Could Direct Killing by Larger Dingoes Have Caused the Extinction of the Thylacine from Mainland Australia?

Invasive predators can impose strong selection pressure on species that evolved in their absence and drive species to extinction. Interactions between coexisting predators may be particularly strong, as larger predators frequently kill smaller predators and suppress their abundances. Until 3500 years ago the marsupial thylacine was Australia's largest predator. It became extinct from the mainland soon after the arrival of a morphologically convergent placental predator, the dingo, but persisted in the absence of dingoes on the island of Tasmania until the 20th century. As Tasmanian thylacines were larger than dingoes, it has been argued that dingoes were unlikely to have caused the extinction of mainland thylacines because larger predators are rarely killed by smaller predators. By comparing Holocene specimens from the same regions of mainland Australia, we show that dingoes were similarly sized to male thylacines but considerably larger than female thylacines. Female thylacines would have been vulnerable to killing by dingoes. Such killing could have depressed the reproductive output of thylacine populations. Our results support the hypothesis that direct killing by larger dingoes drove thylacines to extinction on mainland Australia. However, attributing the extinction of the thylacine to just one cause is problematic because the arrival of dingoes coincided with another the potential extinction driver, the intensification of the human economy

3D bite modeling and feeding mechanics of the largest living amphibian, the Chinese Giant Salamander Andrias davidianus (Amphibia:Urodela)

Biting is an integral feature of the feeding mechanism for aquatic and terrestrial salamanders to capture, fix or immobilize elusive or struggling prey. However, little information is available on how it works and the functional implications of this biting system in amphibians although such approaches might be essential to understand feeding systems performed by early tetrapods. Herein, the skull biomechanics of the Chinese giant salamander, Andrias davidianus is investigated using 3D finite element analysis. The results reveal that the prey contact position is crucial for the structural performance of the skull, which is probably related to the lack of a bony bridge between the posterior end of the maxilla and the anterior quadrato-squamosal region. Giant salamanders perform asymmetrical strikes. These strikes are unusual and specialized behavior but might indeed be beneficial in such sit-and-wait or ambush-predators to capture laterally approaching prey. However, once captured by an asymmetrical strike, large, elusive and struggling prey have to be brought to the anterior jaw region to be subdued by a strong bite. Given their basal position within extant salamanders and theirPeer ReviewedPostprint (published version

Moa diet fits the bill: Virtual reconstruction incorporating mummified remains and prediction of biomechanical performance in avian giants

The moa (Dinornithiformes) are large to gigantic extinct terrestrial birds of New Zealand. Knowledge about niche partitioning, feeding mode and preference among moa species is limited, hampering palaeoecological reconstruction and evaluation of the impacts of their extinction on remnant native biota, or the viability of exotic species as proposed ecological ‘surrogates’. Here we apply three-dimensional finite-element analysis to compare the biomechanical performance of skulls from five of the six moa genera, and two extant ratites, to predict the range of moa feeding behaviours relative to each other and to living relatives. Mechanical performance during biting was compared using simulations of the birds clipping twigs based on muscle reconstruction of mummified moa remains. Other simulated food acquisition strategies included lateral shaking, pullback and dorsoventral movement of the skull. We found evidence for limited overlap in biomechanical performance between the extant emu (Dromaius novaehollandiae) and extinct upland moa (Megalapteryx didinus) based on similarities in mandibular stress distribution in two loading cases, but overall our findings suggest that moa species exploited their habitats in different ways, relative to both each other and extant ratites. The broad range of feeding strategies used by moa, as inferred from interspecific differences in biomechanical performance of the skull, provides insight into mechanisms that facilitated high diversities of these avian herbivores in prehistoric New Zealand

Geometric morphometrics and finite element analyses reveal the Haast's eagle (Harpagornis moorei) to be a mixed predator-scavenger

The extinct Haast’s eagle (Harpagornis moorei) was 30-40% heavier than the largest extant eagle. There have been speculations about its evolutionary history and ecology, though there is still no consensus on its feeding behaviour. This study aims at understanding the evolution and ecology of Harpagornis by combining 3D geometric morphometrics and finite element analysis (FEA) on three-dimensional models constructed from CT-data of skulls and talons of Accipitridae. Statistical analyses revealed the presence of two independent modules (beak and neurocranium) and of a strong allometric effect in the skull. Size-free shape analysis of the two modules revealed that Harpagornis’ beak was similar to the eagles, while it’s neurocranial morphology was more like a vulture. In most cranial FEA loading cases, there seems to be a dichotomy between Cathartidae on the one side and Accipitridae on the other. FEA on the skull, nevertheless, indicates that Harpagornis and the scavenging species of our dataset are well adapted to perform a pull-back motion. The talon results suggest Harpagornis was an active hunter. Harpagornis’ talon occupies a position in morphospace close to its closest living relative Hieraaetus (smallest extant eagle), suggesting a phylogenetic constraint on talon shape. However, FEA showed that the talon of Harpagornis undergoes similar stresses to that of other hunting raptors which rely on large-sized prey (e.g. Aquila audax). Neurocranial morphology and FEA, however, clearly indicate a feeding behaviour more similar to vultures, possibly because of the large size of its prey (e.g., giant Moa). Harpagornis’ neurocranial adaptation probably allowed a stronger and faster pull back motion to quickly remove large chunks of meat from the prey, similarly to vultures. Moreover, our results document a rapid evolutionary change, which might have allowed Harpagornis to exploit large sized prey. Harpagornis moorei therefore represents an extreme example of how freedom from competition in island ecosystems can rapidly influence morphological adaptation

Variation in avian egg shape and nest structure is explained by climatic conditions

Abstract Why are avian eggs ovoid, while the eggs of most other vertebrates are symmetrical? The interaction between an egg and its environment likely drives selection that will shape eggs across evolutionary time. For example, eggs incubated in hot, arid regions face acute exposure to harsh climatic conditions relative to those in temperate zones, and this exposure will differ across nest types, with eggs in open nests being more exposed to direct solar radiation than those in enclosed nests. We examined the idea that the geographical distribution of both egg shapes and nest types should reflect selective pressures of key environmental parameters, such as ambient temperature and the drying capacity of air. We took a comparative approach, using 310 passerine species from Australia, many of which are found in some of the most extreme climates on earth. We found that, across the continent, egg elongation decreases and the proportion of species with domed nests with roofs increases in hotter and drier areas with sparse plant canopies. Eggs are most spherical in open nests in the hottest environments, and most elongate in domed nests in wetter, shadier environments. Our findings suggest that climatic conditions played a key role in the evolution of passerine egg shape

Virtual Reconstruction and Prey Size Preference in the Mid Cenozoic Thylacinid, <i>Nimbacinus dicksoni</i> (Thylacinidae, Marsupialia)

<div><p>Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing 12 known species, the oldest of which are late Oligocene (∼24 Ma) in age. Except for the recently extinct thylacine (<i>Thylacinus cynocephalus</i>), most are known from fragmentary craniodental material only, limiting the scope of biomechanical and ecological studies. However, a particularly well-preserved skull of the fossil species <i>Nimbacinus dicksoni</i>, has been recovered from middle Miocene (∼16-11.6 Ma) deposits in the Riversleigh World Heritage Area, northwestern Queensland. Here, we ask whether <i>N. dicksoni</i> was more similar to its recently extinct relative or to several large living marsupials in a key aspect of feeding ecology, i.e., was <i>N. dicksoni</i> a relatively small or large prey specialist. To address this question we have digitally reconstructed its skull and applied three-dimensional Finite Element Analysis to compare its mechanical performance with that of three extant marsupial carnivores and <i>T. cynocephalus</i>. Under loadings adjusted for differences in size that simulated forces generated by both jaw closing musculature and struggling prey, we found that stress distributions and magnitudes in the skull of <i>N. dicksoni</i> were more similar to those of the living spotted-tailed quoll (<i>Dasyurus maculatus</i>) than to its recently extinct relative. Considering the Finite Element Analysis results and dental morphology, we predict that <i>N. dicksoni</i> likely occupied a broadly similar ecological niche to that of <i>D. maculatus</i>, and was likely capable of hunting vertebrate prey that may have exceeded its own body mass.</p></div

Immunological insights into the life and times of the extinct Tasmanian tiger (Thylacinus cynocephalus)

The thylacine (Thylacinus cynocephalus) was Australia’s largest marsupial carnivore until its extinction within the last century. There remains considerable interest and debate regarding the biology of this species. Studies of thylacine biology are now limited to preserved specimens, and parts thereof, as well as written historical accounts of its biology. This study describes the development of the immune tissues of a pouch young thylacine, one of only eleven in existence, and the only specimen to be histologically sectioned. The appearance of the immune tissue of the developing pouch young thylacine is compared to the immune tissues of extant marsupials, providing insights into the immunity, biology and ecology of the extinct thylacine