page_title: Lithostrotia
section_title: Definition and synapomorphies
hierarchical_section_title: Lithostrotia / Definition and synapomorphies
caption_attribution_description: English: Caudal pneumaticity varies among sauropods. In the diplodocid Tornieria, the first 15–20 caudal vertebrae have neural arch laminae and fossae, and lateral pneumatic foramina opening into large internal chambers. Images traced from Remes ([51]: fig. 31 [lateral view]) and Janensch ([72]: fig. 7 [cross-section]); the two views are from different vertebrae. In the basal titanosaurian Malawisaurus, caudal pneumaticity is restricted to a handful of proximal caudal vertebrae, in which the neural arches are honeycombed with pneumatic chambers but the vertebral centra are solid. Images traced from Wedel ([12]: fig. 2A [lateral view] and 2C [cross-section]). In the derived titanosaurian Saltasaurus, the first 20–25 caudal vertebrae have large external fossae but small external foramina, and both the neural arches and centra are honeycombed with chambers. Images traced from Powell ([59]: plate 53 [lateral view]) and Cerda et al [20]: fig. 4F [cross-section]); the two views are from different vertebrae.
context_page_description: Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Unchurch et al. in 2004 as the most recent common ancestor of Malawisaurus and Saltasaurus and all the descendants of that ancestor. Lithostrotia is derived from the Ancient Greek lithostros, meaning "inlaid with stones", referring to the fact that many known lithostrotians are preserved with osteoderms. However, osteoderms are not a distinguishing feature of the group, as the two noted by Unchurch et al. include caudal vertebrae with strongly concave front faces, although the farthest vertebrae are not procoelous.
context_section_description: Upchurch and colleagues (2004) define the Lithostrotia as a node-based taxon that includes the last common ancestor of Malawisaurus and Saltasaurus and all descendants of that ancestor. According to this definition the Lithostrotia includes all forms that are more derived than Malawisaurus in phylogenies.
  In addition to defining the group Upchurch and colleagues gave two common derived features (synapomorphies), which serve to distinguish the group from non-members. The first is that all caudal vertebrae apart from the farthest distal were procoelous, meaning their front face was concave. Also, the front (proximal) caudal vertebrae were particularly strong procoelous. This first feature is also shared with Mamenchisauridae.
  Unchurch et al. named Lithostrotia based on the presence of osteoderms in many members, but the eponymous osteoderms do not represent synapomorphy, as the evolutionary history of osteoderms is unknown within the titanosaurs. It may be this trait has developed multiple times independently within the titanosaurs and Lithostrotia, as osteoderms are known in many saltasaurids, Mendozasaurus, Aeolosaurus, Ampelosaurus and various other genera both within and outside Lithostrotia with different morphologies.
caption: Caudal vertebrae of Malawisaurus (top right) and Saltasaurus (bottom) compared with Tornieria
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