Comparative Anatomy Exam 2

Placoderms 

• mainly all dermal bone

Ancesteral Osteichyes (polypterus)

• Pectoral Girdles

Dermal and endochronral bone

attached to the head

Ancesteral Osteichyes (polypterus)

• Pelvic Girdles

not attached to anything

Chonchichtyes

• Pectoral Girdle and pelvic girdle

not attached to anything

Acanthodians

• pectoral girdle 

they dont have one

Acanthodians 

• Pelvic Girdle

Yes?

• they really small and simple and dont articulate with the girdle peices

Teleost

• Pectoral Girdle 

attached to the skull 

Teleost

• Pelvic Girdle 

Not attached to the head 

General Trends with Fishes

Pelvic Girdles may be present

• tend to not be attached to the rest of the body 

• small and wimpy 

General Trends with Fishes

Pectoral Girdles are mostly present

• tend to be larger than pelvic girldes 

• tend to be a mix of dermal and endochondral bone 

Coming out of the water moving to land

• Pectoral girdles:

  • Decrease in dermal bone, increase in endochondral bone

  • Fewer bones

  • Getting bigger

  • Stop attaching at the head - increase in head and neck mobility

Coming out of the water moving to land

• Pelvic girdles:

  • Increase in size, more robust

    • Help with support against gravity and muscle attachment

  • Attach to the vertebral column 

  • All endochondral

numbering digits

Medial — lateral

Sprawling posture (early tetrapods)

• fingers face anterio-laterally 

• toes face laterally (more or less) 

Derived Tetrapods general info

• limbs are now under the body

• limbs are more elongated 

  • limbs can become specialized 

  • makes gait more efficient 

• limbs are like levers 

In Derived Tetrapods

Pectoral Girdles : less number of bones, less dermal bone = more range of motion 

In Derived Tetrapods

Pelvic Girdle

• increase in size and surface area 

• have modifications for specialization 

weird bird stuff

Fusion and Bracing

• Pelvic girdle= synsacrium and some vertebra

• Left and Right clavicles = furcula

• Pectoral girdle fuses to support the keel

• Lost 2 digits and fuse carpals and metacarpals to make part of the wing

• All to make the bird able to withstand the flight muscles

Pterosaurs

• Wings have 4 digits, lost the fifth digit

• Have smaller 1-3 digits 

Bats

• wings are just elongated digits 

Humans are plantigrade meaning

they walk with their whole foot

Dogs and cats are digitigrade meaning

they walk on their toes

Horses are unudidgrade meaning

they walk on their tippy toes (hooved mammals)

Development of the axial skeleton

1. Notochord develops 

2. Mesenchyne develops from sclerotome blocks which surround notochord

3. Mesenchyme cells gather around the notochord to make cartilaginous vertebrae

4. Ribs: Develop within myosepta and then attach to vertebrae

What is mesenchyme

embryonic connective tissue that is formed from mesoderm 

Chondro/Neurocranium is what?

A lidless box that holds the brain (except in sharks there is a lid)

Splanchnocranium is what?

contains all of the arches 

• typically 7 of them 

Dermatocranium is what?

The lid for the brain box

group that have centrum

• persistent notocord that exist throughout life 

sturgeons 

Groups that have no ribs or sternum

1. cyclostomes 

2. placoderms 

3. acanthodians 

4. holocephalans 

groups that have ribs and sternum

1. chondrostei

2. actinsti

3. dipnoi 

groups that have trunk and caudal vertebrae (regionalization)

1. acanthodians 

2. holocephalans 

3. chondrostei

4. actinsti

5. dipnoi 

osteitchythes (boney fish)

• most have centra 

• trunk and caudal vertebrae 

tetrapods : Big picture

• sternum: support and connect the pectoral girdle to the axial skeleton

• Ribs: lose the dorsal set; keep the ventral set 

  • ventral set: 2 headed ribs (capitulum and tuberculum)

• notocord is only in intervertebral disks

• pre and post zygopophysise: lock the vertebae together 

• differentiation of vertebrae 

Extant amphibians generally 

• ribs are variable

Extant amphibians (frogs)

• sternum

• no ribs in adults

Caecillians

• no sternum

• have really long ribs 

Fully aquatic salamanders

• no sternum 

• very reduced ribs 

Fully terestrial salamanders 

• cartilageans sternums 

• big ribs

In amphibians the shape of the cervical vertebrae varies 

• amphicoelus 

  • concave on the anterior side and concave on the posterior side 

• opisthocoelus 

  • concave on the posterior and convex on the anterior side of the vertebrae

Non bird reptiles

• ribs 

  • true ribs: connect to the costal cartilage

  • false ribs: costal cartilage that merges together

  • floating ribs: ribs that dont connect to the sternum at all 

• sternum 

• have regionialization of the vertebrae 

  • cervical, thoracic, lumbar, sacral(2 of them), caudal 

Non bird reptiles vertebae shape

proecoelus

• concave on the anterior side and convex on the posterior side 

Turtles

• no sternum 

• ribs: fused to the carapase 

• trunk vertebrae: fused to the carapase

  • decrease in the total number of vertebrae except cervicals 

Mammals

• ribs 

  • true ribs: connect to the costal cartilage

  • false ribs: costal cartilage that merges together

  • floating ribs: ribs that dont connect to the sternum at all 

• sternum 

• have regionialization of the vertebrae 

  • cervical, thoracic, lumbar, sacral(2 of them), caudal 

Birds = Fuse and Reduce

• Reduce the number of ribs

  • Ribs are hooked together with unicate process

    • Helps to support muscles during flight

• Sternum increases in size and becomes very robust to attach flying muscles

• Generally: Big surface area = lots of muscle attachment

Flightless Birds

• the rib and sternum characteristics are not true because they don’t fly so they don’t need them

vertebrae in all birds

• Cervicals - can be up to 26 depending on the bird (flexible, not often fused)

• Lots of fusion happening and loss of flexibility

  • Synsacrum (lumbar vertebrae + sacral + caudal + pelvis)

  • Pygostyle (caudal vertebrae)

  • Notarium (cervical) in some birds which articulates with pectoral girdle when present

vertebrae shape in birds

• Heterocoelous

  • Anterior view will be saddle/dumbell shape (peanut)

  • Posterior view kind of looks like a blobby x that interlocks with anterior

skull development

• Notoochord - anterior part of notochord becomes base of neuro/chondrocranium

• Mesoderm makes up posterior part of neuro/chondrocranium 

• Splanchno and dermatocranium will be the neural crest

cyclostomes cranial skeleton 

• Chondrocranium

• Splanchocranium - but no jaws 

• Really small hyoid arches

Ostracoderms cranial skeleton 

• Chondro (neuro)cranium

• Splanchnocranium - still no jaws

• Dermatocranium - all of the head shield 

placoderms cranial skeleton 

• Neurocranium

• Splanchocranium with jaws

• Dermatocranium - LOTS that’s the armor

Placoderm Jaw

• Palatoquadrate

• Mandibular cartilage

• Palatoquadrate and mandibular cartilage are hidden under the dermal bone

How did we get Jaws?

1. gill arch theory 

2. heterotrophic theory

Gill arch theory

jaw bones look like gill arches 

• serial theory: mandibular arch came from the first or second branchial arches and the hyoid came from the next branchial arch 

• composite theory: mandibular arch is a fusion of multiple arches 

heterotrophic theory

• Gene expression in larval lampreys and other vertebrates

• Gene expression in neural crest cells in the lamprey lips are different than extant gnathostomes

why have jaws?

• could lead to improved feeding efficientcy 

• could be to improve ventilation 

Chondroitchthes

• no dermatiocranium 

• just have a chondrocranium and spanchocranium 

  • hyoid arch: jaw support can be really mobile 

osteichtyes (Non- tetrapods)

• early: had robust dermatocraniums

• modern: showed a decrease in the amount of dermatocranium 

• Jaws

  • upper: premaxilla, maxilla 

  • lower: dentary 

tiktaalik

• totally fused skulls

  • helps resist high biting forces

• upper jaw is not mobile

  • fused to the skull 

• lower jaw 

  • many bones 

moving towards reptiles

• temporal roofing bones move further into the skull

• brain case increases in size because the brain incre

extant amphibians

• Fused skulls 

• decrease in the number of bones 

• decrease in the size of some bones 

• hyoid arch gets incorporated into the tongue 

• Q-A jaw joint 

moving towards reptiles continued

• temporal fenestrae are around the post orbital and squamosal bones 

• anapsids = no temporal fenstrae 

extant reptiles

• Q-A jaw joint 

• snakes and lizards have kinetic skulls 

  • decrease in the number of fusions 

• mostly made of dermatocranium (all reptiles)

• hyoid arch moves into the tongue 

• diapsids with merged temporal fenstrae 

turtles

• fusion of the skull 

• dont have a secondary palate 

crocs 

• Skulls are fused 

• have a secondary palate 

• kept the diapsid condition 

general bird information

• lots of dermatocranium

• decrease in the number and size of bones to allow for flight 

• kinetic skulls in some beaks 

• hyoid arch can be part of the tongue 

synapsids

• braincase increases in size 

  • this distorts the temporal fenstrae to the point where we cannot see them 

• secondary palate: helps with breathing during eating and strengthens the jaw 

• turbinate bones develop in eutherians 

  • help to warm and humidify the air 

synapsids jaw joint

• dentary increases in size, contacts the squamosal bone 

Early mammals have

• double articulation

  • Q-A and D-S 

one intelligent morning, the fishes hyomandibular became the stapes 

• Intelligent: (IQ) = quadrate to incus 

• Morning: (AM) = Articular to malleous

• hyomandibular to stapes or columella

stylpod equals what

humerus

zeugpod equals what 

radius and ulna 

autopod equals what 

The hand