-dimensional reconstruction of the head region of Speleonectes tulumensis in ventral view. The venom delivery system is indicated in purple. The left maxillule is shown, containing a venom reservoir connected via a duct to a gland in the trunk.…

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from article Kangaroo genome

Tammar wallaby (Macropus eugenii). (a) An adult, female tammar wallaby weighs approximately 6 kg (13 lb) and stands 45 cm (18 in.) in height. (b) A tammar wallaby pouch young at approximately 20 days after birth. At this stage, the hind limb is…

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from article Kangaroo genome

Evolutionary tree of the extant mammalian lineages. MYA, million years ago.

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from article Effects of global warming on polar bears

Wrangel Island, Russia.

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from article Effects of global warming on polar bears

Number of bears recorded on Wrangel Island during ice-free seasons in 2004–2010.

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from article Effects of global warming on polar bears

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from article Effects of global warming on polar bears

Percentage of bears in various physical conditions observed on Wrangel Island during ice-free seasons in 2002–2010.

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from article Effects of global warming on polar bears

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from article Lophogastrida

Lophogaster typicus. Note the lateral plates on the abdominal segments (arrows) and the transverse groove dividing the sixth one (arrowhead). (Adapted from G. O. Sars, 1885)

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from article Tropical forest

Tropical rainforest on Brunei. (Credit: Rodney Keenan)

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from article Tropical forest

Monsoon tropical forest in Queensland, Australia. (Credit: Rodney Keenan)

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from article Tropical forest

Tropical savanna forest in Northern Territory, Australia. (Credit: Rodney Keenan)

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from article Tropical forest

Natural forest areas (in thousands of hectares; 1 hectare = 2.47 acres) in various climatic domains (boreal/polar, temperate, subtropical, and tropical) from 1990 to 2015. The data are derived from the Global Forest Resources Assessment 2015 by the…

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from article Tropical forest

Tropical forest climatic zones around the world. Tropical rainforests are indicated by dark blue; tropical monsoon forests are indicated by a medium shade of blue; tropical savanna forests are indicated by light blue. (Credit: Based on data compiled…

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from article Lophiiformes

A deep-sea anglerfish (Sladenia remiger), also known as a monkfish or goosefish. A lure on the forehead of the fish is used to attract prey. (Photo courtesy of the Indonesia-USA Deep-Sea Exploration of the Sangihe Talaud Region, Okeanos Explorer…

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from article Gerbil

Fat sand rat (Psammomys obesus). This gerbil has highly efficient kidneys. (Photo by Vladimír Motyčka)

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from article Nemertea

Tubulanus capistratus from the Pacific coast; size ranges up to nearly 1 m (3.3 ft) in length. (After L. H. Hyman, The Invertebrates, vol. 2, McGraw-Hill, New York, 1951)

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from article Nemertea

Stylets of Amphiporus griseus. (After W. R. Coe, Biology of the nemerteans of the Atlantic coast of North America, Trans. Conn. Acad. Arts Sci., 35:282, 1943)

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from article Nemertea

Schematic generalized diagram of the internal structure of a nemertean.

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from article Nemertea

Diagram of the multiple protonephridium of a nemertean. (After W. R. Coe, Unusual types of nephridia in nemerteans, Biol. Bull., 58(3):214, 1930)

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from article Nemertea

Pilidium of a nemertean. (After H. G. Bronn, ed., Klassen und Ordnungen des Thier-Reichs, vol. 4, Winter'sche Verlags., Leipzig/Heidelberg, 1903)

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from article Nemertea

Steps a, b, and c in fragmentation in Lineus vegetus. (After W. R. Coe, Revision of the Nemertean Fauna of the Pacific Coasts of North, Central, and Northern South America, Allan Hancock Pacific Expeditions, vol. 2, University of Southern California…

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from article Nemertea

Transverse sections of the body for the two orders of the Anopla nemerteans, showing the arrangement of the muscular layers and the position of the lateral nerve cords and lateral blood vessels: (a) Palaeonemertea and (b) Heteronemertea. (After W.…

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from article Nemertea

Malacobdella grossa. (After W. R. Coe, Biology of the nemerteans of the Atlantic coast of North America, Trans. Conn. Acad. Arts Sci., 35:308, 1943)

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from article Aircraft collision avoidance system

Surveillance with Mode A/C transponders. (Reprinted with permission of MIT Lincoln Laboratory, Lexington, MA)

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from article Aircraft collision avoidance system

TCAS pilot displays. (a) Traffic advisory (TA) display. (b) Vertical resolution advisory (RA) display. (Reprinted with permission of MIT Lincoln Laboratory)

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from article Biogeochemistry

Biogeochemistry is concerned with both the biological uptake and release of nutrients, as shown for nitrogen. (Credit: U.S. Geological Survey)

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from article Biogeochemistry

Carbon cycle. Photosynthetic fluxes between the atmosphere and oceans, and the atmosphere and land, represent net primary productivity. Reservoir units, gigatons (1015 g) C; flux units, gigatons C/yr.

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from article Biogeochemistry

Terrestrial nitrogen cycle; organic nitrogen includes both particulate and dissolved material. Flux units, teragrams (1012 g) N/yr.

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from article Biogeochemistry

Marine nitrogen cycle; organic nitrogen includes both particulate and dissolved material. Flux units, teragrams (1012 g) N/yr.

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from article Biogeochemistry

Phosphorus cycle. Reservoir units, teragrams (1012 g) P; flux units, teragrams P/yr.

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from article Biogeochemistry

Sulfur cycle. Reservoir units, teragrams (1012 g) S; flux units, teragrams S/yr.

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from article Olenellina

A fossilized Olenellus trilobite belonging to the suborder Olenellina. This trilobite was discovered among the Early Cambrian strata of the Eager Formation in British Columbia, Canada. (Credit: Houston Museum of Natural Science)

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from article Sunfish

Bluegill (Lepomis macrochirus). (Photo by Eric Engbretson, U.S. Fish and Wildlife Service)

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from article Archiacanthocephala

Life cycle of the giant thorn-headed worm of hogs.

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from article Field theory (mathematics)

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from article Field theory (mathematics)

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from article Speech perception

The perception of speech (as well as the production of speech) involves interactive processes occurring in various regions of the brain. Researchers also have noted the important contribution that vision makes to normal speech perception. (Copyright…

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from article Speech perception

An auditory spectrogram of the word "telephone." (a) The vertical striations in the bands represent amplitude modulation at the frequency of the voice pitch. Such striations are absent from the initial noise portion corresponding to the voiceless…

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from article Information theory (biology)

Human information processing. The estimates of channel capacity are based on the number of rods in the retina of the eye and the number of hair cells in the inner ear's organ of Corti.

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from article Information theory (biology)

Flow diagram of communication.

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from article Information theory (biology)

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from article Information theory (biology)

Coupling diagram of communication.

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from article Biomass

Wood materials are common sources of biomass. They can be burned directly for energy or processed in industrial facilities to produce renewable biofuels. (Credit: alffoto/Getty Images)

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from article Biomass

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from article Biomass

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from article Invasive forest species

The emerald ash borer (Agrilus planipennis) is a destructive invasive forest species. Native to northeastern Asia, this wood-boring beetle has devastated large areas of forests in North America and Europe. (Credit: Benjamin Smith)

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from article Invasive forest species

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from article Cetacea

Dusky dolphins (Lagenorhynchus obscurus) in the coastal waters of New Zealand. (Credit: Mridula Srinivasan/Assessment and Monitoring Division, Office of Science and Technology, National Marine Fisheries Service, National Oceanic and Atmospheric…

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from article Cetacea

Killer whale (Orcinus orca) in Monterey Bay, California. (Credit: Tory Kallman/Getty Images)

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from article Cetacea

A humpback whale opens its mouth wide to collect prey, and then filters food from the water using its baleen. (Credit: John Tunney/Shutterstock)

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from article Cetacea

Sperm whales (Physeter macrocephalus). (Credit: Gabriel Barathieu)

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from article Cetacea

Skeletal reconstruction of Ambulocetus natans. (Credit: J. G. M. Thewissen)

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from article Cetacea

Cetacean fossils. (a) Left upper premolar. (b) Skull of Dorudon atrox (alternatively Prozeuglodon stromeri) from the early Oligocene of Egypt. (c) Skull of Delphinodon dividum from the middle Miocene of Maryland. (Copyright © McGraw-Hill Education)

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from article Surface (geometry)

Part of a dihedron (the rest has been torn away), showing dihedral angle.

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from article Surface (geometry)

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from article Surface (geometry)

Some quadric surfaces, with parameters a, b, and c. (a) Ellipsoid; 0 < c < b < a. (b) Hyperboloid of one sheet; 0 < a < b < c. (c) Elliptic paraboloid; 0 < a < b and c > 0. (d) Hyperboloid of two sheets; 0 < a < b < c. (e) Hyperbolic paraboloid; c >…

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from article Surface (geometry)