Study of cervical vertebrae on titanosaur sauropod: contribution for phylogenetic analysis

ORTIZ DAVID, LEONARDO; GONZÁLEZ RIGA, BERNARDO J.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

In sauropods, cervical vertebrae are one of most relevant structures of the skeleton. They have been studied in details in most diplodocids, brachiosaurs and camarasaurs. However, this topic has not been described yet in detail in titanosaurs, a group of sauropods that exhibit an amazing diversity on the cervical series. This study is focused on anatomy of cervical vertebrae and their application in phylogenetic analyses. Cervicals show differences in size and shape. Some taxa show lateral expanded neural spines in cervicals, like Isisaurus colberti, Mendozasuaus neguyelap, Bonitasaura salgadoi, Ligabuesaurus leanzai and Quetecsaurus rusconii. However, the anatomical details of these structures are different and must be described with accuracy in the phylogenetic matrix. Fourth main distinct structural patterns are recognized: (1) Mendozasaurus-type, (2) Ligabuesaurus-type, (3) Bonitasaura-type, and (4) Isisaurus-type. In the first one (e.g., Mendozasaurus, Futalognkosaurus) a very wide neural spine is formed by lateral laminae that are not related to the spinopostzygapophyseal or the spinoprezygapophyseal laminae. The same lateral laminae are also present in Quetecsaurus, but they are less developed. In the second type, the huge neural spines of Ligabuesaurus are formed by splayed lateral spinoprezygapophyseal laminae. In the third type, Bonitasaura has a rhomboid-shaped neural spine forming a simple expansion of the distal spine without a clear contribution of anterior or posterior laminae. Therefore, the broad neural spine of Bonitasaura lacks the lateral laminae of Mendozasaurus. In the forth type, neural spine of Isisaurus is linked with the spinopostzigapophyseal laminae. In the character matrix this morphology can be describe by three characters: (A) Lateral expansion of the neural spine: absent (0); present (1); (B) Lateral expansion formed by: lateral spinoprezygapofisial laminae (0); spinopostzygapophyseal laminae (1); lateral laminae (2); thickening without contribution of laminae (3); (C) Wide of the neural spine: less than the 70 percent of the centrum wide (0); between the 70 and 100 percent of the centrum wide (1); more than the centrum wide. This comparative study demonstrate that titanosaurs encompassed a greater cervical diversity than was previously appreciated, topic useful to phylogenetic analyses.