Dennis McCarthy / Excerpt from "Here Be Dragons"
Here Be Dragons
(Oxford University Press)
        "At this point, this trickle of mammals into South America stopped for tens of
millions of years, and the resulting isolation produced many peculiar South American
forms – as isolation always does.  The radiation among the Xenarthra produced the
lumbering, elephant-sized ground sloths and the spectacular and seemingly-
Mesozoic glyptodonts – giant armored armadillos, as big as a small car, with spikes
along their tails.  The caviomorph rodents also flourished, leading to the capybara,
porcupines, chinchilla, guinea pigs, and the now extinct “Ratzillas” --  
, a bison-sized guinea-pig like creature,  and its close relative,
Josephoartigasia monesi, which weighed a metric ton and is the current record-
holder for largest rodent ever.  Some sizable predators evolved as well -- the sabre-
toothed panther-like marsupial,
Thylacosmilus (“pouch sabre”) and the giant
flightless terror birds, the phorusrhacids, some of which stood as large as ten feet
tall.  These birds did not become extinct until just a few million years ago and had they
lived until the present day, it is likely the notion that birds evolved from dinosaurs
would have occurred to biologists much earlier.  The surprising size of a number of
the South American plant-eaters was probably an effective enough adaptation
against the relatively small number of predators there, so they remained slow and
        "Thus, up until a few million years ago, South American flora and fauna were
quite as distinctive as the Australia and New Zealand biota seem today – and just as
vulnerable.  But, in one of those colossal transformational episodes that so often
grips this world, the Isthmus of Panama emerged from the sea, and South America
suddenly became acquainted with the cunning, speed, teeth, and claws of the
Laurasian biotic realm.  As noted, biogeographers refer to the event as an
“interchange,” as plants and animal moved in both directions between the continents.  
But it is certainly clear that North America had the upper hand.  Perhaps, the most
obvious result we find in the fossil record is that North American meat-eaters flooded
southward into this new-found rich and fleshy landscape and discovered a wealth of
large and lumbering herbivores to rend and claw.  As the biologist Stephen Wroe
described it, “At that point, suddenly, wham, the carnivore diversity in South America
goes absolutely stratospheric… You go from having a handful of not particularly big
mammalian carnivores to having arguably the most extraordinary range of big
carnivores in the world."   These predators include massive sabre-toothed cats,
bears, at least six species of canines, and a 400 kg lion that was four times larger
than the marsupial lion.  The gargantuan sizes attained by relatives of the South
American guinea pigs, armadillos, and sloths would not have been enough to protect
them from the northern marauders.  And the rise of the Panamanian link may be
properly described as a South American disaster, not as devastating as the one that
befell their Antarctic relatives, but certainly far gorier.  It produced what perhaps was
the bloodiest spectacle since the fall of the tyrannosaurs....  
Excerpt from Chapter Five:

"The Bloody Fall of South America
Glyptodont – giant armored armadillo
Some of the unique South American animals that
evolved during the continent's isolation from 35
million years ago to just a few million years ago:
Ratzilla -- giant guinea-pig like rodent
South American "Terror Bird"
The emergence
of the Isthmus of
Panama a few
million years ago
allowed deadly
North American
predators into
South America.