Perhistoric Birds

                                 Titanis

 Titanis is a large extinct flightless carnivorous bird of the family Phorusrhacidae, endemic to North America during the Blancan stage of the Pliocene living 4.9—1.8 Ma, and died out during the Gelasian Age of the earliest Pleistocene, existing approximately 3.1 million years.

 The generic name, Titanis, refers to the titans, Ancient Greek gods that preceded the Twelve Olympians, in allusion to the bird's size. The specific name, T. walleri, honors the holotype's collector, Benjamin I. Waller.

  It lived approximately 5-2 million years ago (early Pliocene to early Pleistocene) in North America. Fossil evidence has been found in Gilchrist County, Florida dating from 3.0 to 2.9 million years.
From circumstantial evidence (i.e., bone fractures), it has been suggested that the species did not become extinct until 15,000 years ago,  but more precise dating by McFadden and colleagues refutes such a late date; all known Titanis fossils appear to be at least 2 million years old.Titanis was part of the group of giant flightless birds called the Phorusrhacidae, which are nicknamed "terror birds", and has been thought to represent the youngest species of the lineage (recently, a significantly younger South American example has been reported ). The Phorusrhacidae originated in South America; Titanis is the only known member of the branch of the group that migrated out of that continent during the Great American Interchange. It is estimated that Titanis could run at speeds of 65 km/h. It was 2.5 metres (8 ft 2 in) tall and weighed approximately 150 kilograms (330 lb), but with large variance (perhaps indicating strong sexual dimorphism). Though its skull has not been found, it most probably would have been large, with a huge, axe-like beak, like its relatives.
The wings were small and could not have been used for flight. The wing bones articulated in an unusual joint-like structure, suggesting the digits could flex to some degree. It also had a relatively rigid wrist, which would not have allowed the hand to fold back against the arm to the same degree as other birds. This led one scientist, R.M. Chandler, to suggest that the wings may have supported some type of clawed, mobile hand similar to the hands of non-avian theropod dinosaurs, such as the deinonychosaurs (also popularly known as "raptors"). However, it was later pointed out that this wing joint is not in fact unique, and is present in seriamas (modern members of the same bird group to which Titanis belonged), which do not have any specialized grasping hands.
Overall, Titanis was very similar to the South American Phorusrhacos and Devincenzia, its closest relatives. However, it differs from these in having a shorter, thicker neck, a bulkier head, and an overall more heavily-built bodily structure. Little is known of its body structure, but it seems to have been less wide-footed than Devincenzia, with a proportionally much stronger middle toe. (Onactornis is now considered a junior synonym of Devincenzia).

Dinosaurs

                            Tyrannosaurus Rex

 

                                
    

Tyrannosaurus meaning "tyrant lizard", from Greek τυράννος (tyrannos, "tyrant") and σαύρος' (sauros, "lizard")) is a genus of theropod dinosaur. The species Tyrannosaurus rex (rex meaning "king" in Latin), commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 67 to 65.5 million years ago. It was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 12.8 m (42 ft) in length,up to 4 metres (13 ft) tall at the hips, and up to 6.8 metric tons (7.5 short tons) in weight. By far the largest carnivore in its environment, Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger. The debate over Tyrannosaurus as apex predator or scavenger is among the longest running in paleontology.

More than 30 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including life history and biomechanics. The feeding habits, physiology and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy is also controversial, with some scientists considering Tarbosaurus bataar from Asia to represent a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus. Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 metres (42 ft) long, and was 4.0 metres (13.1 ft) tall at the hips. Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons),to less than 4.5 metric tons (5.0 short tons), with most modern estimates ranging between 5.4 and 6.8 metric tons (6.0 and 7.5 short tons). Packard et al. (2009) tested dinosaur mass estimation procedures on elephants and concluded that dinosaur estimations are flawed and produce over-estimations; thus, the weight of Tyrannosaurus could be much less than usually estimated.

Although Tyrannosaurus rex was larger than the well known Jurassic theropod Allosaurus, it was slightly smaller than some other Cretaceous carnivores, such as Spinosaurus and Giganotosaurus.

The neck of Tyrannosaurus rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs had only two clawed fingers, along with an additional small metacarpal representing the remnant of a third digit. In contrast the hind limbs were among the longest in proportion to body size of any theropod. The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow, reducing its weight without significant loss of strength.

The largest known Tyrannosaurus rex skulls measure up to 5 feet (1.5 m) in length.Large fenestrae (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects Tyrannosaurus’ skull was significantly different from those of large non-tyrannosauroid theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good binocular vision.The skull bones were massive and the nasals and some other bones were fused, preventing movement between them; but many were pneumatized (contained a "honeycomb" of tiny air spaces) which may have made the bones more flexible as well as lighter. These and other skull-strengthening features are part of the tyrannosaurid trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids. The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth. The teeth of Tyrannosaurus rex displayed marked heterodonty (differences in shape). The premaxillary teeth at the front of the upper jaw were closely packed, D-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards. The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers; more widely spaced and also had reinforcing ridges. Those in the upper jaw were larger than those in all but the rear of the lower jaw. The largest found so far is estimated to have been 30 centimetres (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found. Tyrannosaurus is the type genus of the superfamily Tyrannosauroidea, the family Tyrannosauridae, and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American Daspletosaurus and the Asian Tarbosaurus,both of which have occasionally been synonymized with Tyrannosaurus Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as megalosaurs and carnosaurs, although more recently they were reclassified with the generally smaller coelurosaurs.

 The identification of several specimens as juvenile Tyrannosaurus rex has allowed scientists to document ontogenetic changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM 28471, the "Jordan theropod") is estimated to have weighed only 30 kg (66 lb), while the largest, such as FMNH PR2081 ("Sue") most likely weighed over 5,400 kg (12,000 lb). Histologic analysis of Tyrannosaurus rex bones showed LACM 28471 had aged only 2 years when it died, while "Sue" was 28 years old, an age which may have been close to the maximum for the species. Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A Tyrannosaurus rex growth curve is S-shaped, with juveniles remaining under 1,800 kg (4,000 lb) until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young Tyrannosaurus rex would gain an average of 600 kg (1,300 lb) a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only 600 kg (1,300 lb) separated the 28-year-old "Sue" from a 22-year-old Canadian specimen (RTMP 81.12.1). Another recent histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age. This sudden change in growth rate may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur of a 16 to 20-year-old Tyrannosaurus rex from Montana (MOR 1125, also known as "B-rex"). Medullary tissue is found only in female birds during ovulation, indicating that "B-rex" was of reproductive age. Further study indicates an age of 18 for this specimen. Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes. Over half of the known Tyrannosaurus rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile Tyrannosaurus rex fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and so were not often fossilized. However, this rarity may also be due to the incompleteness of the fossil record or to the bias of fossil collectors towards larger, more spectacular specimens. As the number of specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or morphs, similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed 'gracile'. Several morphological differences associated with the two morphs were used to analyze sexual dimorphism in Tyrannosaurus rex, with the 'robust' morph usually suggested to be female. For example, the pelvis of several 'robust' specimens seemed to be wider, perhaps to allow the passage of eggs. It was also thought that the 'robust' morphology correlated with a reduced chevron on the first tail vertebra, also ostensibly to allow eggs to pass out of the reproductive tract, as had been erroneously reported for crocodiles in recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between Tyrannosaurus rex genders. A full-sized chevron was discovered on the first tail vertebra of "Sue", an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As Tyrannosaurus rex specimens have been found from Saskatchewan to New Mexico, differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.

Only a single Tyrannosaurus rex specimen has been conclusively shown to belong to a specific gender. Examination of "B-rex" demonstrated the preservation of soft tissue within several bones. Some of this tissue has been identified as a medullary tissue, a specialized tissue grown only in modern birds as a source of calcium for the production of eggshell during ovulation. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive hormones like estrogen. This strongly suggests that "B-rex" was female, and that she died during ovulation.Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs, aside from birds. The shared presence of medullary tissue in birds and theropod dinosaurs is further evidence of the close evolutionary relationship between the two.