So I thought I'll kickstart this with a favorite of mine. 

Carcharodon Megalodon.

C. megalodon may have been the largest and most powerful macro-predatory fish in vertebrate history. Fossil remains of C. megalodon indicate that it was the biggest shark that ever lived and possibly approached a maxima of around 20.3 metres (67 ft) in length. C. megalodon has been assigned to the order Lamniformes but its phylogeny is disputed. Scientists suggest that C. megalodon looked like a stockier version of the great white shark, Carcharodon carcharias, in life. Fossil evidence confirms that C. megalodon had a cosmopolitan distribution. C. megalodon was a super-predator,[1] and bite marks on fossil bones of its victims indicate that it preyed upon large marine animals.

Yodariquo said:

^

HOLY SHIT!

Yodariquo said:

I'm not particularly convinced the premise of this thread is accurate.  The majority of dinosaurs weren't enormous.  We still have large animals; elephants, hippos, whales, giraffes aren't exactly dwarfed.  The modern blue whale is the largest animal ever known.  Short answer to why were there big things then that aren't around now?  Because most species go extinct.

Just the fact that there were giant reptiles that could step on us is crazy enough for me. In terms of land animals I guess Elephants are are the overall biggest, they don't come close to what was on land before. Weren't there roaches that were bigger than our heads. Maybe fiction has me all confused but there was definitely a whole lot of crazy huge stuff that has no real comparison in todays world.

Chalk it all up to failed experiments in evolution.  When creatures are that large, the populations are never that big.  For instance there were probably never more than 200,000 T-Rex's ever walking the earth at one time.  That's a very small population though it is sustainable. However, populations of that size run into problems during cataclysm.  

See when the giant asteroid or whatever caused the climate change it wiped out about 90% of all the creature populations. Now when you have a population of 10 million (like the small mammels) that's a population that can endure a mass wipeout. One of 200,000 on the other hand. . . would be wiped out to an unsustainable level.  

So there you have it. Giant creatures no longer exist (outside of the ocean) because they cannot be sustained.  Nature learned from its mistake, shrunk everything down, and went about its business.

The largest of the group shown in here might very well have rivaled with the blue whale. 

According to the published description, the shin bone (tibia) of Bruhathkayosaurus is 2 m (6.6 ft) long. This is 29 percent larger than the tibia of Argentinosaurus, which is only 1.55 m (5.08 ft) long. Comparing the bones in the upper forelimb gives a similar result. While the humerus of Bruhathkayosaurus is incomplete, it is extrapolated to have been 2.34 m (7.68 ft) long. This is 30 percent larger than the humerus of Argentinosaurus, which is 1.81 m (5.94 ft) long.

No total body size estimates for Bruhathkayosaurus have been published, but paleontologists and researchers have posted tentative estimates on the Internet. One early estimate by Mickey Mortimer estimated that Bruhathkayosaurus could have reached 40 m (130 ft) to 44.1 m (145 ft) in length and to have weighed from 175 to 220 tons.[3] However, Mortimer later retracted these estimates, reducing his estimated length of Bruhathkayosaurus to 28 – 34 m (90 – 110 ft), and declined to provide a new weight estimate, describing the older mass estimates as inaccurate.[4][5] In a May 2008 article for the Weblog Sauropod Vertebra Picture of the Week, paleontologist Matt Wedel used a comparison with Argentinosaurus and calculated the weight of Bruhathkayosaurus at up to 139 tons.[6]

By comparison, the titanosaur Argentinosaurus is estimated to have reached 34.6 m (114 ft) in length, and to have weighed from 80 to 100 tons. Another huge titanosaurid, Paralititan, was probably 31.9 m (105 ft) long, and weighed 65 to 80 tons.[7] All of these sauropods are known only from partial or fragmentary remains, so the size estimates are uncertain. Length is calculated by comparing existing bones to the bones of similar dinosaurs, which are known from more complete skeletons and scaling them up isometrically. However, such extrapolation can never be more than an educated guess and the length of the tail, in particular, is often hard to judge. Determining mass is even more difficult, because little evidence of soft tissues survives in the fossil record. In addition, isometric scaling is based on the assumption that body proportions remain the same, which is not necessarily the case. In particular, the proportions of the titanosaurs are not well known, due to a limited number of relatively complete specimens.

If the size estimates for Bruhathkayosaurus are accurate, the only other animal approaching its size would be the Blue Whale. Mature Blue Whales can exceed 33 m (110 ft) in length, which is a little shorter than Bruhathkayosaurus, but the record-holder Blue Whale weighed in at 176 tons,[8] which is probably heavier than Bruhathkayosaurus.

Among the dinosaurs, only another poorly known specimen may approach or exceed Bruhathkayosaurus in size. Edward Drinker Cope's Amphicoelias fragillimus would have been longer, reaching 56 to 62 m (185 to 200 ft) in length, but it was a slender diplodocid, weighing only 120 tons. Unfortunately, the only bone recovered (a massive vertebra) is now missing, and only a description and drawing of the specimen remain.[9]

My penis is not extinct and it's fucking huge.

That's right, I defy evolution.

Why do I get the sudden urge to post that story of the Mexicans who stole a massive animatronic T-Rex?

This thread has heightened my suspicion of Steel *strokes chin beard*