hotchpotch/wikipedia-multilingual-ir-pairs huggingface dataset:
磨齒獸屬 分布和重要的化石发现
The first occurrence of Mylodon may have been in the Lower Pleistocene, but finds are rather rare. During this period, the possibly closely related form Archaeomylodon also occurred in the Pampas region, whose foremost canine teeth of the upper dentition were greatly reduced in size, but not yet completely reduced. Among the early and more northerly finds of Mylodon is, for example, a skull from the El Palmar Formation in the Argentine province of Entre Ríos, which dates to the end of the last warm period about 80,000 years ago. Also from the northern distribution areas two partial skeletons are worth mentioning, one of which was found at the Río Anisacate in the Argentine province of Córdoba and the other in Arroyo Quequén Salado near Oriente in the Argentine province of Buenos Aires. Mainly in the Pampas, there was an overlap in the occurrence of Mylodon with the two other major mylodontid sloth representatives Glossotherium and Lestodon during the Upper Pleistocene. However, actual co-occurrence is rarely attested. These include the important archaeological site of Paso Otero in Buenos Aires Province, the locality of Arroyo de Vizcaíno in southern Uruguay, and the Chuí River.
磨齒獸屬 分布和重要的化石发现
As with many of the other large ground sloths, most of the Mylodon material is from the Upper Pleistocene, with a focus toward the end of the last glacial period. It is also the phase when Mylodon again disappeared from the fossil record. From a global perspective, numerous larger animals became extinct during the transition from the Pleistocene to the Holocene, which is why this event is considered a Quaternary extinction wave. In South America, this coincides with the first appearance of humans. Whether the two are causally related is the subject of much controversy. In addition to potential hunting and possible landscape overprinting by early human hunter-gatherer groups, climatic changes may also have had an influence. Numerous archaeological sites, especially in the Pampa region and in the Patagonian area, are between 13,500 and 10,000 years old. The majority of these attest to at least a coexistence of humans and ground sloths over an extended period of time. Direct associations of human cultural products and fossil remains of Mylodon are found, among others, at Gruta del Indio in the eastern foothills of the Andes, at Piedra Museo or Las Buitreras, all in Argentina, and at Tres Arroyos in Tierra del Fuego, respectively.
磨齒獸屬 分布和重要的化石发现
Mylodon is often represented by isolated osteoderms, bones or in the form of coprolites, while human remains are limited to stone artifacts and/or hearths. Whether this also involved a more or less intensive raw material use of sloth bones on the part of humans is in many cases unproven. Numerous bone marks that were originally interpreted as anthropogenically caused are, according to recent studies, due to predation. Evidence of direct hunting by humans of the large ground sloths is even more difficult. One piece of evidence is often considered to be Quebrada de Quereo, a site on an ancient coastline in northern Chile. From here come, among other things, skeletal remains of two individuals of Mylodon, distributed in each case over a narrowly defined area, but in two different stratigraphic units and at a spatial distance of 21 m from each other. One of the individuals was associated with about 70 stone objects, whose anthropogenic origin is under discussion. No cut marks are found on the bones as evidence of any human manipulation. The age of the site is given as 11,600 to 10,900 years before present.
磨齒獸屬 分布和重要的化石发现
One of the most important sites is the Cueva del Milodón near Lago Sofía in the Chilean province of Última Esperanza, known mainly for its surviving skin remains. It is part of a whole system of caves in the region, such as the Cueva del Medio or the Cueva Chica, which line the southern flank of the 556 m high Cerro Benitez like pearls. Cueva del Milodón is a large cave 250 m long, 140 m wide and 30 m high at the entrance and 10 m at the back, respectively. It was discovered in 1895 by the German captain Hermann Eberhard, who also found the first skin remains. The great importance of these finds led to the cave, initially known as "Cueva Eberhardt", being subsequently visited and explored by numerous scientists. As a result, a large number of finds accumulated over time, among which Mylodon with bone remains, and numerous coprolites has a large share. Other finds belong to camels such as Lama, horses such as Hippidion or South American ungulates such as Macrauchenia, in addition, several predators are represented, including the jaguar, Smilodon as a member of the saber-toothed cats, and the giant bear form Arctotherium. Some of the mammal bones have marks that were originally associated with human activity, but the current view is that they are more likely due to predator browsing. In addition to faunal remains, the cave also held a myriad of botanical material. It also yielded one of the most extensive data sequences from the Upper Pleistocene. Several radiocarbon dates, measured from a wide variety of Mylodon finds, span a period from about 16,700 to 10,200 years ago. The upper data are among the most recent obtained directly from finds of the sloth vertebrate.
磨齒獸屬 分类
Mylodon's close relatives include the ground sloths of the genera Glossotherium and Paramylodon. The latter genus has often been confused with Glossotherium, but Paramylodon is a distinct genus that was restricted to the Pleistocene of North America. Glossotherium also shares a long history of taxonomic confusion with Mylodon, and currently the only recognized species is Mylodon darwini. At one time, the elephant-sized Megatherium was thought to be closely related, but is recognized as belonging to a separate family (Megatheriidae).
磨齒獸屬 分类
Below is a phylogenetic tree of the Mylodontidae, based on the work of Boscaini et al.. 2019.
磨齒獸屬 分类
Recent molecular sequence results obtained using collagen and mitochondrial DNA extracted from fossils indicate that the closest living relatives of Mylodon are the two-toed sloths of genus Choloepus. This revelation came as a surprise, since morphological analyses had previously suggested that two-toed sloths were close to Caribbean sloths and Megalonyx, now regarded as representing two separate and distant branches of the sloth evolutionary tree.
Some authors suggest that there were two species, with M. darwini restricted to the Pampas, with the Patagonian remains belonging to the separate species Mylodon listai.
磨齒獸屬 研究历史
The taxonomic history of Mylodon is complex. It has involved confusion and equivocation with other mylodont forms such as Glossotherium and Paramylodon over a long period of time. Some of this complexity can be attributed to the first describer of the genus itself, who is Richard Owen (1804-1892). Owen, one of the most important explorers of the Victorian era, was concerned from 1836 with fossil finds brought back by Charles Darwin from his pioneering voyage on HMS Beagle to South America. The collection also included a mandible from Punta Alta near Bahía Blanca in the south of the Argentina Buenos Aires Province (specimen number NHM 16617). The nearly complete specimen was distinguished by a row of teeth consisting of a total of four molar-like Teeth. In an extensive 1840 paper, Owen referred the mandible to the new genus he had created, Mylodon, and named the species M. darwinii (darwinii is the spelling used by Owen, but in modern times darwini is also often used; according to the Regulations of Zoological Nomenclature, the former version is correct.) He related the genus name to the molar-like teeth (from Greek μυλη (myle) for "molar" and ὀδούς (odoús) for "tooth", thus translating as much as "molar tooth"), with the species epithet darwinii honoring Darwin as finder of the voucher specimen. As a second species besides M. darwinii Owen referred in his paper to M. harlani. This form was based on a mandible and clavicle, both of which came from the Big Bone Lick in Boone County in the U.S. state of Kentucky, and which Richard Harlan had already described in 1831 under the species assignment Megalonyx laqueatus. Owen, however, recognized similarities in the construction of the mandible to his M. darwinii and renamed Harlan's form. Harlan used an essay two years later to comment on Owen's choice of name regarding Mylodon, which he felt was not very descriptive. According to him, the name could be applied to almost any extinct mammalian form because almost all of them had the posterior molars. Moreover, the name would be inappropriate because, starting from the Latin version dens molaris for "molar tooth" and the second part of speech don (from dens for "tooth"), there is a duplication that would translate as "molar tooth-tooth". Regardless, Owen's establishment of the genus Mylodon with two species resulted in the extinct sloth representative being distributed in both South and North America.
磨齒獸屬 研究历史
Owen, in his 1840 work, established the genus Glossotherium in addition to Mylodon, but without designation of a specific species. The basis here was a posterior skull fragment taken from the riverbed of the Arroyo Sarandi in the Uruguay department of Soriano. In contrast to Mylodon, for which Owen assumed a kinship proximity to the other large ground sloths known at the time, such as Megatherium or Megalonyx, he placed Glossotherium in a series with the anteaters and with the pangolins, respectively, and postulated an insectivorous lifestyle for the animals. Two years later, however, Owen discarded the name Glossotherium again. This occurred in the course of processing a nearly complete skeleton that had been discovered the year before in the flood plains of the Río de la Plata north of Buenos Aires. The largely intact skull was characterized by a short and broad snout and by a dentition consisting of a total of 18 teeth, of which the foremost tooth in each case showed a canine design. Based on the similarities in dental structure with the flat, molar-like teeth, Owen placed the skeleton in the genus Mylodon and introduced the new species M. robustus. The skull fragment that he had originally placed in Glossotherium he now associated with M. darwinii. As a result of this study, three species of the genus Mylodon already existed in the 1840s.
磨齒獸屬 研究历史
A skull including mandible found at Pergamino in Buenos Aires Province served the Danish zoologist Johannes Theodor Reinhardt (1816-1882) in 1879 as the basis for a comprehensive description. Characteristic of the skull was the narrow snout and a closed nasal arch, which was formed by the firm adhesion of the nasal bone to the middle jaw bone. Furthermore, the dentition consisted of a total of 16 teeth, the upper front canine-like tooth was reduced in each case, in the lower jaw, however, sat four molar-like teeth each. Reinhardt noticed similarities to M. darwinii in the construction of the lower jaw, but in the skull design his find deviated clearly from the broad-nosed M. robustus by the narrow snout. However, according to Reinhardt, there were matches in Owen's Glossotherium skull fragment with corresponding skull sections in M. robustus. Based on the clear parallels between M. darwinii and his narrow-beaked skull finding, Reinhardt propagated the new genus Grypotherium with Grypotherium darwinii as the type species. A different approach was taken by Florentino Ameghino (1854-1911) about ten years later. He confirmed in 1889, the separation of both M. darwinii and M. robustus not only at the species level, but also at the genus level. Deviating from Reinhardt, but agreeing with Owen, he considered the mandible of M. darwinii and the skull fragment of Glossotherium to belong together. Since in this scenario Glossotherium possessed priority over Mylodon (Owen mentioned the former over the latter in 1840) and Grypotherium, Ameghino introduced the species Glossotherium darwinii. In contrast, he left the status of M. robustus untouched. Arthur Smith Woodward (1864-1944), in turn, followed Reinhardt's reasoning. In a paper published in 1900, he presented findings from ground sloths of southern Patagonia and at the same time revised Charles Darwin's collection. In doing so, he equated the mandible of M. darwinii with Reinhardt's Grypotherium and subsequently recovered Grypotherium darwinii. Smith Woodward assigned the skull fragment of Glossotherium to M. robustus by analogy with Reinhardt.
磨齒獸屬 古生物学
The mylodontids (particularly Mylodon itself) are often considered to be pronounced grazers because of their dental structure with flat chewing surfaces on the molar-like teeth. This is also supported by the high (hypsodont) tooth crowns and the wide mouth with numerous shapes. The ungulates are mostly used as analogous examples, in which shapes with high tooth crowns and broad-lipped mouths are usually grass-eating, such as various cattle, horses or the white rhinoceros. In contrast, those with low tooth crowns and narrow snouts such as the duiker or the black rhinoceros feed largely selective from various leaves and other soft vegetable foods. In contrast to other large mylodontid sloths such as Glossotherium, Paramylodon or Lestodon, the mouth of Mylodon is relatively narrow. A special feature is the closed nasal arch, which is heavily roughened in its front area and thus offers muscle attachment points for a mobile upper lip. Something similar can be said about individual depressions in the vicinity of the infraorbital foramen, which also functioned as starting points for individual muscle strands in the nose and lip area. Maybe Mylodon was more well-adapted to a mixed-vegetation diet, which was picked up with the help of a movable upper lip. The loss of the front teeth in the upper row of teeth also leads to the assumption that, comparable to cattle, there was a horn-like structure on the middle jawbone that could be used to pluck the food.
磨齒獸屬 古生物学
The entire anterior cranial structure of Mylodon is relatively solid, combined with a partially ossified nasal septum, it can be assumed that relatively high chewing forces acted when the food was chopped up. In contrast to the sometimes huge representatives of the Megatheriidae, the joint between the lower jaw and the skull of the Mylodonts was relatively low, roughly at the chewing level of the teeth. The resulting decreasing lever arm of the masseter muscle experiences through the structure of the zygomatic arch, mainly of the descending process, a certain compensation, so that there should have been only minor differences to the Megatheria with regard to the biting force. The extended mandibular joint allows a wide freedom of movement when chewing. Against this, however, is the zygomatic arch, which is not closed and therefore could only withstand the opposing forces of the masseter and musculus pterygoideus to a limited extent. It can therefore be assumed that forwards and backwards directed chewing movements dominated in Mylodon. The flat tooth crowns lead to a comparatively small size of the total available chewing surface. In Mylodon, this amounts to a good 1320 mm2 corresponding to other mylodonts of the same size. The Indian rhinoceros, which is comparable in terms of its dimensions, has, on the other hand, double to four times the value with 2660 to 5190 mm2. The situation is similar with the hippopotamus, the total surface area of which is between 3290 and 5410 mm2. The small total occlusal surface of the teeth in Mylodon probably resulted in a rather low processing capacity for the food in the mouth. This can result in either a high rate of fermentation in the gastrointestinal tract and/or a very slow metabolism concluded. The latter is the case with today's sloths. This is due to the long passage time of the food of up to a week through the large, multi-chambered stomach. It can be assumed that this also applies to the extinct sloths. Possibly this made the stomach of the mylodonts a functional equivalent to the complex stomach of the ruminants, whereby a long passage time of the food enabled efficient digestion, in which even more difficult to access nutrients could be provided, for example from foods with a greater fiber content. Such a digestive system could reduce the amount of processed food in the mouth and thus ultimately also have compensated for the small total chewing surface in Mylodon.
磨齒獸屬 古生物学
Direct analysis of the food resources used is possible, among many other things, due to the numerous dung residues in the form of coprolites. These are available not only from the Cueva del Milodón in the Chilean part of Patagonia, but also from other caves. The coprolites of Mylodon have a diameter of up to 18 cm. Investigations of the plant residues showed 80 to 95% grasses and 5 to 20% sedges. Herbaceous plants, on the other hand, could only be detected in traces. Accordingly, Mylodon led, at least in southwestern Patagonia, a diet consisting almost exclusively of grasses. The food is reflected in the paleohabitat, as pollen analyzes show that the landscape at that time was tundra-like in character and was therefore almost free of trees with only a few low bushes. Occasional evidence of false beeches is interpreted as pollen carried by the wind.
磨齒獸屬 古生物学
A 2021 study on stable isotope ratios concluded that Mylodon must have been at least sporadically omnivorous.
磨齒獸屬 古生物学
In general, large mylodonts are ground-dwelling animals. The lower section of the hind leg, which is very short compared to the upper, is also found in Mylodon, whose tibia is 27 cm in length and only half as long as the thigh bone, 59 cm in length. In comparison, the Megatheriidae possess significantly longer lower leg portions, about the almost equally-proportioned Pyramiodontherium possessing to a 47 cm long shin to a 49 cm long femur. Possibly these differences in the hind leg structure result in much more agile locomotion in the Megatheria in relation to the mylodonts. Similar to other large ground sloths, the hand of Mylodon made contact with the ground with the outer side edge and thus sat up rotated. This is indicated by the long metacarpal bones of the external digits and the decreasing number of phalanges on them. The special hand position protected the long claws of the inner digits, which did not penetrate the ground while walking. A functionally similar but fundamentally different hand position can be found in the ankle duct of the distantly related present-day great anteater. The elbow joint was pointed slightly outwards when standing on four feet and the arms were thus angled slightly inwards, which is evident from the position of the olecranon yields. The hands came to rest slightly within the width of the elbow. Such an orientation of the arms can effectively support the large mass of Mylodon. As a result, the hands would also be in a line with the feet, which is also conveyed, among other things, by footprints from Paramylodon. The laterally limited articular surface of the femoral head severely restricted the mobility of the hindlimbs. The same applies to the forearm, the straight spoke with the laterally elongated head of which did not allow any major rotational movements. These features can be interpreted as adaptations to a purely terrestrial lifestyle. Finally, the muscle attachment points on the first cervical vertebra referenced, which are more developed than for example with Paramylodon. Correspondingly, the occipital joint surfaces are also somewhat further apart. Both can be interpreted as meaning that the more massive skull of Mylodon, caused by the lengthening of the snout region, required greater muscle support.
磨齒獸屬 古生物学
For some of the mylodonts of South America, such as Glossotherium, a partially burrowing way of life is being reconstructed, which results from the construction of the foreleg, among other things. An indicator for this is the upper articular process (olecranon) of the ulna. The longer the olecranon, the higher the leverage of the forearm, since more attachment surface is available for the forearm muscles. In Glossotherium, the olecranon takes up up to 35% of the total length of the ulna. The resulting ability to dig would be comparable to that of the Tolypeutes armadillos, which seldom build their own burrows, but can do so. The previous analyses for Mylodon resulted in a much shorter olecranon, which accounts for only about 22% of the total length of the ulna. However, the fact that proportional estimates for Mylodon refer to a not fully grown specimen is problematic. Other clues can be derived from the construction of the hand. In Mylodon, for example, the metacarpal bones of the second and third ray are very delicate, in contrast to Glossotherium. A weakly pronounced central ray does not seem to support a digging activity, as this is usually most strongly developed in underground mammals. However, the distal articular facet of the third metacarpal bone is flat, which means that the middle finger is generally stiff and stable. The same articulation surface on the second metacarpal is significantly more rounded and thus supports greater mobility of the finger when gripping. This obviously resulted in functional differences between the individual rays of the hand. The rare signs of wear and tear on the last phalanx, which are isolated from the Cueva del Milodón several times, can serve as an additional indicator of digging activities.
磨齒獸屬 古生物学
Especially in southern and southwestern Patagonia, numerous bone changes in finds of Mylodon can be proven to be caused by predatory animals. This includes, above all, the remains from the Cueva del Milodón in southwestern Chile. Some caves in their immediate vicinity, such as Cueva Lago Sofía 4 and Cueva Chica, are interpreted as clumps of predators. The same applies to the Cueva del Puma or the Cueva Fell in the Pali-Aike area of southern Chile. Some of the caves mainly contain smaller skeletal elements such as hand and foot bones or bone plates, which indicate that only part of the carcass was carried into the shelter. Whether this is the result of direct foraging or scavenging cannot be determined in many cases. Other caves, in turn, contained a larger proportion of young Mylodon animals. The largest predators occurring at that time are the puma and the jaguar, as well as the saber-toothed cat Smilodon populator and the extinct bear Arctotherium. The latter two could have reconstructed body weights of over 400 kg, with prey sizes between 1 and 2 t being assumed for the saber-toothed cat, which makes Smilodon a likely predator of Mylodon.
磨齒獸屬 古生物学
In various coprolites produced by Mylodon, eggs of nematodes are preserved. The eggs are ovaloid in shape with lengths of almost 50 μm in length and 29 μm in thickness. In addition, individual beetles could be detected.
磨齒獸屬 灭绝
Mylodon became extinct 12-10,000 years ago at the end of the Pleistocene as part of the Late Pleistocene megafauna extinctions, along with all other mainland ground sloths and most large animals in the Americas. The timing coincides with the arrival of humans in the Americas, as well as climatic change. There is evidence that humans exploited Mylodon for food. At Fell's cave (Cueva Fell) in Chilean Patagonia, fractured and burned bones of Mylodon darwinii have been found in association with human artefacts, dating to around 12,766–12,354 calendar years Before Present (BP). At Piedra Museo in Argentine Patagonia, bones of Mylodon are found in association with human artefacts, dating to around 15,517–12,352 cal yr BP. This exploitation may have been a factor in its extinction.
航行警告電傳廣播
航行警告電傳廣播（英語：，縮寫：「NAVTEX」，又稱「中頻航行專用電報」）是一項國際自動化中頻直接列印服務，用於向船舶提供導航和氣象警報和預報以及緊急海上安全資訊。NAVTEX於20世紀70年代末在歐洲西北部開發，旨在提供一種低成本、簡單且自動化的方法，用於在離岸約250海裡的海上船舶上接收此資訊。
航行警告電傳廣播 技術層面
NAVTEX的傳輸採用窄带直接印字电报(NBDP)技術，並奠基於SITOR巨集B模式，是一种使用CCIR 476字符编码的前向錯誤更正广播，NAVTEX的Message以100波特率的速率传输，采用FSK调制，频移为170赫茲。NAVTEX主要在490千赫及518千赫的中频波段进行，又以518千赫為国际標準频率對航行於沿海海域所有船舶，傳送一般氣象預報和海上安全情報，此处的传输应始终使用英语，在使用NAVTEX的国家级传输中，多以試驗性地透過490千赫使用英語以外的其他語文傳送Message。