Abstract
ABSTRACT A morphological revision is presented here on the cohort Otomorpha, a clade currently interpreted as the most primitive among the large supercohort Clupeocephala. Otomorpha is a morphologically heterogeneous group represented by clupei forms , alepocephaliforms, and ostariophysans (gonorynchiforms, cypriniforms, characiforms, siluriforms, and gymnoti forms) that inhabit various marine and freshwater environments worldwide. Otomorphs have a long (ca. 145 Ma) and diverse fossil record. They are the largest fish teleostean clade worldwide, as well as the largest of the Neotropical Region. While molecular studies strongly confirm the monophyly of Otomorpha, most potential morphological synapomorphies of the group become homoplastic largely due to the peculiar morphological character states (either losses or transformations) present in alepocephaliforms. The fusion of haemal arches with their respective vertebral centra anterior to preural centrum 2 stands as an unambiguous synapomorphy of the clade. The ankylosis or fusion of the extrascapular and parietal bones, and silvery areas associated with the gas bladder are also interpreted as synapomorphies, although they are homoplastic characters mainly due to secondary losses or further transformations of the morphological features in the alepocephaliforms.
Highlights
The largest neopterygian clade, the Infraclass Teleostei, has undergone major changes in the last 20 years mainly due to the development of molecular techniques and studies that changed the content, position and phylogenetic interpretations of numerous clades that were historically based on morphological characters (Arratia, 2015); changes in the Teleostei tree include the recognition of new taxa and the deletion of some nominal orders and families
The search for potential synapomorphies of Otomorpha was focused on skeletal structures beginning with a revision of characters previously proposed as synapomorphies of clupeiforms plus ostariophysans
The additional cartilage is characteristic of the crumenal organ present in alepocephalids and argentinoids (Greenwood, Rosen, 1971; Johnson, Patterson, 1996), whereas this cartilage is absent in the epibranchial organ found in gonorynchiforms with different cartilages
Summary
The largest neopterygian clade, the Infraclass Teleostei, has undergone major changes in the last 20 years mainly due to the development of molecular techniques and studies that changed the content, position and phylogenetic interpretations of numerous clades that were historically based on morphological characters (Arratia, 2015); changes in the Teleostei tree include the recognition of new taxa and the deletion of some nominal orders and families.
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