New data on the dimensions ofBrachiosaurus brancai and their physiological implications

Abstract

There are highly divergent data on the body m a s s (mb) of Brachiosaurus (B.). The range of the body-mass estimations lies between 14900 and 102000 kg for this giant dinosaur [1-6] . This is mainly due to the fact that different specimens and varying techniques are used for the volume (V) estimations, such as equations from the circumferences of femur and humerus [4] or from the volume of models [5]. The precise determination of Vis important for calculating the body surface area (SA) as well as for allometric equations, which are often based on Mb. Herewith, we present a photogrammetric method to determine the metrical dimensions of giant sauropods such as B. The data presented here are based on the skeleton of B. brancai from the Upper Jurassic of Tendaguru (East Africa, Tanzania), mounted and exhibited at the Museum of Natural History in Berlin (Germany). The major part of the skeleton belongs to one single specimen of B. brancai recovered from the Middle Saurian Bed at Tendaguru. The tail originates from another individual of the same species of similar size found in the Upper Saurian Bed. In addition, skeletal remains of B. brancai excavated in different sites in the surroundings of the Tendaguru hill were used for the mounting, partly original and partly modeled. The presacral vertebral column (cervicals, dorsals) and the skull have been replaced by plaster copies modeled from originals of the main skeleton due to their extreme fragility and weight. The right shoulder blade, four dorsal ribs, and some bones of the left forefoot have been modeled in plaster according to counterparts of the other body side. Some missing elements are substituted by bones belonging to individuals of the same size such as the right ilium, the right ischium, and the left lower leg. Other missing items have been replaced by originals (e.g., left femur) or copies of bones from different-sized animals (e.g., sacrum, most hindfoot bones). At the very end of the tail four small pieces were added. Like the missing first caudal vertebra, most of the hemapophyses (chevrons) are plaster imitations [6]. As can be seen in Fig. 1, we divided the presumable shape of B. brancai into XI parts. Each part was separately calculated and the Vi-xi are given in Table 1. From the V found, the Mb was calculated assuming a density of 1000 kg per m 3 tissue [5, 7]. On the basis of the above findings, we investigated further whether the presumable organ volumes derived by allometric equations could be fitted into the anatomical dimensions given by the skeleton. The advantage of the photogrammetrical approach is that when the values are taken from a specimen, the complete shape of the animal is stored in the computer. This allows later derivation of other forms and dimensions, which is almost impossible from a model. In the case of a small model being built from the data and later becoming enlarged, the smallest deviation is multiplied by a factor of 10-50 depending on the size of the model. Therefore, regardless of the size of a model, it is defined by these exact basal metric values. The anatomical data of B. brancai derived by stereophotogrammetry and the presumable physiological data calculated after equations given for endotherms are summarized in Table1, Table2, and Fig. 2. According to these, the Mb of B. braneai is ca. 74420 kg (skeleton 11480 kg). Accordingly, the M b estimations in [1] are similar to our findings, whereas those in [2, 4 6 ] are far too low. It is not clear whether the estimation in [3] for B. refers to the Berlin specimen. If so, it is far too high. The S A (Table 2) was found to be at least (without any skin-