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An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc.

ABSTRACT: The adhesion disc of living remoras (Echeneoidea: Echeneidae) represents one of the most remarkable structural innovations within fishes. Although homology between the spinous dorsal fin of generalized acanthomorph fishes and the remora adhesion disc is widely accepted, the sequence of evolutionary-rather than developmental-transformations leading from one to the other has remained unclear. Here, we show that the early remora †Opisthomyzon (Echeneoidea: †Opisthomyzonidae), from the early Oligocene (Rupelian) of Switzerland, is a stem-group echeneid and provides unique insights into the evolutionary assembly of the unusual body plan characteristic of all living remoras. The adhesion disc of †Opisthomyzon retains ancestral features found in the spiny dorsal fins of remora outgroups, and corroborates developmental interpretations of the homology of individual skeletal components of the disc. †Opisthomyzon indicates that the adhesion disc originated in a postcranial position, and that other specializations (including the origin of pectination, subdivision of median fin spines into paired lamellae, increase in segment count and migration to a supracranial position) took place later in the evolutionary history of remoras. This phylogenetic sequence of transformation finds some parallels in the order of ontogenetic changes to the disc documented for living remoras.

SUBMITTER: Friedman M

PROVIDER: S-EPMC3730593 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc.

Friedman Matt M Johanson Zerina Z Harrington Richard C RC Near Thomas J TJ Graham Mark R MR

Proceedings. Biological sciences 20130717 1766

The adhesion disc of living remoras (Echeneoidea: Echeneidae) represents one of the most remarkable structural innovations within fishes. Although homology between the spinous dorsal fin of generalized acanthomorph fishes and the remora adhesion disc is widely accepted, the sequence of evolutionary-rather than developmental-transformations leading from one to the other has remained unclear. Here, we show that the early remora †Opisthomyzon (Echeneoidea: †Opisthomyzonidae), from the early Oligoce ...[more]

PMID: 23864599

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Project description:Lizards play vital roles in extant ecosystems. However, their roles in extinct ecosystems are poorly understood because the fossil record of lizards consists mostly of isolated bones. This makes it difficult to document changes in lizard morphology and body size over time, which is essential for studies of lizard paleoecology and evolution. It is also difficult to compare available fossil lizard data with existing sources of extant lizard data because extant studies rarely measure individual bones. Furthermore, no previous study has regressed measurements of individual bones to body length across crown lizard groups, nor tested those regressions on fossil skeletons. An extensive dataset of individual bone measurements from extant lizards across crown taxonomic groups is here employed to develop novel methods for estimating lizard body size from isolated fossil elements. These methods were applied to a comparably large dataset of fossil lizard specimens from the robust Paleogene record (66-23 Ma) of the Western Interior of North America. This study tests the hypothesis that anatomical proportions have been conserved within higher-level crown lizard groups since the Paleogene and can therefore be used to reconstruct snout-vent length (SVL) and mass for fossil specimens referred to the same groups. Individual bones demonstrated strong correlation with SVL in extant as well as fossil lizard specimens (R2 ≥ 0.69). Equations for mass estimation from individual bones were derived from the SVL regressions using published equations for calculating lizard body mass from SVL. The resulting body size estimates from regression equations for the entire fossil dataset revealed that lizards reached greatest maximum body size in the middle Paleogene, with the largest size class dominated by anguid lizards that exceeded 1 meter in SVL and 1.5 kg in body mass. Maximum body size decreased to under 400 mm and below 1.5 kg in the late Paleogene. No association was found between changes in maximum lizard body size and marine isotope proxies of global temperature through the Paleogene. This is the first study to investigate body size evolution across lizard clades over a deep time interval and for a large geographic region. The proposed methods can be used to generate body size regressions and provide estimates of body size for isolated lizard bones referred to any crown group.

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An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc.

Publications

An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc.

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