Skeletons Part 2 Lecture Notes PDF

Overview In the first part of the lecture we gained some familiarity with anatomical terminology and the axial and appendicular skeleton Now we will move on to examining the vertebrate skull, focusing on bones, holes, and sutures Idea is to start to gain familiarity with the complexity o...

Overview In the first part of the lecture we gained some familiarity with anatomical terminology and the axial and appendicular skeleton Now we will move on to examining the vertebrate skull, focusing on bones, holes, and sutures Idea is to start to gain familiarity with the complexity of skulls 1 Learning Outcomes In this lecture we will focus on: LO1: Basic anatomical terminology LO2: Head, neck, and trunk - the axial skeleton LO3: Limbs and girdles - the appendicular skeleton LO4: Skulls – the cranial skeleton LO5: Comparisons between vertebrates 2 Skulls Just looking at a skull already tells you a lot about an animal Key feature of vertebrates Common evolutionary origin Made up of many bones 3 Skull - function https://sketchfab.com/michiganherpetology The skull supports and protects the brain and sensory organs Cerebellum Cerebrum Brainstem Orbits Vomeronasal organs Pit organs Nasal cavity Melon Etc. 4  Pachycephalosaurs One of my current research areas is Pachycephalosaur cranial taxonomy Their skulls are highly derived (altered from the ancestral state) To understand and compare them we need to know which bones are which The Witmer lab in Ohio has created 3D scans of a few species You can play with these, selecting/removing individual bones 5 https://people.ohio.edu/witmerl/3D_pachy.htm Cranial anatomy and skull morphology Having scared you with Pachycephalosaurs let’s go back to basics! As you can see there is significant variation in skull morphologies However, vertebrate skulls share many commonalities They are derived from the same bones They have holes (fenestrae) and joints (sutures) 6 Skull anatomy and evolution Understanding skull anatomy allows you to follow major changes over time 7  Early tetrapod skull ventral views Amphibian ancestors We can trace patterns of gain Amniote ancestors and loss through time Allows us to understand relationships between modern vertebrates 8 Skull diagrams - amniotes Individual bones labelled with letters e.g. parietal (p), squamosal (sq), nasal (n) Lines indicate sutures Contact points where bones attach/fuse Large holes are called fenestrae “Windows”; muscle attachment or organs 9  Cranial bones Skull roof nasal (n), frontal (f), parietal (p), postparietal (pp) Circumorbital (around the eye) prefrontal (prf), lacrimal (l), postfrontal (pof), postorbital (po), jugal (j), supraciliary (su) Temporal Quadrate (q), intertemporal (it), supratemporal (st), squamosal (sq), tabular (t), quadratojugal (qj) Marginal jaw Premaxilla (pmx), maxilla (mx) Lower jaw Dentary (d), angular (an), surangular (sur), coronoid (co), splenial (sp), prearticular (pre), articular (ar), mentomeckelian (me) Red = not present in modern animals Orange = present in a few restricted lineages Underlined = missing in turtles 10  Cranial bones Braincase basisphenoid (bsp), orbitosphenoid (osp), basioccipital (bos), exoccipital (exo), supraoccipital (soc), prootic (pro), opisthotic (op), epiotic (ep), sphenethmoid (sph) Palatal vomer (v), palatine (pal), pterygoid (pte), ectopterygoid (ecpt), parasphenoid (par) Red = not present in modern animals Blue = not present in amphibians Orange = present in a few restricted lineages Underlined = missing in turtles 11  Bones In mammals, certain skull bones have been repurposed into the ear bones Articular -> malleus Quadrate -> incus Collumella -> stapes 12 Sutures (aka Cranial sutures) Joints between bones of the skull Right lateral Filled with fibrous connective tissue Change with ontogeny Typically more elastic in youth e.g. Newborn humans have “fontanels”; soft spots where sutures have not yet fused Fuse with age Dorsal 13 Holes and cavities Fenestrae (fenestra) Temporal fenestrae; behind the eye socket Diapsids: supratemporal & infratemporal Synapsids: single temporal fenestra Some archosaurs possess additional fenestrae Antorbital; in front of the eye Mandibular; in the jawbone Fossae (fossa) Cavities and shallow depressions brain: anterior, middle, posterior Foramen (foramina) Pineal foramen Openings and holes in bone Often for passage of nerves or blood vessels Nares (naris) and Orbit(s) 14  Skull diagrams Lateral (right) A little daunting at first! Dorsal General anatomical features of skulls Lateral right Bones (may be labelled with letters) mandible Sutures (joints between bones) Anterior Fenestrae (holes between bones) Skulls can also be divided into regions neurocranium (braincase) Ventral splanchnocranium (jaw supports) dermatocranium (dermal bone: skull roof, Medial right facial bones, external jaw bones) mandible Beznosov, P.A., Clack, J.A., Lukševičs, E. et al. Morphology of the earliest reconstructable tetrapod Parmastega aelidae. 15 Nature 574, 527–531 (2019).  Fish skulls Additional considerations Chondrocranium (cartilage scaffold) Many elements shared with tetrapods Highlighted here 16  Tetrapod skulls Kevin the Ichthyostega 17  Tetrapod skulls Seymouria lived ~ 280 Ma Many elements still present in modern tetrapods Some have been lost Otic notch also unusual 18  Modern amphibians Amphibians have lost or fused many of the bones present in early tetrapod skulls Most of neurocranium does not ossify Skulls simplified compared to ancestors 19  Rhynchocephalia The Tuatara “Classic” diapsid skull Upper and lower temporal fenestrae Temporal bar Parietal foramen (aka parietal “eye”) 20  Squamata - lizards Tegu Derived diapsid skull Loss of lower temporal bar 21  Squamata - snakes Serpentes have a very derived diapsid skull Extreme loss of bone (have lost: l, sq, epi, ju, qu) Jaw bones not fused; use elastic ligaments Venom fangs in some lineages Gaboon viper Fangs tuck into mouth Back-up fangs ready to go 22  Testudines Turtles have robust skulls Also a derived diapsid skull! In this case reverted to “anapsid” structure Loss of temporal fenestrae Green sea turtle 23  Crocodilia Crocodiles, alligators, caimen Robust skulls Secondary palate Retroarticular process 24  Aves Aves have lost some elements and greatly reduced or fused many bones in their skulls Light skeletons are better for flight 25  Monotremes e.g. Echidna Egg-laying mammals No teeth in adults No auditory bulla Elongated maxilla and palatine Tachyglossus 26  Marsupials e.g. Oppossum Marsupials typically have a large facial area Small brain case Rear part of jaw turned inward rather than outward More teeth than placentals 27  Placentals e.g. Cat Placentals tend to have highly specialised teeth Large braincase Complex auditory bullae 28  Placentals - Human Humans have 22 bones in our skulls 8 cranial 14 facial bones 29 Comparisons between taxa – cervical vertebrae Typically 1-4 cervical Fish vertebrae E.g. Rainbow trout 30 Amphibians One cervical vertebra C1 (Atlas) 31 Humans 7 cervical vertebrae 32 Mammals Typically mammals have 7 cervical (neck) vertebrae Manatees and two-toed sloths have 5-6 One mammal has more than 7 Which one? 33 Giraffes? No! 7 cervical vertebrae! 34  Bros planning Three-toed sloth something 8-10 cervical vertebrae! devious 35 Snakes Corn snake: 3 cervical vertebrae 36  Mammenchisaurus 19 cervical vertebrae 37 Swan (Cygnus olor) 25 cervical vertebrae 38 Does anyone know what this is? Does anything look wrong to you? 39 40 Elasmosaurus This is Cope’s original reconstruction of the skeleton of Elasmosaurus Cope described over 1400 taxa and was one of the key players in The Bone Wars Edward Drinker There was just one small problem… Cope (1840-1897) 41 Elasmosaurus Cope’s arch rival Othniel Charles Marsh noticed an important issue with the reconstruction The head was on the wrong end… Othniel Charles Marsh (1831-1899) 42 Elasmosauridae Elasmosaurids hold the record for the most vertebrae and the longest necks Albertonectes vanderveldei is the current champion with 132 vertebrae in total(!) The head was not recovered but otherwise it was mostly complete 76 cervical vertebrae – 7m of this animal was neck! Albertonectes 43 vanderveldei Skeletal case study 44 Dasypeltis A genus of Colubrid snakes from Africa ~ 18 species Non-venomous Usually in forests with high bird abundance Dasypeltis scabra is most well-known species 45 Dasypeltis skull 46 Dasypeltis vertebrae 47 48 49 50 51  Skull provides clues about lifestyle Dasypeltis skull Anaconda Bitis gabonica skull skull Ophiophagus hannah Crotalus horridus skull skull Reduced bone Few and small teeth No fangs (no venom) 52 Skeleton adapted to egg-consumption Specialised vertebrae act like teeth Anteriorly-facing ‘hypapophyses’ Crack the shell by grinding egg against hypapophyses Contents leak out into gut, muscles uses to crush shell and regurgitate it 53 Learning Outcomes - Revisited LO1: Basic anatomical terminology LO2: Head, neck, and trunk - the axial skeleton LO3: Limbs and girdles - the appendicular skeleton LO4: Skulls – the cranial skeleton Anatomical features: bones, sutures, fenestrae, etc. LO5: Comparisons between vertebrates Some examples of differences and similarities between vertebrates; cervical vertebrae 54 Take home message Understanding anatomical terminology allows you to compare similarities and differences within and between taxa The skeleton is a key adaptation of vertebrates and can be divided into two main parts: axial and appendicular Morphology of the skull and skeleton tells you a lot about the organism Every bone has a specific name learn them and what they refer to if you want to get really good at vertebrate taxonomy! 55 Next up: Week 3 Practical – Comparative Skeletal Anatomy Week 3 Seminar – Dr Manabu Sakamoto 56