Vertebrates (L18)

Temporal fenestrae

opening in the temporal region of the skull of some amniotes (involved in muscle attachment)

Vertebrates (Craniates)

clade within Chordates

Tunicates

sister group to the Vertebrates

Vertebrates (groups)

Agnathans and Gnathostomata

Shared Chordate traits (seen at least in some points of life)

dorsal notochord, dorsal nerve cord, muscular post-anal tail, pharyngeal slits, elements of the GI system

Notochord

rod-like structure located under the nerve chord derived from mesoderm

Vertebrate traits

vertebral column, cranium, complex genomes, eyes

The vertebral column replaces

the notochord during development (supports nerve cord)

Cranium

bony, cartilaginous structure surrounding the brain

Complex genomes in vertebrates are due to

two whole genome duplication events

Myllokunmingia

earliest vertebrate (530MYA - early Cambrian)

Myllokunmingia (characters)

agnathan, small tapered animal, pharyngeal arches, notochord, rudimentary vertebrae, lobate extension to head (brain)

Myllokunmingia (possible characters)

optic capsules (eyes), nasal sacs

Agnathan

paraphyletic group of (mostly extinct) fish that lack true bony jaws and teeth

Agnathan species

Hagfish, Lamprey, Conodonts, Ostracoderms

Agnathan peak diversity

Devonian (400 MYA)

Hagfish

Myxiniformes (Latin name)

Lampreys (Latin name)

Petromyzontida

Hagfish

deep sea carrion feeders

Lampreys

marine parasitic fish that feed on blood and tissue fluids of other fish

Hagfish have a single

nasal opening connecting to pharynx

Hagfish inner ear

one semi-circular canal

Hagfish eyes

are reduced and often completely covered in thick skin and muscle

Hagfish slime glands

along body produce mucus

Hagfish tie themselves

in a knot using slime to escape predators and help when feeding

Lampreys attach to prey

using a sucker disc

Lampreys have large

eyes and good colour vision

Lampreys’ internal skeleton

notochord, vertebra-like structure, cartilaginous skull, gill arches, fin rays

Lampreys inner ear

2 vertical semi-circular canal

Conodonts

form apatite fossils (Ca3(PO4)2) only present in vertebrates

Conodont fins

caudal fins with radial supports

Ostracoderms

Paraphyletic group of fish with head shields made of dermal bone

The dermal bone makes

the skull and clavicle in humans

Ostracoderm (groups)

astraspida, anaspida, osteostraci

Astraspida

tubercles on head shield made of dentine covered in enameloid (~human teeth)

Anaspida

(Silurian) paired pectoral fins

Osteostraci (group of Ostracoderms - Agnathans)

(Mid-Silurian to Devonian) paired pectoral fins

Gnathostomata (groups)

Chondrichthyes, Osteichthyes

Chondrichthyes

cartilaginous fishes

Osteichthyes

bony fishes

Osteichthyes (groups)

Actinopterygii, Sarcopterygii

Actinopterygii

ray-finned fishes

Sarcopterygii

lobe-finned fishes

Sarcopterygii (groups)

Coelacanths, Rhipdistia

Sarcopterygii to Amniota

Rhipdistia - Tetrapoda - (Lissamphibia +) Amniota

Dipnoi

Lungfish, part of Rhipdistia

Chondrichthyes (groups)

sharks, rays, skates, sawfish

Earliest accepted shark (~360MYA)

Cladoselache

Chondrichthyan-like fossil record consists of

mostly teeth and scales

Lissamphibia

caecilians, frogs, salamanders

Placoderms

extinct group of jawed fishes

Best known species of Placoderm

Dunkelosteus

Dunkelosteus

dermal bone and mobile head shield, paired pectoral and pelvic fins, caudal and anal fins

Acanthodians

extinct group of shark-like jawed fishes

Acanthodian characters (extinct group of Osteichthyes)

asymmetrical caudal fin, dentine scales (similar to sharks)

Heterocercal

Asymmetrical

Most fish with head armour

went extinct at the end of the Devonian

Ray fins are supported by

narrow bony rods - radials

Actinopterygii are the

dominant fishes found today

Actinopterygii skull

kinetic skull - can shoot out its jaw to catch prey

Actinopterygii have tooth-bearing

maxilla, pre-maxilla, dentary

Earliest Actinopterygii fossil and sister group

Cheirolepis

Fleshy lobe fins are

supported by a single basal bone with muscles to modify the posture of the fin

Coelocanths (living Sarcopterygian group)

Actinistia

Earliest Sarcopterygii fossil leading to Dipnoi lineage

Youngolepis

Gill Arch Hypothesis

all arches were gill-bearing and at some point front arches decoupled from respiration and evolved into jaws

Gill Arch Hypothesis (drawbacks)

no fossil found in which all arches are gill bearing

Arches (jaw development)

premandibular arch, mandibular arch, hyoid arch, vagal arch

Mandibular Confinement Hypothesis

jaw evolved via spatial confinement of the mandibular arch

Ancestral mandibular arch domain is

involved in respiration and sensory activity

Mandibular region was initially

extensive and distinct among pharyngeal arches but acquired common pharyngeal pattern at origin of jaw due to spatial confinement

Mandibular confinement occurred by

shift of domain boundary which restricted space for mesenchymal cells in the mandibular arch

Mesenchymal cells

precursor to adult bone marrow stem cells

Mesenchymal population no longer needed to

differentiate to feeding and ventilation structures so remodelled into the jaw

Embryological evidence shows

mandibular arch must be spatially confined for jaw to develop

Mandibular region is supported by the

hyoid arch

Mandibular region is used to provide

structure to the lower lip and the region of the head posterior to the mouth

Hind limbs

a developmental repetition of forelimbs

Actinopterygian fin [1]

fin rays covered in lepidotrichia, scapula

Lungfish fin [2]

scapula, humerus, series of pterygiophores

Lepidotrichia

jointed dermal bones

Pterygiophores

bone that supports the dorsal fin in fish

Eusthenopteron fin [3]

scapula, humerus, small pterygiophores, paired elements

Paired elements in Eusthenopteron fin are

precursors to ulna/radius and fibula/tibia

Structure is not considered a limb until

it possesses digits

Early tetrapods had [digits]

between 3 to 8 digits

All extant tetrapods have [digits]

5 digits (more derived forms have fewer digits)

Tetrapods have

fewer bones in the skull

Opercular covering of the gills is

first detached then lost (evolution over time)

Sea → Land evolution

dorsal-ventral flattening of skull; more robust ribs; loss of caudal, dorsal and anal fin rays; vertebral column becomes more rigid (zygapophysis)

Non-tetrapod Osteichthyes

Tiktaalik

Tiktaalik

transition fossil; longer snout, larger ribs, bony gill cover gone

Longer snout in Tiktaalik suggests

shift from sucking up to snapping up prey

Early tetrapods used limbs

to prop themselves up in shallow water and scuttle onto marshy areas

Lissamphibia

frogs, salamanders, caecilians

Biphasic

aquatic larvae and terrestrial adults

Genera of extinct salamander-like animals

Albanerpetids

Lissamphibia characters

humid/tropical environments, water-dependent reproduction, four digits, adults retain juvenile features

Temnospondyls

early amphibians from which extant amphibians arose

Early amphibians

Temnospondyls