taxonID	type	description	language	source
03F35F238F44C006E135FED78BC9D855.taxon	biology_ecology	A variety of studies have used biomechanical mod- eling, which incorporates mathematics, physics, and computer programming (41), to infer tyran- nosaur behavior. Tyrannosaurs, especially the large, derived forms, have often been used as exemplars to demonstrate the utility of such computer models. Most studies have suggested that although large tyrannosaurids might have been able to run at slow to moderate speeds at best (top speeds between 5 and 11 ms − 1), they could not run near- ly as fast as large athletic animals today, such as racehorses (~ 20 ms − 1) (12, 41, 42). Consensus also is building that even though large tyranno- saurids were not restricted to a pillar-like columnar limb posture to maximize mechanical advantage, they were still far from having very crouched, more birdlike postures (12, 41, 42). Aspects of tyrannosaurid anatomy, such as the long legs and large pelvic limb muscles, which intuitively seem to indicate fast running capacity, were inherited from small, presumably fast-running ancestors. Modeling studies have incorporated these features and shown that they did not make large tyranno- saurids extremely fast. However, it is worth noting that these studies rely on estimates of muscle size and attachment points, a somewhat conjecturaexercise, albeit constrained by the anatomy of extant relatives (12, 16), that plagues all such functional analyses. Both trace fossils (bite marks, coprolites) and quantitative techniques have helped to reveal what tyrannosaurs ate and how they fed. Tyrannosaurid bite marks have been found on the bones of a wide diversity of species, including various other tyrannosaurs, demonstrating that they were ecological generalists (43). Bite mark patterns show that tyrannosaurids characteristically bit deeply into carcasses, often through bones, and then pulled back, creating long cuts [puncture-pull feeding sensu (44)]. Some T. rex bite marks (44) and coprolites with bone chunks (45) indicate that bone was fractured, ingested, and used for sustenance, a mammal-like attribute not seen in extant reptiles. The bite forces needed to crunch through bone would have been enormous. Biomechanical experiments have replicated the size and depth of fossilized bite marks and suggest that T. rex generated bite forces of at least 13,400 N. Maximal bite forces were probably greater (46). Such large bite forces would have exerted tremendous stress on the skull. Tyrannosaurid skull shape and its relation to bite-induced stress have been extensively studied by finite element analysis. The results indicate that large tyrannosaurids had skulls optimized to endure strong bites, as various sutures absorbed stress and the fused nasals strengthened the snout (11, 47, 48). Similar biomechanical techniques have also been used to examine the role of the tyrannosaur neck in feeding, showing that it was important for generating pulling forces on food items and in inertial feeding (49), and the function of the unusual “ pinched metatarsus ” of the foot in turning, indicating that it was structured to resist shearing and twisting forces (50). Little is known about the ecological community structure for most extinct animals, but large sample sizes permit some understanding of tyrannosaur ecology. Late Cretaceous tyrannosaurids were the first dinosaurs for which population dynamics — the balance between deaths and births that create a population’ s age structure — could be assessed (10) (Fig. 4 C). Like large birds and mammals, but unlike living reptiles, tyrannosaurids probably experienced extremely high neonate mortality, followed by few deaths after 2 years of age (presumably a release from predation), and then increased mortality at mid-life (probably from the rigors of reproduction), so that few individuals had a long reproductive life span. Furthermore, a number of fossil sites have preserved multiple individuals, suggesting that tyrannosaurs were at least occasionally gregarious (51). Bite marks indicate that individuals of the same species bit each other in the face during encounters (52), and many older individuals with gout, bacterial legions, and bone fractures have been reported, showing that disease and injury were common (53). Fig. 4. Tyrannosaur growth and ecology. (A) Histological section of a T. rex dorsal rib, showing growth lines whose counts are used to reveal age and longevity. (B) Growth curves for North American tyrannosaurids derived from growth line counts and body size estimations for individuals showing how size changes with age. No sampled tyrannosaurid adults were more than 30 years old, and accelerated rather than prolonged development was the key to the great size of T. rex (8). (C) survivorship curve for Albertosaurus sarcophagus. This tyrannosaur exhibited high neonate mortality, then few deaths after age two, and then increased mortality at mid-life (8). Multiple lines of evidence indicate that tyrannosaur ecological habits changed during ontogeny. In Late Cretaceous tyrannosaurids, the difference in form between the lightly built, fleet juveniles and the larger, bulkier adults suggests that foraging behavior and targeted prey size changed as tyrannosaurs grew. The deep and muscular adult skull, with reinforced sutures and robust teeth, is well suited for sustaining high bite forces, whereas juveniles had none of these features (9, 39). Furthermore, the longer and more gracile hind limbs of juveniles indicate that they were relatively faster than adults (40), which has been corroborated by biomechanical analysis (12). These differences could have promoted major size-related shifts in ecology and behavior. It is plausible that adults preferentially attack- ed larger, but less mobile, prey than their younger counterparts. Such an ontogenetic shift is not seen in many familiar predators today (e. g., lions), but is present in extant crocodylians (54). As most basal tyrannosauroids are similar in skull and body proportions to juvenile Late Cretaceous tyrannosaurids, it is likely that they behaved and fed in a similar manner. However, detailed biomechanical analyses have yet to be carried out for most nontyrannosaurid tyrannosauroids. Whether T. rex and other large tyrannosaurs were scavengers or predators has generated much speculation and dispute. Bite marks from mass death assemblages of herbivorous dinosaurs show that tyrannosaurs scavenged on occasion (38). However, multiple reports of healed tyrannosaur bite marks on prey bones (55, 56) and tyrannosaur stomach contents containing remains of young dinosaurs (57) indicate that tyrannosaurs were capable of active predation. Like most carnivores, tyrannosaurs probably both scavenged and hunted. One of the largest voids in our understanding of dinosaur biology is the sex of individual specimens. It has been suggested that female tyrannosaurs required a larger pelvic outlet for the passage of eggs, reflected by a greater span between the ischial bones and a smaller or more posteriorly located first tail chevron, but these indices find little neontological support in living archosaurs (58, 59). More recently, medullary bone, a calcium phosphate deposit for the use of shelling in eggs, was reported in one T. rex specimen (60). This provides a surefire identification of sex in dino- saurs, and holds much promise for future studies of dinosaur sex and ecology. Tyrannosaur Biogeography Until recently, all tyrannosaur fossils were limited to Asia and North America, but the discovery and recognition of basal tyrannosauroids over the last decade reveals a more cosmopolitan distribution during their early evolution (5, 22 – 24, 61). Members of the Middle – Late Jurassic proceratosaurid radiation are known from Europe and Asia (5), whereas the Late Jurassic genus Stokesosaurus is known from both Europe and North America (24). However, all well-known tyrannosaurs more derived than Eotyrannus and Stokesosaurus exhibit a purely Asian or North American distribution. Faunal interchange between these continents is characteristic of most Campanian-Maastrichtian dinosaur clades and reflects an increasing Laurasian- Gondwanan provincialism during the final stages of the Age of Dinosaurs (62). Tyrannosaurs, because of their rich fossil record and well-studied phylogenetic relationships, are one of the primary sources of evidence for this long-established biogeographic hypothesis. Emerging evidence, however, indicates that tyrannosaurs were likely present on the southern continents during their early evolutionary history. An isolated pubis from the Early Cretaceous of Australia was recently identified as belonging to a derived tyrannosaur (13). As contemporary Earlymid Cretaceous dinosaurs mostly belong to globally distributed clades (26), the absence of Gondwanan tyrannosaurs during this time had been a puzzling anomaly. Even with this discovery, if it is from a tyrannosaur, tyrannosaurs are absent in the well-sampled mid-Late Cretaceous units of South America, Africa, and Madagascar (63). It is possible that tyrannosaurs were rare on the southern continents during the Early-mid Cretaceous, and it is likely that Gondwanan forms did not persist into the latest Cretaceous, at least as common and ecologically dominant carnivores. Most tyrannosaurs are known from mesic (moderate moisture) or seasonally mesic paleoenvironments, and their fossils are notably absent from xeric (dry) facies, even those that interfinger with tyrannosaur-bearing mesic sediments within the same sedimentary rock basins in Asia (64). This likely indicates that tyrannosaurs preferred wetter habitats, although it may still reflect a sampling bias. Wherever they were present during the Late Cretaceous in North America and Asia, tyrannosaurs were the sole apex predators in their environments. Multiple large tyrannosaurids co-occurred during some intervals in North America and Asia (19, 27), but the Maastrichtian of western North America was solely dominated by T. rex (39). In contrast, most nontyrannosaurid tyrannosauroids are found alongside larger non- tyrannosaur predators, demonstrating that tyrannosaurs did not exclusively dominate the apex predator niche, regardless of where they lived, until the final 20 million years of the Cretaceous.	en	Stephen L. Brusatte, Mark A. Norell, Thomas D. Carr, Gregory M. Erickson, John R. Hutchinson, Amy M. Balanoff, Gabe S. Bever, Jonah N. Choiniere, Peter J. Makovicky, Xing Xu (2010): Tyrannosaur Paleobiology: New Research on Ancient Exemplar Organisms. Science 329: 1481-1485, DOI: 10.1126/science.1193304
