Terrestrial locomotion of the northern elephant seal (Mirounga angustirostris): limitation of large aquatically adapted seals on land?

Brain activity of diving seals reveals short sleep cycles at depth

Sleep is a crucial part of the daily activity patterns of mammals. However, in marine species that spend months or entire lifetimes at sea, the location, timing, and duration of sleep may be constrained. To understand how marine mammals satisfy their daily sleep requirements while at sea, we monitored electroencephalographic activity in wild northern elephant seals (Mirounga angustirostris) diving in Monterey Bay, California. Brain-wave patterns showed that seals took short (less than 20 minutes) naps while diving (maximum depth 377 meters; 104 sleeping dives). Linking these patterns to accelerometry and the time-depth profiles of 334 free-ranging seals (514,406 sleeping dives) revealed a North Pacific sleepscape in which seals averaged only 2 hours of sleep per day for 7 months, rivaling the record for the least sleep among all mammals, which is currently held by the African elephant (about 2 hours per day).

Biomechanical Energetics of Terrestrial Locomotion in California Sea Lions (Zalophus californianus)

Pinnipedia, an order of semi-aquatic marine mammals, adapted a body design that allows for efficient aquatic locomotion but limited terrestrial locomotion. Otariids, like the California sea lion (Zalophus californianus), have enlarged forelimbs and can bring their hindlimbs under the body to locomote quadrupedally on land. Phocids (true seals) have reduced forelimbs and are unable to bring their hindlimbs beneath them during terrestrial locomotion. Due to these differences, phocids are expected have greater energetic costs when moving on land compared to otariids. The mechanical costs of transport and power outputs of terrestrial locomotion were first obtained from one male and two female adult California sea lions through video recording locomotion sequences across a level runway. The center of mass, along with six other anatomical points, were digitized to obtain variables such as velocity (V), amplitude of heave (A), and the frequency (f) of oscillations during the locomotion cycle. These variables represent the principal parameters of a biomechanical model that computes the power output of individuals. The three California sea lions in this study averaged a power output of 112.04 watts and a Cost of Transport of 0.63 J kg-1 m-1. This footage was compared against video footage previously recorded of three phocid species (harbor seal, gray seal, and northern elephant seal). Power output and mechanical Cost of Transport were compared between all four pinniped species following the animals' center of mass. The quadrupedal gait of sea lions showed lower vertical displacements of the center of mass, and higher velocities compared to the terrestrial gait of phocids. Northern elephant seals, gray seal, and the harbor seal showed significantly higher Costs of Transport and power outputs from the sea lions. California sea lions locomote with lower energetic costs, and thus higher efficiency compared to phocids, proving that they are a mechanically intermediate species on land between terrestrial mammals and phocids. This study provides novel information on the mechanical energy exerted by pinnipeds, particularly California sea lions, to then be used in future research to better understand the limitations of these aquatic mammals.

The evolution of asymmetrical gaits in gnathostome vertebrates

The difficulty of quantifying asymmetrical limb movements, compared with symmetrical gaits, has resulted in a dearth of information concerning the mechanics and adaptive benefits of these locomotor patterns. Further, no study has explored the evolutionary history of asymmetrical gaits using phylogenetic comparative techniques. Most foundational work suggests that symmetrical gaits are an ancestral feature and asymmetrical gaits are a more derived feature of mammals, some crocodilians, some turtles, anurans and some fish species. In this study, we searched the literature for evidence of the use of asymmetrical gaits across extant gnathostomes, and from this sample (n=308 species) modeled the evolution of asymmetrical gaits assuming four different scenarios. Our analysis shows strongest support for an evolutionary model where asymmetrical gaits are ancestral for gnathostomes during benthic walking and could be both lost and gained during subsequent gnathostome evolution. We were unable to reconstruct the presence/absence of asymmetrical gaits at the tetrapod, amniote, turtle and crocodilian nodes with certainty. The ability to adopt asymmetrical gaits was likely ancestral for Mammalia but was probably not ancestral for Amphibia and Lepidosauria. The absence of asymmetrical gaits in certain lineages may be attributable to neuromuscular and/or anatomical constraints and/or generally slow movement not associated with these gaits. This finding adds to the growing body of work showing the early gnathostomes and tetrapods may have used a diversity of gaits, including asymmetrical patterns of limb cycling.

The evolutionary biomechanics of locomotor function in giant land animals

Giant land vertebrates have evolved more than 30 times, notably in dinosaurs and mammals. The evolutionary and biomechanical perspectives considered here unify data from extant and extinct species, assessing current theory regarding how the locomotor biomechanics of giants has evolved. In terrestrial tetrapods, isometric and allometric scaling patterns of bones are evident throughout evolutionary history, reflecting general trends and lineage-specific divergences as animals evolve giant size. Added to data on the scaling of other supportive tissues and neuromuscular control, these patterns illuminate how lineages of giant tetrapods each evolved into robust forms adapted to the constraints of gigantism, but with some morphological variation. Insights from scaling of the leverage of limbs and trends in maximal speed reinforce the idea that, beyond 100-300 kg of body mass, tetrapods reduce their locomotor abilities, and eventually may lose entire behaviours such as galloping or even running. Compared with prehistory, extant megafaunas are depauperate in diversity and morphological disparity; therefore, turning to the fossil record can tell us more about the evolutionary biomechanics of giant tetrapods. Interspecific variation and uncertainty about unknown aspects of form and function in living and extinct taxa still render it impossible to use first principles of theoretical biomechanics to tightly bound the limits of gigantism. Yet sauropod dinosaurs demonstrate that >50 tonne masses repeatedly evolved, with body plans quite different from those of mammalian giants. Considering the largest bipedal dinosaurs, and the disparity in locomotor function of modern megafauna, this shows that even in terrestrial giants there is flexibility allowing divergent locomotor specialisations.

In vitro evaluation and in vivo use of a novel surgical stent to minimize suture pressure necrosis

OBJECTIVE

To evaluate the efficacy of stents to distribute pressure when incorporated into tension-relieving sutures.

STUDY DESIGN

An in vitro study and case report.

ANIMAL

One common bottlenose dolphin (Tursiops truncates).

METHODS

Three novel silicone stents, a traditional stent, and a control were tested in vitro by using a suture simulator. Stent surface area was measured by using a pressure mapping sensor. Pressure was derived from the measured surface area and the downward force of the suture simulator. Novel silicone stents were also used in the closure of an incision in a bottlenose dolphin.

RESULTS

No difference was found in surface area or pressure among the three silicone stents (adjusted P > .05). Silicone stents yielded an average, 2.69 cm² more surface area and 842.37 kPa less pressure compared with the control as well as 1.67 cm² more surface area and 110.67 kPa less pressure compared with the traditional stent. The traditional stent yielded 1.02 cm² more surface area and 731.7 kPa less pressure compared with the control. Incision site and silicone stent assessment performed postoperatively revealed no obvious pressure necrosis.

CONCLUSION

Stents improved distribution of suture pressure, and novel silicone stents were more effective compared with traditional stents. Novel silicone stents appear to have preliminary clinical success in vivo.

CLINICAL SIGNIFICANCE

Our study provides evidence that stents effectively help distribute suture pressure, and their incorporation might minimize the risk of suture pressure necrosis. Novel silicone stents should be integrated into tension-relieving suture patterns when closing wounds and incisions, particularly in aquatic animals.