Note that with the exception of the T. rex ``Sue'', most of the specimens that will be discussed here have not yet been properly described or repeatably measured, so we cannot really trust the estimates given for them.
Described by Coria & Selgado in 1995, this carcharodontosaurine is perhaps 14.5m (47 feet) in length, making it the longest currently known. Weight estimates are in the region of seven to eight tonnes, which would also make it probably the heaviest known predator.
This African relative of Giganotosaurus has been known for seventy-odd years, but from relatively small specimens. More recent finds have ranged up to 14m (45 feet) in length with weight estimates of up to seven or eight tons.
There's a particularly impressive photograph by Brendan Smith <email@example.com> showing just how huge this animal's skull is: see dinosauricon.com/images/carcharodontosaurus-bs.html. Now stop and think that Giganotosaurus, a very similar animal, is known to be even larger. Ulp!
The largest fully-excavated, reasonably complete T. rex is the Chicago Field Museum's specimen nicknamed ``Sue''. Sue is about 12.6m (41 feet) in length, and a fairly typical weight estimate would be six tonnes (although like all dinosaur weight estimates, you can easily find people who will tell you that it's way too high, and others who will tell you it's way too low.)
In the summer of 2000, an expedition headed by Dr. John Horner (author of The Complete T. Rex) found five new T. rexes, at least one of which is claimed to be 10% bigger than Sue, but it's too early to say much about these specimens, which have not even been excavated yet.
Another contender for the ``biggest T. rex'' title is ``Rigby's rex'' - an undescribed specimen currently locked away somewhere in Montana, awaiting attention. It's odd in that Rigby describes the skull as being of ``normal size'', but the pubic bone is very large - 133cm, compared with 122cm for ``Sue'' (and 118cm for Giganotosaurus). This suggests either a new, differently-proportioned Tyrannosaurus species (or a new genus), or more likely, two specimens mixed up together - one normal sized, the other truly huge.
The only really good Spinosaurus specimen, found by Stromer's team in north Africa in 1911, was destroyed by allied bombing raids during WWII. The remaining evidence suggests that this animal, big as it is, was sub-adult. The implication is that an adult Spinosaurus would have been in the same league as T. rex - probably somewhat longer, but not as heavily built.
A large Spinosaurus skull, rumoured to be eight feet long, has turned up more recently. If the measurement is correct, this would suggest that the complete animal was longer than any known Giganotosaurus or T. rex, but there are no reliable sources yet.
Generally when people mention Allosaurus, they're referring to the common species Allosaurus fragilis; but there's another species, known from much more fragmentary remains: Allosaurus amplexus (previously in its own genus, ``Epanterias'').
Originally described by Cope way back in 1878, it has rather dropped out of sight. However, anecdotally, its claws are at least twice as heavy as those of a thirty-foot A. fragilis. This suggests that it was about 25% bigger than the A. fragilis (1.253 =~ 2.0), implying a total length of about 11.5m (38 feet).
Allosaurus amplexus is a nomen dubium, at least in the Dinosauricon - see dinosauricon.com/genera/allosaurus.html. Why?
Mickey Mortimor posted a message on the mailing list elucidating some details of large specimens of Allosarus and related genera. It can be found at www.cmnh.org/dinoarch/2001Jan/msg00445.html
This is another allosaurid, which had tallish spines - perhaps 50cm or so - along its back. Size estimates of known specimens range up to 12m (39 feet), with vague promises of larger specimens to be described.
This close relative of Megalosaurus, from the very end of the Jurassic period, is known from rather sketchy remains. But is considered likely to have been about 12m (39 feet) in length, and heavily built with it.
In Patagonia, Phil Currie and Rodolf Coria have recently discovered a bonebed containing several individuals of a new, as-yet unnamed, carcharodontosaurine. The individuals in the bed vary in age and size, but the largest seem to be bigger than Giganotosaurus. As always, we have to ``wait for the paper'' before we can say anything very definite.
``The Monster of Minden'' is a badly-documented late-Jurassic specimen from the Wiehengebirge, Germany. The German edition of National Geographic for November 1999 contains an article in which this animal's ribs are described as 1.5 times as large as those of Allosaurus (which it resembles), and its teeth are claimed to be a foot long (including the root.) This might imply an overall length of 15m (about 49 feet) but again, more information is needed. The specimen has not yet even been referred to any species or genus.
First of all, we need to bear in mind that we have so few specimens of most of these genera that we can't come close to estimating how large they might have grown. Some of the genera are represented only by single specimens - there is no reason to think that these were necessarily anywhere near the top end of the possible size-range. (Consider a random sample of a dozen or so humans, then think about how much larger the biggest people are than the biggest in your sample.)
We also have the difficulty that it's very hard to judge the heaviest of these animals, because no-one can agree how much they weighed.
With that said, the longest fully-described predatory dinosaur as of this writing is ... fanfare, please ... Giganotosaurus carolinii at 14.5m (47 feet). We can be pretty confident that it's bigger than T. rex because the two known specimens are bigger than any T. rex for which actual measurements are known. For example, the femur of the type specimen is 1440mm long, compared with about 1380mm for ``Sue'' - a 4% difference. And comparisons of the dentaries of the two known Giganotosaurus indicate that the second specimen is perhaps 8% larger than the type specimen. So Giganotosaurus is almost certainly the biggest predator we have today.
This of course comes with a proviso that new specimens of T. rex, Acrocanthosaurus and/or Currie & Coria's new Patagonia beastie may surpass it at any moment. And then, of course, someone may well find another Giganotosaurus that's bigger again. And so it goes.
By way of a cautionary tale, it's worth reading the ``Which is the largest species of crocodile?'' article in the Crocodilian Biology Database FAQ - see www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/cbd-faq-q2.htm. This illustrates the difficulty of sifting fact from fiction even when dealing with extant species for which which we can observe numerous fully articulated specimens! Given that dinosaurian remains are so much more fragmentary, it shouldn't surprise us that we run into similar problems when trying to establish which are the biggest dinosaurs. Caveat everyone.
It's interesting to note that there are serious ``biggest predator'' contenders from four different families:
The fact that all these families' largest known representatives are roughly the same size (forty feet in length, give or take) hints that they may all be approaching some fundamental bio-mechanical limit for bipedal carnivores.
Then again, there's a long history of new discoveries breaking through such supposed barriers - remember the ``absolute twenty-foot limit'' on Pterosaur wingspans, which was orthodox right up until they started finding forty-footers? :-) So we should probably not be too quick to jump to conclusions here!
For some nice illustrations of predator sizes, see Gavin Rymill's page at gavinrymill.com/dinosaurs/carnivores