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海巨龙属
来自维基百科，自由的百科全书
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海巨龙属（学名：Thalassotitan，意为“海洋巨人”）是一属已灭绝的大型沧龙，生活于约6600万年前晚白垩纪马斯特里赫特期的摩洛哥。该属下有且仅有残暴海巨龙（T. atrox）一个物种，该物种描述自一组发现于奥勒德阿卜杜恩盆地（Ouled Abdoun Basin）的化石。海巨龙属于倾齿龙族（学名：Prognathodontini），该类群包括倾齿龙等其他沧龙。
该属的发现表明沧龙类在白垩纪晚期已经演化出了占据顶级掠食者生态位的物种。严重磨损的海巨龙牙齿和发现于正模标本附近的、酸蚀过的化石表明，海巨龙可能会捕食小型沧龙科、蛇颈龙、大型鱼类和海龟。
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语源学
海巨龙的属名Thalassotitan组合自古希腊语“θìλασσα”（thálassa，意为“海”）和“τιτìν”（tītā́n，“巨人”），指代海巨龙的巨大体型。种加词atrox则来自拉丁语，意为“残忍的”或“无情的”，指代该物种的顶级捕食者地位和化石上因种内搏斗产生的大量咬痕。[1]
描述
海巨龙是最大的沧龙之一，其头骨可达1.3米，身长 可达9-10米。[1]
像所有的倾齿龙一样，海巨龙的头骨又钝又结实，前颌骨是承载头骨顶端的骨头，从侧面看非常短，但从背面看则宽而凸。前颌骨的身体包含许多被称为神经血管孔的凹坑，这些凹坑被认为容纳了对触摸非常敏感的触觉神经。内腭杆是前颌骨的一个很长的延伸部分，一直延伸到额骨，它在上颌骨(主要承载牙齿的上颌骨)和外鼻孔(容纳鼻孔的开口)之间穿过时很宽，但当它与额骨接触时变窄成一个细长的杆。在上颌骨之间，内鼻骨形成一个明显的低而短的龙骨。上颌骨短而结实，而且很深。它的表面是平的，除了在牙齿上方有一个低而宽的脊衬。
神经血管孔沿此边缘排列，向颅后方延伸时逐渐增大。上颌骨表面质地粗糙，在较大个体中尤为明显，这是由于血管沟网状结构为血管提供容纳空间所致。外鼻孔从第四至第十二上颌齿延伸至其上方。颧骨位于眼部正下方，呈宽阔而坚实的形态。额骨短而宽，近似等腰三角形，中央具大型神经血管孔。松果孔（内含颅顶眼）细长而狭窄。颞上窗——即双眼与颅后部间的巨大孔隙——占据颅骨总长近四分之一，呈近似三角形。齿骨作为下颌牙齿的附着处，短而宽厚，呈向上颌凹陷的弯曲形态。上颌多数骨片紧密缝合：两块齿骨——前上颌骨与上颌骨——通过带有特殊楔槽结构的互锁关节连接；而上颌骨与前额骨则由相互咬合的榫槽关节固定。[1]
Thalassotitan teeth are roughly conical in shape, lightly curved, large in size, and robust in build. They are most similar to the teeth of P. saturator except in being slightly shorter and stockier. Tooth crowns are slightly swollen around its base next to the root, but they do not form a round circumference. The surfaces of the crown are generally smooth but may sometimes have faint ridges depending on individual or ontogenetic variation. The enamel at the tip contain veinous ridges and coarse bumps. Cutting edges are well-developed and finely serrated. Each tooth has two cutting edges, but their positions differ depending on the tooth's position in the jaw. Towards the front of the jaw, the front-facing cutting edges are more pronounced than the diminished back-facing edges. In the middle and near the end of the jaw, both edges are of equal development and located diametrically opposite to each other. At the end of the jaw, the back-facing edges become more pronounced. The tooth roots are massive and barrel-shaped. Deep pits occur within the roots, from which new replacement teeth are formed.[1]
Like all mosasaurs, Thalassotitan had four types of teeth, corresponding to the jaw bones they are located on. On the upper jaw were the premaxillary teeth, maxillary teeth, and pterygoid teeth (located separate from the main jawline near the rear of the skull); while on the lower jaw only the dentary teeth were present. Thalassotitan had in each jaw row from front to back: two premaxillary teeth, twelve maxillary teeth, at least six pterygoid teeth (the pterygoids were not fully preserved), and fourteen dentary teeth. The dentary teeth are generally flatter by the side than the maxillary teeth. Heterodonty is present, meaning that tooth shape changes down the jawline. The first four or five teeth are tall, narrow, and slightly curved, which become stockier, erect, and more robust around the middle of the jawline, then become shorter (as broad as they are tall), hooked, and flatter by the side. The pterygoid teeth are strongly hooked but are also large and robust, nearly approaching the size of the teeth on the main jawlines.[1]
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The postcranial skeleton is not fully known, only fossils representing a little more than the front half of the body have been found.[1]
The general shape of the vertebrae are typical for mosasaurines. They are procoelous, meaning that the front side is deeply cupped concavely and the back side is bulged convexly. The cervical (neck) vertebrae are slightly wider than long. Its atlas holds rectangular or triangular neural arches; another single tall neural arch is also present at the top of the vertebra. The articular surfaces, which atach to the cartilage that connect vertebrae together, is initially heart-shaped but becomes rounded at the rearmost cervicals. The dorsal (back) vertebrae are slightly longer than wide with tall neural arches, rounded articular surfaces, and large rectangular transverse processes. The ribs are short and robust.[1]
The pectoral girdle is robust and most similar with that in P. overtoni and Mosasaurus conodon, albeit more square-shaped than the latter. The two bones making up the girdle, the scapula and coracoid, are similar in sizes. They loosely contact with each other, but their contact point is nevertheless wider than the glenoid fossa. The scapula is shaped like a square, being as long as it is wide. It lacks a defined scapular neck but expands from front to back, forming a fan-like convex blade. The coracoid is also somewhat squarish and lacks a well-defined neck. Its margins are weakly concave in the front and back but very convex at the bottom.[1]
The forelimbs formed long paddles that resembled mosasaurin mosasaurs like Mosasaurus and Plotosaurus but more primitive in possessing longer but fewer phalanges. The humerus is very stocky and resemble that in P. overtoni except in the expansion of the glenoid condyle beyond the postglenoid process. The radius is unusually shaped for a mosasaur. It is as large as the humerus and much larger than the ulna and takes on a crescent-like or subrectangular form, unlike smaller hourglass-shaped radii in typical mosasaurs.[1]
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分类
残暴海巨龙与饱和倾齿龙（左）和柯瑞氏倾齿龙（右）关系最近，三者可能构成一个单系群
海巨龙是沧龙亚科下倾齿龙族的成员，该族还包括倾齿龙属和死颌龙属等近亲。从形态学上看，海巨龙与柯瑞氏倾齿龙和饱和倾齿龙最为相似，Longrich等人（2022）的系统发育分析将海巨龙至于这两者之间，三者形成一个单系群。这种处理使得倾齿龙属成为了不自然的并系群，反映出倾齿龙属整体存在的广泛问题。过去十年的多项研究表明，倾齿龙属总体上并非单系群，亟需重新修订。Longrich等人（2022）建议修订方案可将海巨龙属范围扩大，将原先属于倾齿龙属的柯瑞氏种和饱和种归入海巨龙属。[1] 然而，由于许多沧龙（尤其是倾齿龙类）在关系决定性状上存在高度趋同进化，各研究间的系统发育结果鲜少一致，这使得究竟应修订哪些物种才能稳定倾齿龙族的分类地位成为谜团。例如，部分研究将柯瑞氏倾齿龙与饱和倾齿龙判定为系统发育无关的物种，二者均位于单系的倾齿龙属之外；而另一些研究则对模式种沙维氏倾齿龙的系统位置存在分歧——该物种可能在柯瑞氏倾齿龙和饱和倾齿龙构成的单系群之外（基于Longrich等人于2022年的研究），也可能在该单系群内部，如果后者成立，这在理论上将根据优先权原则使海巨龙属成为一个无效的次异名。[1]
下面的发育树基于Longrich等人于2022年的研究。[1]
| 沧龙亚科 Mosasaurinae |
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古环境学
摩洛哥的磷酸盐矿床揭示了晚马斯特里赫特期极为多样化的环境。[1][2]该海域鱼类资源极其丰富，从硬骨鱼类如矛齿鱼和层齿鱼，到软骨鱼类如白垩鼠鲨、鸦鲨和Rhombodus（一种鲼），应有尽有。[1]该地区还存在大量海洋爬行动物，其中最引人注目的是沧龙类，仅此单一地点就发现了超过10个属的沧龙化石。[3]这可能表明此处发生了生态位分化，不同的捕食者占据不同生态位以避免相互竞争，例如像龙骨齿龙和球齿龙这样牙齿较钝的沧龙会以有壳的动物为食，而海巨龙和沧龙则会狩猎更大的猎物。[1][4]当地其他的海洋爬行动物还包括薄板龙科的窈颈龙、海龟Alienochelys和长吻鳄总科的Ocepesuchus。[5][6]
基于附近一些蛇颈龙、龟类和大型鱼类化石上的消化性损伤，海巨龙似乎在其生态系统中是顶级掠食者。[1]该地区的天空中飞翔着诸多种类的翼龙，包括神龙翼龙类的磷矿翼龙、夜翼龙类的翠鸟翼龙、神鸟翼龙和巴巴里翼龙、以及可能属于无齿翼龙类的特提斯翼龙。[7][8]陆地上已知存在有少数几种恐龙，阿贝力龙类的彻纳恩龙、小型赖氏龙亚科异客龙和咮龙、以及一种暂未命名的泰坦巨龙类。[9][10]海巨龙也与其他巨型沧龙（如倾齿龙、沧龙、匕齿沧龙和似长吻鳄龙）和小型沧龙（如异齿沧龙、大洋龙和多齿龙）。[11][1]
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参考文献
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