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

Ostracoderms and Placoderms Part I: Early Fishes Ostracoderms and Placoderms

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

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

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.

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)

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

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

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

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

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

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

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

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....

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)

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

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

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

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

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

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

Part II: Classification Specifics

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.

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

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

Why is Classification Important?

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

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 O2 environments

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

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

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.

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

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

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.

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.

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)

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

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

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

African Cichlids

North American Darters

Linnaean Classification

Linnaean Classification Rules of Nomenclature still named the same way as 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)

Phylogenetic Classification Genus 1 Genus 3 Genus 2 Species 1 Species 3 Species 2 Species 2 Species 3 Species 2 Species 1 Species 1

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

Character State: Gas Bladder Physoclistous Physostomous

Phylogenetic Classification Terms - homologous: characters that are alike in state due to shared common ancestry - homoplasy: characters that are alike in state for other reasons - independent origin: a trait can evolve independently in two different lineages e.g., countercurrent heat exchangers in mako sharks and tuna.

Phylogenetic Classification Terms - homoplasy (cont.) - reversion: a character may revert to a more primitive state. e.g., some eels lack scales and paired fins like primitive agnathans. Ancestors of eels possessed scales and paired fins, but were lost, thus reverting to the more primitive state.