Description[edit]

Artist's restoration of two M. hoffmannii

A size comparison Mosasaurus hoffmannii with a diver.

Mosasaurus was among the last of the mosasaurids, and among the largest. As with most mosasaurids, the legs and feet of Mosasaurus were modified into flippers, and the front flippers were larger than the hind flippers. The largest known species, Mosasaurus hoffmannii, reached lengths up to 18 metres (59 ft),^[1] slightly longer than its relatives Tylosaurusand Hainosaurus. Mosasaurus was also more robust than related mosasaurids. The skull was more robust than in other mosasaurids, and the lower jaws (mandibles) attached very tightly to the skull. They had deep, barrel-shaped bodies, and with their fairly large eyes, poor binocular vision, and poorly developed olfactory bulbs, experts believe that Mosasauruslived near the ocean surface, where they preyed on fish, turtles, ammonites, smaller mosasaurids, and plesiosaurians. Although they were able to dive, they evidently did not venture into deeper waters.

The skull of Mosasaurus tapered off into a short, conical tip. The jaws were armed with massive conical teeth. Their paddle-like limbs had five digits in front and four in back. The body ended in a strong tail, which other mosasaurid fossils suggest had a fluke similar to those of sharks and some ichthyosaurs. The body probably remained stiff to reduce drag through the water, while the end of the tail provided strong propulsion.

Description[edit]

Restoration of T. proriger

Along with plesiosaurs, sharks, fish, and other genera of mosasaurs, it was a dominant predator of the Western Interior Seaway during the Late Cretaceous. Tylosaurus proriger was among the largest of all the mosasaurs (along with Hainosaurus and Mosasaurus hoffmannii), reaching maximum lengths of 14 m (46 ft).^[1] A distinguishing characteristic ofTylosaurus is its elongated, cylindrical premaxilla (snout) from which it takes its name and which may have been used to ram and stun prey and also in intraspecific combat.

Early restorations showing Tylosaurus with a dorsal crest were based on misidentified tracheal cartilage, but when the error was discovered, depicting mosasaurs with such crests was already a trend^[2][3]

Description[edit]

Size compared with a human

Based on the few fully mature specimens,^[3] Deinonychus could reach 3.4 metres (11.2 ft) in length, with a skull length of 410 mm (16.1 in), a hip height of 0.87 metres (2.9 ft) and a weight of 73 kg (161 lb), though there is a higher estimate of 100 kg (220 lb).^[4][5] The skull was equipped with powerful jaws lined with around seventy curved, blade-like teeth. Studies of the skull have progressed a great deal over the decades. Ostrom reconstructed the partial, imperfectly preserved skulls that he had as triangular, broad, and fairly similar to Allosaurus. Additional Deinonychus skull material and closely related species found with good three-dimensional preservation^[6] show that the palate was more vaulted than Ostrom thought, making the snout far narrower, while the jugals flared broadly, giving greater stereoscopic vision. The skull of Deinonychus was different from that of Velociraptor, however, in that it had a more robust skull roof, like that of Dromaeosaurus, and did not have the depressed nasals of Velociraptor.^[7] Both the skull and the lower jaw had fenestrae (skull openings) which reduced the weight of the skull. In Deinonychus, the antorbital fenestra, a skull opening between the eye and nostril, was particularly large.^[6]

Life restoration

Deinonychus possessed large "hands" (manus) with three claws on each forelimb. The first digit was shortest and the second was longest. Each hind foot bore a sickle-shaped claw on the second digit, which was probably used during predation.^[8]

No skin impressions have ever been found in association with fossils of Deinonychus. Nonetheless, the evidence suggests that the Dromaeosauridae, including Deinonychus, had feathers.^[9] The genus Microraptor is both older geologically and more primitive phylogenetically than Deinonychus, and within the same family.^[10] Multiple fossils of Microraptor preserve pennaceous, vaned feathers like those of modern birds on the arms, legs, and tail, along with covert and contour feathers.^[9] Velociraptor is geologically younger than Deinonychus, but even more closely related (within the subfamily velociraptorinae, see Classification, below). A specimen of Velociraptor has been found with quill knobs on the ulna. Quill knobs are where the follicular ligaments attached, and are a direct indicator of feathers of modern aspect.^[11]

Dinosaur eggs are eggs laid by dinosaurs. When the first scientifically documented remains of dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had laid eggs because they were reptiles.^[1]In 1859, the first scientifically documented dinosaur egg fossils were discovered in France by Jean-Jacques Poech, although they were mistaken for giant bird eggs. The first scientifically recognized dinosaur egg fossils were discovered in 1923 by an American Museum of Natural History crew in Mongolia. Since then many new nesting sites have been found all over the world and a system of classification based on the structure of eggshell was developed in Chinabefore gradually diffusing into the West. Dinosaur eggshell can be studied in thin section and viewed under a microscope. The interior of a dinosaur egg can be studied using CAT scans or by gradually dissolving away the shell with acid. Sometimes the egg preserves the remains of the developing embryo inside. The oldest known dinosaur eggs and embryos are from Massospondylus, which lived during the Early Jurassic, about 190 million years ago.^[2][3]

Description

V. mongoliensis compared in size to a human

Velociraptor was a mid-sized dromaeosaurid, with adults measuring up to 2.07 m (6.8 ft) long, 0.5 m (1.6 ft) high at the hip, and weighing up to 15 kg (33 lb).^[3] The skull, which grew up to 25 cm (10 in) long, was uniquely up-curved, concave on the upper surface and convex on the lower. The jaws were lined with 26–28 widely spaced teeth on each side, each more strongly serrated on the back edge than the front.^[1][4]

Velociraptor, like other dromaeosaurids, had a large manus ('hand') with three strongly curved claws, which were similar in construction and flexibility to the wing bones of modernbirds. The second digit was the longest of the three digits present, while the first was shortest. The structure of the carpal (wrist) bones prevented pronation of the wrist and forced the 'hands' to be held with the palmar surface facing inwards (medially), not downwards.^[5] The first digit of the foot, as in other theropods, was a small dewclaw. However, whereas most theropods had feet with three digits contacting the ground, dromaeosaurids like Velociraptor walked on only their third and fourth digits. The second digit, for which Velociraptor is most famous, was highly modified and held retracted off the ground. It bore a relatively large, sickle-shaped claw, typical of dromaeosaurid and troodontid dinosaurs. This enlarged claw, which could grow to over 6.5 cm (2.6 in) long around its outer edge,^[6] was most likely a predatory device used to tear into or restrain struggling prey.^[6][7]

Skeletal restoration of V. mongoliensis by Jaime A. Headden, 2010.

As in other dromaeosaurs, Velociraptor tails had long bony projections (prezygapophyses) on the upper surfaces of the vertebrae, as well as ossified tendons underneath. The prezygapophyses began on the tenth tail (caudal) vertebra and extended forward to brace four to ten additional vertebrae, depending on position in the tail. These were once thought to fully stiffen the tail, forcing the entire tail to act as a single rod-like unit. However, at least one specimen has preserved a series of intact tail vertebrae curved sideways into an S-shape, suggesting that there was considerably more horizontal flexibility than once thought.^[6][8]

In 2007, paleontologists reported the discovery of quill knobs on a well-preserved Velociraptor mongoliensis forearm from Mongolia, confirming the presence of feathers in this species.^[9]

Feathers

Fossils of dromaeosaurids more primitive than Velociraptor are known to have had feathers covering their bodies and fully developed feathered wings.^[10] The fact that the ancestors of Velociraptor were feathered and possibly capable of flight had long suggested to paleontologists that Velociraptor bore feathers as well, since even flightless birds today retain most of their feathers. In September 2007, researchers found quill knobs on the forearm of a Velociraptor found in Mongolia.^[9] These bumps on bird wing bones show where feathers anchor, and their presence on Velociraptor indicate it too had feathers. According to paleontologist Alan Turner,

V. mongoliensis restored by Matthew Martyniuk (2006) showing the large wing feathers evidenced by fossil quill knobs.

A lack of quill knobs does not necessarily mean that a dinosaur did not have feathers. Finding quill knobs on Velociraptor, though, means that it definitely had feathers. This is something we'd long suspected, but no one had been able to prove.^[11]

Co-author Mark Norell, Curator-in-Charge of fossil reptiles, amphibians and birds at the American Museum of Natural History, also weighed in on the discovery, saying:

The more that we learn about these animals the more we find that there is basically no difference between birds and their closely related dinosaur ancestors like velociraptor. Both have wishbones, brooded their nests, possess hollow bones, and were covered in feathers. If animals like velociraptor were alive today our first impression would be that they were just very unusual looking birds.^[11]

According to Turner and co-authors Norell and Peter Makovicky, quill knobs are not found in all prehistoric birds, and their absence does not mean that an animal was not feathered – flamingos, for example, have no quill knobs. However, their presence confirms that Velociraptor bore modern-style wing feathers, with a rachis and vane formed by barbs. The forearm specimen on which the quill knobs were found (specimen number IGM 100/981) represents an animal 1.5 meters in length (5 ft) and 15 kilograms (33 lbs) in weight. Based on the spacing of the six preserved knobs in this specimen, the authors suggested that Velociraptor bore 14 secondaries (wing feathers stemming from the forearm), compared with 12 or more in Archaeopteryx, 18 in Microraptor, and 10 in Rahonavis. This type of variation in the number of wing feathers between closely related species, the authors asserted, is to be expected, given similar variation among modern birds.^[9]

Turner and colleagues interpreted the presence of feathers on Velociraptor as evidence against the idea that the larger, flightless maniraptorans lost their feathers secondarily due to larger body size. Furthermore, they noted that quill knobs are almost never found in flightless bird species today, and that their presence in Velociraptor (presumed to have been flightless due to its relatively large size and short forelimbs) is evidence that the ancestors of dromaeosaurids could fly, making Velociraptor and other large members of this family secondarily flightless, though it is possible the large wing feathers inferred in the ancestors of Velociraptor had a purpose other than flight. The feathers of the flightless Velociraptor may have been used for display, for covering their nests while brooding, or for added speed and thrust when running up inclined slopes.^[9]

Description[edit]

Neck and skull of ROM skeleton

Barosaurus was an enormous animal, with some adults measuring more than 26 meters (85 feet) in length and weighing more than 20 metric tons (22 short tons).^[2] Barosaurus was differently proportioned than its close relative Diplodocus, with a longer neck and shorter tail, but was about the same length overall. It was longer than Apatosaurus, but its skeleton was less robust.^[3]

Sauropod skulls are rarely preserved, and scientists have yet to discover a Barosaurus skull. Related diplodocids like Apatosaurus and Diplodocus had long, low skulls with peg-like teeth confined to the front of the jaws.^[4]

Most of the distinguishing skeletal features of Barosaurus were in the vertebrae, although a complete vertebral column has never been found. Diplodocus and Apatosaurus both had 15 cervical (neck) and 10 dorsal (trunk) vertebrae, while Barosaurus had only 9 dorsals. A dorsal may have been converted into a cervical vertebra, for a total of 16 vertebrae in the neck. Barosaurus cervicals were similar to those of Diplodocus, but some were up to 50% longer. The neural spines protruding from the top of the vertebrae were neither as tall or as complex in Barosaurus as they were in Diplodocus. In contrast to its neck vertebrae, Barosaurus had shorter caudal (tail) vertebrae than Diplodocus, resulting in a shorter tail. The chevron bones lining the underside of the tail were forked and had a prominent forward spike, much like the closely related Diplodocus. The tail probably ended in a long whiplash, much like Apatosaurus, Diplodocus and other diplodocids, some of which had up to 80 tail vertebrae.^[3]

The limb bones of Barosaurus were virtually indistinguishable from those of Diplodocus.^[3] Both were quadrupedal, with columnar limbs adapted to support the enormous bulk of the animals. Barosaurus had proportionately longer forelimbs than other diplodocids, although they were still shorter than most other groups of sauropods.^[3] There was a single carpal bone in the wrist, and the metacarpals were more slender than those ofDiplodocus.^[5] Barosaurus feet have never been discovered, but like other sauropods, it would have been digitigrade, with all four feet each bearing five small toes. A large claw adorned the inside digit on the manus(forefoot) while smaller claws tipped the inside three digits of the pes (hindfoot).^[3][4]

Description

Life restoration

Like all sauropod dinosaurs, Brachiosaurus was a quadrupedal animal with a small skull, a long neck, a large trunk with a high-ellipsoid cross section, a long, muscular tail and slender, columnar limbs.^[1] The skull had a robust, wide muzzle and thick jaw bones, with spoon–shaped teeth. As in Giraffatitan, there was an arch of bone over the snout and in front of the eyes that encircled the nasal opening, although this arch was not as large as in its relative.^[2] Large air sacs connected to the lung system were present in the neck and trunk, invading the vertebrae and ribs, greatly reducing the overall density.^[3][4] Unusually for a sauropod, the forelimbs were longer than the hind limbs. The humerus (upper arm bone) of Brachiosaurus was relatively lightly built for its size,^[5] measuring 2.04 metres (6.7 ft) in length in the type specimen.^[6] The femur (thigh bone) of the type specimen was only 2.03 metres (6.7 ft) long.^[6] Unlike other sauropods, Brachiosaurus appears to have been slightly sprawled at the shoulder joint,^[5] and the ribcage was unusually deep.^[6] This led to the trunk being inclined, with the front much higher than the hips, and the neck exiting the trunk at a steep angle. Overall, this shape resembles a giraffe more than any other living animal.^[7]

Size

Size compared to a human

Because "Brachiosaurus" brancai (Giraffatitan) is known from much more complete material than B. altithorax, most size estimates for Brachiosaurus are actually for the African form. There is an additional element of uncertainty for North American Brachiosaurus because the most complete skeleton appears to have come from a subadult.^[5] Over the years, the mass of B. altithorax has been estimated as 35.0 metric tons (38.6 short tons),^[7]43.9 metric tons (48.4 short tons),^[8] 28.7 metric tons (31.6 short tons)^[5] and, most recently, 56.3 metric tons (62.1 short tons).^[9] In cases when the authors also provided estimates for Giraffatitan, and found that genus to be somewhat lighter (31.5 metric tons (34.7 short tons) for Paul [1988],^[7] 39.5 metric tons (43.5 short tons) for Mazzetta [2004],^[10] 23.3 metric tons (25.7 short tons) for Taylor [2009],^[5] or 34 metric tons (37 short tons) for Benson et al [2014]).^[9] The length of Brachiosaurus has been estimated at 26 metres (85 ft).^[11]