World prehistoric big ocean

Stupendemys is a genus of giant, extinct freshwater turtles that lived 9–5 million years ago in South America. They were the largest freshwater turtles in history, reaching 2.3–3.3 meters in length, weighing up to 2 tons, and possessing powerful jaws and horn-like protrusions on the carapace of males. They inhabited tropical swamp forests and fed on a diverse diet, including fish, insects, and even other reptiles. Main characteristics: Dimensions: Carapace up to 2.3–3.3 m in length, up to 1.9 m in width, weight up to 2 tons. Appearance: Massive head, powerful webbed paws, long tail; males had horns on their shell. Habitat: Lowland tropical forests, large rivers, swamps of South America (Brazil, Venezuela, Colombia). Diet: Omnivorous, ate fish, insects, vegetation, small animals, and other reptiles. Lifestyle: Sexual dimorphism is suspected (presence of horns in males), males probably used horns for fighting.

Messapicetus is a fossil genus of toothed whales that lived during the Miocene (approximately 7–11 million years ago). It is important for studying the evolution of whales from land-dwelling ancestors to modern toothed whales. Messapicetus was a relatively small whale (up to 5 m) with an elongated, narrow jaw with conical teeth adapted for catching fish and squid. It may have already used echolocation, making it a key link in its evolution. Main characteristics of Messapicetus: Epoch: Miocene (approximately 13.7–11.6 million years ago). Size: Reached 5 meters in length. Diet: Hunted fish and squid, as evidenced by its teeth. Evolutionary significance: Bridge between primitive whales (archaeocetes) and modern toothed whales (odontocetes). Characteristics: Had a long, narrow snout and conical teeth. The skull structure suggests possible echolocation. Place of discovery: The remains have been found in Peru, as well as in other parts of South America and Europe. Species: The best known species is Messapicetus gregarius.

An extinct species of giant Pacific salmon, the largest in the history of the family, reaching 2.7 m in length and 200 kg in weight, known for its huge, horizontally protruding jaw teeth, similar to tusks, and feeding on plankton with the help of gill rakers, which lived 11-5 million years ago.

It had the largest teeth of any whale, and possibly of any vertebrate (excluding proboscidean mammals). The upper teeth reach 36 cm in length and 12 cm in diameter. The estimated total body length ranges from 13.5 m (based on the proportions of a modern sperm whale) to 17.5 m (based on the proportions of Zygophyseter varolai).[6] The age of the skeleton is estimated at 9.9–8.9 million years.[3]

Teeth grew on both the lower and upper jaws. Melville's leviathan likely hunted marine mammals, including other whales. It was also capable of feeding on certain species of large fish.[7][8] However, there are no markings on the bones of the supposed victims. This may be because marine mammals conserve their teeth when attacking large prey.

The Melville's leviathan had a massive, short head, with space for a spermaceti organ. This organ is thought to help modern sperm whales feed while diving deep. However, the Melville's leviathan likely hunted its prey near the surface, so it seems likely that this organ would have served a different function. Possible functions of the Melville's leviathan's spermaceti organ include echolocation (due to its presence in more primitive whales), acoustic screens (with the spermaceti organ acting as a resonance chamber), or aggressive ramming, possibly used when attacking prey.

If male sharks were larger than females, as in Megalodon (where females are larger), this would have altered the dynamics of mating, hunting, and social structure: males would have dominated competition for females and could hunt larger prey, but females would have had a harder time carrying offspring, which could have affected their survival and overall population size, shifting the balance toward male dominance. Consequences of the inversion of sexual size dimorphism (males are larger than females): Competition and mating: Male Dominance: Large males would outcompete smaller males to gain access to females. Increased competition for females: This could lead to more aggressive "chasing" and biting (like in blue sharks, where males bite females during courtship). Hunting and prey: Larger prey: Males would have been able to hunt larger prey than they currently do, which would have given them a nutritional advantage. Change in female role: Females, being smaller, would remain mainly on smaller prey, which could make them more vulnerable. Reproduction and survival: Problems with bearing: If the female is carrying young, her smaller size could be a limiting factor for the development of the fetus. The males have become twice as large, and there are fewer females, because some of them die from aggressive courtship of a partner before they can bear offspring, because they were immediately crushed or died from huge scars from a bite by a male to secure a female.