Why were Cretaceous sauropods so big?
The biggest theropoda ever was maybe 10 tons.
The biggest ornithischians got as big as the biggest mammals on land ever, around 20 tons.
The largest Jurassic sauropods were about the same size of 20 tons.
However, in the Cretaceous some sauropods [and only sauropods] broke the scale at 2's, or 3x the natural weight limit for terrestrial megafauna which seems to be 20 tons throughout history.
- Anonymous3 weeks ago
At the end of the Jurassic there was a cold spell, and lots of large sauropods became extinct, along with lots of other large dinosaurs (Allosaurus for example) and large pterosaurs (flying reptiles). The reason they went extinct is because their large size means they have small amounts of body surface per unit volume. During cold weather, it makes it hard for them to absorb sunlight to warm up. If they cannot warm up, they are sluggish (making them easy prey even for a pint sized predator) and they cannot even digest food, if they have any appetite at all. The climate warmed up again during the Cretaceous. By the end of the Cretaceous, it got warmer again, warmer even than the Jurassic. Large dinosaurs evolved again from smaller ones. During hot weather, the smaller surface area means a large dinosaur can retain heat longer at night so it can be active and they do not have to bask in the sun to be warm enough to move around.
- JimZLv 73 weeks ago
When an animal gets that big it really has some problems to deal with in that it is so heavy that it has to be quite strong to cope. Just the physics or math of it means that a proportional sauropod that is 60 feet long relative to a 30 foot long sauropod will be 8 times as heavy (2x2x2) but only be 4 times as strong (2x2). Strength can be roughly calculated as the cross sectional area of the muscle. So growing large can really slow an animal down. The cretaceous sauropods must have evolved some very efficient muscles, heart, and lungs or it seems that a theropod could just start munching on them. Those giants of the Cretaceous are interesting.
There is a phenomena that happens sometimes with certain toxins where toxins in a plant grow more deadly and the herbivore develops resistance and the plant develops more in a kind of every increasing deadly toxicity trend. I wonder if something similar may have happened with the size of some of the Cretaceous dinosaurs. Maybe the herbivores grew large and then the predators grew larger and the herbivores grew even larger to help survive the predators and reach new food sources etc. etc. Still, it only happened in the Cretaceous so I don't know what would have been different before. The predators seemed pretty similar in the different periods.