Thunder Lizards (Diplodocidae)

Diplodocidae are among the best known sauropod dinosaurs. Several species were described in the late 1800s or early 1900s from the Morrison Formation of North America. Since then, numerous additional specimens were recovered in the USA,Tanzania, Portugal, and Argentina, as well as possibly Spain, England, Georgia,Zimbabwe, and Asia.


To date, the clade includes about 12 to 15 nominal species, someof themwith questionable taxonomic status (e.g., ‘Diplodocus’ hayi or Dyslocosaurus polyonychius), and ranging in age from Late Jurassic to Early Cretaceous. However,intrageneric relationships of the iconic, multi-species genera Apatosaurus and Diplodocus are still poorly known.
The dinosaur clade Diplodocidae includes some of the most iconic sauropods.With their greatly elongated necks and tails, diplodocids constitute one of the typical popular images of sauropods.The clade is historically important, having provided the first published reconstruction of an entire sauropod skeleton (‘Brontosaurus’ excelsus; Marsh, 1883), the first complete sauropod skull to be described (Diplodocus; Marsh, 1884), and the first mounted sauropod specimen (Apatosaurus AMNH 460; Matthew, 1905). Diplodocids range from relatively small to gigantic species (Kaatedocus siberi Tschopp &Mateus, 2012,12–14 m, to Supersaurus vivianae Jensen, 1985, 35–40 m, respectively) with a wide range of body masses (Tornieria africana (Fraas, 1908)), 12 t, to Apatosaurus louisae Holland, 1915a,41.3 t; Campione & Evans, 2012; Benson et al., 2014). The clade includes the well-known genera Apatosaurus Marsh, 1877a, Diplodocus Marsh, 1878, and Barosaurus Marsh, 1890.

1. Seismosaurus 2. Diplodocus 3. Apatosaurus 4. Barosaurus 5. Supersaurus
Their possible first occurrence dates to the Middle Jurassic of England (Cetiosauriscus stewarti Charig, 1980; but see Heathcote & Upchurch, 2003; Rauhut et al., 2005, for an alternative identification of Cetiosauriscus).
Diplodocidae reached a peak in diversity in the Late Jurassic, with finds from North America, Tanzania, Zimbabwe, Portugal and Spain, as well as possibly England and Georgia (Mannion et al., 2012). To date, only one convincing report exists for their presence in the Cretaceous, which is furthermore the only occurrence of the clade in South America (Whitlock, D’Emic&Wilson, 2011; Gallina et al., 2014).
In recent phylogenetic trees, Diplodocidae consistently forms the sister group to the clade Dicraeosauridae, with which they form Flagellicaudata. Flagellicaudata in turn is included with Rebbachisauridae in Diplodocoidea (Tschopp & Mateus, 2013b). The taxonomy of these clades was historically somewhat confused, with “Diplodocidae” being used in the same way as Diplodocoidea today.
Although new taxa continue to be discovered,the vast majority of diplodocid species were described in the late 1800s and early 1900s. The high rate of early descriptions,particularly during the so-called ‘Bone Wars’ of the late 1800s, resulted also in a large number of species that are now considered invalid, questionable, or synonymous (Taylor,2010). Species identification is furthermore hampered by the fact that many holotype specimens are incomplete and fragmentary (e.g., Diplodocus longus YPM 1920), or appear to include bones from more than one individual (e.g., Apatosaurus ajax YPM 1860). Due to the absence of field notes or quarry maps for many of these early discoveries, it is oftendifficult or impossible to confidently assign bones to particular individuals or taxa.Given that most sites in the Upper Jurassic Morrison Formation are multi-taxon assemblages,and that the Morrison Formation has yielded about three-quarters of the diplodocid genera reported so far, it is possible that at least some holotype specimens include material from multiple species. This renders meaningful diagnoses for the species, and thus the identification of new specimens, highly difficult. Nevertheless, detailed studies of original material and their corresponding field notes by McIntosh & Berman (1975), Berman &McIntosh (1978), McIntosh (1981), McIntosh (1990a), McIntosh (1995), McIntosh (2005) and McIntosh & Carpenter (1998) have provided a wealth of important information concerning the composition of diplodocid holotype specimens. This valuable researchallows recognition of diagnostic autapomorphies and character combinations for manytaxa. However, only one study so far has tested the referral of individual specimensto diplodocid species using phylogenetic methods, focusing on the genus Apatosaurusalone.By using individual specimens as operationaltaxonomic units (OTUs), Upchurch, Tomida & Barrett (2004) generally supported thetraditional view of Apatosaurus intrarelationships, which included the species A. ajax, A.excelsus, A. louisae and A. parvus.

Supersaurus (meaning "super lizard") is a

Diplodocus

This genus of dinosaurs lived in what is now western North America at the end of the Jurassic period. Diplodocus is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, between about 154 and 152 million years ago, during the late Kimmeridgian age.The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as Apatosaurus, Barosaurus, Brachiosaurus, Brontosaurus, and Camarasaurus.
Diplodocus is among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and four sturdy legs. For many years, it was the longest dinosaur known. Its great size may have been a deterrent to the predators Allosaurus and Ceratosaurus: their remains have been found in the same strata, which suggests that they coexisted with Diplodocus.
Among the best-known sauropods, Diplodocus were very large, long-necked, quadrupedal animals, with long, whip-like tails. Their fore limbs were slightly shorter than their hind limbs, resulting in a largely horizontal posture. The skeletal structure of these long-necked, long-tailed animals supported by four sturdy legs have been compared with suspension bridges. In fact, Diplodocus carnegii is currently one of the longest dinosaurs known from a complete skeleton with a total length of 25 metres (82 ft). Modern mass estimates for Diplodocus carnegii have tended to be in the 10– to 16-tonne range.
In 1991, paleontologist David Gillette announced that he had found the largest of the enormous sauropod dinosaurs. He called it Seismosaurus halli, and based on the parts of the skeleton that had been prepared at the time, Gillette believed. New reaserch has now been proven that Seismosaurus halli is actually species of Diplodocus, Diplodocus Hallorum or longus.

Diplodocus hallorum, known from partial remains, was even larger, and is estimated to have been the size of four elephants. When first described in 1991, discoverer David Gillette calculated it may have been up to 52 m (171 ft) long,] making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as Amphicoelias). Some weight estimates of this time ranged as high as 113 tonnes (111 long tons; 125 short tons). The estimated length was later revised downward to 33.5 metres (110 ft) based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete Diplodocus carnegii skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which size estimates of D. hallorum are mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates for D. hallorum even further. While dinosaurs such as Supersaurus were probably longer, fossil remains of these animals are only fragmentary.
Diplodocus had an extremely long tail, composed of about 80 caudal vertebrae which are almost double the number some of the earlier sauropods had in their tails (such as Shunosaurus with 43), and far more than contemporaneous macronarians had (such as Camarasaurus with 53). Some speculation exists as to whether it may have had a defensive or noisemaking (by cracking it like a coachwhip) function. The tail may have served as a counterbalance for the neck. The middle part of the tail had "double beams" (oddly shaped chevron bones on the underside, which gave Diplodocus its name). They may have provided support for the vertebrae, or perhaps prevented the blood vessels from being crushed if the animal"s heavy tail pressed against the ground. These "double beams" are also seen in some related dinosaurs.
No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus (such as Galeamopus) are well known. The skulls of diplodocids were very small compared with the size of these animals. Diplodocus had small, "peg"-like teeth that pointed forward and were only present in the anterior sections of the jaws. Its braincase was small. The neck was composed of at least 15 vertebrae and may have been held parallel to the ground and unable to be elevated much past horizontal.
Like other sauropods, the manus (front "feet") of Diplodocus were highly modified, with the finger and hand bones arranged into a vertical column, horseshoe-shaped in cross section. Diplodocus lacked claws on all but one digit of the front limb, and this claw was unusually large relative to other sauropods, flattened from side to side, and detached from the bones of the hand. The function of this unusually specialized claw is unknown.
The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed keratinous spines, much like those on an iguana and up to 18 centimetres (7.1 in) long, on the "whiplash" portion of their tails, and possibly along the back and neck as well, as in hadrosaurids. The spines have been incorporated into many recent reconstructions of Diplodocus, notably Walking with Dinosaurs. However, the original description of the spines noted that the specimens in the Howe Quarry near Shell, Wyoming were associated with skeletal remains of an undescribed diplodocids "resembling Diplodocus and Barosaurus." Specimens from this quarry have since been referred to Kaatedocus siberi and Barosaurus sp., rather than Diplodocus.
Due to a wealth of skeletal remains, Diplodocus is one of the best-studied dinosaurs. Many aspects of its lifestyle have been subjects of various theories over the years. Comparisons between the scleral rings of diplodocines and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals.
Marsh and then Hatcher assumed that the animal was aquatic, because of the position of its nasal openings at the apex of the cranium. Similar aquatic behavior was commonly depicted for other large sauropods, such as Brachiosaurus and Apatosaurus. However, a 1951 study by Kenneth A. Kermack indicates that sauropods probably could not have breathed through their nostrils when the rest of the body was submerged, as the water pressure on the chest wall would be too great. Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees, ferns, and bushes.Scientists have debated as to how sauropods were able to breathe with their large body sizes and long necks, which would have increased the amount of dead space. They likely had an avian respiratory system, which is more efficient than a mammalian and reptilian system. Reconstructions of the neck and thorax of Diplodocus show great pneumaticity, which could have played a role in respiration as it does in birds.
While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested that the oversized neck of Diplodocus and its relatives may have been primarily a sexual display, with any other feeding benefits coming second. However, a 2011 study refuted this idea in detail.
While no evidence indicates Diplodocus nesting habits, other sauropods, such as the titanosaurian Saltasaurus, have been associated with nesting sites. The titanosaurian nesting sites indicate that they may have laid their eggs communally over a large area in many shallow pits, each covered with vegetation. Diplodocus may have done the same. The documentary Walking with Dinosaurs portrayed a mother Diplodocus using an ovipositor to lay eggs, but it was pure speculation on the part of the documentary author. For Diplodocus and other sauropods, the size of clutches and individual eggs were surprisingly small for such large animals. This appears to have been an adaptation to predation pressures, as large eggs would require greater incubation time and thus would be at greater risk.
Based on a number of bone histology studies, Diplodocus, along with other sauropods, grew at a very fast rate, reaching sexual maturity at just over a decade, and continued to grow throughout their lives.

Barosaurus lentus

A close relative of Diplodocus, Barosaurus is virtually indistinguishable from its harder-to-pronounce cousin, save for its long neck (one of the longest of any dinosaur, with the exception of the eastern Asian Mamenchisaurus).
No one knows how big a Barosaurus is because according to specimen is known as ROM 3670 it is up to about 27.5 meters long, but according to a specimen known as BYU 9024 it is up to about 170 feet (52 meters) long and up to 100 tons.
Like the other sauropods of the late Jurassic period, Barosaurus wasn"t the brainiest dinosaur that ever lived--its head was unusually small for its massive body, and easily detached from its skeleton after death--and it probably spent its entire life foraging the tops of trees, protected from predators by its sheer bulk.
The sheer length of Barosaurus" neck raises some interesting questions. If this sauropod reared up to its full height, it would have been as tall as a five-story building--which would have placed enormous demands on its heart and overall physiology. Evolutionary biologists have calculated that the ticker of a such a long-necked dinosaur would have had to weigh a whopping 1.5 tons, which has prompted speculation about alternate body plans (say, additional, "subsidiary" hearts lining Barosaurus" neck, or a posture in which Barosaurus held its neck parallel to the ground, like the hose of a vacuum cleaner).

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