Hi, I usually read that Andrewsarchus is considered the biggest flesh-eating mammal ever to have walked on earth. But I also found something about an animal called Megisthotherium. What was it like and which of the two has to be considered the biggest? Thanx for any answer!

Hi Andrea,

to the best of my knowledge the two beasts in question are about the same size. Andrewsarchus is only known from one skull and Megisthotherium is known from a wider variety of cranial and post-cranial material, including a humerus. This means that the size of Megistotherium can be more accurately approximated than for Andrewsarchus, which has size estimates based on the morphology of better known relatives.

I remember as an undergraduate receiving a brief lecture on naming Megistotherium from Bob Savage, he said:
"You know what Megatherium means don't you?" I said "Yes, big beast". Bob then pointed at a cast of a Megistotherium skull and said "So this is Megistotherium - The BIGGEST beast!"

So in memory of Bob, I'd say that Megistotherium is the biggest (although others will disagree, I'm sure).

*Blast, Paolo submitted at the same time, hence the overlap!*

Hi Andrea

The fossil records of both Andrewsarchus and Megistotherium are pretty poor, with both only being known from a skull or two and a few bones (the fossil record of mammals largely consists of teeth anyway, so I suppose it's not too bad).  This means that getting a precise measure of the overall size of the creatures is very hard, but from what I've read they were both about the same size.  Both were probably about 4-6 metres long, although the skull of Megistotherium was a bit larger than that of Andrewsarchus.

Interestingly, Andrewsarchus was a hoofed mammal (called an ungulate), and is thought to have been closely related to the same group that includes cows, camels, and whales!

Last edited by Phil Jardine (21st May 2007 12:21:43)

As already stated in the previous answers, both of these animals were similar in size. However, _Megistotherium osteothlastes_ (with a 650-mm long skull) has been down-sized in recent years due to the discovery that it and its close relatives had particularly big skulls compared to their bodies (near-complete skeletons are known for _Hyainailouros sulzeri_, a close relative of _Megistotherium osteothlastes_ that may even belong to the same genus). A 2001 study on body size in giant animals gave _Megistotherium_ a weight of 880 kg and _Andrewsarchus_ a size range of 600 to 900 kg. However, the estimate for _Megistotherium_ was based on an old reconstruction where the body proportions were probably innaccurate. Clearly, we're making educated guesses, and don't know as much as we'd like to.

Darren wrote: "A 2001 study on body size in giant animals gave _Megistotherium_ a weight of 880 kg and _Andrewsarchus_ a size range of 600 to 900 kg."

Hang on, that's pathetic.  We have bears that weigh more than that, don't we?

To the best of my knowledge the largest extant terrestrial carnivore is the Kodiak bear (an Alaskan and Russian variety of Brown bear), overlapping in mass range with the Polar bear. In the wild male Kodiak bears will often weigh 600-700kg, but in zoos they can be substantially heavier (around 900kg). The heaviest reported is over 1,135kg.

So I guess these palaeo-beasties aren't really any more impressive size-wise than their extant counterparts.

True, but the average bear is not much of a hunter really. OK, they *are* carnivorous (they do actively hunt and kill prey), but the reconstructions I have seen of those mentioned above would make them far more effective predators than a kodiak or a polar bear (i.e. fater and with better endurance) and may well have been exclusive carnivores where fully terrestrial bears are at least omnivorous (polar bears count as semi-aquatic animlas and therfore, not a fully terrestrial carnivore).

That said I have seen papers referring to Andrewsarchus at least as being omnivorous. Overall through it looks like we are limited to under 1t for mammalian predators which is a bit poor compared to both crocs and dinosaurs. Even giant carnivorous birds like Dinornis reached into the hundreds of kilos despite being bipeds and having a light skeleton. Maybe mammals aren't that great after all! ;-)

I would like to point out that the biggest animal we know of is a mammal...

"I would like to point out that the biggest animal we know of is a mammal..."

Well -- the biggest animal that we have a good proportion of the skeleton of.  As you probably know, there is evidence of sauropods on a par with and maybe bigger than blue whales, although nothing wholly convincing yet.  Parts of this story are very well told on Darren Naish's (old) Tetrapod Zoology site:
http://darrennaish.blogspot.com/2007/01 … art-i.html
http://darrennaish.blogspot.com/2007/01 … rt-ii.html

I'll wait to be wholly convinced - I've noticed that estimated masses for most extinct taxa tend to reduce with increasing evidence...