|Size in metres||humerus
|average sized individual||0.75 m||0.498 m||1.35 m||1.21 m|
A relatively small sauropod, Dicraeosaurus or "forked lizrd" gets its name from the high, forked spines jutting up from the vertebrae [Field Guide to Dinosaurs p.132]. These were used to anchor powerful neck and tail muscles. The neck was very short, consisting of only 11 or 12 vertebrae, and the head was - for a sauropod - unusually large in proportion to the body. The forelimbs were very short (humerus to femur ratio 62%) but stoutly built. This was obviously a low-feeder, grazing on the undergrowth and low trees such as cycads. It is also the most primitive of the Diplodocoidea, presumably a late survivor of a line that must have appeared in the late Bathonian, although no traces of these early Dicraeosaurids have been found.
Dicraeosaurus was a common element in the Tendaguru megafauna, making up 22% of identified specimens in the Middle Saurian Bed, but (because of its small size) only 7.5% of the actual megafauna biomass.
Dicraeosaurus sattleri Janensch
Upper Saurian Bed, Tendaguru, Mtwara, Tanzania
late Kimmeridgian/Early Tithonian
2 partial skeltons without skulls; altogether postcrania of about a dozen specimens
Overall length about 8.5 metres; Weight 1.0 tonnes
D. sattleri is considerably smaller than the earlier D. hansemanni;
with a weight of only a tonne, and a hip height of about 2 metres, it had
a body about the size of a large draft horse, with a long tail at one end
and a snaky neck at the other.
We tend to think of sauropods evolving towards greater and greater size, as with the brachiosaurs and brontosaurs. But Dicraeosaurus illustrates the opposite trend, and shows that not all sauropods were huge. This was probably a lively animal, browsing on the undergrowth and the lower branches of the trees of the Tendaguru forest, and sometimes rearing up to reach higher morsels. It was always in danger from the carnivorous Ceratosaurus, and may have gained some protection by living in large herds, like wildebeast do today.
Like all the Diplodocids, the Apatosaurs were huge terrestrial herbivores with a snake-like neck and whiplash tail, that probably fed on lower crown layers of trees and on undergrowth.
Apatosaurus excelsus (Marsh 1879)
(syn. Brontosaurus, Elosaurus)
Morrison Formation; Wyoming, Utah, and Oklahoma, United States
late Kimmeridgian to early Tithonian
6 partial skeletons without skulls, hundreds of post-cranial elements,
Length: 18 to 21 metres, Weight: 13 to 20 tonnes
Apatosaurus ajax (Marsh 1879)
(syn Atlantosaurus, Brontosaurus)
Morrison Formation; Colorado, United States
2 partial skeletons, braincases,
Length: 24 metres, Weight: upto 30 tonnes
The last and largest of all the brontosaurii, this was a huge animal, as big as the bigger brachiosaurii. The humerus or upper arm bone alone measured 2 metres in length, compared with 1.75 metres maximum for A. exelsus. It seems that as the Morrison ecosystem progressed, there was a tendancy for these giants to evolve into larger and larger forms. The Apatosaurs, Diplodocii, Camarosaurs, Brachiosaurs, Allosaurs, and Stegosaurs all followed this trend, so the early Tithonian dinosaurs were among the most gigantic of these beasts that are known. The same tendancy to increased science also occurs at the very end of the Cretaceous (Campanian-Maastrichtian); in both cases this progession to gigantism was followed by a mass-extinction.
Barosaurus gracilus Janesch 1961
Middle Saurian Bed, Tendaguru Beds, Mtwara, Tanzania
[Middle or Late Kimmeridgian, Central Gondwana]
Many isolated limb elements; altogether the remains of at least 15 individuals
Overall length about 16 metres; Live weight about 4.2 tonnes
B. gracilus is the earliest and smallest of the Barosaurs, a line of sauropods which, like the Euhelopids, developed extraordinarily long necks. These enabled the beasts to both graze over a wide area of ground or swampland, and feed from the foliage of tree-ferns and cycads. Although the skull is not known, they probably had adelicate diplodocus-like head, with weak peg-like teeth that could only have been useful on soft vegetation, and it is unlikely that they fed much on the conifer forests that sustained the great brachiosaurs.
Occuring on both sides of the Jurassic Proto-Atlantic seaway, the Barosaurii would have evolved from an ancestral form some time during the late Callovian or early Oxfordian. In the moist Tendaguru rainforest megafauna there was only one evolutionary line of Diplodocid, the small African Barosaurs. But in the drier American Morrison megafauna are found three distinct lines: large Barosaurs, Diplodocii, and the famous Brontosaurs (Apatosaurs).
Initially the Barosaurs were a relatively unimportant element of the Tendaguru megafauna, making up 10% of identified specimens in the Middle Saurian Bed, and 4% of the actual megafauna biomass. It is much more common in the succeeding Lower Transitional sands, where it accounts for 50% of identified specimens and 40% of the megafauna biomass. With the eventual dissapearance of the Brachiosaurs in this region (possibly due to changing environmental factors) the Baraosaurs increased in size and number, and became the dominant element of the Tendaguru fauna.
Barosaurus africanus (Fraas 1908)
Upper Saurian Bed, Tendaguru, Mtwara, Tanzania
late Kimmeridgian/early Tithonian
More than 3 partial skeletons, a few skull elements, isolated postcrania; altogether the remains of at least 41 individuals
|Size in metres||humerus
|average sized individual||0.97 m||0.74 m||1.34 m||1.34 m|
Overall length 20 metres;
Shoulder height about 3 metres; Hip height about 4 metres
Live weight 8.3 tonnes
Strangely, the great Brachiosaurus brancai, so common during the earlier Tendaguru, is totally absent in the later fauna. Instead, we find a larger species of Barosaurus, and a less abundant newcomer, Tornieria. In numbers Barosaurus africanus dominates the later Tendaguru fauna the way Brachiosaurus dominated the earlier fauna, being more common than Dicraeosaurus and Torniera put together. But in individual bulk Barosaurus is only half the weight of Brachiosaurus, and lived a different lifestyle. Whereas Brachiosaurus browsed giraffe-fashion from high branches, Barosaurus fed on undergrowth and low branches, its enormously elongated snaking neck conveying the head to select vegetation.
Barosaurus lentus Marsh 1890
(syn. B. affinis)
Morrison Formation; South Dakota and Utah, United States
5 partial skeletons without skulls, isolated limb elements,
Overall length 23 to 27 metres; Weight about 15 tonnes
The American form is the largest of the three Barosaurus species; and identical to Diplodocus apart from its elongate neck. It has been suggested that it should be included in the latter genus. But the cervicals (neck vertebrae) are 33% longer distinguishes Barosaurus as a distinct type.
from the DINOSAURS AND THE HISTORY OF LIFE - GEOLOGY V1001x site
Morrison Formation; Colorado and Utah, United States
Length: 25 metres, Weight: 10 tonnes
The earliest of the American Diplodocii, a lineage of huge slender sauropods, it gave rise to D. carnegii, which in turn was supplanted by the even bigger D. ("Amphicoelus") altus [Bakker, Dinosaur Heresies, p.400].
Diplodocus carnegii Hatcher 1901
Morrison Formation; Wyoming and Utah, United States
5 skeletons without skulls, 2 skulls, hundreds of isolated post-cranial elements,
Length: 27 metres, Weight: 10 tonnes
The successor and probably descendent of D.longus, Diplodocus carnegii is a slightly larger form.
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page historypage uploaded 6 May 1999