Jobaria
Encyclopedia
Jobaria was a sauropod dinosaur discovered in the Sahara Desert in 1997. It was named after "Jobar", a creature of local legends, and is thought to have been about 18 metres long. It was found in the Tiourarén Formation
, originally thought to represent the Hauterivian
to Barremian
stages of the early Cretaceous
Period, or approximately 136 to 125 million years ago (Sereno et al. 1994). However, re-interpretation of the sediments showed that they are probably mid-Jurassic
in age, dating Jobaria to the Bathonian
to Oxfordian stages, between 164 and 161 mya.
Jobaria seems to be a very primitive sauropod. It has been interpreted either as a basal
macronaria
n (Upchurch et al., 2004), or as a non-neosauropod
eusauropod, basal to the neosauropod clade
.
The backbone and tail of Jobaria are simple compared to the complex vertebrae and whiplash tail of the later North America sauropods Diplodocus
and Apatosaurus
.
Paul Sereno
concluded, after comparing the ratios of humerus
and femur
circumferences in Jobaria to extant elephant
s, that Jobaria may have been able to rear up on its hind legs. As the weight distribution of Jobaria indicates that it was supported by the rear limbs rather than the forelimbs (as in elephants), it has been speculated that as elephants can rear up, then Jobaria would have been able to more easily.
Tiouraren Formation
The Tiouraren Formation is a geological formation in Niger whose strata were originally thought to be Early Cretaceous. However, re-interpretation of the sediments showed that they are probably mid-Jurassic in age. Dinosaur remains are among the fossils that have been recovered from the...
, originally thought to represent the Hauterivian
Hauterivian
The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous epoch or a stage in the Lower Cretaceous series. It spans the time between 136.4 ± 2 Ma and 130 ± 1.5 Ma...
to Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
stages of the early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period, or approximately 136 to 125 million years ago (Sereno et al. 1994). However, re-interpretation of the sediments showed that they are probably mid-Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
in age, dating Jobaria to the Bathonian
Bathonian
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...
to Oxfordian stages, between 164 and 161 mya.
Jobaria seems to be a very primitive sauropod. It has been interpreted either as a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
macronaria
Macronaria
Macronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...
n (Upchurch et al., 2004), or as a non-neosauropod
Neosauropoda
Neosauropoda is a division-level clade of sauropods within Dinosauria, and consists of the group leading to Diplodocoidea and Macronaria. Haplocanthosaurus was a typical basal neosauropod from around 150 million years ago, in the Late Jurassic...
eusauropod, basal to the neosauropod clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
.
The backbone and tail of Jobaria are simple compared to the complex vertebrae and whiplash tail of the later North America sauropods Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
and Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
.
Posture
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
concluded, after comparing the ratios of humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
circumferences in Jobaria to extant elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, that Jobaria may have been able to rear up on its hind legs. As the weight distribution of Jobaria indicates that it was supported by the rear limbs rather than the forelimbs (as in elephants), it has been speculated that as elephants can rear up, then Jobaria would have been able to more easily.