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Family Brachiosauridae

Middle Jurassic to Middle Cretaceous
(Bathonian to Albian / Cenomanian)


Brachiosaurus altithorax
illustration by Steve Kirk - Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals

Together with the Camarosaurs and Titanosaurs, the Brachiosaurs comprise clade Macronaria, one of the two main lineages of advanced Sauropods. The Brachiosaurus were a family of huge sauropods that includes some of the largest land animals. The brachiosaurs and their cousins, the camarosaurs, were distinguished by having forelimbs as long as or longer than their hind limbs, giving them high shoulders and a sloping back. This, and their long vertical necks, gave them a curiously giraffe-like appearance. They were high-grazers, able to feed on the leaves of trees too high for other sauropods to reach.They relied on sheer size as a defense against predators. These animals, are distinguished by their long necks and long arms. The best-known species is the Tanzanian Giraffatitan (more commonly known as Brachiosaurus), but many other species are also known. Generally, brachiosaurids have long arms relative to the hindlimbs and very long, upwards diagonally-held necks. They are the only dinosaurs with forelimbs longer than the hind, hence the name "Brachiosaurus" - arm lizard.

As with the camarasaurs the skull (left) is large, the teeth long and spatulate (spoon-shaped). The upper front of the lightly-constructed skull (the nasal bones) is highly vaulted, with large, elevated nares (nostril holes) indicating nostrils close to the top of the head. This led to several bizarre theories. One was that the animal hid from preditors at the bottom of deep lakes, feeding on water weeds and only poking its "snorkal" through the surface to breath. This is physiologically absurd, as water pressure would make breathing at such a depth impossible. The other theory is that brachiosaurs possessed an elephant-like trunk, as all mammals with trunks (tapirs, elephants, etc) have vaulted elevated nares. However, no reptile is known to have the facial muscles necessary for a trunk, and no indications of scars or blood-vessels have been found in any dinosaur indicating a trunk-like organ. A more plausible theory is that the inflated nares were a cooling mechanism. Living during the tropical hothouse conditions of the Jurassic, such enormous animals were in danger of overheating. Blood therefore was conveyed to the top of the head, where it was cooled via heat-exchange and perhaps also membranes of skin (african elephants use their large ears for the same purpose - the frozen remains of woolly mammoths show their ears were a lot smaller).

brachiosaur image (above) from Prof. Paul Olsen's  Dinosaurs and the history of life - Geology V1001x pages

The neck was long and giraffe-like, with elongated individual vertebrae; the back also sloped ina giraffe-like fashion. These animals were, like the Camarasaurs, high browsers, and may indeed have been able to reach even higher branches than the camarasaurids could. Unlike the caamarasaurs the neural spines were undivided and small, and the neck, although large and stiff, was probably not equipped with the sort of powerful tendons Camarasaurs had, and could not have been held as erectly. Most reconstructions are in error in that they show the neck held in a very high, camarasaur-like posture.

The non-zonal fibro-lamellar bone structure indicates fast, uninterrupted growth from the baby to the adult stage, and these animals were perhaps fairly metabolically active (another reason for the vaulted nares as a heat sink.

With average lengths of 18 to 25 metres, and usual adult weights 15 to 45 tonnes (the largest species reaching 30 to 35 meters in length and perhaps 60 to 80 tonnes in weight), the Brachiosaurs were the largest animals of their time. Like the elephants of today, they were lords everything they surveyed. Not even Ceratosaurs, Allosaurs, or Torvosaurs, the top predators of the Jurassic, would think of taking on a full-grown brachiosaur, any more than a lion would mess with an adult elephant.

The following cladogram is a simplified version of the ones at Mikko's phylogeny site and Justin Tweet's Thescelosaurus! pages. I have also made the completely arbitrary assumption that the three species of Morrison Camarasaurs which suceed each other chronologically are also an evolutionary succession (a chronospecies so to speak). There are of course many more species than those listed in this diagram, but most of them are of questionable relationships.

<==o MACRONARIA ["BRACHIOSAURIA"]
   |--o Camarasauridae
   `-+-o Brachiosauridae Riggs, 1903a 
      |   `-+- Lapparentosaurus madagascariensis Bonaparte, 1986b
      |      `-+-- Atlasaurus imelakei Monbaron, Russell, and Taquet, 1999
      |         `-+-- Giraffatitan brancai (Janensch, 1914)
      |             |?-- Bothriospondylus suffosus Owen, 1875
      |             |?-- Pelorosaurus conybearei Mantell, 1850
      |             |?-- Cedarosaurus weiskopfae Tidwell, Carpenter, and Brooks, 1999
      |             |?-- Sonorasaurus thompsoni Ratkevich, 1998
      |             `-+-- Sauroposeidon proteles  Wadel, Cifelli & Sanders, 2000
      |                `--o Brachiosaurus Riggs, 1903a
      |                     |-- B. altithorax Riggs, 1903a
      |                     `-- B. atalaiensis Lapparent & Zbyszewski, 1957
       `--o Titanosauriformes

Brothriospondylus madagascariensis Bonaparte, 1986b

Based on juvenile remains previosuly referred to the genus Bothriospondylus, this early species appears to be very similiar to, and perhaps a direct ancestor of Brachiosaurus. Like the approximately contemporary Atlasaurus this is a Gondwanaland form, and it is possible that the Brachiosaurs evolved in central Gondwana; China being dominated by Shunosaurine and Europe by Cetiosaurine Cetiosaurids

Atlasaurus imelakei Monbaron, Russell, and Taquet, 1999

Comments: Originally called "Cetiosaurus" mogrebiensis, Atlasaurus imelakei is one of the earliest and most primitive of the brachiosaurs.

Bothriospondylus suffosus Owen, 1875

Comments: Not particularly well known, this sauropod appears to be closely related to Brachiosaurus

Brachiosaurus atalaiensis Lapparent & Zbyszewski, 1957

Comments: The huge B. atalaiensis was probably a descendent of the earlier Kimmeridgian "Ornithopsis" leedsi. Like the contemporary Tendaguru Brachiosaurus (Giraffititan) brancai this was a slender animal.

Brachiosaurus (Giraffatitan) brancai Janensch, 1914

size of selected skeletal elements Size in metres humerus (upper arm) ulna (lower arm) scapula (shoulder balde) femur (thigh bone) Fair-sized individual 1.60 m 1.01 m 1.45 m 1.55 m Large individual [in Berlin Museum] 2.13 m 1.28 m 2 m   Left, a sketch of the famous Berlin Museum Brachiosaur; this is the tallest skeleton ever mounted. It is actually a composite of a number of specimens. Note - the position of the neck in this sketch is very unrealistic, the neck would actually have been held at a 45o angle image from Prof. Paul Olsen's Dinosaurs and the history of life - Geology V1001x site

Comments: Originally considered to be a species of Brachiosaurus, Giraffatitan is now generally placed in its own genus, although it may or may not be a subgenus of Brachiosaurus. It differs from the American Brachiosaurus altithorax in its more gracile build and different form of neck vertebrae. Most representations of Brachiosaurus are actually based on this species, which isknown from more and more complete remains than any other brachiosaurid. It is a long-armed taxon based on a partial postcranial and larger individuals are known. The skull has an unusually tall rounded crest containing the nostrils.

The Giraffatitan brachiosaurs were gigantic terrestrial herbivores, "giraffe-elephants" adapted to feeding on the crowns of trees. They dominated the Tendaguru megafauna, making up about 27% of all large animals (in terms of numbers of individuals identified in the Middle Saurian Bed), but in terms of actual biomass that figure would be closer to 78%. The large numbers would seem to indicate herding behaviour (like Camarasaurs in the Morrison) The whole fauna could be rightfully called a Brachiosaur fauna. The only other identified sauropods were the small Dicraeosaurs and Barosaurs, both in the vicinity of three to four and a half tonnes, and grasers upon lowlying and (in the case of Barosaurus) medium-height vegetation.

Brachiosaurus (Brachiosaurus) altithorax Riggs, 1903a Horizon: Upper Morrison formation, Colorado and Utah
Age: Early Tithonian
Place: western Laurasia
remains: two partial skeletons, also an old skull has recently been shown to belong to this species.
Length: 22 to 27 metres or more
Weight: 25 to 45 or 50 tonnes

Comments: A more heavily built species than the slightly earlier Giraffatitan, this species is similar, but less well known. Most restorations are actually based on Giraffatitan. This was one of the largest animals ever to live. The so-called "Ultrasaurus" and "Supersaurus" are actually based on partial remains of giant Brachiosaurs (in the case of Supersaurus mixed up with other species). B. altithorax did not seem to be as common as G. brancai, which may indicate a siolitary behaviour, in contrast to the herding Giraffititan. Alternatively, the rarety may be dues to local preservation and environmental factors; perhaps altithorax frequented areas taht were not conducive to fossilisation

Sonorasaurus thompsoni Ratkevich, 1998

Comments: A "pygmy" brachiosaurid, this animal nevertheless shows strong similarities with its larger Jurassic cousins.

Pelorosaurus conybearei Mantell, 1850

Comments: known from assorted postcrania, and skin-impresisons showing small, hexagon-like tubercles, Pelorosaurus a poorly known, fairly typical brachiosaurid, somewhat smaller than its Jurassic counterparts. A number of specimens assigned to this genus have been placed elsewhere, or are considered too fragmentary to identify properly.

Cedarosaurus weiskopfae Tidwell, Carpenter, and Brooks, 1999

Comments: Some material referred to Pleurocoelus (but not the type material) may belong here. "Pleurocoelus" (Hollow Side) is a name given to a number of smallish (8 or 10 meters) early Cretaceous American brachiosaurs known from the Arundal formation of Maryland. Astrodon (Star Tooth) is a synonym. Pleurocoelus altus was once thought to be the adult form of P. nanus, but more recently is has been suggested as an entirely different sauropod. The proportionately large pleurocoels of the Arundel type material is likely to be a juvenile trait; juvenile Camarasaurus material was once identified as Pleurocoelus because of the very large pleurocoels. It is likely the genus, like so many partial dinosaur remains, the Pleurocoelus may eventually turn out to be invalid, i.e. nomen dubum (that is, it is sauropod and apparently brachiosaur but not complete enough to diagnose further) and may be assigned other genera. To confuse matters even further, it has recently been suggested that Cedarosaurus and some of the Pleurocoelus material is not even brachiosaurian, but titanosaur instead.

image from Oklahoma Museum of Natural History

Sauroposeidon proteles Wedel, Cifelli, and Sanders, 2000

Comments: Currently holding the status of the largest dinosaur ever (although the late Cretaceous titanosaur Argentinosaurus was certainly just as large), this enormous creature is known from four tree-trunk sized cervicals, and had the longest neck of any known animal, possibly twelve meters in length. It could have stood upto 18 meters tall. The drawing shows the comparison with a standard Brachiosaurus.

Links

Brachiosauridae - Thescelosaurus!

Brachiosauridae - Palaeos

ABCNEWS.com: Dino May Have Been Tallest about Sauroposeidon

Dinosauricon

Brachiosauridae Mikko's phylogeny site

Bob Bakker, "Bakker's field guide to Jurassic Park dinosaurs". pp.33-43, Earth September 1993

D.Russell, P. Béland, & J.S.McIntosh, "Paleoecology of the dinosaurs of Tendaguru (Tanzania)" in  Ecosystèmes Continentaux du Mésozoïque, Mémoires de la Société Géologique de France, 1980, no.139, pp.169-175.

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