VNH sect 2 notes 1 - Professor PDF

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VNH Sect 2 notes (lect) Sections in black are directly typed during lecture. Sections in blue are stories I’ve inserted to tie some of the topics together; they may not be an accurate interpretation of Dr. Ford’s comments. Sections in purple are topics that I think off as being outside of the flow of the story or as being meta-topics.

Vertebrate Story so far: Jaws & Paired fins…

Next part of story… Conquest of Land Lobe finned fish with fins that are good for walking along bottom (benthic) Walking catfish on land that walk from pond to pond (mudskippers in Australia) Happened pretty early Devonian – age of fish (diversified), but also when first organisms emerged onto land Also air and back to sea… (i.e., birds and whales)

In the Devonian, known as the age of fish, the fish have dominated life on Earth and have diversified greatly. The first organisms have appeared on land and are starting to emerge from the water. Benthic dwelling lobe-finned fish have developed perching limbs that will become useful as appendages capable of supporting weight and providing locomotion on land.

Leaving the water…. Why? To take advantage of food sources? // Predation? During the Devonian, fish diversified greatly and expanded to fill lots of environmental niches. Predation pressure or unexploited food sources may have driven some of them to prefer shallow coastal habitats and these early pioneers may have been benthic dwelling lobe-finned fish with fins designed for perching that were capable of some function as “legs”. Some of these fish inhabited shallow areas that were becoming increasingly drier or were going through more intense periods of drought and it became advantageous to be able to use their fins for crossing sections of land in search of water. Estivation (the ability to enter a dormant state by burrowing into the mud until the environment is re-filled with water) became an important trait for these creatures.

Early tetrapods also diversified during the Devonian adapting to flight and even back to the sea (see fig to right (Lepospondyl)).

What are the critical environmental differences? Climate –

Gravity:

Moving to land; no longer immersed

Oxygen:

Oxygen in atmosphere instead of dissolved in water

Drying:

Exposed to atmosphere; skin must change

What adaptations were necessary to shift to land? Lungs instead of gills: Locomotion:

Legs instead of fins

Bone: axial (backbone) and appendicular (arms and legs) skeleton; need strong skeletons to deal with gravity now that they are no longer suspended in water Fish - skeleton is for locomotion (V/W Myomeres) Land – need it for support Osmolarity: Eggs: amniotic – must be impermeable and can withstand being on land Homologies: Have same structures that are in fish but evolved to land Hands & feet – fins

Tetrapods – considered first terrestrial vertebrates Extant amphibians are representative of first land verts Evolved first pre-Devonian (*?extrapolated how?)

Fig 9.2 Lungfish and Coelacanths are outgroups to tetrapods Choana – found at the posterior (back part) of the nasal passage between the nasal cavity and the throat in tetrapods with secondary palates, including humans and other mammals (as well as crocodilians and most skinks). In animals with secondary palates, they allow breathing when the mouth is closed.[1] They are also known as the choanae ("funnel"). In tetrapods without secondary palates their function relates primarily to olfaction (sense of smell). Early bony fishes (~420 mya) had two pair of nostrils, one pair for incoming water (known as the anterior or incurrent nostrils), and a second pair for outgoing water (the posterior or excurrent nostrils), with the olfactory apparatus (for sense of smell) in between. In the first tetrapodomorphs (~415 mya) the excurrent nostrils migrated to the edge of the mouth… In all but the most basal (primitive) tetrapodomorphs, the excurrent nostrils have migrated from the edge of the mouth to the interior of the mouth. In tetrapods that lack a secondary palate (basal tetrapods and amphibians), the choanae are located forward in the roof of the mouth, just inside the upper jaw. These

internal nasal passages evolved while the vertebrates still lived in water. [3] In animals with complete secondary palates (mammals, crocodilians, most skinks) the space between the primary and secondary palates contain the nasal passages, with the choanae located above the posterior end of the secondary palate. Fish Most fish do not have choanae, instead they have two pairs of external nostrils. In lungfish, the inner nostrils are regarded as an example of parallel evolution. The fossil lungfish Diabolepis shows an intermediate stage between posterior and interior nostril and supports the independent origin of internal nostrils in the lungfish.

Amphibians in Batrachomorpha and Lepospondyls are outgroups to amniotes benthic perching fins- become hands and feet // fin rays lost Occipital condyles: is a rounded projection that is present on the posterior (bottom) of the dinosaur's skull. It articulates with the first cervical (neck) vertebra and, in effect, attaches the head of the dinosaur to its body. Functionally it allows the head to move from side to side, up and down, as well as to rotate. The presence of a single occipital condyle in dinosaurs, crocodilians and birds is contrasted with the condition in synapsids, amphibians, and mammals including Homo sapiens, where two occipital condyles are present. (https://en.wikipedia.org/wiki/Occipital_condyle)

Anapsids (turtles) and Synapsids (mammals) are outgroups to Diapsids (reptiles) Amniotes – eggs that can be laid on land All the animals you see on this evogram are synapsids, the group that gave rise to the mammals. Sometimes synapsids are called "mammal-like reptiles;" however, that is misleading because synapsids are not reptiles. Synapsids and reptiles are two distinct groups of amniotes, animals that produce young that are enveloped with a membrane called an amnion that prevents desiccation. All reptiles (including birds) have eggs with amniotic membranes (which some lay and others retain inside their bodies until hatching). And of course all mammals (the clade of synapsids still alive today) reproduce using an amnion, and those that lay eggs (e.g., the platypus and echidna) produce amniotic eggs. (http://evolution.berkeley.edu/evolibrary/article/0_0_0/evograms_05)

Diapsids (Reptiliomorpha) Two temporal fenestrations – allows for increased skull attachment points and therefore increased jaw strength The two subclades of crown tetrapods are Batrachomorpha and Reptiliomorpha. Batrachomorphs are all animals sharing a more recent common ancestry with living amphibians than with living amniotes (reptiles, birds, and mammals). Reptiliomorphs are all animals sharing a more recent common ancestry with living amniotes than with living amphibians.

Continental drift

Paleozoic era Tetrapod dist. before and after drift caused by plate tectonics Salamandridae evolved before Northern and Southern continents separated // when Laurasia separated from Gondwana Pangaea lasted ~160 my before breaking apart Sarcopterygiians led to amphibians

Lepospondyls

– like amphibians

Labyrinthodonts – Ancestral to Leposondyls and all other extant terrestrial verts. Shows fossil evidence supporting hypothesis of modern day asymmetric distribution of amphibian groups, marsupials, etc b/c of vicariance. Lepospondyls and Labyrinthotodonts were anamniotic (but not amphibians because they came before ampibians) Carboniferous climate: Devonian – lots of areas with drought periods Species that estivated – when it became drier eventually needed to be able to go find other habitats – needed to be able to move over land terrain Insects and other prey are taking hold on land Major adaptive radiations took place during the Carboniferous as the terrestrial habitat became more amenable to colonization.

Generalized lobe-finned fish (Sarcopterygii) Synapomorphies Kidney => develops bladder Hyomandibula – connects jaw to skull => eardrum & stapes Operculum – to protect gills but gills still feathery Anamniotes – eggs dumped into water although some live bearing Pelvic and thoracic fins => hind and forelimbs Plesiomorphic traits- refers to the ancestral trait state, usually in reference to a derived trait state Generalized primitive non-amniotic tetrapod “Labyrinthodont” (Stegocephalia) Ancestral to all extant terrestrial vertebrates incl. Tiktaalik and Acanthostega Still anamniotic – must still seek water to lay eggs Lungs: gills were feathery so that water could flow over and maximize surface area // Still adapted to aquatic habitat While most labyrinthodonts remained aquatic or semiaquatic, some of the reptile-like amphibians adapted to explore the terrestrial ecological niches as small or medium-sized predators. They evolved increasingly terrestrial adaptions during the Carboniferous, including stronger vertebrae and slender limbs, and a deeper skull with laterally placed eyes. They probably had watertight skin, possibly covered with a horny epidermis overlaying small bony nodules, forming scutes, similar to those found in modern caecilians. To the modern eye, these animals would appear like heavyset, lizards betraying their amphibious nature only by their lack of claws and by spawning aquatic eggs. In Carboniferous, smaller forms gave rise to the first reptiles. (https://en.wikipedia.org/wiki/Labyrinthodontia)

They evolved from Physostomes (as opposed to physoclists) that had a swim bladder (precursor to lungs) that allowed them to gulp air and fill bladder, which was advantageous in semi-aquatic habitat. Physostomes are fishes that have a pneumatic duct connecting the gas bladder to the alimentary canal. This allows the gas bladder to be filled or emptied via the mouth. This not only allows the fish to fill their bladder by gulping air, but also to rapidly ascend in the water without the bladder expanding to bursting point. In contrast, fish without any connection to their gas bladder are called physoclisti (evolved from physostomes but lost the air bladder) and it is called a swim bladder. The physostome fish encompass the bichirs, gars, a number of carps, trouts, herrings, catfish, eels and the lungfish. While the gas bladder in fish mainly serves as a buoyancy organ, some physostomes (though not all) can use their gas bladder as a lung, allowing them to live from atmospheric oxygen in conditions where aquatic oxygen levels have dropped to a point which would kill other fish.

Cladogram just of lungs Surfactant – chemical used to break water bonds Alveolae has thin layer of water to dissolve air so that it can diffuse into blood Would take a lot energy to pull apart all those H-bonds… So surfactant is like soap; disrupt H-bonding Premature infants often have trouble breathing because surfactant does not develop until very end of pregnancy Inside of lungs very convoluted to increase surface area

Vestibular apparatus for balance Stapes - is one of three ossicles in mammals. In non-mammalian four-legged animals, the bone homologous to the stapes is usually called the columella; however, in reptiles, either term may be used. In fish, the homologous bone is called the hyomandibular, and is part of the gill arch supporting either the spiracle or the jaw, depending on the species. Bladder – don’t want to leave a trail of urine and helps conserve water

Circulation to lungs (pulmonary circuit) Now have to send blood to lungs instead of gills Fish: single pump (atrium & ventricle) Heart >> gills >> flesh Amphibians:

(2 atria & 1 ventricle)

Sixth arch becomes pulmonary artery Heart>> Mixed in ventricle >> some pumped to lungs some pumped to tissues (2 atria) >> tissue

Lymphatic system Gravity problem of circulatory system on land -Stand at attention for a long time – pass out because blood is pooling in extremities 2nd system needed to return blood in tissues Capillaries feed oxygen out into tissues (leaky – fluid also leaks out) Lymphatic system returns water to the blood

Pulmonary vs Systemic Archosaurs have 4 chambered heart – complete separation of two systems

Axial skeleton Fig 8.3 Need to get off the ground or you would rub all the skin off your belly Before have vertebra that touch each other – now need … Zygagophyses – vertebra need cross connections to help support each other while allowing flexibility // Can connect ribs to these as well

Bone marrow – bone can continue to grow as the animal grows in size Haversian canal - series of microscopic tubes in the outermost region of bone called cortical bone that allow blood vessels and nerves to travel through them.

Appendicular skeleton Fig 8.5 Hylonomus Can push vertebral column off of the ground Still using “wiggling” movement that fish use but now with feet attached (lateral undulation) Wiggle between planted and advanced feet position

As lineages moved into shallower water and onto land, the vertebral column gradually evolved as well. You may have noticed that fishes have no necks. Their heads are simply connected to their shoulders, and their individual vertebrae look quite similar to one another, all the way down the body. Mobile necks allow land animals to look down to see the things on the ground that they might want to eat. In shallow water dwellers and land dwellers, the first neck vertebra evolved different shapes, which allowed the animals to move their heads up and down. Eventually, the second neck vertebra evolved as well, allowing them to move their heads left and right. Later tetrapods evolved necks with seven or more vertebrae, some long and some short, permitting even more mobility. The vertebrae you are probably most familiar with (like our own!) consist of a spool-like centrum, which connects in front and back with other centra. On top of the centra are vertebral spines and arches to which muscle segments attach, and lateral to the centra are the ribs; these anchor muscles that flex as the animals move. Fishes swim with simple lateral motions, so their arches are relatively straight and needle-like, and so are their ribs. When you eat fish and pick out the bones, these are mostly what you're finding. Because fishes live in the water, gravity is not a big problem for them. But on land, a quadruped with a backbone between forelimbs and hindlimbs faces the same problems as a bridge designer: sag. As the fleshy-finned organisms began to venture onto land, they evolved a series of interlocking articulations on each vertebra, which helped them overcome sag and hold the backbone straight with minimal muscular effort. As the limbs and their connections to the rest of the skeleton evolved, limb bones took on distinct roles and many bones were lost. The humerus and the femur were already connected to two outer bones (the radius and ulna in the forelimb, the tibia and fibula in the hindlimb). This is something that evolved about 30 million years before vertebrates came onto land. However, muscular connections between these bones began to change on the road to land and allowed the limbs to be used for terrestrial locomotion. The ankle was originally composed of many small bones arranged in two rows, but gradually many of these small bones were lost. The first animals to get close to walking on land had eight digits on each limb. Over time, some of these digits were lost, leading to animals with seven digits, then six, and then five, which is common condition now seen in living tetrapods. (http://evolution.berkeley.edu/evolibrary/article/evograms_04)

Limb modifications Endochronal ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral ossification. Endochondral ossification is also an essential process during the rudimentary formation of long bones,

Allows diversification of movement as longer denser bones capable of supporting body weight become specialized to ecological niche environments.

2.19.16 Eating on Land Neck muscles to support weight of head (skull is heavy on land) Mylohyoid - muscle is derived from the first pharyngeal arch.// paired muscle running from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth Adductor mandibulae – able to attach to temporal fenestration increasing bite strength

Hearing on land Related to jaw because we use some of the bones of the hyoid (jaw => inner ear) Water is compressible // sound waves // Lateral line system… On land air waves are airborne and must be transmitted to some kind of receiver: Tympanum is a membrane that conducts sound waves to mechanical motion of the ossicles Ossicles transduce the mechanical signal to create waves in the cochlea fluid filled cochlea contains hair cells involved in hearing by transducting signal into neural signals These cochlear hair cells are related to the lateral line system in fish Collumela – one bone in amphibians connected to tympanic membrane vs 3 in mammals // evolved from hyomandibular arch – top part of hyomandible (arch) became the columella; bottom part becomes mandible // articular and quadrate are still part of the jaw Vestibular apparatus still occupies the same area but is not involved in hearing – involved in balance In jawed fish- hyostilic jaw // hyoid was involved in connection of jaw to skull jawless fish – 2nd gill arch became hyomandibular bone In reptiles, the eardrum is connected to the inner ear via a single bone, the columella, while the upper and lower jaws contain several bones not found in mammals. Over the course of the evolution of mammals, one lower and one upper jaw bone (the articularand quadrate) lost their purpose in the jaw joint and were put to new use in the middle ear, connecting to the stapes and forming a chain of three bones (collectively called theossicles) which transmit sounds more efficiently and allow more acute hearing. In mammals, these three bones are known as the malleus, incus, and stapes (hammer, anvil, and stirrup respectively). (https://en.wikipedia.org/wiki/Evolution_of_mammalian_auditory_ossicles)

Kidneys: On land you have issues with drying out Kidneys are already in place… Gills no longer there (could drink water and excrete salts in gills before) Kidneys replace that function… Bladder for water retention and Urea cycle for excreting nitrogenous waste, which before would be removed by dilution in water. Urea is an adaptation that allows nitrogenous waste to be stored in a less toxic form than ammonia.

Non-amniote skin: Still impermeable Amphibian skin still has lipids, etc that slow down water loss… Glands in skin that excrete mucous that coat surface of skin to help with water loss Also poison glands – defensive Also glands involved in communication (pheromones) Scales come later… when we lose wet skin

Amphibians (Class) Lissamphibians (subclass) Monophyletic The "lepospondyl hypothesis" of modern amphibian origins proposes that lissamphibians are monophyletic (that is, they form their own clade) and that they evolved from lepospondyl ancestors.

Batrachomorpha (clade) Present during Devonian // Look like sarcopterygian when they emerged from water But… see more walking ability Drought wet/dry periods Lissamphibia = amphibian Extinct:

Lepidospondyls and Temnospondyls

Synapomorphies of amphibians: Skin glands (mucous – poison (granular glands)) Columella: derived from hyoid arch – hearing In fish hyoid is part of operculum with tympanic membrane corresponds to stapes in mammals Green rods - Vision (a special type of visual cell, unknown in caecilians) Pedicellate teeth – more like fish? Levator bulbi muscle – enlarges mouth // when...