Gondwanaland prey vs. Laurentinian predators

I wasn’t sure if this was a General Question or the beginning of a Great Debate. I finally decided to come here, as this commentary seemed likely to draw more questions than answers.
There was just a special about birds on PBS. One of the themes was that flying is expensive, and that, when lack of predators makes it possible, birds will happily give it up, and become flightless.
Now, every even approximately oceanic island lacks a native predator population (aside from a few eagles and snakes), so every e.a.o.i. has (or had, prior to their occupation by humans) its flightless birds – rails, ducks, ratites, etc. It seems that predators don’t get to, or don’t survive on, islands – even New Zealand lacks native predators. Until you get to Australia, whether it is to be considered an island or a continent, there just isn’t a predator population (and Tasmanian devils, despite their reputation, aren’t very impressive predators). It would seem that several million square kilometers are the minimum size for a predator population to evolve and survive.
But, wait, there’s more…
The breakup of Pangaea into Laurentia and Gondwanaland seems to have led to two very different types of fauna: ratites, marsupials, edentates, and primates in Gondwanaland; miacids and ungulates in Laurentia; and (excepting the stunning, but so far short-term, success of humans) Laurentian fauna seem to invariably have the upper hand when they come into conflict.
Is this solely due to the fragmentation of Gondwanaland into pieces too small (South America, Australia, etc.) to support a really competitive fauna, or is there something deeper at work here?


“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”

I used to know this, but I’ve long since forgotten – which continents did the two mega-continents separate into?

Also, a quick definition of the classes of animals you mentioned would be appreciated (I know, of course, marsupials and primates, but the others are foreign to me).
Powers

Powers:

Laurentia is now North America and Eurasia. Gondwanaland is South America, Africa, India, Australia, and Antarctica.

Miacids are the stem group that most carnivorous mammals are derived from. Cats, dogs, bears, sea lions, wolverines, etc. Ungulates are mammals with hoofs. Deer, antelope, horses, etc.

Ratites are the latge flightless birds like ostriches, emus, and moas. Edentates are the anteaters and armadillos.

Definitions done with, I think Akatsukami is overlooking the role of non-mammalian carnivores in the SOuthern landmasses. I seem to recall that the top predator in Australia was a giant goanna (a monitor lizard the size of a car) and the equivalent niche in South America was occupied by flightless birds. I don’t think Australia’s ecology was changed much until humans colonized the land, I know that the South American predators were replaced by Northern models when the isthmus of Panama rose. With the continual faunal exchange between North America and Asia, the predator types that managed to prosper are those most adept at competing with other predators, so the South Americans hardly had a chance.

Let me think on this a little and check some reference books…

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“You cannot reason a man out of a position that he did not reach through reason.”

Sometime in the last couple of months Scientific American had an article on the large marsupial predators of Ausatralia. They did develop, but they did die out. There is speculation that this may have coincided with the arrival of humans (and with them, dingos).

Sorry, just have to but in here.
Goannas the size of cars? From which orifice did this escape? The largest goanna that I have seen is 2 metres long, and they are relatively flat too. Just like most lizards. The tasmanian tiger was just like a dog really and the tasmanian devil is a scavenger. Maybe you are thinking of a komodo dragon, but they may be as long as a car, but not as big as one.

As to why the creatures didn’t really develop into predator prey types is because of a lack of natural resources. In Australia and so on there is not the overabundance of lush vegetation that is found in Europe and America. This means that Species keep their populations down in order to maximise the resources for everyone. As there were lower numbers of herbivores, there are lower numbers of carnivores. It may also pay to look at the herbivores. Emus and kangaroos can run away pretty damn quick, so it takes a bit more to catch them than may be worth it, which is why no large predators evolved.

Also once isolated the only animals that could join the island had to swim or fly. Which is why most of the predators in the pacific are lizards/snakes. In New Zealand the biggest predator at the moment is the cat. Not a special one just the domestic cat. In the outer islands they shoot every cat that they see. Because most of the fauna has not had experience with a prolific hunter they don’t know how to react. Is this beside the point? Sorry, I’ll try and communicate something intelligible later.


What’s the ugliest part of your body?
Some say your nose, some say your toes,
But I think it’s your Mind - Frank Zappa

Excuse me if I’ve missed something. I’ve read the OP several times and still can’t wrap my brain around exactly what the question is.

I did read this in the OP:

and then Dr. Fidelius clarified some definitions with…

If Africa and India were part of Gondwanaland that means that it was the home of some of the fiercest carnavores on Earth. Africa is the home of a huge variety of great cats, wild canines and some quite formidable (albeit herbovorous) megafauna as well. India also has its share of tigers and elephants.
Unless these beasts migrated from Laurentine after Africa and India collided with it, the premise of the OP seems to be quite flawed. Zoology isn’t my strong suit so I am prepared to be humbled by any authoritative correction.

FloChi:

With extensive borrowning from Eric R. Pianka’s work on Varanid evolution:
Megalania prisca is a Pleistocene fossil (19,000-26,000 years BP) from Australia, estimated to have reached 7 m in total length and to have weighed more than 600 kg (Hecht 1975; Auffenberg 1981; Rich 1985). [Cladistic systematics will undoubtedly require that the fossil taxon Megalania eventually be reassigned to the genus and subgenus Varanus (Kluge, pers. comm.)] These spectacular creatures must have been even more formidable than modern-day saltwater crocodiles. The major prey of these gigantic monitor lizards is thought to have been large diprotodont marsupials (rhinoceros-sized beasts, now extinct, that were relatives of wombats and koalas). Being contemporaneous with aboriginal humans in Australia, in all probability, Megalania also ate Homo sapiens. Megalania teeth were over 2 cm long, curved, with the rear edge serrated for cutting and tearing the skin and flesh of its prey as these powerful predators pulled back on their bite. Many other species of Varanus also possess such teeth. Several authors have suggested that Varanus komodoensis and Megalania prisca are/were ecological equivalents of large saber-toothed cats, using a slashing bite to disembowl large mammals (Akersten 1985; Auffenberg 1981; Losos and Greene 1988). Water buffalo as large as 590 kg have been killed by Varanus komodoensis, more than three times their own mass (Auffenberg 1981). [Cladistic systematics will undoubtedly require that the fossil taxon Megalania eventually be reassigned to the genus and subgenus Varanus (Kluge, pers. comm.)]
http://www.zo.utexas.edu/faculty/pianka/varanus.html

Giant goannas.

PapaBear:

The “northern” families invaded Africa and India as plate techtonics brought those land masses into contact. Most of the more familiar extant fauna are imports, adapted to their current homes. Invasion of Africa was easier in the past, before the Mediterranean filled, and India picked up its “northern” animals before the Himalayas were raised up high enough to limit immigration. You can tell when the invasions occurred from the fossil records of the areas.

DrFidelius writes:

I didn’t mean to suggest that the Southern Hemisphere is or was without carnivores, and, if I wrote what could be misinterpreted that way, I apologize. Still, the super-duper-goannas of Australia, and the flightless predatory birds of South America, are long gone, at least in terms of human history. Why?
DrFidelius may have struck on something when he wrote:

That would suggest that critters (not just predators; North America has its opossums and armadillos, but those didn’t represent the whole of aboriginal South American fauna by a long short) that have to contend with lots of species are more adept, by virtue of that fact, than those that must compete with a few, and that large land masses will have more diverse environments, and by virtue of that fact more numerous species, than small ones.
Is the fragmenting of Gondwanaland the cause of its fauna being disfavored, then?
I was going to comment on African animals being Laurentian in origin, but I see by scrolling down that DrFidelius has beat me to it, so I won’t.


“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”

South America, pre-Isthmus of Panama, carnivores of:

> Borhyaenidae: a wide range of marsupial carnivores, many catlike and doglike, ranging up to small bear in size. Included a marsupial saber-tooth (Thylacosmilus sp.)

> Phorusrhacidae: large crane-like flightless birds of prey. Had beaks like your last nightmare.

> Didelphidae: the opossum family. Included a wide variety of small predators filling the weasel/raccoon niches in the ecology.

The present jaguar/ocelot/coatimundi S.A. predators are immigrants in the couple of million years just prior to the last Ice Age and during it. All the previous predators except some of the didelphids went extinct.