You may have heard claims of 18, 19, 20 meter Spinosaurus, hell, I've heard them as high as 25 meters. Personally, I find the idea of an 82 foot Spino a bit ridiculous.
I will split this critcism of these claims up into several sections.
Criticism One: It May not Have Been Able to Support its Weight.
-*** Not a viable criticism for reasons explained by me in the comments***-
I often hear claims from fanboys of 20+ tonne weights for Spinos around the 20 meter range. Estimates larger would likely approach the 30 tonne range.
Let's use Giraffatitan as a means of criticism.
The main criticism here is that Giraffatitan would only be slightly heavier than Spinosaurus (partially due to weight-reducing air-sacs found in most sauropods, but no theropod as far as I know has been found with similar sacs), and yet, Giraffatitan was a pillar-legged quadruped, whilst Spinosaurus had relatively thin legs, and was bipedal.
One rebuttal for this point could be that T. rex had relatively thin legs compared to elephants, and was also bipedal. First of all, Spinosaurus was even slimmer than Tyrannosaurus in its legs, and additionally had to carry a heavy Spine. Elephants also have thinner legs than Sauropods.
However, remember the weight-reducing sacs I mentioned above? Spinosaurus is not known to have such sacs, nor any theropod for that matter, making it extremely unlikely that Spinosaurus had this feature. The fact that pretty much all large Sauropods had this trait suggests that such a trait was necessary to obtain such immense sizes. As Spinosaurus lacked this trait, it suggests it could not grow to the claimed sizes.
Criticism Two: It Wouldn't fit in its Ecosystem.
Not in terms of size, of course. I mean in terms of its niche. Fanboys will often claim that Spinosaurus didn't primarily rely on fish, or will outright deny the fish-eating theory all together.
The main issue is "what would it hunt?"
- Small dinosaurs? Could you really look at someone with a straight face and tell them a 20 meter, 20 tonne carnivore fed primarily on small dinosaurs? Of course not. Spinosaurus couldn't have eaten them in the manner baleen whales eat krill or other small animals, its mouth wasn't even remotely adapted for that, nor did or could said small animals swarm up in the way krill do. Spinosaurus would have to eat them one at a time, wasting absurd energy for a minor gain. Nor could it run them down or sneak up on them anyways. Eating small animals doesn't fit woth the fanboy style anyways.
- Smaller carnivores? There's a reason carnivores generally eat herbivores. It's not because herbivores taste better, it's because their populations are more able to take hits. Carnivores typically only make up 5-10% of fossils. As such, hunting them would not be in Spinosaurus' favour, as they would quickly kill off their food source.
- Ouranosaurus? Are you really telling me a 20 tonne carnivore with a huge sail on its back can sneak up on, run down, or hunt a lightly built hadrosaur in any way?
- Paralititan? The first issue is that Spinosaurus has very few of the adaptations of a Sauropod hunter. The second issue is that this would put it in direct competition with Carcharodontosaurus. Presumably, Spinosaurus would be better at it than Carcharodontosaurus (because Spinosaurus has to be the best at everything). The issue is that it would quickly drive Carcharodontosaurus to extinction.
- Fish? Now we're talking! Fossilized fish have been found at nearly a tonne in weight in Spinosaurs' ecosystem, and would have been an abundant resource. Spinosaurus had gripping conical teeth and a thin, gharial-like snout. With large claws found on other Spinosaurs in similar, fish abundant areas (such as Suchomimus or Baryonyx), it is likely the case that Spinosaurus' large claws were primarily adapted for hunting fish. Its large sail could have funtioned like a herons' wings (and it had a long, thin mouth like a heron). Its shorter hind legs would help it swim more proficiently. The point is, Spinosaurus was a very marine adapted animal, and could not have functioned as the terrestrial super-terror many fanboys imagine it as.
Criticism Three: No Evidence.
The only evidence I have ever been pointed to outside of vauge "there's research papers somewhere" was the claim of NMC 41852, claimed by a member of this wiki to be 23 meters long. Skeptical, I looked into the claim. Replying with the following comment:
"I've done some research into NMC 41852, I found this:
'It is noteworthy that NMC 41852, which is missing the distal and proximal ends, compares quite favourably with the humerus of Baryonyx, the only notable difference being that the humeral shaft is more elongate in the former. The widely expanding distal margin however, suggests a similar outline to that of Baryonyx. Furthermore, the height of the deltopectoral crest and the internal tuberosity is the same in both specimens. The proximal end also appears to be expanding posteriorly in a similar way. Increasing the humerus of Baryonyx to about twice its size (several cranial remains of Spinosaurus are about twice the size of corresponding elements in Baryonyx), renders it similar in size and morphology to NMC 41852. That Spinosaurus is a very large theropod, and very likely the longest theropod in the Kem Kem by a considerable margin further adds to the likelihood of this identification. Considering that no evidence exists for an as yet unknown very large taxon with a giant humerus, it is most parsimonious to refer this specimen to Spinosaurus in the light of the noticeable morphological similarities with Baryonyx' Source
Baryonyx was most recently estimated at 7.5 meters long in 2010 Source
This would give us a length for NMC 41852 of 15 meters. Even the outdated estimate for Baryonyx's length, 9.5-10 meters, would stretch out the length of NMC 41852 to 19-20 meters, a whole 10-13 feet short of the claimed 23 meters. Keep in mind though, that to believe it was 19-20 meters based on a knowingly outdated estimate of Baryonyx's length is to decieve yourself. One can only claim to be rational based on the most recent, reliable, and updated sources.
NMC 41852 was, based on all reliable evidence and information, 15 meters long, or about 49 feet."
However, I should further point out that this could be applied to Spinosaurus as a whole, and not just NMC 41852, based on the quote "several cranial remains of Spinosaurus are about twice the size of corresponding elements in Baryonyx." Meaning Spinosaurus in general was likely around 15 meters on average.
And finally, I am brought to the largest specimen of Spinosaurus, estimated at a likely size of 15.6 meters or 51 feet. Keep in mind though, that the most likely estimate should be regerded as the estimate. Just because it could have been longer than the average estimate doesn't mean it was, and even so, it only reached around 16.7 meters at a maximum (and 14.7 as a minimum estimate). Source
And in reference to me saying above "just because it could have been the case doesn't mean it was," I leave you all with a final quote (basically implying that I shouldn't even have had to make this whole blog, but I did anyways).
"What can be asserted without evidence can also be dismissed without evidence."
- Christopher Hitchens