Fish History & Classification

1. Fish History & Classification http://main.nbii.gov/portal/community/Communities/Geographic_Perspectives/Mid-Atlantic/Featured_Projects/EKey_-_Electronic_Key_for_Identifying_Freshwater_Fishes/ Chapter 11

2. Part I: Early Fishes Ostracoderms and Placoderms

4. Refresher of geologic time scale • Paleozoic Era 570 - 240 million years before present (mybp) • Cambrian 570 - 505 mybp • Ordovician 505 - 438 mybp • Silurian 438 - 408 mybp • Devonian 408 - 360 mybp • Carboniferous 360 - 290 mybp • Permian 290 - 240 mybp

5. Refresher of geologic time scale • Mesozoic Era 240 - 63 mybp • Triassic 240 - 205 mybp • Jurassic 205 - 138 mybp • Cretaceous 138 - 63 mybp • Cenozoic Era 63 mybp - present • Paleogene 63 - 24 mybp • Neogene 24 mybp - present

6. What happened when? • Notice where major evolutionary events occured. • Ancestors of fish did not happen spontaneously. • Continuous development was (is) working on each taxonomic group all the time.

7. Ostracoderms (shell-skins) - earliest vertebrates in fossil record • Originated in late Cambrian Period? (> 500 mybp) - first record is from Ordovician • Were abundant and diverse through the Ordovician and Silurian Periods (approx. 100 million years) • Became extinct by the late Devonian Period (approx. 380 - 400 mybp)

8. What group preceded Ostracoderms? • Earliest vertebrates probably like modern Cephalochordates (Amphioxus) • Bilateral symmetry • Free-swimming (perhaps neotonous larva) • with cephalic sensory structures • with branchial gill apparatus • without bone, jaws or paired fins

9. Traits of Ostracoderms* • Boney armor - first record of bone in fossils - protection from predators • Internal skeleton - made of cartilage • Heterocercal tail • Lacked true jaws - were pump-filter feeders • Lacked paired fins - weak swimmers • Benthic habitat • Small size - none longer than 15 cm

10. Ostracoderm classification • Two classes: • Class Pteraspidomorphi (sp. diplorhina = “two nares”) • they literally had two separate olfactory bulbs in the brain. • those with a different shell, i.e. dermal armor

11. Ostracoderm classification • Class Cephalaspidomorphi (“single nostril”) • jawless fish

13. Success of Ostracoderms • First use of bone • for protection, not support • possibly used as auxiliary supply of Calcium? • Use of filter feeding to exploit common and abundant food source: plankton and suspended organic matter

14. Limitations (failures) of Ostracoderms • Habitat limitations • restricted to benthos (no kiddin’!?!) • weak swimmers due to heavy armor • weight • inflexibility • Food limitations • no jaws - restricted to plankton, suspended organics - slow growth

15. Fate of Ostracoderms* • Extinct within 100 million years - by late Devonian • Lineage debated... • possibly lampreys (Petromyzontiformes) • possibly Chondrichthyes • possibly Osteichthyes

16. How good were they? • Ostracoderms were key to vertebrate evolution! • Gave rise to jawed vertebrates! • Jaw evoluation considered as the single "greatest development in vertebrate evolution“ (Romer (1962) I know I like mine....

17. Placoderms - earliest gnathostomes(jawed vertebrates) • Originated after the Ostracoderms: • Originated in Silurian Period (440 mybp) • Abundant and Diverse in Devonian Period • Extinguished in Carboniferous Period (350 mybp)

18. Two key traits account for Placoderm success: • True jaws • opened new realm of food sources - larger prey items vs. filter-feeding - allowed faster growth to larger sizes • Paired fins • coevolved with acquisition of jaws: • greater control of movement • more effective pursuit and capture of prey

20. Additional traits first appeared in Placoderms • Bony dermal plates (produced by dermal cells) with three layers: • enamel layer - outer surface - hard & shiny • spongy layer - large vacuoles • lamellar layer - layered strata with flat vacuoles • Bony internal skeleton

21. Traits shared with Ostracoderms • Negatively buoyant (due to heavy plates) • Occupied benthic and near-benthic habitats (epi-benthic) • Dorsoventrally depressed (flat)--common among benthic fishes • Strictly marine

22. Differences from Ostracoderms • Placoderms reached larger sizes • up to 10 m (33 feet) in length • why? - food source, mobility • Placoderms had slightly lighter and more flexible (articulated) armor

23. Success of Placoderms • Diversity: • greater than any other group of fishes present in Devonian • seven orders within single class • Duration: • 440 - 350 mybp

24. Fate of Placoderms • Probably evolutionary “dead-end” • Plesiomorphies with Chondrichthyes & Osteichthyes: jaws, paired fins, internal skeleton - suggest common ancestor • Apomorphies: armor, jaw structure, depressed form - suggest they are NOT ancestral to Chondrichthyes & Osteichthyes

25. Part II:Classification Specifics

26. REM: Taxonomy – The theory and practice of describing, naming, and classifying organisms. Systematics – The classification of living organisms into hierarchical series of groups emphasizing their phylogenetic interrelationships. Nomenclature – The system of scientific names applied to taxa.

27. Why is Classification Important? • Communication- “Okay...I get that...” • Prediction- “Don’t get that...”

28. Why is Classification Important? • Communication • - apply consistent names to organisms • - Genus and species name for each organism is unique • - same name used everywhere • - important in keeping track of losses of biodiversity • - know which and how many species at certain time • to how severe the loss is in the present (management) • - Ex. Western United States = water habitats altered

29. Why is Classification Important?

30. Why is Classification Important? • Prediction • - reflects evolutionary history • - members of a group will share a more common • ancestor with each other than with members of • other groups • - will have inherited similar traits • - use shared history to infer that closely related • species share similar traits

31. Suborder Anabantoidei • Gouramies • - possess apparatus that allows extraction of O2 • gulped air. (labyrinth organ) • Betta • - systematically classified as gouramies • - possess apparatus?....yep! • - able to live in low O2environments

32. Why is Classification Important? • Prediction (cont.) • - environment • - can impose an adaptive regime on species that • live there • - results in shared features of unrelated species • -Gars and pikes • - similar body form due to ecological niche

33. Taxonomic Categories Phylum -- Chordata Subphylum Vertebrata Superclass Gnathostomata Grade Teleostomi Class -- Osteichthyes Subclass -- Actinopterygii Infraclass -- Neopterygii Division -- Teleostei Order -- Perciformes Family -- Centrarchidae Genus -- Micropterus Species -- salmoides

34. Taxonomic Categories • Current system based exclusively on shared • common ancestry • All categories that taxonomists apply to fish are • artificial (descriptive) except for one…species • Species is a real entity (biological)…other • categories are artificial assemblages • - most biologists believe that species are • real entities that exist in nature.

35. What is a species? Biological Species Concept (Mayr 1940) Biological Species : A group of actually (or potentially) interbreeding natural populations genetically isolated from other such groups by one or more reproductive isolating mechanisms. • most commonly applied species concept • - Some associated problems

36. What is a species? • Problem: • hybridization • -fish are notorious for this practice • -hybrids are often sterile (or thought to be! (HSB?) • -some are fertile and able to backcross with • either parent

37. Why are there so many species? • random genetic changes • differences in the selective environment • Anagenesis: change in a species over time • - species exist as a single population and whole species • will change over time and not branch off into • multiple discrete species.

38. Why are there so many species? • formation of multiple species from a single • ancestral species is due to isolation of the population into • distinct populations or gene pools. • Why? • - each population undergoes anagenesis and • eventually individual populations are distinct • enough to be recognized as separate species.

39. Why are there so many species? • What causes isolation? • - vicariant event: a geological or climactic event • - Isthmus of Panama = the most studied • -- around 3.5 mya • -- tropical Atlantic separated from tropical Pacific • Allopatric speciation: single species diverge into two species • in separate geographic locations • (squirrels/mountains)

40. Why are there so many species? • Sometimes populations of closely related species will • coexist in an environment. • Genetic independence achieved through premating • and postmating reproductive isolating mechanisms

41. Why are there so many species? • Postmating • - hybrid sterility • - inviability • Why is hybridization rampant among fish? • - external fertilization • - eggs and sperm drift in the proximity of gametes from • a different species • Avoidance: • - sexual selection: partners choose appropriate mates • - males are brightly colored to attract females

42. Why are there so many species? • Premating • - sexual selection: partners choose appropriate mates • - males are brightly colored to attract females • - males especially colorful in genera that have a large • number of coexisting species • Ecological differences • limits degree of competition • food preference, timing and location of spawning

43. African Cichlids

44. North American Darters

45. Linnaean Classification

46. Linnaean Classification • Rules of Nomenclature • still named the same wayas Linnaeus and Artedi did in 1758 • genus name is always capitalized • species name is lower case • oldest valid name sticks with the species • genus names are unique among all biota • species names are unique within a genus • International Code of Zoological Nomenclature • American Fisheries Society (US)

47. Phylogenetic Classification Genus 1 Genus 3 Genus 2 Species 1 Species 3 Species 2 Species 2 Species 3 Species 2 Species 1 Species 1

49. Phylogenetic Classification • Cladistics • lumps together groups that are assumed to share a • common ancestor. • Clade: group that contains an ancestor and all of its • descendents. • - Guidelines defining clade from Willi Hennig (bug man) • - shared derived characters • derived character: is different from some primitive • common ancestor.

50. Character State: Gas Bladder Physoclistous Physostomous