that's good I like them both and as long as brachiosaurus could move it's neck up or was a different species i'm happy was brachiosaurus neck in a vertical position when is was running at full speed
Probably since when you are running at full speed a vertical neck helps you avoid smashing your head into trees.... that said, Brachiosaurus probably wasn't a very fast runner. As far as brachiosaurs go, Giraffatitan was probably a bit faster since its legs were longer relative to its torso. On the other hand, there were some brachiosaurs like the "Archbishop" whose torsos were so compact relative to limb length that stride length was limited by the shortness of the torso, and thus limited maximum speed as well. So if I was to guess which large brachiosaur was the fastest, I 'd probably say Giraffatitan or something with similar proportions.
Giraffatitan looks fast
Given its huge stride length, it could easily outrun a human even if the actual top speed was not very high. The long arms gave it huge reach and longer strides. Not that any sauropods were super-fast, and Giraffatitan counted far more on size than speed when faced with predators, but it could easily leave any diplodocid or camarasaur in the dust. Their shorter legs would have a hard time keeping up. However, brachiosaurs were relatively short in the shin, so this may have reduced their speed somewhat. But there is an advantage to having long arms so you are not constantly tripping over yourself with your hindlegs. I look at stegosaurs and dicraeosaurs and sometimes wonder how these wimpy-armed animals could manage anything more than a slow walk without falling head-first and eating dirt.
There's a recent series on youtube about "killer dinosaurs", one episode covers Acrocanthosaurus and shows it chasing a rather fast Paluxysaurus. The animation, while not top-notch, does show based on limb biomechanics that brachiosaurs could run surprisingly fast for their size (to top things off, Acro had short feet for its size and was fairly slow as far as big predators went, so it really was a tough chase). I'd love to see Atlasaurus in action, basically a huge mega-arms browsing platform with a surprisingly undersized neck for a brachiosaur - as if to say, don't stretch out your neck for food, just run to it!
There's a recent series on youtube about "killer dinosaurs", one episode covers Acrocanthosaurus and shows it chasing a rather fast Paluxysaurus. The animation, while not top-notch, does show based on limb biomechanics that brachiosaurs could run surprisingly fast for their size (to top things off, Acro had short feet for its size and was fairly slow as far as big predators went, so it really was a tough chase). I'd love to see Atlasaurus in action, basically a huge mega-arms browsing platform with a surprisingly undersized neck for a brachiosaur - as if to say, don't stretch out your neck for food, just run to it!
Thank you for furthering my understanding of the subject; I appreciate it.