海巨龍屬

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奥勒德阿卜杜恩盆地（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占據顶级掠食者生態位的物種。嚴重磨損的海巨龙牙齿和發現於正模标本附近的、酸蝕過的化石表明，海巨龙可能會捕食小型沧龙科、蛇颈龙、大型鱼类和海龟。

語源學
海巨龙的属名Thalassotitan組合自古希腊語“θìλασσα”（thálassa，意為“海”）和“τιτìν”（tītā́n，“巨人”），指代海巨龙的巨大体型。種加詞atrox則來自拉丁語，意為“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內搏鬥產生的大量咬痕。

描述

海巨龙是最大的沧龙之一，其头骨可达1.3米，身长 可達9-10米。

頭骨

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。

Neurovascular foramina line this margin, increasing in size as they progress towards the back of the skull. The texture of the maxilla's surface is rough, which is especially apparent in larger individual, caused by a network of veined grooves to house blood vessels. The external nares extend from and to above the fourth and twelfth maxillary teeth. The jugal bone, which is located just below the eye, is broad and robust. The frontal bone is short and broad, shaped almost like an isosceles triangle, with large neurovascular foramina at the center. The pineal foramen, which contains the parietal eye, is small and long. The supratemporal fenestrae, large openings between the eyes and the back end of the skull, take up nearly a quarter of the entire skull length and are somewhat triangular. The dentary, the tooth-bearing bone of the lower jaw, is short, wide, robust, and curved concave towards the upper jaws. Many bones of the upper jaw are tightly sutured together; its two tooth-bearing bones the premaxilla and maxilla were connected through interlocking joints containing an unusual series of flanges and grooves while an interdigitating set of tongue-and-groove joints secure the maxilla and prefrontal bone.

牙齒

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.

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.

顱後骨骼
The postcranial skeleton is not fully known, only fossils representing a little more than the front half of the body have been found.

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.

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.

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.

分類

Thalassotitan is a member of the Prognathodontini tribe of the Mosasaurinae subfamily, with other members including Prognathodon and Gnathomortis. Morphologically, it is most similar to the giant mosasaurs P. currii and P. saturator, and a phylogenetic analysis by Longrich et al. (2022) recovered Thalassotitan in a clade between the two. This creates an unnatural paraphyletic relationship that reflects a wider issue with the genus Prognathodon as a whole. Several studies over the past decade found that Prognathodon is in general not monophyletic and in need of revision. Longrich et al. (2022) suggested such a revision may include an expansion of the Thalassotitan genus to include P. currii and P. saturator. However, due to a high degree of convergent evolution in the relationship-determining traits among many mosasaurs (especially among prognathodontines), phylogenetic results between each study are seldom consistent, mystifying exactly which species must be revised to stabilize the Prognathodontini. For example, some studies recovered P. currii and P. saturator as phylogenetically unrelated species with either falling outside a monophyletic Prognathodon, while other studies yield variable placements for the type species P. solvayi as either outside a monophyletic P. currii-P. saturator clade in support of Longrich et al. (2022) or within it, which would in theory invalidate Thalassotitan as a junior synonym under the principle of priority.

The following cladogram is modified from Longrich et al. (2022).

{{clade| style=font-size:85%;line-height:85%
|label1=Mosasaurinae
|1={{clade
 |1=Kourisodon
 |2={{clade
    |1=Clidastes
    |2=
    }}
}}}}

古環境學
 
The phosphate deposits of Morocco have revealed an extremely diverse environment of late maastrichtian age. The oceans of the area were full of an abundance of fish, from bony fish like Enchodus and Stratodus to cartilaginous fish like Cretalamna, Squalicorax and Rhombodus. There was also an abundance of marine reptiles, most notably the mosasaurs, with more than 10 genera alone known from this single site. This possibly suggests that niche partitioning took place here, in which predators take on different niches to avoid competition with one another (for example, mosasaurs like Carniodens and Globidens had blunt teeth for crushing shellfish while Thalassotitan and Mosasaurus hunted much larger food). Other marine reptiles include the elasmosaurid plesiosaur Zarafasaura, the sea turtle Alienochelys and the gavialoid crocodilian Ocepesuchus .

It seems that Thalassotitan was an apex predator in its ecosystem, with evidence being digestive damage found on some of the fossils in the nearby vicinity including those of plesiosaurs, turtles, and large fish. In the skies flew multiple species of pterosaurs including the azhdarchid Phosphatodraco, the nyctosauromorph Alcione and Simurghia, the nyctosaurid Barbaridactylus, and the possible pteranodontid Tethydraco. On land three species of dinosaurs are known, these being the abelisaur Chenanisaurus, the small lambeosaurine hadrosaur Ajnabia and a so far unnamed titanosaur. Thalassotitan lived alongside other giant mosasaurs like Prognathodon, Mosasaurus and Gavialimimus, as well as smaller mosasaurs like Xenodens, Halisaurus and Pluridens.''

參考文獻