more articulated and ossified. These seem to correspond with developmental levels of 45–50, and 64-day-old embryos of the american alligator. The last and more advanced stage is D where the embryos had completely ossified vertebral centra and a partially reduced neurocentral suture in their cervical vertebrae. Additionally, most therizinosaurian characters are more notorious in this phase, such as the edentulous premaxilla. The most mature embryo is represented by CAGS-01-IG-5, which had a clearly more developed ossification than alligator hatchlings. This indicates that embryonic therizinosaurids reached a more mature skeleton than other archosaur hatchlings in ovo and stayed within the egg for a longer period to enlarge their proportions despite the advanced ossification. Based on the developmental states preserved within embryos, Kundrát and colleagues suggested a rough incubation period between 1.5 and 3 months. Given that some embryos had their bones ossified and the fact that no adults were found in association with the nests, therizinosaurid hatchlings were highly precocial (capable of locomotion from birth) and able to leave their nests to feed alone, independently of their parents. Subterraneously constructed nests could be an indicative of the lack of parental care during the incubation period, furthermore, the skeletal maturity of stage D embryos was considerably adapted to allow immediate locomotion after birth, potentially suggesting a superprecocial behaviour. The independence from their parents may also be supported by the development of the teeth of the hatchlings that is consistent to an omnivorous diet. Paleoecology Therizinosaurids were very specialized herbivores that evolved a convergent life-style to the more recent ground sloths. They are so similar in some aspects that this idea is also reflected in the name of several species, such as Nothronychus (slothful claw) or Suzhousaurus megatherioides (Megatherium-like). Multiple of their anatomical and physiological traits such as leaf-shaped, coarsely serrated teeth, strong arm build with large claws, a notoriously elongated neck and the development of a keratinous beak situate therizinosaurids as browser herbivores. More specifically, therizinosaurids inhabited high-browsing niches in their ecosystems and commonly lived in semi-arid to wetland-like habitats composed of high vegetation as seen on the fluvial-lacrustrine setting of most specimens. As reflected by at least 31 therizinosaurid footprints at the Cantwell Formation of Alaska, some species formed small herds, which is consistent with the complex brain and ear structure in these theropods. The co-occurrence with hadrosaurids on this area may also indicate that these very different dinosaurs benefited from