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

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.

KEYWORDS:

• Batoid
• embryo
• egg case
• abortion
• collagen fibres
• yolk sac

Acknowledgments

The authors would like to thank the colleagues who collaborated in carrying out crucial parts so as to make this work possible: Prof. Ruggero D’Anastasio, of the University of Chieti and Pescara, Italy, who performed the observations and photographs under the binocular microscope; Dr Lorenzo Arrizza, of the Microscopy Center of the University of L’Aquila (directed by Professor Luca Lozzi), Italy, for all the laboratorial activities with SEM, with the EDX, and with the “Expanded Focus Microscope”; Dr Keisuke Furumitsu, of Nagasaki University, Japan, for his support in discussing egg cases and giving his information for egg cases of Hemitrygon akajeri; Donatella Del Pizzo and Luciano Lullo, who took the photographs that illustrate this paper. Finally, the authors thank the three anonymous reviewers of this paper who – with their comments and observations – have substantially improved the scientific content of this work.

Disclosure statement

No potential conflict of interest was reported by the authors.