在所有岛上处于食物链底端的恐龙中，有一种小型的草食恐龙被称为双坚颌龙。它一天到晚只做一件事情，就是贪婪地吞嚼远远超过自身体型的食物。 双坚颌龙的喙嘴的完美进化使它能够在摄取植物果实的同时还能避开那些不易消化的纤维。除非被攻击，双坚颌龙进食的过程中通常都会忽略周边的生物。 某些时刻，它会成为一种非常具有进攻性（尽管并没什么威胁）的生物，用超出自己所受到的威胁级别的尖叫和飞扑来恫吓对手。 你可能认为这样小只且弱势的生物会群聚一起生活，然而双坚颌龙却是一种独居生物。不过人们都知道它会从岛上的人类那里偷东西，不管它们是否孤独。
Common name: Pegomastax
Species: Pegomastax fructarator
Time: Early Jurassic
Among the bottom of the Island's dinosaur food chain is a small herbivore called Pegomastax fructarator. It is content to spend all day alone, gorging itself on far more food than you might reasonably expect for a creature of its tiny stature. Its beak appears perfectly evolved for collecting food from plants while avoiding indigestible fibrous strands. Pegomastax is likely to spend its time greedily foraging; this behavior can turn it into a very aggressive (though rather unthreatening) opponent, shrieking and whooping far above its actual threat level. It has been known to steal belongings from humans on the Island, regardless of whether they're alone or not.
You would expect a creature this small and weak to live in flocks, but Pegomastax seems to be rather solitary in nature. While not pretty, and far too small to ride, tribes often keep Pegomastax around for two reasons. Firstly, they are an excellent farming aid, its skill at scavenging means that it collects an extraordinary quantity of seeds and berries, while also handily gathering rare flowers, mushrooms and other ingredients necessary to cook up special concoctions. The other reason being that tamed Pegomastax can be utilized by tribes to steal items from others. Their nimble feet and quick fingers allow them to get away with loot unscathed and potentially undetected!