Spectember 2023 #06: Some Big Reptiles

An anonymous request asked for a “large ankylosaur-like herbivorous notosuchian“:

A shaded sketch of a speculative ankylosaur-like animal related to modern crocodilians. It has a chunky body covered in interlocking armor plates, with a row of spikes down each side of its body and a longer pair of upward-pointing spikes on the bulbous tip of its tail. It has four squat legs, also armored, with hoof-like claws, and a short wide snout with large forward-facing nostrils.

Mitafosuchus pachysomatus is descended from Simosuchus-like notosuchians in Madagascar that survived through the K-T extinction.

Highly convergent with the now-extinct ankylosaurs, it’s a 5m long (~16’4″) squat tank-like herbivore with hoof-like claws, and a wide short snout used for grazing on low vegetation. Heavy interlocking osteoderm amor covers most of its body, protecting it against the big carnivorous crocodyliformes that also still survive in this version of Cenozoic Madagascar.


Another anon wanted to see a “giant warm blooded lizard”:

A shaded sketch of a speculative giant lizard descended from tegu. It has a small head with a slender snout, a crest on its head and a small pair of horns behind its eyes. Its neck is long and thick with a hanging fleshy dewlap, a chunky body with a sloping back, four legs in a semi-upright stance, and a long thick tail.

Atopohippus zestamenus is a descendant of invasive Argentine giant tegu lizards that became established on an island archipelago. At 2m tall (~6’6″) and around 6m long (~20′) it’s an example of island gigantism, and occupies a high-browsing-herbivore ecological niche similar to giant tortoises and prosauropods.

Its ancestors’ seasonal endothermy has become full endothermy in this species, partly due to young individuals having a very rapid growth rate and metabolism – their main defense against the predators on their island home (primarily carnivorous tegu-descendants and large birds of prey) is to simply get to a big body size as fast as they possibly can.