LECTURE 5 - OUTLINE Evolution & Classification - Part I

Evolution & Classification 1. Overview - vertebrate origins 2. Overview - extant fishes

Agnatha 3. Phylogenetic relationships 4. Conodonta 5. Pteraspidomorphi

BIOL 4340 – Lecture 5 - 1

Overview : origin of vertebrates

Gnathostome(s)Sacabambaspis - raptorial feeders - pharyngeal expansion rapid & strong - rapid mouth closure & strong bite Agnathan(s) - exploited expanded pharyngeal pump - deposit feeders, mud grubbers etc. - transitional raptorial feeders 1. expansion of pharyngeal pump 2. definitive mouth closure Prevertebrate(s) - suspension feeders - feeding based on ciliary “pumps” - developed muscular pharyngeal pump 1. encircling band of muscles - pharynx 2. cartilage replaced collagen - pharyngeal bar BIOL 4340 – Lecture 5 - 2

1 MBP (millions of years before present)

- each column, first known fossil trace

- widths, estimates of abundance and diversity

- traditional broad groups across top

- conodonts missing

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Overview : extant fishes Phylum Chordata Subphylum Vertebrata (Craniata) Superclass Agnatha Superclass Gnathostomata (jawless vertebrates) (jawed vertebrates)

Class Myxini Class Chondrichthyes (hagfishes) Subclass Holocephali Class Cephalaspidomorphi (ratfish) (lampreys) Subclass Elasmobranchii (sharks/skates/rays)

BIOL 4340 – Lecture 5 - 4

2 Overview : extant fishes Phylum Chordata Subphylum Vertebrata (Craniata) Superclass Gnathostomata (jawed vertebrates) Class Sarcopterygii Class Actinopterygii Subclass Coelocanthimorpha Subclass Chondrostei (coelocanths) (sturgeons/bichirs) Subclass Dipnoi Subclass Neopterygii (lungfish) (gars/bowfin) Division Teleostei (all “modern” fishes)

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Superclass Agnatha (jawless vertebrates) Phylogenetic Relationships hi i p h or rp o om m id a o p nt id as o i sp al od in ra h n x e ep (e.g. lancelet) o y Pt C C M Gnathostomata

Loss: mineralized dental tissue; eyes jaws ? true bone cells Cephalochordata (outgroup) lateral line

tripartite brain : extant : extinct neural crest, ectodermal placodes

3 Conodonts Cambrian (544 - 505 mbp) - Triassic (250 - 208 mbp) Gk. kōnos , cone; odous , tooth Conodont elements - tooth-like microfossils - generally < 1 mm long - used for dating marine sediments

Molluscs? Chordates? Aquatic Plants? - origins unknown until ~1973 !! - origins unknown until ~1983

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Conodonts Cambrian (544 - 505 mbp) - Triassic (250 - 208 mbp) - laterally compressed animal bearing a complete set of conodont elements

- chordate hallmarks present

Conodont elements - evidence of wear & tare - mineralized dental tissue 1. calcium phosphate 2. enamel 3. dentin *

*dentin laid down by odontoblasts, indirect

evidence for the presence of a neural crest BIOL 4340 – Lecture 5 - 8

4 Class Pteraspidomorphi (“ostracoderms”)

Late Cambrian (544 - 505 mbp) - Late Devonian (410 - 360 mbp) Gk. ostrakon , shell; derma , skin First vertebrates to possess; - paired appendages - lateral-line system - bone (acellular) Bone located almost exclusively as an outer exoskeleton

Endoskeleton; - fibrous tissue - cartilaginous elements - occasionally bone cephalic plates fused, head shield

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Class Myxini (hagfishes)

Cambrian (544 - 505 mbp) - to date

Myxinikela siroka scale bar = 1 cm

- functional eyes - no slime glands BIOL 4340 – Lecture 5 - 10

5 Class Myxini (hagfishes)

Cambrian (544 - 505 mbp) - to date slime gland pores

- scaleless, worm-like, 3 pairs of barbels surrounding mouth - 1 to 14 lateral gill openings & a series of slime gland pores - caudal fin present but no paired fins or dorsal fin - eyes degenerate (blind) and no lateral-line system

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