【激龙属】
激龙（属名：Irritator）是棘龙科恐龙的一个属，生存于大约1.13亿至1.1亿年前早白垩世阿尔比阶的巴西。激龙所知于Araripe Basin发现的一个接近完整的颅骨，该颅骨曾为Fossil dealers所得并卖给State Museum of Natural History Stuttgart。1996年，该标本成为模式种查氏激龙（Irritator challengeri）的正模标本。属名取自英文irritation（生气、恼怒）一词以反映古生物学家发现颅骨已被收集者严重破坏并改动时的心情，种名致敬亚瑟·柯南·道尔小说中的虚构角色Professor Challenger。
部分古生物学家将利氏崇高龙（Angaturama limai，所知于1996年描述的一个吻尖）视为该属的潜在次异名，两者皆来自阿勒莱皮盆地的同一地层。之前也有人提出激龙和崇高龙颅骨属于同一标本，尽管该假说受到质疑，但还需要更多重叠化石材料以确认两者是否为同种生物。罗穆阿尔多组还出土了其它棘龙科骨骼，其中一些可能属于激龙或崇高龙，根据这些化石制作了一具骨骼模型，并于2009年在巴西国家博物馆展出。
估计激龙身长在ft之间、重约short ton，使其成为已知最小的棘龙科之一。细而浅的长吻上排列着笔直而无锯齿的圆锥形牙齿。一片很薄的矢状嵴在头顶纵向延伸，强健的颈部肌肉很可能附着于此。鼻孔处于远离吻尖的位置，嘴部上侧坚硬的Secondary palate可在进食时加固双颚。查氏激龙正模是迄今为止保存最完整的棘龙科颅骨，属于一只未成年个体。崇高龙吻尖呈Rosette (design)向两侧伸展，其上长有修长的牙齿及异常高的嵴。一具疑似骨骼表明其与其它棘龙科一样第一指爪较大、背部长有神经棘帆。
激龙曾先后被错误鉴定为翼龙目及手盗龙类。1996年，这种动物被确认为棘龙科兽脚类。正模颅骨在2002年重新描述之前就已进行彻底制备，从而证实了这一分类。激龙和崇高龙皆属于棘龙亚科。有人提出，激龙像现在的鳄鱼一样具有广食性，可能主要捕食鱼类及可以捕到的任何其它小型猎物。已有化石证据表明一只激龙个体吃过翼龙，该个体要么真的狩猎了这只翼龙，要么仅在清理其尸体。激龙可能具有Semiaquatic习性，栖息在为干旱区所包围的沿海泻湖热带环境中，与其它肉食性兽脚类、海龟、Crocodyliformes及大量翼龙和鱼类物种共存。
== 研究历史 ==
巴西东北部地区的地图，上面标出了Araripe Basin和São Luís-Grajaú Basin中三具棘龙亚科化石标本的发现地。从上到下分别为奥沙拉龙、激龙和崇高龙。
激龙正模标本出土于巴西东北部地区圣安娜-杜卡里里附近的白垩岩结核中，包含一只带有下颌的巨大颅骨后段。该化石被化石贩子得到，并卖给德国State Museum of Natural History Stuttgart的卢珀·威尔德（Rupert Wild）。鉴于Chapada do Araripe地区以大量翼龙类发现而闻名，而这家德国博物馆也经常购买此类化石，因此其当时被假定为一只巨型原始翼龙类的颅骨。由于其被视为有着非凡重要性的独特发现，因此联系了德国和英国翼龙专家对标本进行研究。当时，一篇将其描述为翼龙类的论文已经提交上去，但同行评审否认了作者――德国古生物学家埃伯哈德·弗雷（Eberhard Frey）和英国古生物学家大卫·马提尔（David Martill）――的结论，并提出化石属于兽脚类恐龙。
正模标本颅骨的过时重建，据马提尔和同事1996年的解释所绘。基于这种重建作出的外观描述（类似底部的复原图）后来出现在许多恐龙书籍和百科全书中。
颅骨轻微侧向压扁，且正如化石常见状态一般被部分压碎。右侧保存完好，左侧在收集过程中严重损坏。颅骨最后段的上表面有部分风化，下颌前端遗失，两者皆由石化过程中的破坏造成。部分标本亦作为凝岩球结核的一部分而碎裂。上颌吻尖也已经遗失。鉴于未发现风化迹象，因此它很可能是在化石收集期间或之后断裂。某些骨头上存在明显腐蚀痕迹，表明有人曾试图对其进行酸处理。颅骨中部有一处垂直骨折，表明其显然被车身填料密封过。为使其看起来更完整、更有价值，化石贩子用石膏对颅骨做了大面积遮盖，此手段为查帕达杜阿勒莱皮的当地收藏家广泛采用，尤其是用作处理鱼化石。直到标本被送往英国大学进行CT扫描成像，买家才知道其被改动过。 这表明收藏者试图通过将上颌骨（上颚主要骨骼）的一部分移至Rostrum (anatomy)（鼻部）前侧来重建颅骨。该颅骨（编号SMNS 58022）于1996年2月由古生物学家大卫·马提尔（David M. Martill）、亚瑟·科鲁克尚克（Arthur R. I. Cruickshank）、埃伯哈德·弗雷（Eberhard Frey）、菲利普·斯默（Philip G. Small）和玛丽亚·克拉克（Maria Clarke）首次作出科学描述，成为新属新种查氏激龙（Irritator challengeri）的正模标本。马提尔和团队在论文中写道，属名Irritator源自“作者发现鼻部被人为拉长时所产生的愤怒（irriation）之感（此处轻描淡写）。”模式种查氏激龙以阿瑟·柯南·道尔小说《失落的世界》中Professor Challenger这一角色命名。两年前，弗雷和马提尔还以该小说家的名字命名了Crato Formation翼龙新种——柯南道尔亚氏翼龙。
马提尔和同事首次描述查氏激龙时，正模标本仍有大部分裹在Calcareous岩石基质中。在美国古生物学家汉斯－戴尔特·苏伊士（Hans-Dieter Sues）的监督下，多伦多大学密西沙加分校技术员黛安娜·斯科特（Diane M. Scott）负责从岩石中彻底取出颅骨，以便在2002年进行详细重新描述。这项对制备完成标本的检查（由苏伊士、弗雷、马提尔和斯科特等人发表）否认了马提尔和同事的许多原始观察结果，后者基于对受损且大部分被遮盖的颅骨的误判。颅骨全长估计为abbr=on，比之前的数据更短。最初鉴定为突出头冠的骨头被证明是一块脱落的不明骨骼碎片。与先前研究一样，苏伊士及其同事认为，非洲棘龙属是与激龙最相似的分类单元，因为两者具有许多相同牙齿特征，包括几乎笔直的圆锥形牙冠、薄薄的珐琅质、无锯齿且纵向伸长的清晰边缘。由于当时对棘龙颅骨所知甚少，这些相似之处足以让作者提出激龙可能为棘龙的次异名，但苏伊士和同事指出，需要更多重叠颅骨材料来作进一步鉴别。随着对棘龙颅骨的了解增加，后期研究皆坚持视两者为不同分类单元。
尽管发现地点尚不确定，但该标本很可能来自Romualdo Formation（原为Santana Formation的罗穆阿尔多段）。该猜想为介形虫Pattersoncypris的微体化石和Ichthyodectidae的鱼鳞所证实，两者皆发现于罗穆阿尔多组。对当地化石贩子的询问透露出一个靠近查帕达杜阿勒莱皮侧翼圣安纳杜卡里里的布克塞克（Buxexé）村附近、海拔约sp=us的地点。由于罗穆阿尔多组确实暴露于此，且包裹正模的基质与此处岩石有相同颜色及纹理，因此可将该地区视为化石的可能发现地。查氏激龙是罗穆阿尔多组首个被描述的恐龙，其正模标本代表已知保存最完整的棘龙科颅骨。
=== 与崇高龙的异名争议 ===
激龙已知颅骨材料，由古生物学家海梅·海登（Jaime A. Headden）绘制；吻尖来自崇高龙标本。
与查氏激龙生存于同一时期及地点的另一种棘龙科――利氏崇高龙（Angaturama limai），由巴西古生物学家Alexander Kellner（Alexander W. A. Kellner）和狄奥内戈斯·德·阿梅达·坎波斯（Diogenes de Almeida Campos）于1996年2月命名。正模标本编号USP GP/2T-5，保存于圣保罗大学，由一个来自罗穆阿尔多组的单个吻尖组成，是使用最初为挖掘翼龙化石而开发的技术从一个石灰质结核中取出。属名取自巴西土著图皮人文化中的守护神昂迦图拉玛（Angaturama），种名纪念于1991年将标本告知克尔纳的已故巴西古生物学家穆里洛·德·利玛（Murilo R. de Lima）。
上颌齿。由塞里斯和舒茨于2017年提出。
1997年，英国古生物学家Alan J. Charig（Alan J. Charig）和Angela Milner（Angela C. Milner）将崇高龙视为激龙的潜在次异名，指出两个属皆有缩小的鼻孔、修长的双颚和典型棘龙科特征。Paul Sereno（Paul Sereno）和同事在1998年同意此观点，并提出崇高龙和激龙正模可能属于同一标本。包括Éric Buffetaut（Éric Buffetaut）和茂哈马德·夸亚（Mohamed Ouaja）（2002年）、Cristiano Dal Sasso（Cristian Dal Sasso）和同事（2005年）、托尔·贝汀（Tor G. Bertin）（2010年）、Darren Naish（Darren Naish）（2013年）以及马达尼·本尤塞夫（Madani Benyoucef）和同事（2015年）在内的作者皆支持此结论。苏伊士和同事在激龙重新描述中指出，两者正模标本吻部宽窄相同，且皆有横截面圆润、边缘明显且无锯齿的牙齿。他们还指出，崇高龙前颌上的矢状嵴可能与激龙鼻骨上的相一致。已有人对这些结论提出质疑。克尔纳和坎波斯（2000年）及伊莱恩·马卡多（Elaine B. Machado）和克尔纳（2005年）认为化石来自两个不同属，而利氏崇高龙正模显然比激龙更为横向扁平。
巴西古生物学家马克斯·塞里斯（Marcos A. Seles）和恺撒·舒茨（Cesar L. Schultz）于2017年在对两者化石的检查中指出两件标本在保存状况等其它方面也存在差异：激龙标本颜色更浅且有一条竖向裂缝，崇高龙标本则具有很多孔洞；激龙牙齿上的损坏也相对更轻。塞里斯和舒茨还鉴定出一个疑似重叠的部位即左上颌第三颗牙齿，并注意到，根据近缘属重爪龙的比例，崇高龙颅骨应大于激龙。因此作者得出结论称两件标本并非属于同一个体，并指出需要更多重叠遗骸确认前者是否为后者的异名。如果将崇高龙和激龙看作相同属，鉴于后者命名时间几乎比前者早了一个月，则应根据Principle of Priority视后者为有效学名。由于对牙齿位置的解释不同，古生物学家马克·沙德（Marco Schade）及同事（2023年）未能证实牙齿部位存在重叠，也未能提供数据解决此问题。
=== 颅后材料及额外发现 ===
棘龙亚科骨盆及骶椎（标本MN 4819-V），展示于巴西国家博物馆。
除颅骨、鼻骨碎片及单个牙齿外，罗穆阿尔多组还出土了可能属于棘龙科Postcrania遗骸，其中有许多迄今仍未描述并全部归入棘龙亚科。2004年该地层又出土部分神经弓（MN 4743-V）。巴西古生物学家乔纳斯·比腾考特)were unearthed at the formation. Brazilian paleontologist Jonathas Bittencourt and Kellner assigned these, due to their structure, to the Spinosauridae. It is uncertain whether this specimen can be referred to Irritator or Angaturama, given that both are based only on skull material. In 2007, Machado and Kellner tentatively referred a rib fragment (MN 7021-V) to the Spinosauridae. However, the most complete spinosaur specimen retrieved from the Romualdo Formation is MN 4819-V, a partial skeleton lacking the skull. First reported in 1991, the specimen was referred by Kellner to the Spinosauridae in 2001 because of its tall sacral neural spines and the enlarged condition of the hand claw. The skeleton was fully described in 2010 in an as-of-yet unpublished master's thesis by Machado. An incomplete hind limb (MPSC R-2089) mentioned in 2013 might also pertain to the Spinosauridae. In 2018, Tito Aureliano and his team described LPP-PV-0042, part of a left tibia from a particularly large individual. As is common with fossils from the Araripe Basin, the majority of spinosaurid material from the Romualdo Formation was collected under uncontrolled circumstances for use in the illegal fossil trade. As such, many specimens are partly damaged and without precise geological field data.
Some of the Romualdo Formation postcrania were used as the basis for the creation of a replica Angaturama skeleton, later mounted at the Federal University-owned Museu Nacional do Rio de Janeiro (National Museum of Rio de Janeiro). The skeleton depicted the animal carrying an anhanguerid pterosaur in its jaws. It was the centerpiece of the Dinossauros no Sertão (Dinosaurs of Sertão) exhibit, which opened to the public in March 2009, becoming the first large carnivorous Brazilian dinosaur to be put on display. Some of the original postcranial elements (including the fossil pelvis and sacral vertebrae) were presented alongside the mount. In press releases of the exhibit's opening, Kellner informally implied MN 4819-V as belonging to Angaturama. This is also reflected in the specimen's inclusion in the skeletal mount. In 2011, a third Brazilian spinosaur, Oxalaia quilombensis, was named and described from the Alcântara Formation of the Itapecuru Group, part of the São Luís Basin. This larger species, known only from an isolated snout tip and upper jaw fragment, lived during the Cenomanian stage, around six to nine million years after Irritator and Angaturama. Oxalaia quilombensis is differentiated from Angaturama limai by its broader, more rounded snout and lack of a sagittal crest on the premaxillae. In September 2018, a fire broke out at the palace housing the Museu Nacional, largely destroying the fossil collections and possibly the exhibited Angaturama skeleton and fossil elements. The holotype of Oxalaia quilombensis, which was stored in the same building, may also have been destroyed.
==描述==
Estimated size of Irritator (light green) and Angaturamas (dark green) holotype specimens with a human
Even by maximal size estimates, Irritator was smaller than other known spinosaurids. Gregory S. Paul calculated its length at sp=us and weight at short ton. Thomas R. Holtz Jr. published a higher estimate of sp=us, with a weight between abbr=. Estimates by Dougal Dixon were lower at sp=us long and sp=us high. When scaled by Aureliano and colleagues, the reconstructions from the study by Sales and Schultz provided a length of sp=us for the Irritator challengeri holotype, and sp=us for the Angaturama limai holotype. Some of the skull bones of the former holotype had not yet fully co-ossified (fused), indicating that the specimen belonged to a subadult. The partial spinosaurine skeleton MN 4819-V represented a moderately-sized individual, estimated by Machado at sp=us in length. Many elements from this specimen were incorporated into the skeletal mount in the National Museum of Rio de Janeiro, which had a length of sp=us and a height of sp=us. However, spinosaurids from the Romualdo Formation possibly attained greater sizes. Although LPP-PV-0042 is represented only by a tibia fragment, Aureliano and colleagues estimated its length at roughly sp=us. Bone histology indicates that this individual was a subadult, so the mature animal may have been larger.
===查氏激龙正模标本解剖学===
Holotype skull of Irritator challengeri from left (top) and right side views
The holotype skull of Irritator challengeri, although heavily damaged in certain places, is largely complete; missing only the tip of the snout and the front of the mandible. The preserved skull is abbr=on tall and abbr=on wide, its full length has been estimated at abbr=on, based on comparisons with Baryonyx. Irritators skull was long, narrow, and somewhat triangular in cross section. The braincase was inclined backwards, and deeper than it was long. Extending from it was an elongate and low snout, with both sides relatively flat and slightly angled towards the skull midline. Only the rear ends of the paired premaxillae (frontmost snout bones) remain intact, forming the front upper and lower borders of the external nares (bony nostrils). As in all spinosaurids, the maxillae (main upper jaw bones) extended below and past the nostrils in a long, low branch that formed the lower border of this opening, consequently separating the premaxillae and nasal bones in that location. Irritators maxillary sinuses (located in the body of the maxillae) bore a large oval opening, as in Allosaurus. The nostril openings were oval and, as in all spinosaurids, positioned farther back on the skull than in typical theropods. Irritators nostrils were both proportionately and absolutely smaller than in Suchomimus and Baryonyx, but larger than those of Spinosaurus. The opening behind the orbit (eye socket), the lateral temporal fenestra, was very large, while the antorbital fenestra, in front of the eyes, was long and elliptical. The orbit itself was deep and wider at the top (where the eyeball was placed) than the bottom. The lacrimal bone separated the orbit from the antorbital fenestra, forming the upper and lower rear margins of the latter with two processes that enclosed a 40-degree angle; similar to Baryonyx, where it enclosed 35 degrees. Unlike in Baryonyx, Irritators lacrimal did not form a bony horn core. The prefrontal bones were large and sturdy, while the thinner frontal bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit.
Life restoration combining specimens of Irritator and Angaturama
A thin sagittal crest, constructed from the elongate nasal bones, extended along the skull midline before stopping just above the eye in a slightly flattened bulge. Although the complete shape and height of this structure is unknown in Irritator, these head crests were commonplace in spinosaurids, having possibly served a display function when the animal was alive. The preserved part of Irritators crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of Spinosaurus. Like others in its family, Irritator possessed a long and bony structure on the roof of its mouth called a secondary palate, separating the oral from the nasal cavity. This is a feature observed in extant crocodilians, but absent in most theropod dinosaurs. Also like its relatives, Irritator had two additional openings on the skull roof (called the postnasal fenestrae) as well as long and only partially diverging basipterygoid processes (bony extensions connecting the braincase with the palate). The back of the lower jaw was deep, its rear upper surface consisting mainly of the large surangular bone, which articulated with the shallower angular bone below it. The mandibular fenestra, a sideways-facing opening in the lower jaw, was oval and comparatively large. The dentary (tooth-bearing bone of the mandible) is unknown in Irritator, save for a possible remnant at the front of the surangular. Irritator challengeris holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes.
dentition
Irritator had straight or only faintly recurved conical teeth, bearing sharply defined but unserrated edges. Flutes (lengthwise ridges) were present on its tooth crowns, a common dental trait among spinosaurids. Both sides of Irritators teeth were fluted, as in Spinosaurus, whereas Baryonyx exhibited them only on the lingual (inward facing) side of its teeth. Irritators teeth were circular in cross section, as opposed to the laterally flattened condition of most theropod teeth. The enamel (first layer of the teeth) was thin, with a finely wrinkled texture also observed in Baryonyx. Both of Irritators maxillae preserve nine teeth, although the left maxilla's tooth crowns are more intact, and there are traces of a tenth tooth in the rock matrix. The teeth were deeply inserted into the jaw and widely spaced towards the front of the maxilla. The first and second preserved maxillary teeth were the largest, at abbr=on and abbr=on in crown length. The seven remaining teeth became progressively smaller towards the rear, one of the last ones measuring abbr=on in estimated crown length. CT scans performed on the specimen revealed replacement teeth on both sides of the upper jaw. Their roots ran deep into the maxillae and converged close to the midline, nearly reaching the top of the skull. Based on comparisons with Irritators relatives, the maxillae were probably lined with a total of 11 teeth each, similar to the number of 12 teeth in MSNM V4047, an upper jaw fossil referred to Spinosaurus. The hindmost tooth of the Irritator specimen's left maxilla was not yet fully erupted, and only the tip of it was visible.
===利氏崇高龙正模标本解剖学===
Holotype of Angaturama limai from various angles
The holotype of Angaturama limai consists only of the front part of the upper jaw, comprising the tips of the paired premaxillae and the frontmost ends of the maxillae. The specimen measures abbr=on in height and abbr=on in length, with the width of the palatal region being abbr=on. The suture between the maxilla and premaxilla was jagged at the front and straightened out towards the rear. The lower margin of the premaxillae was concave, with the concavity reaching its apex at the sixth premaxillary tooth. The front of the snout was expanded, forming the spoon-shaped terminal rosette characteristic of spinosaurids. This concave underside of the premaxillae would have complemented a convex and enlarged mandible tip. The premaxillae connected with each other on the bottom to form Angaturamas secondary palate, which was also partially contributed to by two processes extending from the maxillae. The snout was strongly compressed laterally, and the premaxillae gently tapered towards the top to form a tall sagittal crest abbr=on in thickness. This crest was larger and extended farther forwards on the snout than in other known spinosaurids. The frontmost upper border of the premaxilla had a small bulge that overhung the base of the crest. This bulge was apparently damaged on its upper surface, indicating that the top of the crest may have extended even farther over and forwards from that point. The front of Angaturamas snout hence had a vertically straight or concave margin, atypical from the more smoothly-sloping snouts of other spinosaurs.
In the premaxilla, a broken-off tooth with partial tooth crown was recovered. The strongly extended and straight teeth with unserrated conical crowns, which measured abbr=on in length, were singly embedded. This indicates continuous tooth replacement where new teeth were pushed up between the old ones. Judging by the alveoli (tooth sockets), the premaxilla had seven teeth altogether, the third tooth being the largest. The frontmost three teeth of the maxilla were also preserved. The premaxillary teeth increased in size from the first to third, shrank from the third to the sixth, and enlarged again from the sixth premaxillary to third maxillary positions. A abbr=on diastema (gap in tooth row) was present between the last premaxillary and first maxillary tooth.
===颅后===
Hand and arm bones of specimen MN 4819-V, the most complete spinosaurid hand known
Though no skeletal remains were discovered with the original Angaturama snout tip, one partial skeleton (MN 4819-V) from a different location may belong to the genus. But since there is no overlapping material between the two specimens, direct comparisons cannot be made. MN 4819-V comprises a largely intact pelvis, some dorsal (back) and caudal (tail) vertebrae, five sacral (hip) vertebrae, a partial right tibia and fibula (shin and calf bones), most of the right femur (thigh bone), and part of an ulna (forearm bone). It also has the most complete hand known from a spinosaurid, including metacarpals, phalanges, one carpals, and one claw. Like in all spinosaurids, the claw of the first finger (the "thumb") was enlarged.
The pelvic bones are well-preserved, with the right side better articulated than the left. The fused sacral vertebrae are still attached to the pelvis, which lacks the distal ends of both of its pubic bones and ischia (lower and rearmost hip bones). The ilium (main hip bone) is abbr=on long. The preacetabular ala (front expansion) of the ilium was curved on the bottom and was somewhat shorter and deeper than the postacetabular ala (rear expansion). The preacetabular ala were somewhat enlarged at the front, in contrast to the more slender condition of the postacetabular ala. The brevis fossa (groove at the bottom of the postacetabular ala) was concave, as was the rear margin of the ischium. The pubis bore a relatively large and almost closed obturator notch, an indentation in the lower margin of the rear part of the bone that allowed for the passage of the obturator nerve. The upwards projecting neural spines of the sacrum were elongated, as is typical in spinosaurs. In life, these would have been covered in skin, forming a "sail" down the animal's back. MN 4819-V is distinguished from Suchomimus due to its longer and shallower ilium with a less curved upper margin, and from Baryonyx by having a more developed obturator process, a blade-like structure on the bottom of the ischium.
==分类==
Size of various spinosaurids (Irritator in purple, first from left) compared with a human
Martill and his team originally classified Irritator as a maniraptoran dinosaur in the clade Bullatosauria (a group no longer considered monophyletic), as a close relative to the feathered ornithomimosaurs and troodontids. Given that its dental morphology, particularly long snout, and assumed fin-shaped crest were features unknown in "other" maniraptorans, the researchers erected the new family Irritatoridae within the clade. They recognized Irritators affinities with Spinosaurus, in that they both had similarly shaped and unserrated teeth, but noted that the latter's mandible would not conform with the front of Irritators upper jaw, and that other non-avian dinosaurs like Compsognathus and Ornitholestes also bore no serrations on some or all of their teeth. Some of these claims were questioned in 1996 by Kellner who found that Irritators skull lacked the one autapomorphy (distinguishing feature) diagnosed in maniraptorans at the time, which was having its jugal (cheek) bone forming part of the antorbital fenestra. He also pointed out that since Irritator challengeris holotype lacked the tip of its snout, it would not be possible to know if Spinosauruss dentary could complement it or not. Based on comparisons with Spinosaurus, Kellner resolved Irritator as a spinosaurid and synonymized Irritatoridae with that family. Irritator was then assigned to the Baryonychidae along with Angaturama, Baryonyx, Suchomimus, and Spinosaurus by Oliver W.M. Rauhut in 2003. Thomas Holtz and colleagues in 2004 considered the Baryonychidae synonymous with Spinosauridae, and moved these genera to the latter family. Most later revisions have upheld these classifications. As spinosaurids, Irritator and Angaturama are placed within the superfamily Megalosauroidea, with Spinosauridae being a possible sister taxon to the Megalosauridae.
external nares, or bony nostrils, (labeled e.n.)
In 1998, Sereno and colleagues defined two subfamilies within the Spinosauridae based on craniodental (skull and tooth) characteristics. They were Spinosaurinae, where they placed Spinosaurus and Irritator; and Baryonychinae, to which they assigned Baryonyx, Suchomimus, and Cristatusaurus. Spinosaurines were distinguished by their unserrated, straighter, and more widely spaced teeth, as well as smaller first teeth of the premaxilla. In 2005, Dal Sasso and colleagues assumed Irritators nostrils as being located above the middle of the maxillary tooth row; more posteriorly than in baryonychines, but less so than in Spinosaurus. Sales and Schultz in 2017 found that Irritators nostrils were in fact positioned closer to the front of the jaw, as in Baryonyx and Suchomimus; this more forward nostril placement was typically considered characteristic of baryonychines. Nevertheless, Irritator also bore unserrated teeth, a trait associated with spinosaurines. Sales and Schultz thus noted that the Araripe Basin spinosaurids Irritator and Angaturama might represent intermediate forms between the earlier baryonychines and later spinosaurines, and that further research may eventually render the former a paraphyletic (unnatural) group.
Irritator is further distinguished from Baryonyx, Suchomimus, and Cristatusaurus by having slightly over half as many teeth in the maxilla, and from Spinosaurus due to its comparatively larger and more forwardly positioned nostril openings, which, unlike in Spinosaurus, are also formed by the premaxilla. The narrow sagittal crest, which ends in a knob-like process above the frontals, is another autapomorphy separating Irritator from other spinosaurids. Although Angaturama limais snout is generally narrower than in other spinosaurids, this might be due to damage sustained by the fossil; the holotype appears partly crushed and broken on its lower margin, with some of the preserved teeth having been sectioned off along their length. Therefore, Angaturamas only valid autapomorphy is its sagittal crest, which extends farther forwards on the rostrum and is more exaggerated than in other known spinosaurid skulls.
Topology A: Benson and colleagues (2009)
Topology B: Sales and Schultz (2017)
==古生物学==
===食性与进食===
Head of an Indian gharial, which has similarities to the head of Irritator
In 1996, Martill and colleagues theorized that Irritator challengeri, with its elongated snout and unserrated conical teeth, likely had at least a partly piscivorous (fish-eating) diet. Although much of the holotype's morphology turned out to be greatly different than they thought, later studies supported these observations. Spinosaurids had very narrow and elongated jaws with relatively homogeneous pointed teeth, an arrangement found particularly in animals like the Indian gharial—the most piscivorous extant crocodilian. The long conical teeth, which in spinosaurines did not possess serrated edges, were suitable for grabbing and holding prey. They differed from teeth of other theropods, which seemed geared towards tearing or cutting off seized body parts.
Closeup of reconstructed skull and neck
Irritator shared with crocodilians a stiff secondary palate and reduced antorbital fenestrae. In 2007, a finite-element analysis study by British paleontologist Emily J. Rayfield and colleagues found that these attributes, present in other spinosaurids as well, made the skull more resistant to torsion from prey item loads when feeding. The authors pointed out that in contrast, most theropods lacked secondary palates and had large antorbital fenestrae, exchanging strength for lighter skull builds. The nostrils of Irritator were shifted far back from the snout tip; this, along with the secondary palate, which separated the animal's nasal passages from the inside of its mouth, made respiration possible even if most of the jaw was underwater or held prey. In particular, the sagittal crest of Irritator is an indication for pronounced neck musculature, which would have been necessary to close the jaws quickly against water resistance and withdraw the head rapidly. In 2015, German paleontologist Serjoscha W. Evers and colleagues found evidence for similar adaptations in the African spinosaur Sigilmassasaurus. The neck vertebrae of this genus have a heavily furrowed undersurface. This is consistent with the attachment of powerful neck muscles for use in fishing or rapidly snatching small prey, a trait also observed in extant crocodilians and birds. Sales and Schultz in 2017 found that Irritator and baryonychines might have relied more on their sense of smell for hunting than Spinosaurus did, since they had larger, less retracted nostrils and more room in their skulls for the nasal cavity. Spinosaurus itself probably made heavier use of senses like vision or the mechanoreceptors on the tip of its snout, like those used by crocodilians to sense prey moving in the water.
Skeleton mounted as attacking an anhanguerid pterosaur, National Museum of Rio de Janeiro
Another trait spinosaurs shared with gharials was an enlarged snout tip that wielded a rosette-shaped array of interlocking teeth, adept for impaling and catching fish. Although to a lesser degree than most known spinosaurs, this feature was also present in the Angaturama limai holotype. In 2002, Sues and colleagues pointed out, however, that there would be no reason to assume that the Spinosauridae specialized completely in fishing. They stressed rather that this head morphology indicates a generalistic feeding, particularly on small prey animals. In fact, portions of a young Iguanodon, a terrestrial herbivore, were found inside the fossil skeleton of one Baryonyx. Naish and colleagues in 2004 supported the theory that Irritator hunted both aquatic and terrestrial animals as a generalist within the coastal area and in addition probably searched for carrion. A tooth belonging to Irritator was discovered still inserted into the fossil neck vertebral column of an ornithocheirid pterosaur, likely with a wingspan of abbr=on. This indicates that Irritator ate pterosaurs as well, although it is not known if it actively hunted these animals or simply scavenged the remains. In 2018, Aureliano and colleagues presented a possible scenario for the food web of the Romualdo Formation. The researchers proposed that spinosaurines from the formation may have also preyed on terrestrial and aquatic crocodyliforms, juveniles of their own species, turtles, and small to medium-sized dinosaurs. This would have made spinosaurines apex predators within this particular ecosystem.
===水生习性===
Many spinosaurs likely had semiaquatic habits, as has been shown in studies using techniques like isotope analysis and bone histology. It has been found that they probably took advantage of aquatic prey and environments (usually marginal and coastal habitats) to occupy a distinct ecological niche, therefore avoiding competition with more terrestrial theropods. Spinosaurines appear to have been more adapted for such lifestyles than baryonychines. A 2018 study by British paleontologist Thomas M. S. Arden and colleagues examined the morphology of spinosaurine skull bones for possible aquatic traits. They found that the frontal bones of Irritator, Spinosaurus, and Sigilmassasaurus were similar in being arched, concave on top, and narrowed at the front; features that would have resulted in the eyes being positioned further up on the head than in other theropods. In particular, the broad lower jaw and narrowed frontals of Irritator resulted in the orbits facing at a steep incline towards the midline of the skull, whereas most theropods had laterally facing orbits. These traits would have permitted the animal to see above the waterline when submerged.
In 2018, Aureliano and colleagues conducted an analysis on the Romualdo Formation tibia fragment. CT scanning of the specimen in the University of San Carlos revealed the presence of osteosclerosis (high bone density). This condition had previously only been observed in Spinosaurus aegyptiacus, as a possible way of facilitating submersion in water by making its bones heavier. The presence of this condition on the Brazilian leg fragment showed that compact bones had already evolved in spinosaurines at least 10 million years before the appearance of Spinosaurus in Morocco. According to phylogenetic bracketing—a method used to infer unknown traits in organisms by comparison with their relatives—osteosclerosis therefore might have been the norm in the Spinosaurinae. The significance of these traits was questioned in a later 2018 publication, where Canadian paleobiologist Donald Henderson argued that osteosclerosis would not have changed a theropod's buoyancy to a significant extent.
===Neuroanatomy and senses===
CT scan of the holotype showing endocast and endosseous labyrinth
In 2020, German paleontologist Marco Schade and colleagues analyzed the anatomy of the holotype skull braincase through CT scans, revealing numerous details about behavioral capabilities of Irritator. With the scans, they created a 3D model of the skull and braincase, discovering that Irritator had elongated olfactory tracts and a relatively large floccular recesses (area that pierces through the semicircular canals and connects the brain with the inner ear). The flocculus itself, is an important element in the coordination and control of head and ocular movements during gaze stabilization (visual ability during head movement), by being involved in the coordination of the vestibulo-ocular (VOR) and vestibulo-collic (VCR) reflexes. The flocculus appears to be enlarged in taxa that rely on quick movements of the head body. In addition, the vestibular part of the endosseous labyrinth has a large anterior semicircular canal with a lateral oriented semicircular canal.
Both floccular recesses and semicircular canal suggest that Irritator could coordinate fast head movements and had a downward inclined snout posture, enabling an unobstructed, stereoscopic forward vision, which is important for distance perception and therefore precise snatching movements of the snout. These inferences seem to be an agreement with a piscivore life-style. They also noted that the relatively well-developed cochlear duct may have enable an average hearing frequency of 1950 Hz with a frequency band width of 3196 Hz. However, they considered these ranges as rough estimates and established an overall frequency range of 350–3550 Hz, making Irritator to be placed under bird hearing but above crocodiles.
==古生态学与古生物地理学==
Restoration of the head
Irritator and Angaturama are known from the Romualdo Formation, whose rocks are dated to the Albian stage of the Early Cretaceous Period, about 110 million years ago. During this time, the Southern Atlantic Ocean was opening, forming the series of circum-Atlantic basins of southern Brazil and southwestern Africa, but the northeastern part of Brazil and West Africa were still connected. The Romualdo Formation is part of the Santana Group and, at the time Irritator was described, was thought to be a member of what was then considered the Santana Formation. The Romualdo Formation is a Lagerstätte (a sedimentary deposit that preserves fossils in excellent condition) consisting of limestone concretions embedded in shales, and overlies the Crato Formation. It is well known for preserving fossils three-dimensionally in limestone concretions, including many pterosaur fossils. In addition to muscle fibres of pterosaurs and dinosaurs, fish preserving gills, digestive tracts, and hearts have been found there. The formation is interpreted as a coastal lagoon with irregular freshwater influence that contended with cycles of transgressing and regressing sea levels. The climate of the formation was tropical and largely corresponded to today's Brazilian climate. The regions surrounding the formation were arid to semi-arid, with most of the local flora being xerophytic (adapted to dry environments). Cycadales and the extinct conifer Brachyphyllum were the most widespread plants.
Restoration of Irritator walking down a coastline in the Romualdo Formation environment
This environment was dominated by pterosaurs, including: Anhanguera, Araripedactylus, Araripesaurus, Brasileodactylus, Cearadactylus, Coloborhynchus, Santanadactylus, Tapejara, Thalassodromeus, Tupuxuara, Barbosania, Maaradactylus, Tropeognathus, and Unwindia. The known dinosaur fauna besides Irritator was represented by other theropods like the tyrannosauroid Santanaraptor, the compsognathid Mirischia, an indeterminate unenlagiine dromaeosaurid, and a megaraptoran. The crocodyliforms Araripesuchus and Caririsuchus, as well as the turtles Brasilemys, Cearachelys, Araripemys, Euraxemys, and Santanachelys, are known from the deposits. There were also clam shrimps, sea urchins, ostracods, and molluscs. Various well-preserved fish fossils record the presence of: hybodont sharks, guitarfish, gars, amiids, ophiopsids, oshuniids, pycnodontids, aspidorhynchids, cladocyclids, bonefishes, chanids, mawsoniids and some uncertain forms. According to Naish and colleagues, the lack of herbivorous dinosaurs could mean that the local vegetation was scant and thus incapable of sustaining a large population of them. The abundant carnivorous theropods would have then likely turned to the lush aquatic life as a primary food source. They also hypothesized that following storm events, pterosaur and fish carcasses might have washed up on the shoreline, providing theropods with plenty of carrion. Multiple piscivorous animals were present in the formation, which might in theory have led to high competition. Aureliano and colleagues stated there must have, therefore, been some degree of niche partitioning, where different animals would have fed on prey of varied sizes and locations within the lagoon.
Generalized locations of spinosaurid fossil discoveries from the Albian-Cenomanian, 113 to 93.9 million years ago, marked on a map of that time span
Similarities between the fauna of the Romualdo and Crato Formations to that of Middle Cretaceous Africa suggest that the Araripe Basin was connected to the Tethys Sea, though this link was likely sporadic, because the lack of marine invertebrates indicates the basin had a non-marine depositional setting. Spinosaurids had already achieved a cosmopolitan distribution during the Early Cretaceous. Sereno and colleagues in 1998 suggested that with the opening of the Tethys Sea, spinosaurines would have evolved in the south (Africa, in Gondwana) and baryonychines in the north (Europe, in Laurasia). In following, Machado and Kellner theorized in 2005 that spinosaurines would have then spread to South America from Africa. Sereno and colleagues postulated that divergent evolution between spinosaurines in South America and Africa likely occurred as a consequence of the Atlantic Ocean, whose opening gradually separated the continents and contributed to differences between taxa. A similar scenario was suggested in 2014 by Brazilian paleontologist Manuel A. Medeiros and colleagues for the fauna of the Alcântara Formation, where Oxalaia has been found. But the paleobiogeography of spinosaurids remains highly theoretical and uncertain, with discoveries in Asia and Australia indicating that it may have been complex.
=== Taphonomy ===
The taphonomy (changes between death and fossilization) of the Irritator challengeri holotype specimen has been discussed by some researchers. The skull was found lying on its side. Preceding fossilization, several bones from the back of the braincase, as well as the dentary, splenial, coronoid, and right angular bones from the lower jaw, were lost. Other bones, mostly from the skull rear, had become disarticulated and displaced towards alternate regions of the head before burial. Naish and colleagues in 2004 asserted that the Romualdo Formation dinosaur fauna is represented by animals that died near shorelines or rivers before being carried out to sea, where their floating remains were eventually fossilized. In 2018, Aureliano and colleagues argued against this scenario, stating that the Irritator challengeri holotype's mandible was preserved in articulation with the rest of the skull, whereas it would have likely detached had the carcass been floating at sea. They also noted that the corpse would have quickly sunk due to the osteosclerosis of the skeleton. The researchers, therefore, concluded that fossils from the Santana Group represent organisms that were buried in their natural habitat, instead of having been deposited allochthonously (other than at their present position).