OSMT Exam Questions with verified Solutions 100% Solved 2024

OSMT Exam Questions with verified Solutions 100% Solved 2024 Why doesn't phylogenetic systematics have a fixed number of hierarchical categories like Linnaean systematics? - answerEach branching point is a hierarchical level in the nested structure of phylogenetic systematics. The number of branching points—and therefore the number of possible hierarchical levels—varies substantially from one lineage to another. What aspect of evolution does phylogenetic systematics represent more clearly than Linnaean systematics does? - answerThe branching sequences of evolutionary lineages are represented more clearly by phylogenetic systematics than by Linnaean systematics. In the Linnaean classification of vertebrates, for example, reptiles (Class Reptilia) and birds (Class Aves) appear to be equivalent hierarchical levels. In contrast, a phylogenetic classification shows that birds are a derived group of reptiles. Tetrapoda (see Figure 1.4) is a crown group; Tetrapodomorpha is the corresponding stem group. What organisms are included in Tetrapoda? In Tetrapodomorpha? - answerTetrapoda (tetrapods) includes the living vertebrates with limbs. Tetrapodomorpha includes tetrapods plus all those (extinct) fishes that are closer to tetrapods then they are to lungfishes. Look at Figure 1.4. Why can a human correctly say to another "you are a rhipidistian," but not "you are a lungfish?" How can you describe your relationship to lungfishes? - answerIf you trace the human lineage backward from Eutheria (placental mammals), you will follow progressively more inclusive lineages down as far as Rhipidistia. The next step takes to you Sarcopterygii; lungfishes are a separate lineage from Rhipidistia. You can correctly say that lungfishes are the sister group of Rhipidistia. What inference can you draw from Figure 1.3 about parental care by pterosaurs? - answerThe reasoning that applies to nonavian dinosaurs applies also to pterosaurs. Parental care was probably an ancestral character of the lineage. For the sake of this question, suppose you have firm evidence that phytosaurs did not exhibit parental care. What would be the most parsimonious hypothesis about the appearance or disappearance of parental care in the archosaur lineage? - answerThis is a more interesting question than the previous one, because two plausible sequences of changes could lead to the absence of parental care in the sister group of crocodylians: (1) Parental care was ancestral for archosaurs, but it was lost in the phytosaur lineage. (2) Parental care evolved independently in the crocodylian lineage and in Dinosauria. Both hypotheses require two changes: (1) Parental care was gained in an ancestral archosaur and lost in phytosaurs. (2) Parental care was gained in crocodylians and again in pterosaurs + dinosaurs. The hypotheses are equally parsimonious. Suppose new molecular data showed that tunicates and vertebrates are sister taxa. What difference would this make to our assumptions about the form of the original chordate animal? What additional features might this animal have possessed? - answerThis would mean that the original chordate was a mobile animal throughout life, rather than sessile as an adult. With this scenario, amphioxus serves as a model for what the basic chordate plan might have been like. In addition, the earliest chordate would probably have had the features that are shared by amphioxus and vertebrates (e.g., segmental muscles through the entire trunk, not just the tail), and these would have been ancestral characters for tunicates that were secondarily lost in the sessile adult forms. Why would evidence of sense organs in the head of a fossil nonvertebrate chordate suggest a close relationship with vertebrates; that is, which critical vertebrate feature would have to be present? - answerVertebrate sense organs are formed from neural-crest tissue and epidermal placodes, both of which are unique vertebrate features. The presence of such structures in an adult chordate suggests the presence of these vertebrate embryological tissues, and hence a closer relationship to vertebrates than amphioxus or tunicates (which lack these tissues). Vertebrates have been described as "dual animals," consisting of both segmented and unsegmented portions. How is this duality reflected in their embryonic development and the structure of the nervous system? - answerDuring embryonic development, the mesoderm is divided into the segmented somite (making, among other things, the striated muscles that power locomotion) and the unsegmented lateral plate (making, among other things, the smooth muscles of the gut). The dual nervous system follows this embryological division: the somatic (voluntary nervous system) innervates the striated muscles, and the visceral (involuntary nervous system) innervates the smooth muscles. How could duplication of Hox genes lead to the structural complexity of vertebrates? - answerHox genes control expression of developmental genes in specific regions of the body, and duplication of a Hox gene is believed to allow the paralogs to diverge in function, changing the timing or rate of expression of structural genes, for example. Those changes could lead to differences in the adult phenotype of an organism. We think of the presence of ice caps at the poles as the "normal" condition for Earth, but in fact this situation is less common over geological history than are ice-free polar regions. How does continental movement relate to this? - answerIce will form at the poles only in a globally cool world, and it usually forms over a continental landmass. If the continents are distributed in more equatorial realms, Earth will be warmer and there will be no polar ice. Ocean currents transport vast quantities of heat, and when the positions of the continents allow these currents to flow into polar regions, they can prevent the formation of ice caps. What other aspects of Earth's history might make the world colder, with ice at the poles, and when was this a particular issue for tetrapods? - answerLow levels of carbon dioxide have a reverse greenhouse effect and lead to cooling of the planet (seen especially in the Late Carboniferous and Early Permian). What effect did the Late Carboniferous/Early Permian climate changes have on global vegetation, and how did this affect vertebrate evolution? - answerCooling and drying caused the collapse of the rainforest ecosystems. This left a world less suitable for large non- amniote tetrapods and promoted the diversification and radiation of amniotes. We think of amniotes as being more derived types of tetrapods than non-amniotes. Is there evidence that the replacement of terrestrial faunas dominated by non-amniotes with faunas dominated by amniotes was the result of competition? - answerThere is no real evidence, but the faunal change coincided with profound changes in climate and vegetation that favored the amniote body plan and physiology (see Question 3). What profound change happened to the community structure of tetrapods in the Permian that led to a change for the entire terrestrial vertebrate community? - answerLow levels of carbon dioxide have a reverse greenhouse effect and lead to cooling of the planet (seen especially in the Late Carboniferous and Early Permian). We know that invertebrates colonized the land before vertebrates did. What is a possible reason for this? Did things have to happen this way? - answerThis probably did have to happen. One reason is that the invertebrates provided food for the vertebrates, but a more basic reason is that a complex terrestrial ecosystem requires invertebrates to eat the dead and dying plant material and to return the nutrients to the soil. What is the difference between the effects of the density and the viscosity of water from the perspective of an aquatic vertebrate? - answerDensity and viscosity have overlapping effects on some activities of vertebrates and act independently in other situations.Both the velocity of an animal's movement through water and the ability of an aquatic organism to ventilate its respiratory surfaces are slowed by the density and viscosity of water. The high density of water means that an aquatic animal must work to force the water aside, and the high viscosity means that water flows slowly compared with a less-dense fluid such as air.The density of water allows aquatic animals to achieve neutral buoyancy so they can maintain their vertical position in the water column without needing to swim up or down. The viscosity of water plays essentially no role in this behavior.The high density of water renders gravity irrelevant to aquatic animals. Its high viscosity is the main physical property that makes streamlining important for aquatic vertebrates.Because aquatic vertebrates are essentially neutrally buoyant, their skeletons lack the weight-bearing characteristics seen in the skeletons of terrestrial vertebrates.Free of the need to support a massive body, aquatic vertebrates can evolve very large body sizes. The blue whale, the largest aquatic vertebrate, reaches a length of 30 m and weighs 180,000 kg. A few of the huge dinosaurs of the Mesozoic were longer than a whale, but they weighed less. Argentinosaurus is the largest dinosaur currently known; it is estimated to have been about 34 m from nose to tail tip, but it weighed only 91,000 kg. When you walk past the tanks in an aquarium store, you see both physostomous and physoclistous fishes. Goldfishes, for example, are physostomous, and cichlids are physoclistous. Conduct a thought experiment comparing the responses of the two kinds of fishes to changes in air pressure. (Don't actually conduct this experiment, because it would be painful for the fish.) Imagine that you put a goldfish and a cichlid into a jar half filled with water and then screw on a lid to make an airtight seal. Protruding from the lid is a tube to which you can attach a vacuum pump and a valve that allows you to close off the tube.a. Pump some air out of the jar. What effect will that have on the air pressure inside the jar? How will each of the fishes respond to that change in pressure? How are those responses related to being physostomous or physoclistous?b. Now open the valve and allow air to enter the jar, returning the pressure - answera. Pumping air out of the jar reduces the pressure, and that causes the fishes' gas bladders to expand, making them positively buoyant so they float to the surface of the water. The goldfish can burp air out of its gas bladder because it is physostomous, and it quickly restores neutral buoyancy. The cichlid is physoclistous, so it must use its gas gland to move oxygen from the gas bladder to the blood. This is a much slower process than burping out the extra volume, so the cichlid floats on the surface for several minutes after the goldfish has resumed its normal behavior.b. Opening the valve increases the pressure in the jar, and the fishes' gas bladders get smaller, so they are now negatively buoyant and sink to the bottom of the jar. The goldfish swims to the surface and gulps air into its gas bladder, quickly returning to neutral buoyancy. The cichlid must use its gas gland to release oxygen from its blood into the gas bladder. This is a slow process compared with gulping air, and once again the cichlid remains helpless for several minutes after the goldfish has resumed normal behavior, but this time the cichlid is resting on the bottom of the jar. When deep-sea fishes are pulled quickly to the surface, they often emerge with their gas bladder protruding from their mouth .a. Why does this happen, and what does it tell you about whether these deep-sea fishes are physoclistous or physostomous? b. Why could you have figured out whether deep-sea fishes are physostomous or physoclistous simply by considering how air enters the gas bladder of a fish? - answera. When the fishes are pulled rapidly to the surface, the pressure on their gas bladder decreases faster than they can adjust the volume of the bladder, indicting that deep-sea fishes are physoclistous.b. Physostomous fishes gulp air into their gas bladder, but deep-sea fishes live far below the surface where there is no air to gulp.