It’s an oddity that in eight years of SV-POW!, we’ve never written about one of the best of all the Wealden-formation sauropod specimens: the forelimb and associated skin impression NHMUK R1870 that is known as “Pelorosaurusbecklesii.

Let’s fix that. Here is all the bony material (i.e. everything except the skin patch) in a photo taken in the basement of the Natural History Museum back in 2007:

Left forelimb material of

Left forelimb material of “Pelorosaurusbecklesii holotype NHMUK R1870. Left: humerus, in posterior view. Right, from top to bottom: ulna in anterior view; radius in anterior view. Yes, I should have turned the humerus over before taking this photo. What can I tell you? I was young and stupid then.

As you can see, the two lower-limb bones were broken back then (though I believe they have since been repaired), but the breaks are very clean, and it’s actually quite interesting to see inside the bones:

Breakage in bones of the lower left forelimb of

Breakage in bones of the lower left forelimb of “Pelorosaurusbecklesii holotype NHMUK R1870. Left: proximal part of radius in distal view. Right: proximal part of ulna in distal view.

I wish I knew enough about mineralisation to comment intelligently on what we can see there. If anyone has thoughts, do leave them in the comments.

We can look in more detail at those lower-limb bones in a subsequent post, but for now, here’s the humerus:

Pelorosaurusbecklesii holotype NHMUK R1870, left humerus. Top row: proximal view, with anterior to the bottom. Middle row, from left to right: medial, anterior, lateral and posterior views. Bottom row: distal view, with anterior to the top.

As you can see it’s in really nice shape, and pretty distinctive. Way back in my 2007 Progressive Palaeo talk (Taylor 2007), I coded up the humerus (alone, without the other elements) in the Harris-based phylogenetic matrix that I’ve used repeatedly in other projects. It came out as the sister taxon to the titanosaur Malawisaurus (which in that matrix comes out fairly basal within Titanosauria): in fact, it could hardly do anything else, since the coding was exactly the same as that of Malawisaurus.

And indeed it’s been pretty widely accepted that “P.” becklesii is a titanosaur — one of the earliest known, and the only name-bearing one from the Wealden Supergroup, unless you count the extremely indeterminate Iuticosaurus, which predictably enough is based on a single eroded partial mid-caudal centrum. Still, the titanosaurian identity of “P.” becklesii has never been convincingly demonstrated — only inferred by non-cladistic means.

Pelorosaurusbecklesii holotype NHMUK R1870, left humerus in anterodistal view (anterior to the left).

So why the quotes around the genus name “Pelorosaurus“? Because it’s long been recognised that, whatever this specimen might be, it ain’t Pelorosaurus, which is based on the Cetiosaurusbrevis caudals and a much more slender humerus.

Here’s that humerus, so you can see how different it is from that of “Pelorosaurusbecklesii:

Right humerus of Pelorosaurus conybeari holotype NHMUK 28626. Top row: distal view, anterior to bottom. Middle row, left to right: lateral, anterior and medial views. Bottom row: distal, anterior to top. Missed parts reconstructed from the humerus of Giraffatitan brancai (Janensch 1961: Beilage A)

Right humerus of Pelorosaurus conybeari holotype NHMUK 28626. Top row: distal view, with anterior to bottom. Middle row, left to right: lateral, anterior and medial views. Bottom row: distal view, with anterior to top. Missing parts reconstructed from the humerus of Giraffatitan brancai (Janensch 1961: Beilage A)

Paul Upchurch recognised the generic distinctness of “Pelorosaurusbecklesii way back in his (1993) dissertation. But because of Cambridge University’s policy of only making copies of dissertations available for £65, that work is effectively unknown. (Perhaps we should all chip in a fiver, buy a copy and “liberate” it. Or maybe 22 years on, Paul would rather leave it in obscurity and let his reputation continue to rest on his impressive body of later work.)

What has happened to this specimen in the last 22 years? Very little has been published about it. It got a mention in the systematic review of sauropods in Dinosauria II (Upchurch et al. 2004), but the only mention that is more than in passing, as far as I’m aware, is that of see Upchurch’s first published (1995) phylogenetic analysis. From page 380:

The only reliable Lower Cretaceous titanosaurid material, apart from Malawisaurus, comes from Europe, especially England. The earliest of these forms may be represented by the forelimb of ‘Pelorosaurus becklesii‘ (Mantell 1852) from the Valanginian of Sussex. This specimen was considered to be Sauropoda incertae sedis by McIntosh (1990b). However, a skin impression shows polygonal plates of a similar shape and size to those found in Saltasaurus (Bonaparte & Powell 1980). The ulna and radius are robust and the ulna bears the typical concavity on its anteromedial proximal process. Upchurch (1993) therefore argued that this form should be provisionally included within the Titanosauridae.

[Update: as Darren points out in the comment below, Upchurch et al. (2011) figure the specimen in colour and devote three pages to it. They leave it as Titanosauria, and “refrain from naming a new taxon until more comparative data are available” (p. 501).]

Given my interest in the Wealden, it’s surprising that we’ve never blogged about “Pelorosaurusbecklesii before, but it’s true: I’ve mentioned it three times in comments, but never in a post. It’s good to finally fix that!

Next time: the radius and ulna.

References

  • Janensch, Werner. 1961. Die Gliedmaszen und Gliedmaszengurtel der Sauropoden der Tendaguru-Schichten. Palaeontographica (Suppl. 7) 3:177-235.
  • Taylor, Michael P. 2007. Diversity of sauropod dinosaurs from the Lower Cretaceous Wealden Supergroup of southern England. p. 23 in Graeme T. Lloyd (ed.), Progressive Palaeontology 2007, Thursday 12th-Saturday 14th April, Department of Earth Sciences, University of Bristol. 38 pp.
  • Upchurch, Paul. 1993. The Anatomy, Phylogeny and Systematics of Sauropod Dinosaurs. Ph.D dissertation, University of Cambridge, UK. 489 pages.
  • Upchurch, Paul. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London Series B, 349:365-390.
  • Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pages.
  • Upchurch, Paul, Philip D. Mannion and Paul M. Barrett. 2011. Sauropod dinosaurs. pp. 476-525 in: Batten, David J. (ed.), English Wealden Fossils. The Palaeontological Association (London).

Continuing with what seems to have turned out to be Brachiosaur Humerus Week here on SV-POW! (part 1, part 2, part 3), let’s consider the oft-stated idea that brachiosaurs have the most slender humeri of any sauropod. For example, Taylor (2009:796) wrote that:

Discarding a single outlier, the ratio of proximodistal length to minimum transverse width (Gracility Index or GI) in humeri of B. brancai [i.e. Giraffatitan] varies between 7.86 for the right humerus HMN F2 and 9.19 for the left humerus HMN J12, with the type specimen’s right humerus scoring 8.69, slightly more gracile than the middle of the range […] For the B. altithorax type specimen, the GI is 8.50, based on the length of 204 cm and the minimum transverse width of 24 cm reported by Riggs (1904:241). However, the B. altithorax humerus looks rather less gracile to the naked eye than that of B. brancai, and careful measurement from Riggs’s plate LXXIV yields a GI of 7.12, indicating that the true value of the minimum transverse width is closer to 28.5 cm. As noted by Riggs (1903:300-301), the surface of the distal end of this humerus has flaked away in the process of weathering. Careful comparison of the humeral proportions with those of other sauropods (Taylor and Wedel, in prep.) indicates that the missing portion of this bone would have extended approximately a further 12 cm, extending the total length to 216 cm and so increasing the GI to 7.53 – still less gracile than any B. brancai humerus except the outlier, but more gracile than any other sauropod species except Lusotitan atalaiensis (8.91), and much more gracile than the humerus of any non-brachiosaurid sauropod (e.g., Diplodocus Marsh, 1878 sp., 6.76; Malawisaurus dixeyi Jacobs, Winkler, Downs and Gomani, 1993, 6.20; Mamenchisaurus constructus Young, 1958, 5.54; Camarasaurus supremus Cope, 1877, 5.12; Opisthocoelicaudia skarzynskii Borsuk-Bialynicka, 1977, 5.00 – see Taylor and Wedel, in prep.)

Implicit in this (though not spelled out, I admit) is that the humeri of brachiosaurs are slender proportional to their femora. So let’s take a look at the humerus and femur of Giraffatitan, as illustrated in Janensch’s beautiful 1961 monograph of the limbs and girdles of Tendaguru sauropods:

Janensch1961-tendaguru-limbs--plates-AJ--giraffatitan-limb-bones

The first thing you’ll notice is that the humerus is way longer than the femur. That’s because Janensch’s Beilage A illustrates the right humerus of SII (now properly known as MB R.2181) while his Beilage J illustrates the right femur of the rather smaller referred individual St 291. He did this because the right femur of SII was never recovered and the left femur was broken, missing a section in the middle that had to be reconstructed in plaster.

(What’s a Beilage? It’s a German word that seems to literally mean something like “supplement”, but in Janensch’s paper it means a plate (full-page illustration) that occurs in the main body of the text, as opposed to the more traditional plates that come at the end, and which are numbered from XV to XXIII.)

How long would the intact SII femur have been? Janensch (1950b:99) wrote “Since the shaft of the right femur is missing for the most part, it was restored to a length of 196 cm, calculated from other finds” (translation by Gerhard Maier). Janensch confused the left and right femora here, but assuming his length estimate is good, we can upscale his illustration of St 291 so that it’s to SII scale, and matches the humerus. Here’s how that looks:

Janensch1961-tendaguru-limbs--plates-AJ--giraffatitan-limb-bones-scaled

Much more reasonable! The humerus is still a little longer, as we’d expect, but not disturbingly so.

Measuring from this image, the midshaft widths of the femur and humerus are 315 and 207 pixels respectively, corresponding to absolute transverse widths of 353 and 232 mm — so the femur is broader by a factor of 1.52. That’s why I expressed surprise on learning that Benson et al (2014) gave Giraffatitan a CF:CH ratio (circumference of femur to circumference of humerus) of only 1.12.

Anyone who would like to see every published view of the humeri and femora of these beasts is referred to Taylor (2009:fig. 5). In fact, here it is — go crazy.

Taylor (2009: figure 5). Right limb bones of Brachiosaurus altithorax and Brachiosaurus brancai, equally scaled. A-C, humerus of B. altithorax holotype FMNH P 25107; D-F, femur of same; G-K, humerus of B. brancai lectotype HMN SII; L-P, femur of B. brancai referred specimen HMN St 291, scaled to size of restored femur of HMN SII as estimated by Janensch (1950b:99). A, D, G, L, proximal; B, E, H, M, anterior; C, K, P, posterior; J, O, medial; F, I, N, distal. A, B, D, E modified from Riggs (1904:pl. LXXIV); C modified from Riggs (1904:fig. 1); F modified from Riggs (1903:fig. 7); G-K modified from Janensch (1961:Beilage A); L-P modified from Janensch (1961:Beilage J). Scale bar equals 50 cm.

Taylor (2009: figure 5). Right limb bones of Brachiosaurus altithorax and Brachiosaurus brancai, equally scaled. AC, humerus of B. altithorax holotype FMNH P 25107; DF, femur of same; GK, humerus of B. brancai paralectotype HMN SII; LP, femur of B. brancai referred specimen HMN St 291, scaled to size of restored femur of HMN SII as estimated by Janensch (1950b:99). A, D, G, L, proximal; B, E, H, M, anterior; C, K, P, posterior; J, O, medial; F, I, N, distal. A, B, D, E modified from Riggs (1904:pl. LXXIV); C modified from Riggs (1904:fig. 1); F modified from Riggs (1903:fig. 7); GK modified from Janensch (1961:Beilage A); LP modified from Janensch (1961:Beilage J). Scale bar equals 50 cm.

Notice that the femur of Giraffatitan, while transversely pretty broad, is freakishly narrow anteroposteriorly. The same is true of the femur of Brachiosaurus, although it’s never been shown in a published paper — I observed it in the mounted casts in Chicago.

Weird.

Calculations

So let’s take a wild stab at recalculating the mass of Giraffatitan using the Benson et al. formula. First, measuring the midshaft transverse:anteroposterior widths of the long bones gives eccentricity ratios of 2.39 for the femur and 1.54 for the humerus (I am not including the anterior prejection of the deltopectoral crest in the anteroposterior width of the humerus) . Dividing the absolute transverse widths above by these ratios gives us anteroposterior widths of 148 for the femur and 150 mm for the humerus. So they are almost exactly the same in this dimension.

If we simplify by treating these bones as elliptical in cross section, we can  approximate their midshaft circumference. It turns out that the formula for the circumference is incredibly complicated and involves summing an infinite series:

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But since we’re hand-waving so much anyway, we can use the approximation C = 2π sqrt((a²+b²)/2). where a and b are the major and minor radii (not diameters). For the femur, these measurements are 176 and 74 mm, so C = 848 mm; and for the humerus, 116 and 75 mm yields 614 mm. (This compares with FC=730 and HC=654 in the data-set of Benson et al., so we have found the femur to be bigger and the humerus smaller than they did.)

So the CF:CH ratio is 1.38 — rather a lot more than the 1.12 reported by Benson et al.  (Of course, if they measured the actual bones rather than messing about with illustrations, then their numbers are better than mine!)

And so to the mass formula, which Campione and Evans (2012) gave as their equation 2:

log BM = 2.754 log (CH+CF) − 1.097

Which I understand to use base-10 logs, circumferences measured in millimeters, and yield a mass in grams, though Campione and Evans are shockingly cavalier about this. CH+CF is 1462; log(1462) = 3.165. That gives us a log BM of 7.619, so BM = 41,616,453 g = 41,616 kg.

Comparison with Benson et al. (2014)

Midshaft measurements and estimates for SII long bones (all measurements in mm)
SV-POW! Benson et al.
Femur Humerus Femur Humerus
Transverse diameter 353 232 240
Transverse radius 176 116 120
Anteroposterior diameter 148 150 146
Anteroposterior radius 74 75 73
Circumference 848 614 730 654
Total circumference 1462 1384
Mass estimate (kg) 41,616 34,000

My new mass estimate of 41,616 kg is is a lot more than the 34,000 kg found by Benson et al. This seems to be mostly attributable to the much broader femur in my measurement: by contrast, the humerus measurements are very similar (varying by about 3% for both diameters). That leaves me wondering whether Benson et al. just looked at a different femur — or perhaps used St 291 without scaling it to SII size. Hopefully one of the authors will pass by and comment.

More to come on this mass estimate real soon!

References

 

Last time we looked at the humeri in the Field Museum’s mounted Brachiosaurus skeleton — especially the right humerus, which is a cast from the holotype, while the left is a sculpture. But Matt’s and my photos of that mount are all pretty much useless scientifically — partly because we were terrible photographers back then, but also partly because the very light background of sky tended to put the skeleton into silhouette and lose a lot of detail.

But fortunately there’s another Brachiosaurus in Chicago!

dscn1156

(We’ve featured this mount once before.)

This in fact the original Brachiosaurus mount that was erected in the Field Museum’s main hall in 1993. When a certain vulgar, over-studied theropod was installed in that hall in 2000, the surprising decision was made to remove the Brachiosaurus to “make room” for it (even though it’s objectively tiny). The mount was not built to be exposed to the elements, so it couldn’t just be moved outdoors. Instead, a new one was made from more suitable materials for the picnic area, and the original mount was moved to O’Hare Airport.

[Aside: what the heck were the museum thinking when they booted Brachiosaurus out of the main hall? However much you love T. rex, and I admit I do, Sue makes a feeble centrepiece compared with a brachiosaur. I can only assume there was some subtle political motivation for reducing their main hall’s Awesome Quotient so dramatically. The poor thing was only there seven years.]

Anyway, the original mount is now at Terminal 1 at O’Hare Airport, where it can be photographed less inadequately than outdoors. Here are those contrasting humeri again: the real cast on the right side of the animal (left side of photo) and the sculpture on the left (right side of photo):

dscn1158

And a zoom into the relevant section:

dscn1158-closeup

As it happens, I flew into a different terminal at O’Hare. But I knew that this mount was in Terminal 1, so before I get the transit to my hotel, I dragged my luggage across to Terminal 1 and begged the ticket clerk to let me through into the departure area so I could look at it. I don’t now remember exactly what the sequence of events was, but I do recall that phone-calls were made and supervisors were consulted. In the end, someone on staff gave me a platform ticket, and I was able to go and spend a quality hour with this glorious object.

It also meant I got to watch nearly every single traveller amble straight past Brachiosaurus giving it literally not even a single glance — see the first photo for an example. Truly depressing.

Anyway, I was able to get some slightly better photos of this cast humerus than I subsequently got of the outdoor mount. Though not very many, because — stop me if you’ve heard this — I was young and stupid then.

Anyway, here is the humerus in anterior view. Or as close to anterior as I could manage. By holding the camera above my head, I could get it nearly level with the distal margin of the mounted bone, so what we have here is really more like anterodistal:

dscn1161-brightened

And here is that some bone in lateral view (again, really laterodistal). From this angle, you can really see how shapeless parts of the lateral border of the cast are — which is odd, because there are sharp lips on the actual fossil.

dscn1163

In terms of general appreciation of the bone, this next one, in anterolaterodistal view,  is probably best — the light caught it in an informative way. Unfortunately, I cut off the distal margin. Sorry.

dscn1164

As you can see, the level of detail in the cast is mostly pretty good. For example, you can clearly make out the broken-off base of the deltopectoral crest (the tall light-coloured oval about a quarter of the way down and a third of the way across the bone). That makes the lumpenness of the distal part of the lateral aspect all the more mysterious.

Finally, here are both humeri, more or less from the left, so that the real cast is in something approaching medial view.

dscn1165

From this angle, you can see that the humerus is noticeably less anteroposteriorly deep than its transverse width. We’ll see this theme cropping up again with brachiosaur limb bones — stay tuned for future posts!

Also of interest: the very nice sculpted humerus on the left side has a complete deltopectoral crest — modelled, I imagine, after those of the various Giraffatitan humeri. It also has a finished distal end which is much broader than that of the cast humerus. In this, it’s probably right, as the real bone suffered from some decay.

And that, I am afraid, is all: stupidly, I neglected to photograph the humerus in posterior aspect, or any of the diagonals other than anterolateral.

Next time: exciting news about the relative breadth of humerus and femur in brachiosaurs!

As we noted yesterday, the humerus of the Brachiosaurus altithorax holotype FMNH P25107 is inconveniently embedded in a plaster jacket — but it wasn’t always. That’s very strange. I have an idea about that which I’ll come to later.

Anyway, although the humerus is now half in a jacket and fully inside a cabinet, we can see it from all angles thanks to the cast that’s part of the mounted skeleton outside the Field Museum. (I can definitively state that this is the greatest picnic area in the universe).

dscn9650

As noted in the previous post, Matt and I were idiots back when we visited Chicago, so our photos are mostly useless. We have lots that show the mounted skeleton as art, but very few that are scientifically useful. But what you can make out from the photo above (especially if you click through) is that the textures of the two humeri are very different.

You can see it more clearly from in front:

dscn9672

(There I am, microscopic and easily overlooked, on the left.)

Here’s a close-up of the humeri from that photo, sharpened and contrast/brightness-balanced so you can more easily see what’s going on:

dscn9672-close-up

Contrast the scarred, pitted surface of the right humerus (on the left of the picture) with the much cleaner and bone-like texture of the left one (on the right of the picture). What’s going on here is that the right humerus of the mounted skeleton is a cast of the original element (bad preservation and all) whereas the left humerus is a sculpture. (Or possibly a cast of one of the Giraffatitan humeri, but I doubt that — it’s a bit too clean and seems more robust than those bones.) The real humerus is very distinctive, especially in the progressive flaking away on the lateral side of the distal end.

Of course you can walk all around the cast humerus and photograph it from every angle — both the posterior that is apparent in the jacket, and the anterior that’s face down and inaccessible.

You can walk all around the cast humerus and photograph it from every angle. But we didn’t. Because, as noted here and yesterday (and previously, come to think of it) we used to be idiots back then. As Matt has pithily observed:

“About every three or four months I realize that I’ve spent my entire life up until now being a dumbass; the problem is that ‘now’ keeps moving and every time I think I’ve finally got everything figured out, I later determine that I was/am still a moron.  I distinctly remember having this feeling for the first time in third grade, age of eight, and I keep hoping it will eventually go away, but that hope seems increasingly unfounded.”

That is a hauntingly familiar feeling.

It seems that this cast-right, sculped-left humerus combo is common in Brachiosaurus mounts — I guess because they’re all cloned from the Field Museum’s original. Here, for example (from this post) is the mount at BYU the North American Museum of Ancient Life:

Utah 2008 07 Matt in lift

Once you’ve seen that humerus mismatch, you can’t miss it.

Finally, then — what about this historical oddity that the humerus was once out of its jacket but is now back in? That doesn’t make a lot of sense to me. I can’t really imagine why you’d do that.

So maybe that never happened? We’ve been taking it for granted that the humerus in the old Field-Museum photo is real, but maybe it’s not. Maybe it was a cast, and that cast is still somewhere in the museum (or indeed incorporated into the mount). Maybe when the fossil humerus was brought back from the field, the jacket was removed from the anterior face and that was cast; then this face was rejacketed, the bone was flipped, the posterior face was exposed (as it still is today) and that was cast. Then the two casts were joined together to make an apparently whole humerus.

If that speculation is right, then it should be possible to detect a join running down the lateral and medial faces of the cast humerus that’s in the mount (and apparently in all other mounts). That’s something I’ll look closely for the next time I’m lucky enough to be in Chicago.

I wish it was possible to know this kind of thing. I’d love it if every time a museum mounted a skeleton they published an account of how it was done, as Janensch (1950b) did for the original Giraffatitan mount in Berlin, and Remes (2011) did for the recent remount. Unfortunately I’ve never heard of such a paper regarding the Chicago mount, and I don’t even know how long ago it was done (or if anyone who was involved is still alive). The Wikipedia page says the mount went up in 1993, but gives no reference for that and doesn’t say who did it. Does anyone know?

Update (11:38pm)

Thanks to Ben (no surname given), whose comment below points to a useful 1993 Chicago Tribune article, “Brach To The Future“. This confirms the date of the mount as 1993, unveiled on Saturday 3rd July. The mount is the work of PAST (Prehistoric Animal Structures, Inc.), who bizarrely don’t seem to have a web-site. PAST president Gilles Danis was involved in the process, so he’d be the person to contact about how it was done.

Oh, and here’s another relevant Tribune article: “Out Of The Past“. Steven Godfrey is the key player in this account, so he’s someone else to track down.

References

  • Janensch, Werner. 1950b. Die Skelettrekonstruktion von Brachiosaurus brancai. Palaeontographica (Supplement 7) 3:97-103, and plates VI-VIII.
  • Remes, Kristian, David. M. Unwin, Nicole. Klein, Wolf-Dieter Heinrich, and Oliver Hampe. 2011. Skeletal reconstruction of Brachiosaurus brancai in the Museum für Naturkunde, Berlin: summarizing 70 years of sauropod research. pp. 305-316 in: Nicole Klein, Kristian Remes, Carole T. Gee, and P. Martin Sander (eds.), Biology of the Sauropod Dinosaurs: Understanding the Life of Giants. Indiana University Press, Bloomington and Indianapolis.

In the comments on Matt’s post about the giant new Argentine titanosaur specimens, Ian Corfe wondered why Benson et al. (2014) estimated the circumference of the humerus of Brachiosaurus altithorax instead of just measuring it. (Aside: I can’t find that data in their paper. Where is it?)

I replied:

Yes, the humerus is half-encased in a jacket, face down (we should post photos some time), which would make the circumference impossible to measure directly. But the mounted Brachiosaurus skeleton right outside the Field Museum (and the identical one at O’Hare Airport) have casts of that humerus, so measuring the circumference shouldn’t require any equipment more exotic than a stepladder. Maybe the anterior aspect was sculpted — but I doubt it, as there certainly was a time when the humerus was out of its jacket and mounted vertically.

Here is the evidence that the humerus wasn’t always in that jacket (from Getty Images):

Femur of Apatosaurus and right humerus Brachiosaurus altithorax holotype on wooden pedestal (exhibit) with labels and 6 foot ruler for scale, Geology specimen, Field Columbian Museum, 1905. (Photo by Charles Carpenter/Field Museum Library/Getty Images)

Femur of Apatosaurus and right humerus Brachiosaurus altithorax holotype on wooden pedestal (exhibit) with labels and 6 foot ruler for scale, Geology specimen, Field Columbian Museum, 1905. (Photo by Charles Carpenter/Field Museum Library/Getty Images)

I have no idea why it was put back in a plaster jacket: does anyone?

Back in 2005, when Matt and I visited the Field Museum, the staff were amazingly, almost embarrassingly, helpful. They mounted a whole elaborate project to remove the humerus jacket from the cabinet that held it, so we could get a better look:

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Unfortunately, Matt and I were doofuses back in the day: terrible photographers who knew embarrassingly little about appendicular material. So nearly all of our photos are worthless. Here is a rare nice one, showing the humerus in posterodistal aspect. You can see how layers have flaked away towards this end:

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Here is the humerus in proximal view — something that’s relevant to my interests, as at tells us about the area of articular cartilage where it connected to the shoulder:

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And finally — because it would be rude not to — here is Matt, going the Full Jensen with the humerus:

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Next time: what we can learn about the humerus from the mounted skeleton outside the museum!

References

Benson Roger B. J., Nicolás E. Campione, Matthew T. Carrano, Philip D. Mannion, Corwin Sullivan, Paul Upchurch, and David C. Evans. (2014) Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology 12(5):e1001853. doi:10.1371/journal.pbio.1001853

My camera had a possibly-fatal accident in the field at the end of the day on Saturday, so I didn’t take any photos on Sunday or Monday. From here on out, you’re either getting my slides, or photos taken by other people.

Powell Museum sauropod humerus

On Sunday we were at the John Wesley Powell River History Museum in Green River, Utah, for the Cretaceous talks. There were some fossils on display downstairs, including mounted skeletons of Falcarius and one or two ornithischians,* and this sauropod humerus from the Cedar Mountain Formation (many thanks to Marc Jones for the photo).

* A ceratopsian and Animantarx, maybe? They were in the same room as the sauropod humerus, so it’s no surprise that I passed them by with barely a glance.

There were loads of great talks in the Cretaceous symposium on Sunday, and I learned a lot, about everything from clam shrimp biostratigraphy to ankylosaur phylogeny to Canadian sauropod trackways. But I can’t show you any slides from those talks, so the rest of this post is the abstact from Darren’s and my talk, illustrated by a few select slides.

Wedel Naish 2014 Sauroposeidon and kin - slide 1 title

Sauroposeidon is a giant titanosauriform from the Early Cretaceous of North America. The holotype is OMNH 53062, a series of four articulated cervical vertebrae from the Antlers Formation (Aptian-Albian) of Oklahoma. According to recent analyses, Paluxysaurus from the Twin Mountain Formation of Texas is the sister taxon of OMNH 53062 and may be a junior synonym of Sauroposeidon. Titanosauriform material from the Cloverly Formation of Wyoming may also pertain to Paluxysaurus/Sauroposeidon. The proposed synonymy is based on referred material of both taxa, however, so it is not as secure as it might be.

Wedel Naish 2014 Sauroposeidon and kin - slide 34 Sauroposeidon characters

Top row, vertebrae of Paluxysaurus. From left to right, the centrum lengths of the vertebrae are 72cm, 65cm, and 45cm. Main image, the largest and most complete vertebra of the holotype of Sauroposeidon. Labels call out features that are present in every Sauroposeidon vertebra where they can be assessed, but consistently absent in Paluxysaurus. Evaluating the proposed synonymy of Paluxysaurus and Sauroposeidon is left as an exercise for the reader.

MIWG.7306 is a cervical vertebra of a large titanosauriform from the Wessex Formation (Barremian) of the Isle of Wight. The specimen shares several derived characters with the holotype of Sauroposeidon: an elongate cervical centrum, expanded lateral pneumatic fossae, and large, plate-like posterior centroparapophyseal laminae. In all of these characters, the morphology of MIWG.7306 is intermediate between Brachiosaurus and Giraffatitan on one hand, and Sauroposeidon on the other. MIWG.7306 also shares several previously unreported features of its internal morphology with Sauroposeidon: reduced lateral chambers (“pleurocoels”), camellate internal structure, ‘inflated’ laminae filled with pneumatic chambers rather than solid bone, and a high Air Space Proportion (ASP). ASPs for Sauroposeidon, MIWG.7306, and other isolated vertebrae from the Wessex Formation are all between 0.74 and 0.89, meaning that air spaces occupied 74-89% of the volume of the vertebrae in life. The vertebrae of these animals were therefore lighter than those of brachiosaurids (ASPs between 0.65 and 0.75) and other sauropods (average ASPs less than 0.65).

Wedel Naish 2014 Sauroposeidon and kin - slide 64 Mannion phylogeny

Check this out: according to at least some versions of the Mannion et al. (2013) tree, Sauroposeidon and Paluxysaurus are part of a global radiation of andesaurids in the Early and middle Cretaceous. Cool!

Sauroposeidon and MIWG.7306 were originally referred to Brachiosauridae. However, most recent phylogenetic analyses find Sauroposeidon to be a basal somphospondyl, whether Paluxysaurus and the Cloverly material are included or not. Given the large number of characters it shares with Sauroposeidon, MIWG.7306 is probably a basal somphospondyl as well. But genuine brachiosaurids also persisted and possibly even radiated in the Early Cretaceous of North America; these include Abydosaurus, Cedarosaurus, Venenosaurus, and possibly an as-yet-undescribed Cloverly form. The vertebrae of Abydosaurus have conservative proportions and solid laminae and the bony floor of the centrum is relatively thick. In these characters, Abydosaurus is more similar to Brachiosaurus and Giraffatitan than to Sauroposeidon or MIWG.7306. So not all Early Cretaceous titanosauriforms were alike, and whatever selective pressures led Sauroposeidon and MIWG.7306 to evolve longer and lighter necks, they didn’t prevent Giraffatitan-like brachiosaurs such as Abydosaurus and Cedarosaurus from persisting well into the Cretaceous.

Wedel Naish 2014 Sauroposeidon and kin - slide 65 Cloverly sauropods

The evolutionary dynamics of sauropods in the North American mid-Mesozoic are still mysterious. In the Morrison Formation, sauropods as a whole are both diverse and abundant, but Camarasaurus and an efflorescence of diplodocoids account for most of that abundance and diversity, and titanosauriforms, represented by Brachiosaurus, are comparatively scarce. During the Early Cretaceous, North American titanosauriforms seem to have radiated, possibly to fill some of the ecospace vacated by the regional extinction of basal macronarians (Camarasaurus) and diplodocoids. However, despite a flood of new discoveries in the past two decades, sauropods still do not seem to have been particularly abundant in the Early Cretaceous of North America, in contrast to sauropod-dominated faunas of the Morrison and of other continents during the Early Cretaceous.

Wedel Naish 2014 Sauroposeidon and kin - slide 66 acknowledgments

That final slide deserves some explanation. On the way back from the field on Saturday–the night before my talk–a group of us stopped at a burger joint in Hanksville. Sharon McMullen got a kid’s meal, and it came in this bag. We took it as a good omen that Sauroposeidon was the first dinosaur listed in the quiz.

For the full program and abstracts from both days of talks, please download the field conference guidebook here.

When Fiona checked her email this morning, she found this note from our next-door neighbour Jenny:

Hi
I seem to remember Mike wanting a mole – I do hope so because I’ve left you a body on your patio in a cereal box!

Cheers Jen x

What a delightful surprise! And here it is:

The SV-POW! mole, intact

The SV-POW! mole, intact

And a close-up of that awesome digging hand:

The SV-POW! mole, right manus

The SV-POW! mole, right manus

I don’t have time to deal with it properly right now, so it’s gone into a plastic box with some small holes in the lid, where I will trust invertebrates to do my work for me — as they did to great effect with the juvenile baby rabbit whose skeleton I must show you some time.

The end-game here is of course to obtain a complete skeleton; but if not that, then at least the upper-arm bones. I’m on record as saying that next to sauropod vertebrae, mole humeri are the bones that move me most; and elsewhere I nominated mole humeri in response to John Hutchinson’s question, “what are the strangest animal bones (in form & function etc) that have ever been discovered?”

Here’s why:

Left: rat humerus (for comparison), Right: mole humerus. The rat humerus is unfused on top, which is why there is a visible gap between the two parts.

Left: rat humerus (for comparison), Right: mole humerus. The rat humerus is unfused on top, which is why there is a visible gap between the two parts.

I stole this picture from an Ossamenta post, The strangest animal bone?. Get yourself over there for more wacky rat-vs.-mole comparisons!

LACM Deinonychus claw

All I want to do in this post is make people aware that there is a difference between these two things, and occasionally that affects those of us who work in natural history.

In one of his books or essays, Stephen Jay Gould made the point that in natural history we are usually not dealing with whether phenomena are possible or not, but rather trying to determine their frequency. If we find that in a particular population of quail most of the birds eat ants but some avoid them, then we know some things: that quail can tolerate eating ants, that quail are not required to eat ants, and that both strategies can persist in a single population.

This idea has obvious repercussions for paleoart, especially when it comes to “long-tail” behaviors. I dealt with that in this post, and also in the comment thread to this one. But that’s not what I want to talk about today.

Sometimes it is useful to talk about things that never happen, or that have at least never occurred in the sample of things we know of. Obviously how certain you can be in these cases depends on the intensity of sampling and the inherent likelihood of a surprising result, which can be hard to judge. If you argued right now that T. rex lacked feathers because no T. rex specimens have been found with feathers, you’d most likely be wrong; it is almost certainly just a matter of time before someone finds direct evidence of feathers in T. rex, given the number of T. rex specimens waiting to be found and the strength of the indirect evidence (e.g., phylogenetic inference, analogy: ornithomimids are known to be feathered even though most specimens are found without feather impressions). If you argue that sauropods are unique among terrestrial animals in having necks more than five meters long, you’re most likely right; being wrong would imply the existence of some as-yet undiscovered land animal of sauropod size, or with seriously wacky proportions (or both), and our sampling of terrestrial vertebrates is good enough to make that extremely unlikely.

LACM baby rex snout

The reason for this post is that sometimes people confuse that last argument, which is about sampling and induction, with the argument from personal incredulity.

For example, in our no-necks-for-sex paper (Taylor et al. 2011), we included this passage:

Sauropoda also had a long evolutionary history, originating about 210 million years ago in the Carnian or Norian Age of the Late Triassic, and persisting until the end-Cretaceous extinction of all non-avian dinosaurs about 65 millions years ago. Thus the ‘necks-for-sex’ hypothesis requires that this clade continued to sexually select for exaggeration of the same organ for nearly 150 million years, a scenario without precedent in tetrapod evolutionary history.

One of the reviewers argued that we couldn’t include that section, because it was just the argument from personal incredulity writ large, like so:

There are no other known cases of X in tetrapod evolutionary history, and therefore we don’t believe that the case in question is the sole exception.

…with the second part of that unstated (by us) but implied. But we disagreed, and argued (successfully) that it was an argument based on sampling, like so:

There are no other known cases of X in tetrapod evolutionary history, and therefore it is unlikely that the case in question is the sole exception.

Now, it is perfectly fair to criticize arguments like that based on the thoroughness of the sampling and the likelihood of exceptions, as discussed above for T. rex feathers. Just don’t mistake arguments like that for arguments from personal incredulity.* On the flip side, if someone makes an argument from personal incredulity, see if the same thing can be restated as an argument about sampling. Maybe they’re correct but just expressing themselves poorly (“I refuse to believe that the moon is made out of cheese”), and maybe they’re wrong and restating things in terms of sampling will help you understand why.

* If you want to get super pedantic about it, they’re both arguments from ignorance. But one of them is at least potentially justifiable by reference to sampling. Absence of evidence is not necessarily evidence of absence, but it may get to be that way as the sampling improves (e.g., there is no evidence of planets closer to the sun than Mercury, and at this point, that is pretty persuasive evidence that no such planets exist).

LACM brachiosaur humerus with Wedels for scale

Parting shot: one thing that has always stuck in my head from Simberloff (1983) is the bit about imagining a large enough universe of possible outcomes. And I’ve always had a perverse fascination with Larry Niven’s “Down in Flames”, in which he pretty much demolished his Known Space universe by assuming that every basic postulate of that universe was false. Neither of these follow directly on from the main point of the post, but they’re not completely unrelated, either. Because I think that they yield a pretty good heuristic for how to do science: imagine what it would take for you to be wrong–imagine a universe in which you are wrong–and then go see if the thing that makes you wrong, whatever it is, can be shown to exist or to work. If not, it doesn’t mean you’re right, but it means you’re maybe less wrong, which, if we get right down to it, is the best that we can hope for.

The photos have nothing to do with the post, they’re just pretty pictures from the LACM to liven things up a little.

References

I was cruising the monographs the other night, looking for new ideas, when the humerus of Opisthocoelicaudia stopped me dead in my tracks. I think you’ll agree it is an arresting sight:

Opisthocoelicaudia right humerus in lateral, anterior, medial, and posterior views, from Borsuk-Bialynicka (1977: figure 7)

Opisthocoelicaudia right humerus in medial, anterior, lateral, and posterior views, from Borsuk-Bialynicka (1977: figure 7)

I’d seen it before, but somehow I had never grokked its grotesque fatness. I mean, damn, Opisthocoelicaudia, you really let yourself go. Especially compared to the slenderness and grace of this juvenile Alamosaurus humerus:

Alamosaurus left humerus in anterior and posterior views, from Lehman and Coulson (2002: figure 7).

Alamosaurus left humerus in anterior and posterior views, from Lehman and Coulson (2002: figure 7).

Now, I realize that part of the slenderness of this Alamosaurus humerus might be because it’s a juvenile–other alamosaur humeri are a bit more robust–but it’s still a striking contrast. I couldn’t help but superimpose them, scaled to the same midshaft width:

Alamosaurus and Opisthocoelicaudia humeri superimposed

I flipped the Alamosaurus humerus left-to-right to match that astonishing lump of Opisthocoelicaudia. The result reminds me of one of Abrell and Thompson’s Actual Facts:

If you put Woodrow Wilson inside William Howard Taft, he would have stuck out by a good 18 inches.

None of that probably signifies anything more than that I am easily amused. And also,  Opisthocoelicaudia is Just Plain Wrong. You hear me, Opisthocoelicaudia? Don’t make me make you cry mayonnaise!

References