Dimetrodon ( (listen) or , meaning "two measures of teeth") is an extinct genus of non-mammalian synapsids that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Ma). It is a member of the family Sphenacodontidae. The most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the southwestern United States, the majority coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878.
Dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the first appearance of dinosaurs. Reptile-like in appearance and physiology, Dimetrodon is nevertheless more closely related to mammals than to modern reptiles, though it is not a direct ancestor of mammals. Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally called "mammal-like reptiles". This groups Dimetrodon together with mammals in a clade (evolutionary group) called Synapsida, while placing dinosaurs, reptiles and birds in a separate clade, Sauropsida. Single openings in the skull behind each eye, known as temporal fenestrae, and other skull features distinguish Dimetrodon and mammals from most of the earliest sauropsids.
Dimetrodon was probably one of the apex predators of the Cisuralian ecosystems, feeding on fish and tetrapods, including reptiles and amphibians. Smaller Dimetrodon species may have had different ecological roles. The sail of Dimetrodon may have been used to stabilize its spine or to heat and cool its body as a form of thermoregulation. Some recent studies argue that the sail would have been ineffective at removing heat from the body due to large species being discovered with small sails and small species being discovered with large sails, essentially ruling out heat regulation as its main purpose. The sail was most likely used in courtship display with methods such as threatening rivals or showing off to potential mates.
- "Dimetrodon" | 2020-02-18 | 19 Upvotes 6 Comments
Elephant cognition is the study of animal cognition as present in elephants. Most contemporary ethologists view the elephant as one of the world's most intelligent animals. With a mass of just over 11 lb (5 kg), an elephant's brain has more mass than that of any other land animal, and although the largest whales have body masses twenty times those of a typical elephant, a whale's brain is barely twice the mass of an elephant's brain. In addition, elephants have a total of 300 billion neurons. Elephant brains are similar to humans' and many other mammals' in terms of general connectivity and functional areas, with several unique structural differences. The elephant cortex has as many neurons as a human brain, suggesting convergent evolution.
Elephants manifest a wide variety of behaviors, including those associated with grief, learning, mimicry, play, altruism, use of tools, compassion, cooperation, self-awareness, memory, and communication. Further, evidence suggests elephants may understand pointing: the ability to nonverbally communicate an object by extending a finger, or equivalent. It is thought they are equal with cetaceans and primates in this regard. Due to such claims of high intelligence and due to strong family ties of elephants, some researchers argue it is morally wrong for humans to cull them. Aristotle described the elephant as "the animal that surpasses all others in wit and mind."
- "Elephant intelligence" | 2008-03-05 | 32 Upvotes 10 Comments
Homo floresiensis ("Flores Man"; nicknamed "hobbit") is a pygmy archaic human which inhabited the island of Flores, Indonesia, until the arrival of modern humans about 50,000 years ago.
The remains of an individual who would have stood about 1.1 m (3 ft 7 in) in height were discovered in 2003 at Liang Bua on the island of Flores in Indonesia. Partial skeletons of nine individuals have been recovered, including one complete skull, referred to as "LB1". These remains have been the subject of intense research to determine whether they represent a species distinct from modern humans; the dominant consensus is that these remains do represent a distinct species due to genetic and anatomical differences.
This hominin had originally been considered remarkable for its survival until relatively recent times, only 12,000 years ago. However, more extensive stratigraphic and chronological work has pushed the dating of the most recent evidence of its existence back to 50,000 years ago. The Homo floresiensis skeletal material is now dated from 60,000 to 100,000 years ago; stone tools recovered alongside the skeletal remains were from archaeological horizons ranging from 50,000 to 190,000 years ago.
- "Homo floresiensis" | 2013-10-14 | 12 Upvotes 3 Comments
The sand cat (Felis margarita), also known as the sand dune cat, is the only cat living chiefly in true deserts. This small cat is widely distributed in the deserts of North Africa, the Middle East and Central Asia. Starting in 2002, it was listed as near threatened on the IUCN Red List because the population was considered fragmented and small with a declining trend. It was downlisted to least concern in 2016.
Owing to long hairs covering the soles of its feet, the sand cat is well adapted to the extremes of a desert environment and tolerant of extremely hot and cold temperatures. It inhabits both sandy and stony deserts, in areas far from water sources.
- "Sand Cat" | 2015-12-02 | 47 Upvotes 15 Comments
Musth or must (an Urdu word, from Persian, lit. drunk) is a periodic condition in bull (male) elephants characterized by highly aggressive behavior and accompanied by a large rise in reproductive hormones.
Testosterone levels in an elephant in musth can be on average 60 times greater than in the same elephant at other times (in specific individuals these testosterone levels can even reach as much as 140 times the normal). However, whether this hormonal surge is the sole cause of musth, or merely a contributing factor, is unknown.
Scientific investigation of musth is problematic because even the most placid elephants become highly violent toward humans and other elephants during musth.
- "Musth" | 2020-04-06 | 77 Upvotes 15 Comments
A whale fall occurs when the carcass of a whale has fallen onto the ocean floor at a depth greater than 1,000 m (3,300 ft), in the bathyal or abyssal zones. On the sea floor, these carcasses can create complex localized ecosystems that supply sustenance to deep-sea organisms for decades. This is unlike in shallower waters, where a whale carcass will be consumed by scavengers over a relatively short period of time. Whale falls were first observed in the late 1970s with the development of deep-sea robotic exploration. Since then, several natural and experimental whale falls have been monitored through the use of observations from submersibles and remotely operated underwater vehicles (ROVs) in order to understand patterns of ecological succession on the deep seafloor.
Deep sea whale falls are thought to be hotspots of adaptive radiation for specialized fauna. Organisms that have been observed at deep-sea whale fall sites include giant isopods, squat lobsters, bristleworms, prawns, shrimp, lobsters, hagfish, Osedax, crabs, sea cucumbers, and sleeper sharks. In the past three years whale fall sites have come under scrutiny, and new species have been discovered, including potential whale fall specialists. It has been postulated that whale falls generate biodiversity by providing evolutionary stepping stones for multiple lineages to move and adapt to new environmentally-challenging habitats. Researchers estimate that 690,000 carcasses/skeletons of the nine largest whale species are in one of the four stages of succession at any one time. This estimate implies an average spacing of 12 km (7.5 mi) and as little as 5 km (3.1 mi) along migration routes. They hypothesize that this distance is short enough to allow larvae to disperse/migrate from one to another.
Whale falls are able to occur in the deep open ocean due to cold temperatures and high hydrostatic pressures. In the coastal ocean, a higher incidence of predators as well as warmer waters hasten the decomposition of whale carcasses. Carcasses may also float due to decompositional gases, keeping the carcass at the surface. The bodies of most great whales (baleen and sperm whales) are slightly denser than the surrounding seawater, and only become positively buoyant when the lungs are filled with air. When the lungs deflate, the whale carcasses can reach the seafloor quickly and relatively intact due to a lack of significant whale fall scavengers in the water column. Once in the deep-sea, cold temperatures slow decomposition rates, and high hydrostatic pressures increase gas solubility, allowing whale falls to remain intact and sink to even greater depths.
The nocturnal bottleneck hypothesis is a hypothesis to explain several mammalian traits. In 1942, Gordon Lynn Walls described this concept which states that placental mammals were mainly or even exclusively nocturnal through most of their evolutionary story, starting with their origin 225 million years ago, and only ending with the demise of the non-avian dinosaurs 66 million years ago. While some mammal groups have later evolved to fill diurnal niches, the approximately 160 million years spent as nocturnal animals has left a lasting legacy on basal anatomy and physiology, and most mammals are still nocturnal.
- "Mammals are shaped by descent from nocturnal animals" | 2022-08-17 | 203 Upvotes 76 Comments