“…Taken together, these structures occupy at least 7.3% and 6.7% of the internal volume of the premaxilla and maxilla, respectively (Table 1), and an accessory sinus is linked to the premaxillary fenestra at the base of the ascending ramus of the maxilla. Several branches of these maxillary neurovascular structures closely approach the sinus although they do not appear to interact with it directly.Figure 4Lateral view of left premaxilla and maxilla, denoting maxillary anatomy as suggested by Hendrickx and Mateus 56 . Graphs denote changes in canal area versus canal count (i.e.…”
The discovery of large, complex, internal canals within the rostra of fossil reptiles has been linked with an enhanced tactile function utilised in an aquatic context, so far in pliosaurids, the Cretaceous theropod Spinosaurus, and the related spinosaurid Baryonyx. Here, we report the presence of a complex network of large, laterally situated, anastomosing channels, discovered via micro-focus computed tomography (μCT), in the premaxilla and maxilla of Neovenator, a mid-sized allosauroid theropod from the Early Cretaceous of the UK. We identify these channels as neurovascular canals, that include parts of the trigeminal nerve; many branches of this complex terminate on the external surfaces of the premaxilla and maxilla where they are associated with foramina. Neovenator is universally regarded as a ‘typical’ terrestrial, predatory theropod, and there are no indications that it was aquatic, amphibious, or unusual with respect to the ecology or behaviour predicted for allosauroids. Accordingly, we propose that enlarged neurovascular facial canals shouldn’t be used to exclusively support a model of aquatic foraging in theropods and argue instead that an enhanced degree of facial sensitivity may have been linked with any number of alternative behavioural adaptations, among them defleshing behaviour, nest selection/maintenance or social interaction.
“…Taken together, these structures occupy at least 7.3% and 6.7% of the internal volume of the premaxilla and maxilla, respectively (Table 1), and an accessory sinus is linked to the premaxillary fenestra at the base of the ascending ramus of the maxilla. Several branches of these maxillary neurovascular structures closely approach the sinus although they do not appear to interact with it directly.Figure 4Lateral view of left premaxilla and maxilla, denoting maxillary anatomy as suggested by Hendrickx and Mateus 56 . Graphs denote changes in canal area versus canal count (i.e.…”
The discovery of large, complex, internal canals within the rostra of fossil reptiles has been linked with an enhanced tactile function utilised in an aquatic context, so far in pliosaurids, the Cretaceous theropod Spinosaurus, and the related spinosaurid Baryonyx. Here, we report the presence of a complex network of large, laterally situated, anastomosing channels, discovered via micro-focus computed tomography (μCT), in the premaxilla and maxilla of Neovenator, a mid-sized allosauroid theropod from the Early Cretaceous of the UK. We identify these channels as neurovascular canals, that include parts of the trigeminal nerve; many branches of this complex terminate on the external surfaces of the premaxilla and maxilla where they are associated with foramina. Neovenator is universally regarded as a ‘typical’ terrestrial, predatory theropod, and there are no indications that it was aquatic, amphibious, or unusual with respect to the ecology or behaviour predicted for allosauroids. Accordingly, we propose that enlarged neurovascular facial canals shouldn’t be used to exclusively support a model of aquatic foraging in theropods and argue instead that an enhanced degree of facial sensitivity may have been linked with any number of alternative behavioural adaptations, among them defleshing behaviour, nest selection/maintenance or social interaction.
“…The spinosaurid record reflects this in that there are only ten taxa in our dataset (only nine classified species) but abundant fossil occurrences are known from specific sites (Läng et al . ; Medeiros et al . ; Benyoucef et al .…”
Non‐avian theropods were a highly successful clade of bipedal, predominantly carnivorous, dinosaurs. Their diversity and macroevolutionary patterns have been the subject of many studies. Changes in fossil specimen completeness through time and space can bias our understanding of macroevolution. Here, we quantify the completeness of 455 non‐avian theropod species using the skeletal completeness metric (SCM), which calculates the proportion of a complete skeleton preserved for a specimen. Temporal patterns of theropod skeletal completeness show peaks in the Carnian, Oxfordian–Kimmeridgian and Barremian–Aptian, and lows in the Berriasian and Hauterivian. Lagerstätten primarily drive the peaks in completeness and observed taxonomic diversity in the Oxfordian–Kimmeridgian and the Barremian–Aptian. Theropods have a significantly lower distribution of completeness scores than contemporary sauropodomorph dinosaurs but change in completeness through time for the two groups shows a significant correlation when conservation Lagerstätten are excluded, possibly indicating that both records are primarily driven by geology and sampling availability. Our results reveal relatively weak temporal sampling biases acting on the theropod record but relatively strong spatial and environmental biases. Asia has a significantly more complete record than any other continent, the mid northern latitudes have the highest abundance of finds, and most complete theropod skeletons come from lacustrine and aeolian environments. We suggest that these patterns result from historical research focus, modern climate dynamics, and depositional transportation energy plus association with conservation Lagerstätten, respectively. Furthermore, we find possible ecological biases acting on different theropod subgroups, but body size does not influence theropod completeness on a global scale.
“…These results show that left-skewed M-S distributions of herbivorous non-avian dinosaurs, and relative scarcity of medium- to small-sized species of this group, could easily have arisen because of size-specific competition for niche space in this mass range. Similarly, the increased availability of medium-sized prey in dinosaur-dominated ecosystems could account for the normal M-S distribution so far recorded for theropods, as well as a higher carnivore:herbivore species ratio in dinosaur versus mammal communities [25]–[27]. Thus, our approach offers an ecological explanation for patterns observed in the fossil record, such that we might even expect these patterns rather than predicting that taphonomic effects have taken place.…”
Section: Discussionmentioning
confidence: 60%
“…We simulate communities comprising size-structured populations across the full range of body size classes expected for both vertebrate groups, and hypothetical life tables for each population based on predicted survivorship schedules (type B1 for dinosaurs, type 1 for mammals). Results are compared with M-S distributions from the fossil record (and of extant mammals and birds), to test the hypotheses that 1) middle- and large-sized carnivorous dinosaurs were relatively more diverse than carnivorous mammals [25]–[27] because the former had access to a wider diversity and abundance of prey in this size range [23]; and 2) dinosaurs were poorly represented amongst small-to-middle size class species due to high competition intensity with juveniles from larger species in this range [4]. We also discuss trends in prey size selection that emerge in terms of resource partitioning that occurs amongst different-sized carnivorous dinosaurs in our models.…”
Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs’ successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.
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