femur, coracoid, and sacrum of the Brachiosaurus holotype that had been prepared at the Field Columbian Museum. Since then, the classification of these sauropods has been through many changes. Marsh's multifamily theory of sauropod classification prevailed until 1929, when Werner Janensch proposed a two-family theory based on differences in sauropod teeth. Macronarians with broad, spatulate teeth, were placed in the family Brachiosauridae, while sauropods with more slender and peg-shaped teeth were considered titanosaurids. This put diplodocids and titanosaurids together in one group based on their similar teeth, despite the many other differences between the taxa. Today, about four to five groups within the Macronaria are considered families (with names ending in ~). In 1997, Salgado, Coria and Calvo studied the traits that had been used to set the Brachiosauridae apart and determined that they were in fact plesiomorphic, original, for all basal Titanosauriformes. They proposed that some characteristics that had been used to differentiate Brachiosaurus were synapomorphies for the Titanosauriformes as a whole. They concluded that the family Brachiosauridae was actually a "grade" of not specially related primitive titanosauriforms, and not a stable separate clade. They partly based this conclusion on similar humerus:femur length ratios known for titanosauriforms, basal titanosaurs, and more basal sauropods. However, in 1998 Sereno & Wilson published data contrary to the conclusions in Salgado et al.'s article, indicating that the Brachiosauridae were a separate clade in the Titanosauriformes. After 1998, new brachiosaurid species have been named, generally confirming that the Brachiosauridae were a natural group. Important findings In 1943, de Lapparent described the "French Bothriospondylus" from the Oxfordian of France which dates to the Late Jurassic, which was identified in 2013 by Philip Mannion as a brachiosaurid and named Vouivria damparisensis in 2017. This specimen represents the oldest undisputed record of the brachiosaurid group. The following diagram is a timeline of important brachiosaurid discoveries, the date given being that of the naming of the genus. The actual excavation was often much earlier, in the case of Vouivria eighty-three years and of Duriatitan at least 136 years. Paleobiogeographic distribution Definitive brachiosaurid remains have been found from the Late Jurassic Period to the Early Cretaceous, from about 157 to 93 million years ago. In addition, Macronaria in general first appear in the Late Jurassic. However, the almost simultaneous appearance of Camarasaurus, Brachiosaurus, and a possible titanosaur suggest that they originated earlier, closer to the Mid-Jurassic. Trackway evidence also