Abstract
We describe a dentary of a new titanosaur sauropod, Baalsaurus mansillai, gen. et sp. nov. from the Late Cretaceous of Patagonia, Argentina. The material comes from the Portezuelo Formation, Neuquén Group. Titanosaur sauropods lower jaws are scarce and only nine taxa with dentaries have been described. There are two types of morphology in titanosaur dentaries; "L" shaped or "U" shaped based on the shape, without a phylogenetic issue. In this paper; we recognize a new taxa, Baalsaurus mansillai, represented by an "L" shaped dentary with three apomorphic characters that are not present in other taxa: dentary alveoli with 10 teeth in the anterior ramus, a ventrally and anteriorly inclined symphysis and a wide ventral Meckelian groove surrounded by a thin lamina that forms a keel on the ventral border of the dentary.
Highlights
Since more than 100 years ago, titanosaur sauropods have been some of the most common record of dinosaur fossils from Gondwanan continents
Isolated bones from the lower jaw have been described for some taxa such as in Antarctosaurus wichmanianus (Huene 1929), Ampelosaurus atacis (Le Loeuf 2005), Bonitasaura salgadoi (Apesteguia 2004, Gallina and Apesteguia 2011), Rapetosaurus krausei (Curry Rogers and Forster 2004) and Quaesitosaurus (Kurzanov and Banikov 1983), Karongasaurus gittelmani (Gomani 2005), Brasilotitan nemophagus (Machado et al 2013) Choconsaurus bayleiwillisi (Simón et al 2018)
Diagnosis: Baalsaurus differs from other titanosaurs in the following combination of features: a) dentary alveoli with 10 alveoli on the anterior ramus, b) dentary with ventrally and anteriorly inclined symphysis and c) wide ventral meckelian groove surrounded by a thin lamina that form a keel in the ventral border of the dentary
Summary
Since more than 100 years ago, titanosaur sauropods have been some of the most common record of dinosaur fossils from Gondwanan continents. Diagnosis: Baalsaurus differs from other titanosaurs in the following combination of features: a) dentary alveoli with 10 alveoli on the anterior ramus, b) dentary with ventrally and anteriorly inclined symphysis and c) wide ventral meckelian groove surrounded by a thin lamina that form a keel in the ventral border of the dentary. The dentary in dorsal view is L-shaped forming a strong 90 degrees angle between anterior and posterior ramus giving a square jaw morphology (different to Nemegtosaurus and Rapetosaurus but similar to Antarctosaurus). Sauropod pencil like teeth are restricted to diplodocids and titanosaurs; jaw movement, tooth morphology and wear surface is different (Calvo 1994a, b). The long axis of the dentary symphysis in Baalsaurus inclines anteroventrally differently to Antarctosaurus wichmanianus, Sarmientosaurus, Quaesitosaurus, Karongasaurus, Nemegtosaurus and Tapuiasaurus where it is perpendicular to the long axis of the lower jaw, while in Malawisaurus, Bonitasaura and Diplodocus (McIntosh and Berman 1975) it inclines posteroventrally. The Meckelian groove opens in the ventral symphysis differently to Nemegtosaurus that opens on the ventral third of the articular surface
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