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38-686: During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics , the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained

76-433: A basal taeniodont, Schowalteria is fairly derived, perhaps more so than later taenidonts. It shares with them similar speciations towards herbivory and possibly fossoriality, but unlike them it also possesses evidence of transverse ( ungulate -like) mastication , making it even more specialised towards processing vegetation. As one of the largest mammals of its time period and a rather specialised herbivore, Schowalteria

114-511: A break in rainfall during mid-season when the Intertropical Convergence Zone or monsoon trough moves poleward of their location during the middle of the warm season; Typical vegetation in these areas ranges from moist seasonal tropical forests to savannahs . When the wet season occurs during the warm season, or summer , precipitation falls mainly during the late afternoon and early evening hours. The wet season

152-584: A northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated

190-671: A range similar (though not confirmed) to Repenomamus giganticus , while posterior analysis showcase it to be as large as latter taeniodonts. Schowalteria occurs in the Trochu deposits of Alberta , dating to the Maastrichtian stage of the Cretaceous period. This site is part of the larger Edmonton Group , that probably represented a warm, temperate environment. Mammal remains are very common in this site, such as various metatherians and multituberculates . Schowalteria

228-532: A very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

266-498: Is a genus of extinct mammal from the Cretaceous of Canada . It is the earliest known representative of order Taeniodonta , a specialised lineage of eutherian mammals otherwise found in Paleocene and Eocene deposits. It is notable for its large size, being among the largest of Mesozoic mammals, as well as its speciation towards herbivory, which in some respects exceeds that of its later relatives. Currently, Schowalteria

304-516: Is a taeniodont eutherian. It was initially recovered as a fairly derived member related to stylinodonts , but more recent examinations show it to be a more basal species within the group, less related to them than Onychodectes . Atlantogenata [REDACTED] Boreoeutheria [REDACTED] † Palaeoryctida † Ambilestes † Procerberidae † Alveugena † Schowalteria clemensi † Stylinodontoidea [REDACTED] † Conoryctidae † Onychodectidae In spite of being

342-500: Is a time when air quality improves, freshwater quality improves and vegetation grows significantly due to the wet season supplementing flora, leading to crop yields late in the season. Floods and rains cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients are washed away and erosion increases. The incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for

380-402: Is considered to be a monotypic genus, with only one species, S. clemensi . It is known from only one skull. Schowalteria shares some speciations with later taeniodonts, namely similar canine and incisor morphology, similar facial proportions and zygomatic arch construction, though unlike them its occlusal surface is worn nearly completely flat, and the wear facet completely encompasses

418-477: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

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456-585: Is that the tropics represent a ' Garden of Eden ', a heaven on Earth, a land of rich biodiversity or a tropical paradise. The alternative is that the tropics consist of wild, unconquerable nature. The latter view was often discussed in old Western literature more so than the first. Evidence suggests over time that the view of the tropics as such in popular literature has been supplanted by more well-rounded and sophisticated interpretations. Western scholars tried to theorise why tropical areas were relatively more inhospitable to human civilisations than colder regions of

494-605: The Andes as far south as the northernmost parts of Chile and Perú . The climate is changing in the tropics, as it is in the rest of the world. The effects of steadily rising concentrations of greenhouse gases on the climate may be less obvious to tropical residents, however, because they are overlain by considerable natural variability. Much of this variability is driven by the El Niño-Southern Oscillation (ENSO) . The Tropics has warmed by 0.7–0.8 °C over

532-543: The Deccan Traps , both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered photosynthesis , leading to a massive disruption in Earth's ecology . A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate . Tropics The tropics are the regions of Earth surrounding

570-504: The Equator , where the sun may shine directly overhead . This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's axial tilt ; the width of the tropics (in latitude) is twice the tilt. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone ). Due to the overhead sun,

608-732: The Pantropic . The system of biogeographic realms differs somewhat; the Neotropical realm includes both the Neotropics and temperate South America, and the Paleotropics correspond to the Afrotropical , Indomalayan , Oceanian , and tropical Australasian realms . Flora are plants found in a specific region at a specific time. Some well-known plants that are exclusively found in, originate from, or are often associated with

646-579: The Waterberg Biosphere of South Africa , and eastern Madagascar rainforests. Often the soils of tropical forests are low in nutrient content, making them quite vulnerable to slash-and-burn deforestation techniques, which are sometimes an element of shifting cultivation agricultural systems. In biogeography , the tropics are divided into Paleotropics (Africa, Asia and Australia) and Neotropics (Caribbean, Central America, and South America). Together, they are sometimes referred to as

684-667: The axial tilt of the Earth . The Tropic of Cancer is the Northernmost latitude from which the Sun can ever be seen directly overhead , and the Tropic of Capricorn is the Southernmost. This means that the tropical zone includes everywhere on Earth which is a subsolar point at least once during the solar year . Thus the maximum latitudes of the tropics have equal distances from the equator on either side. Likewise, they approximate

722-858: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

760-846: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

798-533: The Northern Hemisphere. A popular explanation focused on the differences in climate. Tropical jungles and rainforests have much more humid and hotter weather than colder and drier temperaments of the Northern Hemisphere, giving to a more diverse biosphere. This theme led some scholars to suggest that humid hot climates correlate to human populations lacking control over nature e.g. 'the wild Amazonian rainforests'. Schowalteria Schowalteria

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836-399: The angle of the Earth's axial tilt. This angle is not perfectly fixed, mainly due to the influence of the moon, but the limits of the tropics are a geographic convention, and their variance from the true latitudes is very small. Many tropical areas have both a dry and a wet season. The wet season , rainy season or green season is the time of year, ranging from one or more months when most of

874-459: The average annual rainfall in a region falls. Areas with wet seasons are disseminated across portions of the tropics and subtropics , some even in temperate regions. Under the Köppen climate classification , for tropical climates , a wet-season month is defined as one or more months where average precipitation is 60 mm (2.4 in) or more. Some areas with pronounced rainy seasons see

912-523: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

950-460: The geographic region; these usages ought not be confused. The Earth's axial tilt is currently around 23.4° , and therefore so are the latitudes of the tropical circles , marking the boundary of the tropics: specifically, ±23°26′09.8″ (or 23.43605°). The northern one is called the Tropic of Cancer , and the southern is the Tropic of Capricorn . As the Earth's axial tilt changes, so too do

988-660: The large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held

1026-961: The last century—only slightly less than the global average—but a strong El Niño made 1998 the warmest year in most areas, with no significant warming since. Climate models predict a further 1–2 °C warming by 2050 and 1–4 °C by 2100. Tropical plants and animals are those species native to the tropics. Tropical ecosystems may consist of tropical rainforests , seasonal tropical forests , dry (often deciduous) forests , spiny forests, deserts , savannahs, grasslands and other habitat types. There are often wide areas of biodiversity , and species endemism present, particularly in rainforests and seasonal forests. Some examples of important biodiversity and high-endemism ecosystems are El Yunque National Forest in Puerto Rico , Costa Rican and Nicaraguan rainforests, Amazon Rainforest territories of several South American countries, Madagascar dry deciduous forests ,

1064-635: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

1102-538: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

1140-406: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

1178-503: The paracone and metacone, leaving only an outline of the buccal side of the bases of these cusps remaining, differing radically from the more "normal" teeth wearing patterns of other taenidonts. Based on the skull's proportions, it was initially comparared in size to Didelphodon vorax , making it one of the largest mammals of the Mesozoic at the time of its discovery, and posterior measurements have cited larger sizes; Anne Weil posits

Late Cretaceous - Misplaced Pages Continue

1216-516: The tropical and polar circles . The tropics constitute 39.8% of Earth's surface area and contain 36% of Earth's landmass . As of 2014 , the region was home also to 40% of the world's population , and this figure was then projected to reach 50% by 2050. Because of global warming , the weather conditions of the tropics are expanding with areas in the subtropics , having more extreme weather events such as heatwaves and more intense storms. These changes in weather conditions may make certain parts of

1254-701: The tropics receive the most solar energy over the course of the year, and consequently have the highest temperatures on the planet. Even when not directly overhead, the sun is still close to overhead throughout the year, therefore the tropics also have the lowest seasonal variation on the planet; "winter" and "summer" lose their contrast. Instead, seasons are more commonly divided by precipitation variations than by temperature variations. The tropics maintain wide diversity of local climates, such as rain forests , monsoons , savannahs , deserts , and high altitude snow-capped mountains . The word "tropical" can specifically refer to certain kinds of weather , rather than to

1292-469: The tropics include: Tropicality refers to the image of the tropics that people from outside the tropics have of the region, ranging from critical to verging on fetishism. Tropicality gained renewed interest in geographical discourse when French geographer Pierre Gourou published Les pays tropicaux ( The Tropical World in English), in the late 1940s. Tropicality encompassed two major images. One,

1330-568: The tropics uninhabitable. The word "tropic" comes via Latin from Ancient Greek τροπή ( tropē ), meaning "to turn" or "change direction". The tropics are defined as the region between the Tropic of Cancer in the Northern Hemisphere at 23°26′09.8″ (or 23.43605°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′09.8″ (or 23.43605°) S; these latitudes correspond to

1368-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

1406-726: The wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature. However, regions within the tropics may well not have a tropical climate. Under the Köppen climate classification, much of the area within the geographical tropics is classed not as "tropical" but as "dry" ( arid or semi-arid ), including the Sahara Desert , the Atacama Desert and Australian Outback . Also, there are alpine tundra and snow-capped peaks, including Mauna Kea , Mount Kilimanjaro , Puncak Jaya and

1444-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

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