Comment on Brachiosaurid skull comparison by Paleo-King
Wait!
You're telling me we don't have adult Brachiosaurus and Giraffatitan skulls?!
Frankly, this... Well, i didn't expect it!
You're telling me we don't have adult Brachiosaurus and Giraffatitan skulls?!
Frankly, this... Well, i didn't expect it!
Nope. The skulls are all from individuals that are not done growing. You should have known they never find adult skulls! LOL.
The biggest Giraffatitan skull (HMN S116) was found close to the SII skeleton and is probably the same individual. This animal was around 75 feet long or maybe a bit longer. The associated scapula classed as specimen HMN Sa9 (possibly also from the same individual, or at least cross-scales well with it) is not fused to a coracoid. SII's coracoid is also not fused to a scapula. This animal was not done growing. And remember, HMN XV2 was around 15% larger. Maybe even bigger than that, since we only have the tibia, and as sauropods reach adulthood the legs slow their growth allometrically relative to the body as a whole. HMN Fund no. is also bigger than SII, since its tail scales up about 12% bigger than than HMN Aa, which is almost certainly past of the same individual as SII (I know, their cataloging system was crazy. oh well).
Fund no. (tail) and XV2 (tibia) may be parts of the same animal. It was probably around 95-100 ft. long which means a skull around 1m long. No telling if THIS beast was an adult either, since there's no shoulder material!
The two referred Brachiosaurus skulls are definitely not from adult individuals, they scale up considerably smaller than the holotype animal (unfused coracoid again!) assuming similar estimated proportions (and guess who estimated those proportions?
). The Felch Quarry skull is not that big, if you visit the Cleveland Museum you will see how small it is next to their cast of the AMNH T. rex skull. The Potter Creek Brachiosaurus, the biggest referred specimen we know of, would have had a skull roughly around 1m, that rivals many T. rex skulls in size. And again, no shoulder material for that one either, so whether it was still immature is anyone's guess.
The biggest Giraffatitan skull (HMN S116) was found close to the SII skeleton and is probably the same individual. This animal was around 75 feet long or maybe a bit longer. The associated scapula classed as specimen HMN Sa9 (possibly also from the same individual, or at least cross-scales well with it) is not fused to a coracoid. SII's coracoid is also not fused to a scapula. This animal was not done growing. And remember, HMN XV2 was around 15% larger. Maybe even bigger than that, since we only have the tibia, and as sauropods reach adulthood the legs slow their growth allometrically relative to the body as a whole. HMN Fund no. is also bigger than SII, since its tail scales up about 12% bigger than than HMN Aa, which is almost certainly past of the same individual as SII (I know, their cataloging system was crazy. oh well).
Fund no. (tail) and XV2 (tibia) may be parts of the same animal. It was probably around 95-100 ft. long which means a skull around 1m long. No telling if THIS beast was an adult either, since there's no shoulder material!
The two referred Brachiosaurus skulls are definitely not from adult individuals, they scale up considerably smaller than the holotype animal (unfused coracoid again!) assuming similar estimated proportions (and guess who estimated those proportions?
). The Felch Quarry skull is not that big, if you visit the Cleveland Museum you will see how small it is next to their cast of the AMNH T. rex skull. The Potter Creek Brachiosaurus, the biggest referred specimen we know of, would have had a skull roughly around 1m, that rivals many T. rex skulls in size. And again, no shoulder material for that one either, so whether it was still immature is anyone's guess.
Of course, it's worth considering that full fusion of all synostoses and sutures can occur very late in life--the human skull, for example, often still has open sutures into its owner's 30s or 40s. Sexual maturity in dinosaurs appears to have occurred long before 'adult' morphology, skeletal fusion, or size were all necessarily reached--so defining 'adult' precisely can be difficult. When you consider that truly 'adult' individuals, as defined by skeletal fusion, were probably extremely rare, the fact that their fossils are so uncommon is less surprising!
That's true. How do you really define what is 'adult'? Even human definitions of adult age have changed over time and depending on culture and rulers. It was not uncommon to get married around age 13 or 14 in medieval times in many places. Technically if you go by gray matter density, 25 is the minimum adult age. But fertility-wise it's already "past prime". Different measures.
It's known that sexual maturity for sauropods (in females at least) happened at around 50% of maximum known size, based on medullary bone. So what we consider "immature" for skeletal ontogeny was likely fully mature when it came to banging out egg caches.
So for all we know HMN t1 could have been mature for reproductive purposes, but was hardly mature skeletally. The huge-nosed SMN SII/S116 (assuming it was male) may or may not have been sexually mature. There really isn't a good way to test for that in male skeletons. We could also have a case of dimorphic development rates where females mature much faster, like in sperm whales today. On the other hand if t1 was a female and S116 and the smaller S66 were both males, as the nasals and maxillae indicate may be the case, then possibly even S66 was reproductively mature since it was already showing "mature" male face proportions.
It's hard to tell if Giraffatitan had sexual dimorphism in skull shapes, but I've seen some convincing arguments that Europasaurus did, since a lot of skulls for it have been found. Most of these still have yet to be published, but there was a detailed presentation in SVP 2011.
It's known that sexual maturity for sauropods (in females at least) happened at around 50% of maximum known size, based on medullary bone. So what we consider "immature" for skeletal ontogeny was likely fully mature when it came to banging out egg caches.
So for all we know HMN t1 could have been mature for reproductive purposes, but was hardly mature skeletally. The huge-nosed SMN SII/S116 (assuming it was male) may or may not have been sexually mature. There really isn't a good way to test for that in male skeletons. We could also have a case of dimorphic development rates where females mature much faster, like in sperm whales today. On the other hand if t1 was a female and S116 and the smaller S66 were both males, as the nasals and maxillae indicate may be the case, then possibly even S66 was reproductively mature since it was already showing "mature" male face proportions.
It's hard to tell if Giraffatitan had sexual dimorphism in skull shapes, but I've seen some convincing arguments that Europasaurus did, since a lot of skulls for it have been found. Most of these still have yet to be published, but there was a detailed presentation in SVP 2011.
Man, one meter long skull for a sauropod... It's something i'd def want to see!
Me too. Maybe someday the Humboldt Museum will reconstruct HMN S116 and put it on display, at least that would be a start. HMN t1 is already pretty large in person, but seeing a bigger skull next to it will really get some attention.