An Early Jurassic Sauropod Tooth From Patagonia (Cañadón Asfalto Formation): Implications for Sauropod Diversity

Abstract

Abstract. Eusauropods were a group of herbivorous dinosaurs that evolved during the Early Jurassic and dominated the terrestrial ecosystems throughout the Jurassic and Cretaceous. A peak of diversity is represented by the Late Jurassic, when most of the lineages of the derived clade, Neosauropoda, are represented. Different lineages of eusauropods differ in several morphological aspects, including a great diversity in gathering strategies, inferred by their dentition morphology and wear facets. Here we describe a new tooth morphotype that can be well differentiated from any other tooth recovered from the Cañadón Asfalto Formation (Lower-Middle Jurassic). Therefore, this new tooth morphology increases the evidence of a high diversity of sauropods during that time as well as providing evidence of advanced characters in the dentition of some Early Jurassic sauropods (e.g., subcylindrical and narrow crowns with single apical wear facet).Key words. Sauropoda. Wear facets. Narrow-crowned. Broad-crowned. Argentina. Abstract. UN DIENTE DE SAURÓPODO DEL JURÁSICO TEMPRANO DE PATAGONIA (FORMACIÓN CAÑADÓN ASFALTO): IMPLICANCIAS PARALA DIVERSIDAD DE SAURÓPODOS. Los eusaurópodos fueron un grupo de dinosaurios herbívoros que evolucionaron durante el Jurásico Temprano y que dominaron los ecosistemas terrestres a lo largo de todo el Jurásico y Cretácico. Durante el Jurásico Superior se observa un pico en su diversidad, cuando la mayoría de los linajes de Neosauropoda, un clado derivado, se encuentran bien representados. Los diferentes linajes de Eusauropoda difieren en distintos aspectos morfológicos, incluyendo una gran diversidad de estrategias de alimentación, inferidas por la morfología de sus dientes y las facetas de desgaste. Aquí describimos un nuevo morfotipo de diente que puede ser bien diferenciado de cualquier otro diente recuperado de la Formación Cañadón Asfalto (Jurásico Inferior a Medio). Por lo tanto, este nuevo morfotipo incrementa la evidencia de diversidad de saurópodos durante ese momento, dando cuenta de caracteres derivados en la dentición de algunos saurópodos del Jurásico Inferior (e.g., dientes sub-cilíndricos con coronas angostas y una única faceta de desgaste apical).

Cranial anatomy ofBellusaurus sui(Dinosauria: Eusauropoda) from the Middle-Late Jurassic Shishugou Formation of northwest China and a review of sauropod cranial ontogeny

“…A low ridge extends apicobasally along the midline of the lingual surface of the crown, from the mid-crown mesiodistal expansion to the apex of the tooth, producing shallow troughs on either side. The teeth of non-diplodocoid and non-titanosaurian sauropods also exhibit apicobasal labial grooves near their mesial and distal margins ( Upchurch, 1995 , 1998 ; Wilson & Sereno, 1998 ; Mannion et al, 2013 ; Mannion, Allain & Moine, 2017 )—a feature identified as a synapomorphy of eusauropods and their closest outgroups ( Wilson & Sereno, 1998 ; Carballido & Pol, 2010 ; Carballido et al, 2017 )—but these are very weakly developed in Bellusaurus , manifesting as flat or shallowly concave surfaces. Tooth size decreases distally along the tooth row, and smaller teeth bear a shorter crown and are more distinctly recurved.…”

“…19A , 19B and 20GG – 20HH ). That most tooth wear consists of low-angled, V-shaped wear facets suggests an interlocking upper and lower jaw occlusion typical of eusauropods ( Chatterjee & Zheng, 2002 ; Carballido et al, 2017 ). In IVPP V17768.20, the enamel has been worn away basally, and the paired wear facets meet on the lingual aspect of the tooth.…”

Peer Review #2 of "Cranial anatomy of Bellusaurus sui (Dinosauria: Eusauropoda) from the Middle-Late Jurassic Shishugou Formation of northwest China and a review of sauropod cranial ontogeny (v0.1)"

“…A low ridge extends apicobasally along the midline of the lingual surface of the crown, from the mid-crown mesiodistal expansion to the apex of the tooth, producing shallow troughs on either side. The teeth of non-diplodocoid and non-titanosaurian sauropods also exhibit apicobasal labial grooves near their mesial and distal margins (Upchurch, 1995;Upchurch, 1998;Wilson & Sereno, 1998;Mannion et al, 2013;Mannion, Allain & Moine, 2017) -a feature identified as a synapomorphy of eusauropods and their closest outgroups (Wilson & Sereno, 1998;Carballido & Pol, 2010;Carballido et al, 2017) -but these are very weakly developed in Bellusaurus, manifesting as flat or shallowly concave surfaces. Tooth size decreases distally along the tooth row, and smaller teeth bear a shorter crown and are more distinctly recurved.…”

“…Among the teeth bearing paired, V-shaped wear facets, IVPP V17768.20 and IVPP V8299.3 exhibit markedly asymmetrical facets, the distal edge being more deeply worn and developing a pronounced shoulder (Figure 19A-B; Figure 20GG-HH). That most tooth wear consists of low-angled, V-shaped wear facets suggests an interlocking upper and lower jaw occlusion typical of eusauropods (Chatterjee & Zheng, 2002;Carballido et al, 2017). In IVPP V17768.20, the enamel has been worn away basally, and the paired wear facets meet on the lingual aspect of the tooth.…”

Phylogenetic analysis of Gondwanan basal eusauropods from the Early-Middle Jurassic of Patagonia, Argentina

“…Though used in many phylogenies, it has not received much revision since it was named and fi rst described in 1979 and 1986 by Bonaparte, and therefore its current phylogenetic position is unclear. Moreover, the strata from whence Patagosaurus and Volkheimeria were unearthed contain at least three other (as yet unnamed) sauropod taxa Rauhut, 2003a;Holwerda et al, 2015;Becerra et al, 2017;Carballido et al, 2017). This shows a higher taxic diversity than elsewhere in Gondwana or Laurasia in contemporaneous beds.…”