Abstract
A small juvenile turtle is described from the Early Cretaceous Jehol Biota, shedding light on the juvenile morphology and ontogeny of Manchurochelys manchoukuoensis. Several juvenile features are uncovered, such as a small and circular carapace (less than half of the adult), wide vertebral scales, and lateral carapacial fontanelles. In contrast to the adult morphology, which has an oval carapace, closed lateral fontanelles, and longer vertebrals 2–4, the juvenile of M. manchoukuoensis is more comparable to that of Sinemys lens, except for earlier occurrence of the well-ossified carapace of the latter. Differs from Changmachelys bohlini, and Ordosemys liaoxiensis, in which the circular carapace is relatively independent of ontogenetic age, and the lateral fontanelles are only closed in adult stage of O. liaoxiensis. Therefore, the trajectory of ontogenetic change appears to be highly diversified in the sinemydids.
Highlights
As part of the basal eucryptodires, the sinemydid turtles are dominated and widely distributed in the Early Cretaceous of East Asia (e.g., Hirayama, Brinkman & Danilov, 2000; Rabi, Joyce & Wings, 2010; Joyce et al, 2016)
As known in Sinemys lens (Brinkman & Peng, 1993), the ontogenetic series show the morphology varied from the juvenile to adult, with the carapacial outline is nearly rounded in the juvenile and becomes to an oval in an adult; vertebral scales 2–4 are wide in juveniles but much narrower in adults
Based on the juvenile specimen, our study firstly reveals the juvenile morphology and ontogeny of Manchurochelys manchoukuoensis, such as a circular carapace, wide vertebral scales, and lateral carapacial fontanelles, which distinct from the adult condition
Summary
As part of the basal eucryptodires, the sinemydid turtles are dominated and widely distributed in the Early Cretaceous of East Asia (e.g., Hirayama, Brinkman & Danilov, 2000; Rabi, Joyce & Wings, 2010; Joyce et al, 2016). Sinemydids (Manchurochelys manchoukuoensis, Ordosemys liaoxiensis, Liaochelys jianchangensis, Xiaochelys ningchengensis) have been discovered from the Jehol Biota and a large number of well-preserved fossils have been described (e.g., Tong, Ji & Ji, 2004; Zhou, 2010a; Zhou, 2010b; Zhou & Rabi, 2015). As known in Sinemys lens (Brinkman & Peng, 1993), the ontogenetic series show the morphology varied from the juvenile to adult, with the carapacial outline is nearly rounded in the juvenile and becomes to an oval in an adult; vertebral scales 2–4 are wide in juveniles but much narrower in adults. The ontogenetic change is relatively less developed in O. liaoxiensis (Tong, Ji & Ji, 2004) and Changmachelys bohlini (Brinkman et al, 2013)
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