帝鳄属（属名：Sarcosuchus）又称为肌鳄、帝王鳄，意思为“肌肉鳄鱼”，是种已灭绝鳄类。它们生存在于早白垩纪的非洲，是曾经存活过的最大型鳄类动物之一。它几乎是现今咸水鳄的3倍大，重量约是4到6公吨。 直到最近，对于这种动物的了解仅来自于少数牙齿与鳞甲，是由法国古生物学家艾伯特·拉伯（Albert-Félix de Lapparent）在1940年代到1950年代于撒哈拉沙漠发现。然而在1997年与2000年，保罗·塞里诺（Paul Sereno）发现6个新标本，其中一个标本有将近一半的完整头颅骨与大部分的脊柱。所有其他巨鳄都只有少数局部头颅骨，所以帝鳄是实际上最大的巨鳄。 描述[编辑]当帝鳄成长完全时，它们应该跟公车一样长，约9到10.5米长，重达6000公斤。[1]而现今最大的鳄鱼咸水鳄，仅有帝鳄的2/3长（6.3米），重约1,200公斤。 最大型的帝鳄应该是年龄最老的。根据一个成长80%个体（以已知最大型的帝鳄个体作为基准）的皮内成骨（Osteoderms骨质外皮，）上的成长环，显示帝鳄在它50到60年的预期寿命间持续地成长。现代鳄鱼以更快速度成长，花约12年成长到它们的成年体型，成年后成长速率更为缓慢。[2] 它的头颅与成人一样大，约1.78米。上颌的长度大于下颌，形成咬合不正。颌部相当狭窄，尤其是幼年体。口鼻部占了75%的头颅长度。[2] 帝鳄的巨型颌部有132个粗厚牙齿，汉斯·拉尔森（Hans Larsson）形容它们像是铁路道钉。牙齿呈圆锥形，适合用来抓取、夹住猎物，而非现代鳄鱼狭窄的撕裂用牙齿（类似某些陆地肉食性动物）。帝鳄的颌部咬合力可达到18,000磅 80,000牛顿，让猎物很难逃脱。[3] 它拥有一排覆盖沿者背部排列的鳞甲或皮内成骨（Osteoderms），最大的鳞甲达1米长。鳞甲可当装甲用，可能辅助支撑它们的巨大身体，但也限制了它们的灵活性。 帝鳄的口鼻部末端有个奇特的凹处，称为“鼓泡”（Bulla），相当于长吻鳄的“壶”（Ghara）。不像长吻鳄，所有帝鳄的口鼻部末端都有这凹处。这显示它并非帝鳄的性选择特征，而只有雄长吻鳄拥有口鼻部末的凹处。这结构的用途仍然不清楚。保罗·塞里诺与其他爬虫类专家对于凹处用途的看法，从帮助嗅觉到发声器官都有。[4] 行为与食性[编辑]如同真鳄类，帝鳄也许有广范围的发声范围。帝鳄可能使用这些声音来界定领地范围、吸引异性、与它们后代沟通。 帝鳄的眼窝略朝上，显示这动物可能花大部分时间浸在水中，观察岸边的猎物。[2] 它们似乎以白垩纪的大型鱼类与乌龟为食。突出的颌部与结实的牙齿是用来抓取与压碎，它们的主要猎物可能是大型动物与较小的恐龙，它们埋伏在水中，并将猎物拖入水中，将猎物压碎、淹死、撕裂。 帝鳄可能与同一地层发现的似鳄龙产生猎食的冲突，似鳄龙是身长12米的兽脚类恐龙，有类似长吻鳄的颌部。保罗·塞里诺宣称，因为这群动物非常大，它们可以轻易地猎食大型恐龙，包括非洲地区的长颈部、小头部的巨大蜥脚类恐龙。 其他鳄类生物学家怀疑这巨型动物的猎食能力。帝鳄长而瘦的口鼻部非常类似现代长吻鳄、伪长吻鳄、狭吻鳄的狭窄口鼻部，上述物种都是以鱼类为食，不能追踪大型猎物。与现代尼罗鳄与已灭绝的恐鳄相比，尼罗鳄与恐鳄都有非常宽广、厚重的头颅骨，适合咬食大型猎物。由于该地当时有大量的总鳍鱼类动物，所以许多专家认为帝鳄只是种大型鱼食性动物，是现代长吻鳄的布满鳞甲版本，而非恐龙杀手。 然而，未成年帝鳄与现代狭窄口鼻部鳄鱼，两者口鼻部宽度类似，但成年帝鳄的口鼻部极度扩展。[2]若计算口鼻部相较于身体比例，帝鳄比尼罗鳄还狭窄，但宽度仍比长吻鳄宽。此外，帝鳄的牙齿并未如同大部分鱼食性鳄类般互相交错，显示它主要以鱼类为食，而以陆地动物为补助，如同尼罗鳄。 与帝鳄住在同一水域的总鳍鱼类经常身长超过2-3米，重达90公斤。这增加了猎食中型或小型陆地动物的可能性，而非以这些大型鱼类为食，许多这种鱼类拥有一层保护用的皮内成骨。 环境[编辑]在1亿1000万年前的早白垩纪，撒哈拉沙漠是个热带平原，上面散布着湖，有河流与溪流过，岸边布满植被。根据目前所发现的化石，水生的帝鳄可能繁盛于这些温暖、浅水、淡水栖息地。 现代真鳄类的体型与外形上非常相似，倾向于生存在不同区域；帝鳄是鳄形动物之一，鳄形动物体型与外型上差异很大，大 多生存于同一区域。有四种鳄形动物跟帝鳄在同一岩石层发现，包括有者8公分长头颅的矮小鳄类。它们占据多样且不同的生态位，而非互相竞争食物资源。 科学研究[编辑]帝鳄化石来自于数个个体，包括一个脊柱、四肢骨头、髋骨、背上的鳞甲、超过六个头颅骨。许多鳄形动物的头颅骨厚又重，所以发现头颅骨的机率比发现身体其他部分还高。这与恐龙的状况相反，恐龙头颅骨易碎，很少成为化石记录。 史前爬行动物的皮内成骨，因为上面有成长环，如同树的年轮，可用在判断年龄。[5]一个80%的成年体发现了40个成长环，显示它至少存活了40年。然而这种计算年龄法是有争议的。其他学者提出在中生代缺乏极端气候的环境下，很难以计算年轮的方法计算动物的年龄。[6] 因为没有发现过完整骨骸，所以是用测量最大的头颅骨，然后与现代鳄鱼相比，计算出帝鳄的长度。现代鳄鱼头颅与身体的比例，不管年龄或性别都是一样的。[2]主要的差异在于长口鼻部鳄鱼，头部占的比例比宽口鼻部鳄鱼还大。帝鳄的长度是以长吻鳄与咸水鳄的比例平均作为计算。塞里诺也测量印度与哥斯达黎加的现存鳄鱼作为他研究中的计算数据。 在一个国家地理学会的特别计划里，佛罗里达州立大学的格里高利·艾利克森（Gregory Erickson）、佛罗里达大学的Kent Vliet、北亚历桑纳大学的Kristopher Lapping，他们在佛罗里达州一个鳄鱼公园里诱使美国短吻鳄咬一个上有测量仪器的棒子。他们所测量最大型短吻鳄的咬力是2,125磅（9,452牛顿）。在比较过60种动物的咬力后，他们认为动物的咬力与体型成正比。以此方法计算帝鳄的咬力，所得结果是18,000磅（80,000牛顿）。 巨型鳄类[编辑]巨型鳄类似乎是趋同演化的好例子，因为根据Schwimmer的研究，大型鳄类时常在演化史上重复出现。这可能部分导因于身体结构，背上的装甲骨板能协助支撑巨大的身体，部分导因于环境，水能使它们巨大的身体漂浮。 恐鳄是另一种巨大鳄类，它们能以与现代鳄鱼同样的速度成长，每年0.5米。它较现代鳄鱼大，因为它持续成长，花35年达到成年体，而非现代鳄鱼的10年。所有这些不同的巨型鳄类必须生活在有大量温暖浅水、充足猎物的良好生存环境。 恐鳄生存于晚白垩纪的北美，是一个与帝鳄关系较远的巨型鳄类。对于恐鳄的了解只来自头颅，头颅比帝鳄的小，但恐鳄拥有宽广口鼻部，类似短吻鳄，而帝鳄拥有狭窄口鼻部，类似长吻鳄。这意味者恐鳄的头颅占了身体较小的部分，而长口鼻部帝鳄的体型可能一样或更大。帝鳄体型上的对手有中新世巴西的普鲁斯鳄、中新世与鲜新世印度的鸟嘴鳄，但它们的化石并不完整。 巨型鳄类彼此间的关系可见于以下简略的演化树：
分类[编辑]帝鳄并非现代鳄鱼的始祖。在种系发生学定义里，它也不是鳄鱼。鳄鱼是鳄目演化支。鳄目包括所有现代物种，例如鳄鱼本身、短吻鳄，与它们的最近史前近亲。帝鳄是大头鳄科的成员，与今日鳄鱼血缘很远。 鳄类通常用在较宽广的定义。第一种类似鳄的爬行动物（鳄形超目），出现于约2亿3000万年前的晚三叠纪，从主龙类分化出，外表看起来类似现代鳄鱼。它们拥有修长的腿、长形身体由鳞甲包覆。 直到1980年代，大头鳄科被分类于假设的中鳄亚目之下，此亚目又在鳄目之下。然而，Benson与Clark在1988年确定中鳄亚目是并系群，包含现代鳄鱼的始祖。 一个简略的生物演化树：
在巴西发现了帝鳄近亲的牙齿与皮内成骨。这可能是非洲与南美间陆桥比原本推测的时间还要晚存在的证据。 另一方面，基于口鼻部的结构，帝鳄的近亲包括大头鳄类的特里鳄（Terminonaris）、森林鳄，以及较轻型的远亲大头鳄。这些帝鳄的近亲是狭窄口鼻部、以鱼为生、生存在咸水环境；帝鳄是宽广口鼻部，住在河边。 挖掘过程[编辑]化石是在尼日Gadoufaoua的Ténéré沙漠发现，该沙漠是撒哈拉沙漠的一部分。第一个帝鳄的牙齿与鳞甲是在40年代到50年代发现，由法国古生物学家艾伯特·拉伯发现。直到1964年，地理学家发现其头颅，并引起菲利普·塔丘特的注意。他带者化石回到巴黎，头颅由France de Broin检验。在1966年，他们正式地将这种动物叙述、命名，学名为帝鳄（Sarcosuchus imperator），意思是“肌肉-鳄类-帝王”。正模标本为MNN 604，是尼日国立博物馆（Musee National du Niger）的第604号标本，研究之后标本归还回尼日。 第二、三次主要的考察是保罗·塞里诺在1997年与2000年的考察。他在El Rhaz地层发现部分的骨骼、大量的头颅、20吨的已分类化石，该地层时间是晚白垩纪的阿普第阶到阿尔比阶。他们花了一年完成帝鳄标本。挖掘的结果在2001年12月公布。这个挖掘团队有芝加哥大学与国家地理学会的驻会探险家保罗·塞里诺、耶鲁大学与多伦多大学的汉斯·拉尔森、纽约骨科医学院的Christian Sidor、尼日的Boubé Gado。 照片集[编辑]SarcosuchusFrom Wikipedia, the free encyclopedia For the theropod dinosaur, see Sarcosaurus.
Sarcosuchus (/ˌsɑːrkoʊˈsuːkəs/; meaning "flesh crocodile") is an extinct genus of crocodyliform and distant relative of living crocodylians that lived 112 million years ago. It dates from the early CretaceousPeriod of what is now Africa and South America and is one of the largest crocodile-like reptiles that ever lived. It was almost twice as long as the modern saltwater crocodile and weighed up to 8 tonnes (7.9 long tons; 8.8 short tons). The first remains were discovered during several expeditions led by the French paleontologist Albert-Félix de Lapparent, spanning from 1946 to 1959, in the Sahara. These remains were fragments of the skull, vertebrae, teeth, and scutes. In 1964, an almost complete skull was found in Niger by the French CEA, but it was not until 1997 and 2000 that most of its anatomy became known to science, when an expedition led by the American paleontologist Paul Sereno discovered six new specimens, including one with about half the skeleton intact and most of the spine. Contents[hide]Description[edit source]Sarcosuchus was a giant relative of crocodiles, with fully grown individuals estimated to have reached up to 11–12 m (36–39 ft) in total length and 8 tonnes (8.8 short tons) in weight.[1] It had somewhat telescoped eyes and a long snout comprising 75% of the length of the skull. There were 35 teeth in each side of the upper jaw, while in the lower jaw there were 31 teeth in each side. The upper jaw was also noticeably longer than the lower one leaving a gap between them when the jaws were shut, creating an overbite. In young individuals the shape of the snout resembled that of the living gharial but in fully grown individuals it became considerably broader.[1][2] Bulla[edit source]At the end of its snout, Sarcosuchus presented an expansion, known as a bulla, which has been compared to the ghara seen in gharials. However, unlike the ghara, which is only found in male gharial, the bulla is present in all Sarcosuchus skulls that have been found so far, suggesting that it was not a sexually dimorphic trait. The purpose of this structure remains enigmatic. Opinions from researchers range from it being an olfactory enhancer to being connected to a vocalization device.[citation needed] Osteoderms[edit source]The osteoderms, also known as dermal scutes, of Sarcosuchus were similar to those goniopholodids like Sunosuchus and Goniopholis, they formed an uninterrupted surface that started in the posterior part of the neck up to the middle of the tail like is seen in Araripesuchus and other basal crocodyliforms, different from the pattern seen in living crocodiles, which present discontinuity between the osteoderms of the neck and body.[1] Size[edit source]A common method to estimate the size of crocodiles and crocodile-like reptiles is the use of the length of the skull measured in the midline from the tip of the snout to the back of the skull table,[1] since in living crocodilians there is a strong correlation between skull length and total body length in subadult and adult individuals irrespective of their sex,[3] this method is preferred for Sarcosuchus due to the absence of a complete enough skeleton. Two regression equations were used to estimate the size of S. imperator, they were created based on measurements gathered from 17 captive gharial individuals from northern India and from 28 wild saltwater crocodileindividuals from northern Australia,[1] both datasets supplemented by available measurements of individuals over 1.5 m (4.92 ft) in length found in the literature.[1][4] The largest known skull of S. imperator (the type specimen) is 1.6 m (5.25 ft) long, and it was estimated that the individual it belonged to had a total body length of 11.65 m (38.2 ft),[1] its snout-vent length of 5.7 m (18.7 ft) was estimated using linear equations for the saltwater crocodile[5] and in turn this measurement was used to estimate its body weight at 8 tonnes (8.8 short tons).[1] This shows that Sarcosuchus was able to reach a maximum body size not only greater than previously estimated[1] but also greater than that of the Miocene Rhamphosuchus,[6] the Late Cretaceous Deinosuchus[7][8] and the Miocene Purussaurus.[9] Classification[edit source]Sarcosuchus is commonly classified as part of the clade Pholidosauridae,[1][10][11] a group of crocodile-like reptiles (Crocodyliformes) related but outside Crocodylia (the clade containing living crocodiles, alligators and gharials).[1] Within this group it is most closely related to the North American genus Terminonaris.[1] Most members of Pholidosauridae had long, slender snouts and they all were aquatic, inhabiting several different environments, some forms are interpreted as marine, capable of tolerating saltwater while others, like Sarcosuchus, were freshwater forms, the most primitive members of the clade, however, were found in coastal settings, zones of mixing of freshwater and marine waters.[11] Sarcosuchus stands out among pholidosaurids for being considered a generalist predator, different from most known members of the clade which were specialized piscivores.[1] Simplified cladogram after Fortier et al. (2011).[11]
Discovery and naming[edit source]Early findings[edit source]During the course of several expeditions on the Sahara from 1946 to 1959, led by the French paleontologist Albert-Félix de Lapparent, several fossils of a crocodyliform of large size were unearthed in the region known as the Continental Intercalaire Formation, some of them were found in Foggara Ben Draou, in Mali and near the town of Aoulef, Algeria (informally named as the Aoulef Crocodile) while others came from the Ain el Guettar Formation of Gara Kamboute, in the south of Tunisia, the fossils found were fragments of the skull, teeth, scutes and vertebrae. In 1957, in the region now known as the Elrhaz Formation in the north of Nigerseveral isolated teeth of great size were found by H. Faure. The study of this material by French paleontologist France De Broin helped identify them as coming from a new long snouted crocodile.[10] Later, in 1964, the research team of the French CEA discovered an almost complete skull in region of Gadoufaoua, in the north of Niger, said skull was shipped to Paris for study and became the holotype of the then new genus and species Sarcosuchus imperator in 1966. The genus name comes from the Greek "sarco" meaning flesh and "suchus" meaning crocodile.[10] Fossils from Brazil[edit source]In 1977, a new species of Sarcosuchus was named, S. hartti, from remains found in the late 19th century in the Recôncavo Basin of Brazil.[2] In 1867, American naturalist Charles Hartt found two isolated teeth and sent them to the American paleontologist O. C. Marsh who erected a new species of Crocodylus for them, C. hartti,[12] this material, along with other remains were assigned in 1907 to the genus Goniopholis as G. hartti.[13] Now residing in the British Museum of Natural History the fragment of the lower jaw, dorsal scute and two teeth compromising the species G. hartti were reexamined and conclusively placed in the genus Sarcosuchus.[2] Recent findings[edit source]The next major findings occurred during the expeditions led by the American paleontologist Paul Sereno in 1995 (Aoufous Formation, Morocco), 1997 and the follow-up trip in 2000. Partial skeletons, numerous skulls and 20 tons of assorted other fossils were recovered from the deposits of the Elrhaz Formation, which has been dated as late Aptian or early Albian stages of the Late Cretaceous. It took about a year to prepare the Sarcosuchus remains.[1][14] Fossils were found in 2010 in the Ifezouane Formation of Morocco. Fossil teeth from the area of Nalut in northwestern Libya, possibly Hauterivian to Barremian in age, might be referable to S. imperator.[15] Paleobiology[edit source]Growth pattern[edit source]Sereno took thin sections from trunk osteoderms of an estimated subadult individual (~80% of estimated maximum adult size).[1] Approximately 40 lines of arrested growth (LAG) were counted in these thin sections, suggesting that S. imperator took 50 to 60 years to reach adult size.[1] Given that extant wild crocodylians rarely reach these advanced ages,[3][16] Sereno suggested that S. imperator achieved its large size by extending its period of rapid, juvenile, growth.[1] A similar growth strategy has been suggested for the equally titanic crocodylian Deinosuchus, based on similar criteria.[7] Diet[edit source]Based on the broader snout of fully grown S. imperator when compared to the living gharial and other narrow-snouted crocodiles, along with a lack of interlocking of the smooth and sturdy-crowned teeth when the jaws were closed, Sereno et al.[1] hypothesized that S. imperator had a generalized diet similar to that of the Nile crocodile, which would have included large terrestrial prey such as the abundant dinosaurs that lived in the same region.[1] However, a 2014 analysis of a biomechanical model of its skull suggested that unlike Deinosuchus, Sarcosuchus may not have been able to perform the "death roll" maneuver used by extant crocodylians to dismember their prey.[17][18] This suggests that if S. imperator did hunt big game, it probably did not dismember prey in the same fashion as extant crocodylians. Habitat[edit source]The remains of S. imperator were found in a region of the Ténéré Desert named Gadoufaoua, more specifically in the Elrhaz Formation of the Tegama Group, dating from the late Aptian to the early Albian of the Early Cretaceous,[19] approximately 112 million years ago.[1] The stratigraphy of the region and the aquatic fauna that was found therein indicates that it was an inland fluvial environment, entirely freshwater in nature with a humid tropical climate.[1][10][19]S. imperator shared the waters with the holostean fish Lepidotus and the coelacanth Mawsonia.[2] The dinosaur fauna was represented by the iguanodontian Lurdusaurus, which was the most common dinosaur in the region, and its relative Ouranosaurus; there were also two sauropods, Nigersaurus and a currently unnamed sauropod while the theropod fauna included the spinosaurid Suchomimus, the carcharodontosaurid Eocarcharia and the abelisaurid Kryptops.[19][20] Meanwhile, S. hartti was found in the Recôncavo Basin of Brazil, specifically in the Ilhas Formation of the Bahia series, it was a shallow lacustrine environment dating from the late Aptian, similar in age to the habitat of S. imperator, with similar aquatic fauna, including Lepidotus and two species of Mawsonia. The dinosaur fauna is of a very fragmentary nature and identification does not go beyond indeterminate theropod and iguanodontid remains.[2] |
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来自： KyunraWang > 《远古生物》
