Postcranial skeleton of Cricosaurus araucanensis (Crocodyliformes: Thalattosuchia): morphology and palaeobiological insights

Abstract

Herrera, Y., Fernández, M.S. & Gasparini, Z., 2013. Postcranial skeleton of Cricosaurus araucanensis (Crocodyliformes: Thalattosuchia): morphology and palaeobiological insights. Alcheringa 37, 1–14. ISSN 0311-5518.

The metriorhynchid crocodyliform Cricosaurus araucanensis (Gasparini & Dellapé) has been documented from Tithonian (Upper Jurassic) strata of the Vaca Muerta Formation exposed in the Neuquén Basin, northwest Patagonia, Argentina. Postcranial components of this species were mentioned but not described in the original analysis. Subsequently, other authors described the forelimbs. The postcranial elements of metriorhynchids are poorly documented in comparison with their skulls, but new data from C. araucanensis reveal delayed ossification of the caudal neurocentral sutures indicating skeletal paedomorphosis affecting not only the appendicular skeleton but also the posterior region of the vertebral column. The morphology of the caudal region (transverse processes of the first caudal vertebrae ventrally deflected) and the reduction in the femur of the fourth trochanter suggest a reduction of the hypaxial musculature allowing increased epaxial musculature. This pattern of musculoskeletal arrangement is consistent with the swimming style and propulsion by lateral undulation of the tail, as proposed by previous authors.

Yanina Herrera [yaninah@fcnym. unlp.edu.ar], Marta S. Fernández [[email protected]] and Zulma Gasparini [[email protected]], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n, W1900FWA La Plata, Argentina, CONICET. Received 23.7.2012; revised 16.10.2012; accepted 22.10.2012.

Cricosaurus araucanensis(Crocodyliformes: Thalattosuchia)的颅后骨骼: 形态学和古生物学含义

所记录的地蜥鳄类鳄鱼Cricosaurus araucanensis (Gasparini & Dellapé)采自Vaca Muerta组的Tithonian(上侏罗统) 层位; 该地层出露于阿根廷Patagonia西北部Neuquén盆地。该种颅后骨骼成分在原先的分析中被提及过但未被描述过。因此, 其他一些研究者就描述了前肢。与颅骨相比, 颅后骨的资料记录较少, 但Cricosaurus araucanensis的新资料发现尾部神经中部缝合线的滞后骨化现象, 说明骨骼幼态持续不仅影响了附肢骨骼, 还影响了脊椎柱的后部分。尾部形态(第一尾椎的横突向腹部弯曲) 和第四转子股骨的缩减表示下轴肌肉的缩减导致上轴肌肉的增加。这种肌肉和骨骼的安排与游泳方式和尾巴侧向摆动产生推力是一致的, 就像以前的研究者所认为的那样。

Key words:

• Metriorhynchidae
• neurocentral suture
• paedomorphosis
• Jurassic
• Vaca Muerta Formation
• Neuquén Basin
• Argentina

Acknowledgements

We are especially grateful to L. Acosta Burllaile (MLP) for preparation of the specimens; to R. Schoch (SMNS), W. Joyce, P. Havrlik and M. Aiglstorfer (GPIT) for providing assistance and access to the collections in their care. C. Dal Sasso (Museo di Storia Naturale di Milano) provided the photographs of cf. Pelagosaurus sp. (MSNM V4012). The authors thank the anonymous reviewers and editor for their suggestions that greatly improved this article. We thank N. Toledo (MLP) for his comments and C. Deschamps (MLP) for corrections to the English grammar. This research was supported by the following grants: Agencia Nacional de Promoción Científica y Tecnológica (PICT 2008-0261), Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 0426) and Programa de Incentivos Universidad Nacional de La Plata N607 (Argentina). Direct examination of specimens at Stuttgart (SMNS) and Tübingen (GPIT) was only possible with the support of the Deutscher Akademischer Austausch Dienst to YH, during her PhD.