Natural History of Sharks, Skates, and Rays Early Chondrichthyes MARE 394 Dr. Turner Summer 2008

Defining Elasmobranchs What kind of Thyes?...Chondrichthyes What kind of Fish?...Cartilagenous Fish What kind of Brates?...Vertebrates… What kind of Dates?...Chordates…

Phylum Chordata 3 subphylum: Subphylum Urochordata – tunicates, sea squirts Subphylum Cephalochordata – lancelets Subphylum Vertebrata – fishes, amphibians, reptiles, birds, mammals

Subphylum Urochordata – Sessile, feeding – Mobile, non-feeding 4 chordate traits: Dorsal hollow nerve chord, notochord, pharyngeal gill slits, post anal tail

Subphylum Cephalochordata 4 chordate traits: Dorsal hollow nerve chord, notochord, pharyngeal gill slits, post anal tail

Who did the what now? “Well, whenever I'm confused, I just check my underwear. It holds the answer to all the important questions.” – Grandpa Simpson Neoteny is the retention of juvenile traits in an adult Specifically, paedomorphosis is the developmental process by which these changes take place 6

Subphylum Vertebrata Characteristics that distinguish vertebrates: Extensive skull Backbone - a dorsal row of hollow skeletal elements (vertebrae) which enclose and protect nerve (spinal) cord

Fishes Simplest & oldest of all living vertebrates “I wish, I wish I did not kill that fish” – Homer Simpson Simplest & oldest of all living vertebrates Sharks (400-500 MYBP) Most abundant vertebrates (by # & species) ~29,500 living spp of fishes (>482 families) 58% Marine; 1% diadromous fish travel between salt & fresh water 9

Fishes Superclass Agnatha (jawless fish) Class Myxini (hagfish) Class Cephalospidomorpha (lamprey) Superclass Gnathostoma (jawed fish-cart) Class Chondrichthyes (cartilaginous fish) Superclass Osteichthyes (jawed fish-bony) Class Actinopterygii (ray-finned fish) Class Sarcopterygii (lobe-finned fish)

Super

Class Myxini (hagfish) - Cartilage skull - Lack jaws & vertebrae Superclass Agnatha Class Myxini (hagfish) - Cartilage skull - Lack jaws & vertebrae - All Marine (30 spp.) - Scavengers - Produce slime 12

Class Cephalospidomorpha Superclass Agnatha Class Cephalospidomorpha (lamprey) - Cartilage skull - Lack jaws & vertebrae - Freshwater & Marine (35 spp.) - Parasites – attach to host - Rasping tongue - Some diadromous 13

(sharks, skates, rays, ratfish) Superclass Gnathostoma Class Chondrichthyes (sharks, skates, rays, ratfish) - Cartilage skeleton (jaws & vertebrae) - Marine & few FW (750 sp.) - Traces of bone in scales & teeth - Buoyancy via liver – squaline oil - Spiral valve – corkscrew intestine SA:V ratio; compact - Internal fertilization of eggs - Claspers – modified pelvic fins ♂ Placoid scales 14

(sharks, skates, rays, ratfish) Superclass Gnathostoma Class Chondrichthyes (sharks, skates, rays, ratfish) Skates differ from Rays: Skates have a more muscular tail, two dorsal fins & often a caudal fin, lay eggs Skates & Rays differ from Sharks: Enlarged pectoral fins that attach to side of head, no anal fin, ventral gill openings, dorsal eyes & spiracles Ratfishes (Chimaeras): Possess an operculum or gill cover over gill slits, adults have no scales, ♂ clasper on head 15

Shark Ray Skate Ratfish 16

Class Cephalospidomorpha - Freshwater & Marine (35 sp.) - Parasites – attach to host - Rasping tongue - Some diadromous

Early Vertebrates Earliest vertebrates - early Cambrian 530 mybp (million years before present).. Early relatives of agnathans (jawless fishes) first 500+ mybp

Early Fishes

Early Fishes 1. Ordovician (505-438 mybp) 2. Silurian (438-408) 3. Devonian (408-360) 4. Carboniferous (360-290) 5. Permian (290-240) 6. Triassic (240-205) 7. Jurassic (205-138) 8. Cretaceous (138-63) 9. Cenozoic (63-24) 10. Quaternary (24-0) A. Hemicycapsis, B. Pterapsis, C. Cyathapsis, D. Drepanapsis, E. Coccosteus, F. Helodus, G. Cladoselache, H. Raja, I. Chimaera

Early Fishes Conodonts – (550 mybp) – known from small (<2mm) teeth found in fossil deposits Large eyes and eel-like bodies, notochord Closer to jawed fishes than lamprey & hagfishes

Early Fishes Hagfishes - (Class Cephalaspidomorpha)– (550 mybp?) – marine, jawless, eel-like fishes; scavengers Single nostril, rudimentary eyes, ventral mouth, tongue with rows of keratinized teeth

Early Fishes Lampreys – (Class Myxini) – anadromous or freshwater, lawless, eel-like fishes Predatory & non-predatory forms Keratinized teeth on buccal funnel & tongue

Early Fishes Ostracoderms – some of the earliest fishes Lack jaws, have paired fins, bony armor, cartilaginous skeleton, heterocercal tail (460 mya)

Early Fishes Placoderms – Earliest jawed fishes Heavy bony skeletons No special affinities with modern fishes

Placoderms Most likely sister group to the combined lineages of Acanthodii, Chondrichthyes, and Osteichthyes; share: 1) jaws with common structure 2) Two pairs of paired fins w/ bony girdles 3) three semicircular canals in inner ear

Early Fishes Acanthodii – “spiny sharks” – oldest known jawed vertebrates (440 mybp) Small (<20cm), large eyes, streamlined bodies, dentine-tipped scales

Early Fishes Chondrichthyes – What are they Doctor? Sharks, rays, & skates… But that’s not important right now…

Early Fishes Osteichthyes – bony fishes – loosely defined group Defined by common structures and lack of characters that define chondrichthyes

Early Cartilagenous Fishes Chondrichthyan fishes most successful measured by historical endurance; ability to survive extinctions Defined by cartilagenous skeleton mineralized by calcifications (tesserae) and modification of mixopterygia (claspers) in ♂

Early Cartilagenous Fishes Two sister taxa: Elasmobranchii (sharks, rays, skates) & Holocephali (chimeras)

Evidence of Early Chondrichthyans Easier group to define than bony fishes: 1) only approximately 850 species 2) fossil groups are poorly known

Evidence of Early Chondrichthyans Scales & spines from early chond. Identified in Lower Silurian (430 mybp) to Devonian (350 mybp) Difficult to nail down due to similar mophology among scales & spines of thelodonts & acanthodians (spiny sharks) at this time

Evidence of Early Elasmobranchii Appeared in middle Devonian (350 mybp); rays appeared during Jurassic (200 mybp) Few well preserved specimens; difficult to piece together evolution Two early forms: cladoselachian & xenacanth sharks

Evidence of Early Elasmobranchii Two early forms: Cladoselachian Xenacanth

Order Cladoselachiformes Lacked: claspers, an elongate skull, amphistylic jaw suspension, no anal fin, Had: triangular, paired fins, multicusped teeth Predator in marine systems

Order Xenacanthiformes Had: 2 anal fins, tail diphycercal (pointed) Predator in freshwater systems

Order Hybodontiformes Ancestral to modern sharks Appeared during Permian (260 mybp) Fed on large, active invertebrates – first with large, sharp teeth

Order Chimaeriformes Appeared during Devonian (350 mybp) with Elasmobranchs Modern forms during Jurassic (170 mybp)

Modern Cartilagenous Fishes Monophyletic group Common origin – distinct from bony fishes

Modern Cartilagenous Fishes Beyond cartilage have several traits in common…. 1. Simple box-like cranium 2. Upper jaws (palatoquadrate cartilage) not fused to cranium; lower jaw is a single element (Meckel’s cartilage) 3. 4-7 internal & external gill openings 4. Vertebral column is notochord supported by calcified vertebrae

Modern Cartilagenous Fishes 5. Pectoral & pelvic fins are supported internally by a girdle skeleton ; externally by rays (lepidotrichia) of flexible connective tissue 6. Basal skeleton on ♂ anal fins – claspers (paired copulatory organs) 7. Most have covering of small placoid scales (dermal denticles)

Modern Cartilagenous Fishes

S-U-C-C-E-S-S Success due to adaptive characteristics: 1) buoyancy 2) respiration 3) external covering 4) feeding 5) movement 6) sensory systems 7) osmoregulation 8) reproduction

Buoyancy -no swimbladder -combination of methods to reduce density Cartilage less dense than bone (1.1 vs 2.0) Large, oil-filled liver (0.8) (water 1.0) Hydrodynamic lift from heterocercal tail & pectoral fins

Respiration 3 basic means of respiration 1) Two-pump system (like teleosts) – pump O2 water across gills in slow-moving, bottom oriented sharks 2) Ram ventilation – push water across gills during swimming; fast-moving sharks 3) Spiracles – used to bring water across gills; small round opening precede gills on lateral sides of head – on top of head in rays – almost absent in pelagic sharks

External Covering All have placoid scales Rays – few rows on back; sometimes modified into spines Sharks – skin overlapping into lightweight, protective coat fast-swimming sharks have channels between scales to minimize turbulence

External Covering Slow-moving sharks more “armored” - dorsal spines Rays – barb/sting Skates – denticles Teeth are modified placoid scales

Feeding Most are specialized predators – teeth dictate type of feeding Triangular, blade-like teeth – large fish & marine mammals Long, thin, pointed – whole fish Rows of small, sharp teeth – small inverts Flattened, pavement-like teeth – hard-shelled inverts Pointed in front/flattened in back – small inverts (grasping and crushing)

Feeding Teeth continually shed & replaced; may loose 30,000 in lifetime Jaws loosely attached to cranium - can throw jaws or create suction Large stomach & spiral valve intestine

Movement Large heterocercal tail Counter-current heat exchangers in pelagic sharks (Lamnidae) Pectoral fins (Mylobatidae) – fly through the water

Movement Homocercal Heterocercal

Sensory Systems Odor – olfaction detects dissolved chemicals in the water Low frequency sounds – inner ear and lateral line system; “hear” and “feel” sound waves respectively Ampullae of Lorenzini – pit organs filled with an electrically conductive gel used for detecting weak electrical currents & magnetic fields

Ampullae of Lorenzini

Osmoregulation Osmoregulators – regulate internal salt concentration approximately 1/3 seawater Utilize large quantities or organic salts (urea & trimethylene oxide) Invade marine, estuarine (brackish) and freshwater systems

Reproduction Osmoregulatory and and reproductive systems likely evolved simultaneously; Long gestation periods of embryos (in egg or ♀, would not be possible without ability to withstand high concentrations of waste

Reproduction Unlike most bony fishes (teleosts) put most energy into relatively small number of large, active, young (ecological term?) Wide variety of means to this end: egg laying (oviparity) to live bearing (viviparity); all stages inbetween