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海巨龍屬
来自维基百科，自由的百科全书
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海巨龍屬（學名：Thalassotitan，意為「海洋巨人」）是一屬已滅絕的大型滄龍，生活於約6600萬年前晚白堊紀馬斯垂克期的摩洛哥。該屬下有且僅有殘暴海巨龍（T. atrox）一個物種，該物種描述自一組發現於奧勒德阿卜杜恩盆地（Ouled Abdoun Basin）的化石。海巨龍屬於傾齒龍族（學名：Prognathodontini），該類群包括傾齒龍等其他滄龍。
該屬的發現表明滄龍類在白堊紀晚期已經演化出了佔據頂級掠食者生態位的物種。嚴重磨損的海巨龍牙齒和發現於正模標本附近的、酸蝕過的化石表明，海巨龍可能會捕食小型滄龍科、蛇頸龍、大型魚類和海龜。
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語源學
海巨龍的屬名Thalassotitan組合自古希臘語「θìλασσα」（thálassa，意為「海」）和「τιτìν」（tītā́n，「巨人」），指代海巨龍的巨大體型。種加詞atrox則來自拉丁語，意為「殘忍的」或「無情的」，指代該物種的頂級捕食者地位和化石上因種內搏鬥產生的大量咬痕。[1]
描述
海巨龍是最大的滄龍之一，其頭骨可達1.3米，身長 可達9-10米。[1]
像所有的傾齒龍一樣，海巨龍的頭骨又鈍又結實，前頜骨是承載頭骨頂端的骨頭，從側面看非常短，但從背面看則寬而凸。前頜骨的身體包含許多被稱為神經血管孔的凹坑，這些凹坑被認為容納了對觸摸非常敏感的觸覺神經。內腭杆是前頜骨的一個很長的延伸部分，一直延伸到額骨，它在上頜骨(主要承載牙齒的上頜骨)和外鼻孔(容納鼻孔的開口)之間穿過時很寬，但當它與額骨接觸時變窄成一個細長的杆。在上頜骨之間，內鼻骨形成一個明顯的低而短的龍骨。上頜骨短而結實，而且很深。它的表面是平的，除了在牙齒上方有一個低而寬的脊襯。
神經血管孔沿此邊緣排列，向顱後方延伸時逐漸增大。上頜骨表面質地粗糙，在較大個體中尤為明顯，這是由於血管溝網狀結構為血管提供容納空間所致。外鼻孔從第四至第十二上頜齒延伸至其上方。顴骨位於眼部正下方，呈寬闊而堅實的形態。額骨短而寬，近似等腰三角形，中央具大型神經血管孔。松果孔（內含顱頂眼）細長而狹窄。顳上窗——即雙眼與顱後部間的巨大孔隙——佔據顱骨總長近四分之一，呈近似三角形。齒骨作為下頜牙齒的附着處，短而寬厚，呈向上頜凹陷的彎曲形態。上頜多數骨片緊密縫合：兩塊齒骨——前上頜骨與上頜骨——通過帶有特殊楔槽結構的互鎖關節連接；而上頜骨與前額骨則由相互咬合的榫槽關節固定。[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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分類
殘暴海巨龍與飽和傾齒龍（左）和柯瑞氏傾齒龍（右）關係最近，三者可能構成一個單系群
海巨龍是滄龍亞科下傾齒龍族的成員，該族還包括傾齒龍屬和死頜龍屬等近親。從形態學上看，海巨龍與柯瑞氏傾齒龍和飽和傾齒龍最為相似，Longrich等人（2022）的系統發育分析將海巨龍至於這兩者之間，三者形成一個單系群。這種處理使得傾齒龍屬成為了不自然的並系群，反映出傾齒龍屬整體存在的廣泛問題。過去十年的多項研究表明，傾齒龍屬總體上並非單系群，亟需重新修訂。Longrich等人（2022）建議修訂方案可將海巨龍屬範圍擴大，將原先屬於傾齒龍屬的柯瑞氏種和飽和種歸入海巨龍屬。[1] 然而，由於許多滄龍（尤其是傾齒龍類）在關係決定性狀上存在高度趨同進化，各研究間的系統發育結果鮮少一致，這使得究竟應修訂哪些物種才能穩定傾齒龍族的分類地位成為謎團。例如，部分研究將柯瑞氏傾齒龍與飽和傾齒龍判定為系統發育無關的物種，二者均位於單系的傾齒龍屬之外；而另一些研究則對模式種沙維氏傾齒龍的系統位置存在分歧——該物種可能在柯瑞氏傾齒龍和飽和傾齒龍構成的單系群之外（基於Longrich等人於2022年的研究），也可能在該單系群內部，如果後者成立，這在理論上將根據優先權原則使海巨龍屬成為一個無效的次異名。[1]
下面的發育樹基於Longrich等人於2022年的研究。[1]
| 滄龍亞科 Mosasaurinae |
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古環境學
摩洛哥的磷酸鹽礦床揭示了晚馬斯特里赫特期極為多樣化的環境。[1][2]該海域魚類資源極其豐富，從硬骨魚類如矛齒魚和層齒魚，到軟骨魚類如白堊鼠鯊、鴉鯊和Rhombodus（一種鱝），應有盡有。[1]該地區還存在大量海洋爬行動物，其中最引人注目的是滄龍類，僅此單一地點就發現了超過10個屬的滄龍化石。[3]這可能表明此處發生了生態位分化，不同的捕食者佔據不同生態位以避免相互競爭，例如像龍骨齒龍和球齒龍這樣牙齒較鈍的滄龍會以有殼的動物為食，而海巨龍和滄龍則會狩獵更大的獵物。[1][4]當地其他的海洋爬行動物還包括薄板龍科的窈頸龍、海龜Alienochelys和長吻鱷總科的Ocepesuchus。[5][6]
基於附近一些蛇頸龍、龜類和大型魚類化石上的消化性損傷，海巨龍似乎在其生態系統中是頂級掠食者。[1]該地區的天空中飛翔着諸多種類的翼龍，包括神龍翼龍類的磷礦翼龍、夜翼龍類的翠鳥翼龍、神鳥翼龍和巴巴里翼龍、以及可能屬於無齒翼龍類的特提斯翼龍。[7][8]陸地上已知存在有少數幾種恐龍，阿貝力龍類的徹納恩龍、小型賴氏龍亞科異客龍和咮龍、以及一種暫未命名的泰坦巨龍類。[9][10]海巨龍也與其他巨型滄龍（如傾齒龍、滄龍、匕齒滄龍和似長吻鱷龍）和小型滄龍（如異齒滄龍、大洋龍和多齒龍）。[11][1]
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參考文獻
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