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Description
Originating in the Late Jurassic, the macro-predatory carcharodontosaurs came to be the top predators of the much of the world during the Cretaceous. By the Late Cretaceous, however, they had largely been replaced by tyrannosaurs in the Northern Hemisphere while abelisaurids and neovenatorids competed with them for domination of the south; carcharodontosaur success seems largely dependent on the presence of their preferred prey, giant sauropods. Perhaps this explains why their most successful Cenozoic lineages were to be found in South America and Africa, both of which have (or had) a rich array of sauropods. Though sauropods were present in Australia and Asia during much of the Cenozoic, carcharodontosaurs appear to have lost out to other predators on these continents by the Early Eocene. Their status on ancient Antarctica is unknown.

The best known and most magnificent lineage were the South American steroidosaurids. As their name suggests, these titans resembled a carnosaur on steroids! Characteristics of the group include massive shark-like heavily serrated teeth that are reduced in number, greatly expanded post-orbital region of the skull and lower jaw to house enormous jaw muscles, lacrimal bones united into a low midline crest, a very wide gape, an extremely muscular neck, tiny forelimbs, enlarged vertebral spines often forming a ridge over the hips and tail, relatively short and robust legs with small feet, and a long tail. Capable of growing over 15 meters in length, these were without a doubt the heaviest terrestrial carnivores that have ever lived, though they are exceeded by some spinosaurs in length. Appearing abruptly in the Late Eocene, these animals appear to have coevolved with the numerous South American sauropods free from other influences due to the continent's isolation. It is thought that millions of years of harassment by the steroidosaurids is what drove the evolution of the radical armor of many of South America's sauropods, which seem like overkill in modern times. Their feeding method is quite clear thanks to the scrape marks frequently found on sauropod bones. They were ambush predators that trailed sauropod herds (as evidenced by numerous trackways), rushing out from cover with a sudden burst of speed to inflict a large bite on the hind limbs or flanks and then tearing off a massive chunk of flesh using their serrated teeth and powerful necks; like an overgrown coockiecutter shark. The markings on the sauropod bones typically show signs of healing, indicating that the predators only fed as needed. Steroidosaurids are known from seven sights across South America, but only two genera are well known. The largest and longest lived genus, Steroidosaurus, is known from complete skeletons while most others are known from just teeth and craniums. A Miocene genus known as Carcharotitan is known from decent skull material and shows that it had armor plating over much of its face, including scute like plates and callouses in front of its eyes, likely to defend itself from the various spiny defenses of certain sauropods. Steroidosaurids were always uncommon components of the landscape, but during the Mid Pliocene they went into a sudden and drastic decline and were wiped by the Late Pliocene. They appear to have been one of the first victims of the American Faunal Exchange, though it's likely no other predator could touch them, their sauropod prey was vulnerable to the new competition and shortly after sauropod numbers crashed, the great steroidosaurs were no more.

The history of Africa's carcharodontosaurs is imperfectly known. A unique group of modest sized (to 10 m) species with large but lightly constructed skulls and long limbs appears to have been present, adapted at stalking long distances across the newly formed savannas in search of smaller prey. Only a single genus, Neocarcharia, has been named, though its holotype may actually be actually be a chimaera. It is thought drying conditions and an increasingly diverse array of competing abelisaurids drove them to extinction by the Early Miocene.

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Sorry about all that text. This is the post-Oligocene extinct group that won the vote. When I originally started planning things, the African varieties were going to be extant and known as Savanna-Stalkers, but I decided to scrap that idea. I was especially glad after the announcement of the undescribed giant abelisaur, with beasts like that the around it's entirely possible carcharodontosaurs were already extinct in Africa by the Late Cretaceous!

Introduction to the Saurocene

Made in Sketchbook Express

Description
Originating in the Late Jurassic, the macro-predatory carcharodontosaurs came to be the top predators of the much of the world during the Cretaceous. By the Late Cretaceous, however, they had largely been replaced by tyrannosaurs in the Northern Hemisphere while abelisaurids and neovenatorids competed with them for domination of the south; carcharodontosaur success seems largely dependent on the presence of their preferred prey, giant sauropods. Perhaps this explains why their most successful Cenozoic lineages were to be found in South America and Africa, both of which have (or had) a rich array of sauropods. Though sauropods were present in Australia and Asia during much of the Cenozoic, carcharodontosaurs appear to have lost out to other predators on these continents by the Early Eocene. Their status on ancient Antarctica is unknown.

The best known and most magnificent lineage were the South American steroidosaurids. As their name suggests, these titans resembled a carnosaur on steroids! Characteristics of the group include massive shark-like heavily serrated teeth that are reduced in number, greatly expanded post-orbital region of the skull and lower jaw to house enormous jaw muscles, lacrimal bones united into a low midline crest, a very wide gape, an extremely muscular neck, tiny forelimbs, enlarged vertebral spines often forming a ridge over the hips and tail, relatively short and robust legs with small feet, and a long tail. Capable of growing over 15 meters in length, these were without a doubt the heaviest terrestrial carnivores that have ever lived, though they are exceeded by some spinosaurs in length. Appearing abruptly in the Late Eocene, these animals appear to have coevolved with the numerous South American sauropods free from other influences due to the continent's isolation. It is thought that millions of years of harassment by the steroidosaurids is what drove the evolution of the radical armor of many of South America's sauropods, which seem like overkill in modern times. Their feeding method is quite clear thanks to the scrape marks frequently found on sauropod bones. They were ambush predators that trailed sauropod herds (as evidenced by numerous trackways), rushing out from cover with a sudden burst of speed to inflict a large bite on the hind limbs or flanks and then tearing off a massive chunk of flesh using their serrated teeth and powerful necks; like an overgrown coockiecutter shark. The markings on the sauropod bones typically show signs of healing, indicating that the predators only fed as needed. Steroidosaurids are known from seven sights across South America, but only two genera are well known. The largest and longest lived genus, Steroidosaurus, is known from complete skeletons while most others are known from just teeth and craniums. A Miocene genus known as Carcharotitan is known from decent skull material and shows that it had armor plating over much of its face, including scute like plates and callouses in front of its eyes, likely to defend itself from the various spiny defenses of certain sauropods. Steroidosaurids were always uncommon components of the landscape, but during the Mid Pliocene they went into a sudden and drastic decline and were wiped by the Late Pliocene. They appear to have been one of the first victims of the American Faunal Exchange, though it's likely no other predator could touch them, their sauropod prey was vulnerable to the new competition and shortly after sauropod numbers crashed, the great steroidosaurs were no more.

The history of Africa's carcharodontosaurs is imperfectly known. A unique group of modest sized (to 10 m) species with large but lightly constructed skulls and long limbs appears to have been present, adapted at stalking long distances across the newly formed savannas in search of smaller prey. Only a single genus, Neocarcharia, has been named, though its holotype may actually be actually be a chimaera. It is thought drying conditions and an increasingly diverse array of competing abelisaurids drove them to extinction by the Early Miocene.

...................................................................................................................................................................................................

Sorry about all that text. This is the post-Oligocene extinct group that won the vote. When I originally started planning things, the African varieties were going to be extant and known as Savanna-Stalkers, but I decided to scrap that idea. I was especially glad after the announcement of the undescribed giant abelisaur, with beasts like that the around it's entirely possible carcharodontosaurs were already extinct in Africa by the Late Cretaceous!

Introduction to the Saurocene

Made in Sketchbook Express