In both timelines, the Amazon Rainforest is a place filled with an innumerable number of species, ranging from the wildly diverse endoparasitic fish, to the large durocephalid cenoceratopsians. In such a thick, heavily forested place like the Amazon, it's easy for even creatures of gihugrongo-sized proportions to hide with relative ease from spexsplorers. One such creature has done just that: the mapinguari.
One of Spec's least known cryptids, the mapinguari is said to be a large, feathered animal that stands up to 10 feet tall. Its distinguishing feature is its pair of claws, which are large and sharp enough to bring down a bull k'z'k tuskhorn (as reported by one person).
The first reports of the mapinguari come from the logbook of Captain Chadd Johnson, leader of the "Neo-Orellana Expedition", which was one of the first expeditions to head into the Spec-Amazon. The two-month journey discovered many species we're now familiar with, such as cazadins, pseudosauropods, viriosaurs, etc. In one entry, Captain Johnson describes being woken up in the middle of the night by loud noises which he says "could only be described as bone-chilling". He, and 2 other men investigated the noise. And what they found next, they wish they could forget.
In a small forest glade, the group encountered two "monstrosities", as Johnson put it. They were hard to describe due to the low light, but he estimates that the creatures were 8-10 feet tall, had long necks, and wicked claws. As they drew closer to get a better look at the animals, one of the men tripped, setting off a dangerous chain of events.
Upon hearing the man trip, one of the animals, presumably a bull, reared up into a defensive position. Immediately, the group ran for their lives, with the animal chasing them half-way to the boat.
While later reports haven't been as detailed as that of Captain Johnson's, they do describe a similar creature: big, feathered, wicked claws, and in one case, a vegetarian.
These descriptions provided quite a challenge to spec-cryptozoologists until the discovery of two fossil therizinosaurs in the Esenada Formation in Argentina. These fossils show that during the Pliocene, some therizinosaurus occupied niches similar to those of the HE ground sloths. These fossils looked very to the descriptions of the mapinguari.
Could the mapinguari be the last surviving member of this segnosaur radiation? Without a specimen, or even film of some kind, it'll be just another one of the thousands of species yet to found in the natural maze known as the Amazon Rainforest.