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[dinosaur] Crocodylian bite marks in taphonomy + ichthyosaur and shark convergence + aquatic adapations

Ben Creisler

Some recent non-dino papers:

Stephanie K. Drumheller and  Christopher A. Brochu (2016)
Phylogenetic taphonomy: a statistical and phylogenetic approach for exploring taphonomic patterns in the fossil record using crocodylians.
PALAIOS (advance online publication)
DOI: 10.2110/palo.2016.030

Actualistic observations form the basis of many taphonomic studies in paleontology. However, surveys limited by environment or taxon may not be applicable far beyond the bounds of the initial observations. Even when multiple studies exploring the potential variety within a taphonomic process exist, quantitative methods for comparing these datasets in order to identify larger scale patterns have been understudied. This research uses modern bite marks collected from 21 of the 23 generally recognized species of extant Crocodylia to explore statistical and phylogenetic methods of synthesizing taphonomic datasets. Bite marks were identified, and specimens were then coded for presence or absence of different mark morphotypes. Attempts to find statistical correlation between trace types, marking animal vital statistics, and sample collection protocol were unsuccessful. Mapping bite mark character states on a eusuchian phylogeny successfully predicted the presence of known diagnostic, bisected marks in extinct taxa. Predictions for clades that may have created multiple subscores, striated marks, and extensive crushing were also generated. Inclusion of fossil bite marks which have been positively associated with extinct species allow this method to be projected beyond the crown group. The results of this study indicate that phylogenies can and should be further explored for use as predictive tools in a taphonomic framework.


Theagarten Lingham-Soliar (2016)
Convergence in Thunniform Anatomy in Lamnid Sharks and Jurassic Ichthyosaurs.
Integrative and Comparative Biology (advance online publication)
doi: 10.1093/icb/icw125

Among extinct ichthyosaurs the Jurassic forms Ichthyosaurus and Stenopterygius share a number of anatomical specializations with lamnid sharks, characterized in the white shark, Carcharodon carcharias. These features allow their inclusion within the mode of high-speed thunniform swimming to which only two other equally distinctive phylogenetic groups belong, tuna and dolphins—a striking testaments to evolutionary convergence. Jurassic ichthyosaurs evolved from reptiles that had returned to the sea (secondarily adapted) about 250 million years ago (MYA) while lamnid sharks evolved about 50 MYA from early cartilaginous fishes (originating ca. 400 MYA). Their shared independently evolved anatomical characteristics are discussed. These include a deep tear-drop body shape that helped initially define members as thunniform swimmers. Later, other critical structural characteristics were discovered such as the crossed-fiber architecture of the skin, high-speed adapted dorsal and caudal fins, a caudal peduncle and series of ligaments to enable transmission of power from the musculature located anteriorly to the caudal fin. Both groups also share a similar chemistry of the dermal fibers, i.e., the scleroprotein collagen.


Alexandra Houssaye, P. Martin Sander, and Nicole Klein (2016)
Adaptive Patterns in Aquatic Amniote Bone Microanatomy—More Complex than Previously Thought.
Integrative and Comparative Biology (advance online publication)

Numerous amniote groups adapted to an aquatic life. This change of habitat naturally led to numerous convergences. The various adaptive traits vary depending on the degree of adaptation to an aquatic life, notably between shallow water taxa still able to occasionally locomote on land and open-marine forms totally independent from the terrestrial environment, but also between surface swimmers and deep divers. As a consequence, despite convergences, there is a high diversity within aquatic amniotes in e.g., shape, size, physiology, swimming mode. Bone microanatomy is considered to be strongly associated with bone biomechanics and is thus a powerful tool to understand bone adaptation to functional constraints and to make functional inferences on extinct taxa. Two opposing major microanatomical specializations have been described in aquatic amniotes, referred to as bone mass increase and a spongious organization, respectively. They are assumed to be essentially linked with the hydrostatic or hydrodynamic control of buoyancy and body trim and with swimming abilities and velocity. However, between extremes in these specializations, a wide range of intermediary patterns occurs. The present study provides a state-of-the-art review of these inner bone adaptations in semi-aquatic and aquatic amniotes. The analysis of the various microanatomical patterns observed in long bones, vertebrae, and ribs of a large sample of (semi-)aquatic extant and extinct amniotes reveals the wide diversity in microanatomical patterns and the variation in combination of these different patterns within a single skeleton. This enables us to discuss the link between microanatomical features and habitat, swimming abilities, and thus functional requirements in the context of amniote adaptation to an aquatic lifestyle.


Frank E. Fish (2016)
Secondary Evolution of Aquatic Propulsion in Higher Vertebrates: Validation and Prospect.
Integrative and Comparative Biology (advance online publication)
doi: 10.1093/icb/icw123

Re-invasion of the aquatic environment by terrestrial vertebrates resulted in the evolution of species expressing a suite of adaptations for high-performance swimming. Examination of swimming by secondarily aquatic vertebrates provides opportunities to understand potential selection pressures and mechanical constraints, which may have directed the evolution of these aquatic species. Mammals and birds realigned the body and limbs for cursorial movements and flight, respectively, from the primitive tetrapod configuration. This realignment produced multiple solutions for aquatic specializations and swimming modes. Initially, in the evolution of aquatic mammals and birds, swimming was accomplished by using paired appendages in a low-efficiency, drag-based paddling mode. This mode of swimming arose from the modification of neuromotor patterns associated with gaits characteristic of terrestrial and aerial locomotion. The evolution of advanced swimming modes occurred in concert with changes in buoyancy control for submerged swimming, and a need for increased aquatic performance. Aquatic mammals evolved three specialized lift-based modes of swimming that included caudal oscillation, pectoral oscillation, and pelvic oscillation. Based on modern analogs, a biomechanical model was developed to explain the evolution of specialized aquatic mammals and their transitional forms. Subsequently, fossil aquatic mammals were described that validated much of the model. However, for birds, which were adapted for aerial flight, fossil evidence has been less forthcoming to explain the transition to aquatic capabilities. A biomechanical model is proposed for birds to describe the evolution of specialized lift-based foot and wing swimming. For both birds and mammals, convergence in morphology and propulsive mechanics is dictated by the need to increase speed, reduce drag, improve thrust output, enhance efficiency, and control maneuverability in the aquatic environment.


Richard W. Blob, Christopher J. Mayerl, Angela R. V. Rivera, Gabriel Rivera, and Vanessa K H. Young
“On the Fence” versus “All in”: Insights from Turtles for the Evolution of Aquatic Locomotor Specializations and Habitat Transitions in Tetrapod Vertebrates.
Integrative and Comparative Biology (advance online publication)

Though ultimately descended from terrestrial amniotes, turtles have deep roots as an aquatic lineage and are quite diverse in the extent of their aquatic specializations. Many taxa can be viewed as “on the fence” between aquatic and terrestrial realms, whereas others have independently hyperspecialized and moved “all in” to aquatic habitats. Such differences in specialization are reflected strongly in the locomotor system. We have conducted several studies to evaluate the performance consequences of such variation in design, as well as the mechanisms through which specialization for aquatic locomotion is facilitated in turtles. One path to aquatic hyperspecialization has involved the evolutionary transformation of the forelimbs from rowing, tubular limbs with distal paddles into flapping, flattened flippers, as in sea turtles. Prior to the advent of any hydrodynamic advantages, the evolution of such flippers may have been enabled by a reduction in twisting loads on proximal limb bones that accompanied swimming in rowing ancestors, facilitating a shift from tubular to flattened limbs. Moreover, the control of flapping movements appears related primarily to shifts in the activity of a single forelimb muscle, the deltoid. Despite some performance advantages, flapping may entail a locomotor cost in terms of decreased locomotor stability. However, other morphological specializations among rowing species may enhance swimming stability. For example, among highly aquatic pleurodiran turtles, fusion of the pelvis to the shell appears to dramatically reduce motions of the pelvis compared to freshwater cryptodiran species. This could contribute to advantageous increases in aquatic stability among predominantly aquatic pleurodires. Thus, even within the potential constraints of a body plan in which the body is encased by a shell, turtles exhibit diverse locomotor capacities that have enabled diversification into a wide range of aquatic habitats.