title: Pigmented anatomy in Carboniferous cyclostomes and the evolution of the vertebrate eye.
abstract: The success of vertebrates is linked to the evolution of a camera-style eye and sophisticated visual system. In the absence of useful data from fossils, scenarios for evolutionary assembly of the vertebrate eye have been based necessarily on evidence from development, molecular genetics and comparative anatomy in living vertebrates. Unfortunately, steps in the transition from a light-sensitive 'eye spot' in invertebrate chordates to an image-forming camera-style eye in jawed vertebrates are constrained only by hagfish and lampreys (cyclostomes), which are interpreted to reflect either an intermediate or degenerate condition. Here, we report-based on evidence of size, shape, preservation mode and localized occurrence-the presence of melanosomes (pigment-bearing organelles) in fossil cyclostome eyes. Time of flight secondary ion mass spectrometry analyses reveal secondary ions with a relative intensity characteristic of melanin as revealed through principal components analyses. Our data support the hypotheses that extant hagfish eyes are degenerate, not rudimentary, that cyclostomes are monophyletic, and that the ancestral vertebrate had a functional visual system. We also demonstrate integument pigmentation in fossil lampreys, opening up the exciting possibility of investigating colour patterning in Palaeozoic vertebrates. The examples we report add to the record of melanosome preservation in Carboniferous fossils and attest to surprising durability of melanosomes and biomolecular melanin.
authors.affiliation: Department of Geology, University of Leicester, Leicester LE1 7RH, UK sg21@le.ac.uk.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Gabbott
authors.affiliation: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
authors.forename: Philip C J
authors.identifier: 0000-0003-3116-7463
authors.initials: PC
authors.lastname: Donoghue
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester M20 6RT, UK.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Sansom
authors.affiliation: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
authors.forename: Jakob
authors.initials: J
authors.lastname: Vinther
authors.affiliation: Texas Materials Institute, The University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Andrei
authors.initials: A
authors.lastname: Dolocan
authors.affiliation: Department of Geology, University of Leicester, Leicester LE1 7RH, UK.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Purnell
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005123:Eye / Q000033:anatomy & histology*; D005580:Fossils; D006196:Hagfishes / Q000033:anatomy & histology*; D007798:Lampreys / Q000033:anatomy & histology*; D010802:Phylogeny; D010858:Pigmentation; D014714:Vertebrates
keywords: Mazon Creek; cyclostomes; melanosomes; retinal pigment epithelium