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When it comes to studying organisms, having size independent measures for maturity are important for many aspects of organismal biology, and may be crucial for determining taxonomic affinity, and morphological signals associated with ontogenetic age (i.e., juvenile vs. adult) and sexual dimorphism. This is because the size of an organism can be the result of many factors that are not necessarily indicators of maturity (Chabreck and Joanen, 1979; Ferguson, 1984; Mazzotti et al., 1986; Deeming and Ferguson, 1989; Brandt, 1991). This problem is particularly pronounced when researchers are studying extinct species. The purpose of my research project was to investigate and understand patterns of morphological variation in the phytosaur premaxilla and maxilla and to determine the degree to which morphological variation is a result of ontogeny. For example, such patterns might include the number, size and location of alveoli or the presence of prenarial crests. I conducted this research by gathering information on the premaxilla and maxilla of all phytosaur elements present in the University of Texas at Austin Vertebrate Paleontology Lab collection. I then performed statistical analysis on the data, and compared my results to those of previous authors to see if I could identify any ontogenetic signal. I did not identify size-independent ontogenetic influence on morphology with certainty but I did find some possible features that merit additional investigation in future studies. Those include the presence of one to three diastemas located primarily at the anterior end of the premaxilla, a wide interpremaxillary fossa but small alveolar ridge, and alveoli whose size mirror the width of the premaxilla (for example wide areas in the premaxilla are associated with larger alveoli whereas narrow areas in the premaxilla are associated with smaller alveoli). My study also confirmed the previous findings of Hungerbühler (2002) that the alveoli of phytosaurs are heterodont and exist in three distinct location-specific patterns, and the work of other researchers that prenarial crests are present only in larger specimens (Camp, 1930; Ballew, 1986; Hungerbühler, 2002; Stocker, 2010). / text

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Gudgeon (Hypseleotris spp.) are the most widespread and abundant native Australian freshwater fish and the dominant zooplanktivore in Maroon Dam, the site of Australia's first whole-lake biomanipulation experiment. The spatial (littoral and pelagic) and temporal (diurnal and seasonal) distribution and diet of Hypseleotris was examined following the addition of 100,000 piscivorous Australian Bass (Macquaria novemaculeata) to Maroon Dam in the summer of 1998/99. A strong spatial and temporal ontogeny was observed, with smaller (<16 mm SL) Hypseleotris dominating the pelagic, an intermediate (12-20 mm SL) size class diurnally migrating between littoral and pelagic, and larger fish (>20 mm SL) remaining in the littoral throughout the day and night. Spatial ontogeny affected diet also, with fish consuming a decreasing proportion of zooplankton and an increasing proportion of macro-invertebrates as fish length increased and habitat use changed. A bioenergetics model was constructed to examine these distribution and diet patterns. Laboratory derived consumption and respiration parameters were combined with caloric densities and commonly accepted excretion and activity scalars to produce modeled growth estimates that were validated against Hypseleotris age-at-growth data collected from a diversity of habitats. Using this model, it was concluded that the spatial and temporal ontogeny and diet of Hypseleotris in Maroon Dam described the most energetically advantageous life history. Unlike many zooplanktivores in northern hemisphere lakes, Hypseleotris did not appear to engage in migratory predator avoidance behaviour. This is discussed in a context of Australia's paucity of pelagic piscivores. It is concluded that top-down biomanipulation by stocking of native piscivores has only a limited application in Australia, and that other biomanipulation techniques may prove more successful.

Marsupial evolution and morphological diversity is traditionally viewed against the background of marsupial life history, central to which are the highly altricial neonates that actively move towards the teat. It has been suggested that this mode of birth leads to a constraint on the marsupial postcranial diversity. However, apart from phylogenetic investigations, few empirical studies have assessed diversity, patterns of adaptation, or ontogeny of the marsupial postcranium. This thesis contributes to the debate by providing diverse, large-scale empirical data on selected issues of marsupial postcranial evolution, using multidisciplinary approaches with focus on quantitative analysis. Chapter 1 provides an overview on previous research on this topic. Chapter 2 assesses the phylogenetic and functional-anatomical implications of marsupial carpal diversity. Chapter 3 is a phylogenetically informed morphometric analysis of diprotodontian manual digits, demonstrating locomotor adaptations similar to those in placentals and allowing the development of a new locomotor predictor ratio. Chapter 4 shows that functional correlates of digit proportions in Diprotodontia also exist in the placental hystricomorph rodents, which resemble Diprotodontia in ecological diversity. Chapter 5 applies the results from Chapters 2-4 to the mostly extinct diprotodontian suborder Vombatiformes, revealing functionally related parallelism in the hand of vombatiforms and kangaroos and questioning previous concepts of locomotion in early vombatiforms. Chapter 6 focuses on the evolution of marsupial syndactyly using a multidisciplinary approach including morphometrics and ossification sequence analysis. The results suggest that syndactylous digits evolve as a functional unit; syndactyly may arise through alteration of developmental patterns as suggested by ossification sequence heterochrony. Chapter 7 is a combined analysis of ossification sequences in marsupial and placental postcrania. The results suggest that the special locomotor and developmental requirements on marsupial neonates may metabolically and mechanically impact postcranial ossification patterns, delaying hindlimb development and accelerating ossification of the anterior torso. Chapter 8 summarises the research presented in this thesis and suggests directions for future work on marsupial postcranial evolution, particularly with respect to integrating information on postcranial diversity with ontogenetic work on morphogen expression patterns.

Undergraduate honors paper--Mount Holyoke College, 2008. Dept of Biological Sciences. / Includes bibliographical references (leaves 45-47).