Bruet et al. [9] revealed materials design principles present in the penetration resistance of the ganoid scales of Polypterus senegalus, a small fish that reaches only approximately 200 g in mass and 20 cm in length. Its scales have multiple layers, each with unique properties, deformation mechanisms, and a specialized manner in which cracking and failure occur in order to absorb energy and protect the fish. Song et al. [3] demonstrated how the structure of the ganoid scale provides toughness, penetration resistance and non-catastrophic pathways for energy dissipation.
During this rotational deflection, the matching curvature of adjacent scales maintains full protective coverage without the formation of gaps. It is also important that the scales do not separate from their foundation during curvature. This effect is shown in figure 5a, and δ, the gap between scales, may be calculated as a function of scale length (l) and bending radius (R) through the relationship
Pangolin V3 2 6 Crack Full 13
Nanoindentation of ganoine normal and parallel to the scale surface. (a,b) The variation of modulus corresponds to the layers of ganoine. (c) In the transverse direction of the scale, a high load indent causes cracks to grow; crack semi-length, c, is marked. (d) In the normal direction to the scale, smaller cracks caused by a high load indent correspond to an increased toughness. (Online version in colour.)
An additional penetration test performed with an alligator tooth is shown in figure 10b, which results in the failure of the tooth at 500 N. The cracking of the alligator tooth is induced by the hardness of the ganoine layer, which prevents deformation and a distribution of the load across the alligator tooth. This shows that, with the ganoine layer, the gar scale is sufficiently strong to withstand local loads due to alligator bite force. Additionally, the hardness of ganoine may play a role in inducing the failure of teeth.
Penetration tests into the ganoine reveal robust toughening features. Figure 11a is an indent caused by penetration of a steel indenter into the ganoine surface of the scale. After loading to 1000 N, damage to the ganoine is apparent as some crushing takes place, but the cracks do not propagate through the thickness of the scale. Cracking occurs directly beneath the indenter, and some cracks radiate out from the indenter but are contained within the ganoine layer. This is directly related to the fracture toughness, which is enhanced by the twisted cross-plied mineral, and a likelihood of multiple cracking within the ganoine, as observed in the conch shell [25]. Similarly, in a compression test of a portion of the scale with the ganoine layer intact (figure 11b), failure occurs in the ganoine layer but does not propagate to the interface with the bone layer. Close observation of the failure surface of ganoine (figure 11c) shows that, as cracks progress, they must twist and deflect since they follow the interfaces of cross-plied mineral bundles. This deflection toughens the mineral and inhibits the propagation of cracks, which are often arrested prior to penetrating the mineral layer. Figure 11d shows the containment of a crack in the ganoine layer.
Toughening in the ganoine region. (a) Cracking of ganoine from penetration test loaded to 1000 N shows partial mineral failure, while bone remains intact. (b) Failure of ganoine during a compression test: failure is contained within the ganoine and does not propagate to bone. (c) Fracture surface of ganoine shows cross-plied mineral bundles that provide toughening. (d) A crack is arrested in the ganoine. (Online version in colour.)
With sufficient load, the bone will also crack. Energetically, it is expected that cracks propagate straight through the scale, along tubules (shown in figure 3), which create stress concentrations. Figure 13a,b shows an actual cracking path and overall jagged fracture surface, which results in a significant increase in the energy required to progress the crack. This meandering, possibly caused by the orientation of mineral crystals in the bone (shown in figure 13c), forces cracks to traverse highly mineralized fibrils with exceptional toughness, strength and elasticity. This closely aligns with the results by Yang et al. [13], which indicated that fracture toughness is enhanced for orientations where fibrils span the crack wake. Figure 13d shows one instance where collagen fibrils bridge a crack and aid in stopping propagation.
Toughening features of bony region: mineralized collagen fibrils. (a) The crack path as it penetrates through the bone layer is jagged. (b) The fracture surface of a hydrated scale. (c) A collagen fibril is shown with mineral crystals oriented across the fibril. This orientation is found throughout the scale. (d) Collagen fibrils stretch across a crack and prevent its propagation. (Online version in colour.)
Toughening features of bony region: tubule effects. (a) A crack in a dry scale progresses by jumping from one tubule to the next. (b) A crack in a wet scale progresses without strong influence of the tubules. Adapted from Yang et al. [13]. (c,d) Simulations calculate stress in the presence of tubules when wet and dry. Stress concentrations around dry tubules correspond closely with three times the applied load, while stress concentrations around wet tubules are reduced by 38%. (e) The material responses applied for the elastic and elastoplastic responses. (Online version in colour.)
We gratefully acknowledge Dianne and Gary Ulery for generously providing a supply of alligator gar scales. We thank Eric Bushong for assistance with recording of μ-CT data and Jerry Jung for assistance in the data reconstruction. Discussions with Prof. Joanna McKittrick, Prof. Robert Ritchie, Eric Hahn, Wen Yang, Tarah Sullivan and Bin Wang were helpful in the development of our ideas.
Submerged in the twisty kelp, Last Lioness struggles to kick free with her wrenched leg and manages to extricate herself from the kelp and surfaces with a gasp! Grandma Orca and the resident orca pod are hot on the flukes of the transient orcas as both pods "leave at full sprint for a mile and a half at 30 miles an hour or better", well beyond the field of battle (Pailthorp 2021). At Protection Island, protective Grandma Orca saved the Last Lioness, even if incidentally, before departing the field of battle in pursuit of possible threats to her pod. In the intertidal zone, Last Lioness limps toward her sisters, broken kelp twisted around her body. Rushing to their briefly lost sister, the Lionesses reunion in the sea surf involves rubbing heads together and licking each other's faces.
The combatants meet on the home turf of the Lionesses in the Okavango Delta. The Lionesses are getting HANGRY- mole meals and weasel sneaks do not a full stomach make! The Lionesses set out into the twilight for a hunting foray. MMMagic transports the Lodge of Beavers to NW Botswana, where the Okavango River flows from the highlands of Angola splitting into myriad braided rivers and streams to form a complex wetland of islands, marshes, lakes and lagoons. While once widespread throughout much of Eurasia, Beavers never ecosystem engineered in Africa, so the Lodge of Beavers gets busy making new heath & home. Mama Beaver and a juvenile gnaw on some nearby sycamore fig trees, similar in ways to their preferred willow trees at home. Large Papa Beaver is in the shallows, investigating fig sticks for how well they'll work for territorial displays. Standing on back legs, holding a FIG STICK in his forepaws, Papa Beaver slams the branch against the water surface, making impressive splashes. The rainy season is winding down and 230kg sable antelope forage, as 50-100kg warthogs trot about and a troop of baboons wades to a grove of preferred sleeping trees. From the tall marsh grasses, the Lionesses survey the scene of possible prey. One lioness thinks "Sable antelope is the right size, but the weaponry is daunting" (Hayward & Curley 2005). Another lioness muses how leopards more typically slum it with the primate diet. The last lioness thinks "warthogs are slow, less vigilant, they aren't packing a lot of meat but will do in a pinch" (Hayward & Curley 2005). Then the #3 Lioness spots large Papa Beaver, wonders what he is, stalks closer, and urinates in the water. Her pee drifts on the water toward swimming Mama Beaver and although beavers were never in Africa, lions once widely roamed Eurasia. Mama Beaver responds to the smell of predator urine by tail slapping the water surface to alert her family and she immediately dives down. Now alerted, the Beavers on land rush into the water as the Lionesses halfheartedly charge because really, this isn't the prey the lionesses are looking for. Together the Lodge of Beavers swim out to a deeper Okavango River channel and off the field of battle, beyond the claw reach of the lionesses! PRIDE OF LIONESSES OUTLASTS LODGE OF BEAVERS! Narration written by Katie Hinde; summarized by Melanie Beasley.
Black Bear (3) vs Wapiti Elk (6). Black Bears were once widespread in North America, but have been extirpated from large portions of their historical range. Actual Living Scientist (and narrator of this battle) Jessica Light has looked at Black Bear distributions in Texas, but the range of Black Bears has been expanding in other parts of the continent. The population introduced to Hot Springs National Park has been successfully expanding across Arkansas and into Missouri. Wapiti is another species that was once common throughout North America prior to local extirpations (mostly via hunting & habitat loss) and has been rebounding where reintroduced, including in Arkansas along the Buffalo National River.
When MMMagic transports our Wapiti from Great Smoky Mountains National Park to Hot Springs National Park in Arkansas, Wapiti is ready to roll. It's dusk and both Black Bear and Wapiti are hangry. Springtime ushers in new plant growth, perfect for our herbivorous (plant-eating) Wapiti & our omnivorous (I'll eat anything) Black Bear. In fact, Black Bear springtime diet is primarily plants, especially in summer. Wapiti has stumbled upon a particularly productive patch of young grass to graze on. Wapiti are ruminants; they have a multi-chambered stomach full of microorganisms that help pull all the nutrients out of whatever Wapiti eats. Nearby, Black Bear also has found his own spot to graze, but these springtime grasses are not very nutritious and he doesn't have all those digestive system microorganisms. Black Bear needs more and better to support his growing girth. Black Bear huffs over to Wapiti, lunging to scare him off of this prime grassy real estate. He is not at all dissuaded by Wapiti's significantly larger size. Wapiti takes a step back, lifts his head high and eyes the Black Bear, measuring up the threat. Black Bear doesn't wait and aggressively lunges at Wapiti again, stomping the grasses. Wapiti is having none of this brash Black Bear bluff. Wapiti snorts a strong exhale and stomps his forefeet, smashing more young plants, & charges at Black Bear, who doesn't flinch. He and Wapiti circle each other. Neither are willing to give up precious calories to the other, but they are tearing up more grass as they aggressively lunge back and forth. Breathing heavily, Black Bear & Wapiti pause and continue to eye each other while contemplating their limited, precious resource. Wapiti stomps his feet, ready for more. Black Bear has taken on Wapiti before, but rarely full-grown bulls... Black Bear rethinks a battle with Wapiti over this patch of grass, which is now all ripped up. Black Bear retreats in search of healthier and less actively defended fields! ELK DISPLACES BLACK BEAR! Narration written by Jessica Light; summarized by Margaret Janz 2ff7e9595c
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