page_title: Rhabdodontidae
section_title: Evolution
hierarchical_section_title: Rhabdodontidae / Evolution
context_page_description: Rhabdodontidae is a family of herbivorous ornithopod dinosaurs whose earliest stem members appeared in the middle of the Lower Cretaceous. The oldest dated fossils of these stem members were found in the Barremian Castrillo de la Reina Formation of Spain, dating to approximately 129.4 to 125.0 million years ago. With their deep skulls and jaws, Rhabdodontids were similar to large, robust iguanodonts. The family was first proposed by David B. Weishampel and colleagues in 2003. Rhabdodontid fossils have been mainly found in Europe in formations dating to the Late Cretaceous.
  The defining characteristics of the clade Rhabdodontidae include the spade-shape of the teeth, the presence of three or more premaxillary teeth, the distinct difference between the two maxillary and dentary teeth ridge patterns, and the uniquely shaped femur, humerus, and ulna. Members of Rhabdodontidae have an adult body length of 1.6 to 6.0 meters.
context_section_description: Rhabdodontids first appeared during the Barremian stage of the Early Cretaceous, and an extensive fossil record shows that they remained extant until the Maastrichtian stage at the end of the Late Cretaceous. During much of the Late Cretaceous, an isolated island habit in the western Tethyan archipelago contributed to the evolution of rhabdodontids in two main ways. First, the rhabdodontid dentition is relatively primitive, which is consistent with their habitat being sheltered from expansive mixing leading to a long period of dominance. Second, the fossil record contains three genera of rhabdodontids – Mocholdon, Zalmoxes, and Rhabdodon – that make up two geographically separated lines in the archipelago.
  Traditionally, it has been thought Mochlodon and Zalmoxes were insular dwarfs. The smaller sizes of Mocholodon (1.6 to 1.8 m) and Zalmoxes (2.0 to 2.5 m) relative to Rhabodon (5.0 to 6.0 m) and the island locale that all three genera shared led to the hypothesis of island nanism in the case of the former two. However, Ősi et al. (2012) proposed that Rhabdodon underwent gigantism on the mainland, as opposed to Zalmoxes and Mochlodon experiencing nanism on island habitats. Ösi and colleagues used femur length to estimate body size through evolution in the rhabdodontid lineage. The conclusion was that in the eastern lineage comprising Zalmoxes and Mochlodon, the size ranges of both were too close to that of the ancestral rhabdodontid to support the hypothesis of nanism. Ösi and colleagues instead came to the conclusion that Rhabdodon in the western lineage is a case of gigantism in the group Rhabdodontidae.
caption: Adult body sizes of Mochlodon, Zalmoxes and Rhabdodon.
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