FOSSIL COLEOIDS FROM THE LAGERSTÄTTE OF SÂHEL AALMA (UPPER CRETACEOUS, LEBANON)

The origin and divergence of modern decabrachians (squids, cuttlefishes) and vampyropods (octopods) remain elusive. Many paleontologists are currently working on exceptionally well-preserved Mesozoic gladius-bearing coleoids, which are reported from a few Konservat-Lagerstätten only. Among those are the Upper Cretaceous Lebanon Lagerstätten, a group of sites that provides the only record of exceptionally well-preserved fossil coleoids for the entire Cretaceous period.

The study of 17 specimens of coleoid cephalopods from the Santonian chalky limestones of Sâhel Aalma, from the Dubertret collection stored at the MNHN of Paris, reveals a diversity much higher than previously assumed for this Lagerstätte. Five species can be identified: Dorateuthis syriaca and Palaeoctopus newboldi (that were already reported from this site), as well as 3 species previously unknown in Sâhel Aalma: Glyphiteuthis libanotica, Glyphiteuthis n. sp. and Rachiteuthis n. sp. Consequently, we document the first unambiguous Santonian occurrence of the genera Rachiteuthis and Glyphiteuthis. We agree with previous authors in that the diagnostic characters for D. syriaca have yet to be clarified. In addition, morphological differences are so tenuous between D. syriaca and the Jurassic Senefelderiteuthis tricarinata and Plesioteuthis priscathat we suggest they might be seen as a single species.

The 17 studied specimens show numerous well-preserved soft-part characters. Some of them were previously unknown and have a major phylogenetic significance. For example, we document for the first time two transverse rows of sessile suckers in D. syriaca. We also confirm the presence of posterior salivary glands in D. syriaca specimens. On the contrary, the presence of eye capsules is challenged for Teudospeina coleoid specimens previously described from the plattenkalks of Hâqel and Hâdjoula. Well-preserved muscular fibers are also described for the first time on fossil coleoids from the Lebanon Lagerstätten.

Finally, the soft-part anatomy of the studied gladius-bearing coleoids (i.e. absence of tentacles, transverse pairs of suckers, sessile suckers, crop) strongly suggests that they are closely related to modern vampyropods.