Thefossilizedremains of fisheggshave an extensiverecordgoing at least as far back as theDevonianand spanning into theCenozoic era.The eggs of many different fishtaxahave contributed to this record, includinglobe-finned fish,placoderms,andsharks.Occasionally eggs are preserved still within the mother's body, or associated with fossilembryos.Some fossil eggs possibly laid by fish cannot be confidently distinguished from those laid byamphibians;for example, theichnogenusMazonovais known from impressions of eggs which resemble eggs of both fish and amphibians. Paleontologist B.K. Hall has observed that the discovery of fossil fish eggs, embryos andlarvaelink the sciences of paleontology withevo-devo.[1]
Fish taxa known from egg fossils
editCartilaginous fishes
editFossilizedegg casesthat may have been laid by anelasmobranchorchimaeroidare known from as far back as the Devonian period. Egg sacs that can more confidently be referred to those taxa are known from theCarboniferoustoOligocene,although no embryos are known from these.[2]
Shark eggs have been recognized in the fossil record. More than thirty fossil sharkegg caseshave been discovered at the Bear River Seep Deposit of Washington state in the US.[3]These capsules are up to 5 cm in length and resemble those of moderncatsharkspecies in the genusApristurus.[4]Since fossil teeth attributable to this genus go back to the lateEoceneepoch, an ancientApristurusspecies might very well be the mother of the fossil egg cases. A less likely candidate mother would be the genusScyliorhinus,which also has a fossil record stretching back to the Eocene. However, modernScyliorhinusegg capsules are smoother than the Bear River Seep Deposit fossils, casting doubt on this possibility.[5]
Lobe-finned fishes
editSome well-preserved embryos have been found withyolksacs in the CarboniferousactinistianRhabdoderma exiguum.[6]These range in development from specimens still inside the egg to individuals who had partially resorbed their yolk sac. These specimens were part of theMazon Creek faunaofIllinois.[7]
Placoderms
editOne possible specimen of the DevonianplacodermCowralepis mclachlanicontained many unhatched egg sacs.[2]
Confounding factors
editSome fossil eggs possibly laid by fish can't be confidently distinguished from those laid byamphibians.Examples are known from various Carboniferous andTriassiclagerstattenthat preserve the eggs of aquatic vertebrates. The identity of the fossils' egglayers can't be confidently ascertained.[2]
See also
edit
Footnotes
edit- ^"4. Phylogenetic perspective on developmental patterns and processes," Cloutier (2010); page 410.
- ^abc"2. Fossil record of fossilized ontogenies," Cloutier (2010); page 401.
- ^"Results and Discussion," Treude (2011); page 178. For location and "BRSD" as standing for Bear River Seep Deposit, see "Abstract," page 175.
- ^"Results and Discussion," Treude (2011); pages 178–179.
- ^"Results and Discussion," Treude (2011); page 179.
- ^"2. Fossil record of fossilized ontogenies," Cloutier (2010); pages 401–402.
- ^"2. Fossil record of fossilized ontogenies," Cloutier (2010); page 402.
References
edit- Cloutier, R. 2010. The fossil record of fish ontogenies: insights to developmental patterns and processes.Semin Cell Dev Biology21: 400–413.
- Treude, T., Kiel, S., Linke, P., Peckmann, J., and Goedert, J.L. 2011. Elasmobranch egg capsules associated with modern and ancient cold seeps: A nursery for non-seep marine predators.Marine Ecology Progress Series437: 175–181.