The First Giants
The giants of the Thanetian
Location: The Forests of the West Antarctic Archipelago
When: Paleocene, Thanetian, 58.2 Million years ago
Eodespotoaves Antipodensis, one of the largest herbivores of the Paleocene
Thanetian Earth
It is three months into the long dark, and while many smaller animals have taken to hibernating, the largest terrestrial animal of the Paleocene, Eodespotoaves Antipodensis (Dawn despot bird of Antarctica), lumbers through the darkness letting out deep bellows from time to time. With polar night soon to give way to twilight, this Jake is lekking to attract a female. Unlike their South American cousins, E. Wilhelmi, which live in flocks of dozens of individuals this polar species lives in fairly small flocks of just a single Tom and his harem. This behavior prevents the animals from overburdening their environment during the lean months of the Antarctic Winter, but it also makes finding a mate more difficult. Instead of the mass lekking of male E. Wilhelmi, the lone male E. Antipodensis must call out into the darkness and hope he hears the response of a female.
He can smell them, the scent of urine in the area is strong and it tells the Jake that, multiple females are ready for breeding. However, the scent of urine from an old Tom hangs around the area like a foreboding miasma. The young Jake could attempt to find Jennies who have recently left their family groups, but such a task would be difficult, as Jennies typically approach existing flocks rather than untested males. Instead of trying to find wandering Jennies, this Jake seeks to unseat a Tom and take his hens. So he will ignore the warning signs and continue to call out into the darkness, for hours, until he is met by a reply… though not of a female.
The big Tom of this territory has decided to answer the young male’s cries with a challenge, announcing his approach long before the two animals can smell or see one another. When the two finally meet, the big Tom is followed by his flock of three hens and one newly arrived Jenny. He is older and larger than the young Jake and has not had to seriously defend his territory or his flock in some time. Lurching forward, he fans his arms out and shouts at the invader, the feathers on his neck bristling with rage as he attempts to intimidate the Jake as he has done to countless would-be rivals.
Yet this time is different. After each of the old Tom’s hisses, the Jake responds with his own, fashing his long claws and strutting like a peacock. Unlike the dull spotted grey of the old Tom’s winter coat, the young male glimmers in the starlight with ultraviolet colors no mammal can see. They make him shine in the Antarctic darkness like a beacon in the night, but the Jake is far too large for any of the archipelago’s predators to seriously consider attempting to bring him down so he proudly and aggressively flashes his feathers in his dance.
He will not be intimidated.
And so it is that, cautiously, the old male begins to advance on his young rival, letting out a low hiss accompanied by a series of barking sounds and the occasional pop and whistle as the pair close in on each other. At first, it seems as if they are slowly sizing each other up, but once they have reached a small enough distance apart from each other, the powerful animals break into a sprint. Unlike their ancestors, all four of their toes come to rest upon the ground as their column-like legs slam them into the snowy earth. Soon the 5.2 meter long and 670 kilo Tom slams into Jake chest first, barreling the overconfident young male over and knocking him to the ground. At 590 kilos, the Jake could dominate most other animals in the Polar forests, but against the old Tom, he is still a size class too small. His quick defeat has prevented the fight from escalating to slaps between the two which likely would have resulted in at least one death, possibly 2, but splayed out on the forest floor, he knows he’s beaten. With this turn of events, the young Jake’s pride is wounded, but that is about all that is.
And so, as the Jake slinks off and the Tom triumphantly struts back to his harem, the polar forest begins to grow quiet once again, only the whistling of the wind breaking the silence.
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The much better known, but slightly smaller, E. Wilhelmi.
Eodespotoaves is the oldest true member of Serpopardinae, Eonychus being part of a grade leading to the subfamily. The longest, tallest, and arguably heaviest terrestrial animal of the Paleocene, (comparable in weight to the Pantodont Barylambda and the Sebecid Basilosuchus though the semi-aquatic boid Titanoboa would have weighed substantially more) E.Antipodensis is known from a fragmentary find on Seymore Island. It was initially assumed to be the same species as E.Wilhelmi, simply being a larger morph because of the climate conditions in Antarctica, but the shape and number of high neural spines on the animal’s tail vertebrae differ enough to identify it as its own species, with some arguing that it should probably be split into its own genus. The high neural spines at the base of the tail are representative of most Serpodardinae. This is because the animals needed to find a way to correct their balance as they got larger. Unlike more basal pre-K-Pg dracoavians, atrophied caudofemoralis muscles which are themselves a result of the lack of a distinguishable raised fourth trochanter and a minimal number of caudal vertebrae with transverse processes are basal to all Kairosdracoavians. This affected their balance as they grew in size. The high neural spines at the base of the tail supported a large fatty and muscled hump and coupled with their increased tail length helped offset their balance, allowing them to reach truly megafaunal sizes.
Such an adaptation may not have been necessary if the animals were able to convergently evolve a quadrupedal posture similar to Sauropods or Ornithischians. However, despite superficially resembling basal Sauropodomorphs like Plateosaurus, Eodespotoaves was not a facultative biped. Its’ wrist bones, like all Serpopards, and indeed all maniraptorans, having long since lost the number of wrist and hand bones that would have given them the ability to articulate in a way necessary for quadrupedal locomotion as far back as the Triassic. While other Serpopardformes will eventually evolve pseudo-quadrupedalism through elbow and even knuckle-walking, these adaptations will come from derived fossorial Dromaeoaves and not the early giants of the Paleogene.
Living in the deltaic forests of the Thanetian Austral Basin E. Antipodensis represented the largest herbivore in all of South America. However, it was hunted by an almost equally large Sebecid. While hypercarnivorous Kairosdracoavians had emerged almost immediately after the post-K-Pg climate stabilized, the Sebecids had been equally quick to recover in South America, preying upon the small mammals and large reptiles of the continent. When larger and more robust Kairosdracoavians entered the continent, it spurred the evolutionary arms race between predator and prey which contributed to the evolution of larger and more robust Sebecids to hunt animals like the early Serpobardids.
When these animals were first discovered, the large ziphodont teeth they left behind were assumed to belong to an early lineage of giant Culebreformes. The discovery of the giant teeth of one middle Eocene behemoth even resulted in its owner being named Tyranoaves Rex (Tyrant Bird King). While the largest of these animals would not emerge until the Eocene, the Paleocene giant, Basilosuchus Imperator had already attained a massive body size. At 4.3 meters long and weighing an estimated 640 kilos, the animal dwarfed its Culebreform competitors, the largest South American member being not that different in size from Sateopteryx, and the speculated size of an as-of-yet-to-be-described Antarctic genus only about two times larger.
The Emperor of the Paleocene
Basilosuchus’ deep skull and large ziphodont teeth were built to inflict massive damage to their prey, the notch in their top jaw likely acting as a meat hook which would have increased bloodloss and general trauma by securing trapped flesh when the animal would yank its massive jaws. Its subdermal osteoderms would have acted as armor against the battering and slashing claws of Eodespotoaves or the horns and tusks of its large mammalian prey. The ultimate predator of its age, Basilosuchus would soon face something far more powerful than itself. Between 59.7 to 58.1 Million years ago, the world was experiencing a brief cooling period. This saw a continued increase in the body size of large endotherms. It allowed for E. Antipodensis to be a giant that was completely covered in feathers and for mammals to reach truly megafaunal sizes, but soon the world will get warmer than it’s been in hundreds of millions of years, and many endotherms will be pressured to grow smaller, and with their shrinking, giants like Basilosuchus will go extinct. The Sebecids will survive and reach even larger sizes in the Middle Eocene but climate change is about to deal the world a great disruption, the PETM is coming.
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