After the dinosaurs went extinct, why didn’t new giant animals come to be?
In: Biology
As other answers point out, there were and are plenty of giant animals after non-avian dinosaurs disappeared. Several species of whale are larger than any dinosaurs were (at least by weight if not length). And the largest land mammals like [*Palaeoloxodon* and *Paraceratherium*](https://i.pinimg.com/originals/f6/19/62/f6196287ce4209a28c226a4cac43b3b1.jpg) would have surpassed pretty much all dinosaurs except for [some of the more impressive sauropods](https://i.pinimg.com/originals/61/5d/92/615d92f3f2a720155126347699a1154d.jpg). Mammals of [all types and all over the world](https://science.sciencemag.org/content/sci/330/6008/1216/F1.large.jpg?width=800&height=600&carousel=1) increased in size after the end of the Cretaceous, and reached about the same average size as we see now within just 15 million years ([Smith et al. 2010](https://science.sciencemag.org/content/330/6008/1216?casa_token=_rctBUafwfUAAAAA:j-YKS47hkoPY5VQJkc225llT5wSqMved50_6MNDDnEJiPDIN8MlDICVqm-Pjhrcj7Oqd2mnboM_aqQ)). The question of why land mammals have still not been able to approach the very largest dinosaurs is not that clear, but it most likely has to do with a combination of factors including breathing and temperature regulation (which sauropods were great at thanks to [large bird-like air sacs](https://static.scientificamerican.com/blogs/cache/file/23C1EE59-CC6F-4542-A5EAACB8E6336F06_source.jpg)), reproduction (laying eggs vs. pregnancy), and differences in available food resources.
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