A batoid hembryo (Chondrichthyes: Batoidea), from the marine upper Cenomanian (Late Cretaceous) Sannine limestone of Hjoula, Lebanon

Abstract

ABSTRACT Here, a fossil egg case that contains a well-preserved embryo is described. The embryo is characterised by (i) a rostral cartilage, (ii) some ribs, (iii) and a well-developed stinger; (iv) absence of thoracolumbar synarcual. This represents an unique combination of characters which demonstrate that the batoid that produced the egg case was a completely new form, possibly a stem–Myliobatiformes, which remains undetermined in the absence – to date – of any comparable adult specimen. SEM morphological analysis demonstrates that the wall of the fossil egg case was multilaminate, made up of collagen fibres (with a thickness of 2–4 μm): an ultrastructure that has been positively compared to the egg case of living Rajiformes (Raja asteria) and Myliobatifirmes (Hemitrygodon akajeri). The egg case also contains a mass that is interpreted as the remains of yolk sac, internally organised in platelets with a diameter of 25–35 μm. Since in living Myliobatiformes the egg cases disappears from inside the uterus before the end of the embryogenesis, the described fossil is interpreted as an embryo that was prematurely emitted by the pregnant mother, such as an abortion of a batoid dated to the Late Cretaceous.