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