University of Bristol

Mike Taylor

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.

How slender were the humeri of Giraffatitan?

Western University of Health Sciences

Matt Wedel

[![Recapture Creek comparo with
measurements](https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=806&h=1024){.aligncenter
.size-large .wp-image-7986 loading="lazy" attachment-id="7986"
permalink="http://svpow.com/2013/03/03/the-recapture-creek-sauropod-the-reveal/recapture-creek-comparo-with-measurements/"
orig-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg"
orig-size="709,900" comments-opened="1"
image-meta="{\"aperture\":\"0\",\"credit\":\"\",\"camera\":\"\",\"caption\":\"\",\"created_timestamp\":\"0\",\"copyright\":\"\",\"focal_length\":\"0\",\"iso\":\"0\",\"shutter_speed\":\"0\",\"title\":\"\"}"
image-title="Recapture Creek comparo with measurements"
image-description="" image-caption=""
medium-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=236"
large-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=709"
srcset="https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=378 378w, https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=118 118w, https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg?w=236 236w, https://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg 709w"
sizes="(max-width: 378px) 100vw, 378px"}](http://svpow.files.wordpress.com/2013/02/recapture-creek-comparo-with-measurements.jpg)

If you're just joining us, this post is a follow-up to [this
one](http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/),
in which I considered the possible size and identity of the Recapture
Creek femur fragment, which ["Dinosaur Jim"
Jensen](http://svpow.com/2011/06/01/how-big-was-brachiosauruss-forelimb/)
(1987: page 604) said was "the largest bone I have ever seen".

True to his word, Brooks Britt at BYU got back to me with measurements
of the Recapture Creek femur fragment in practically no time at all:

> Length 1035 mm, width 665 mm.  However, you cannot trust the
> measurements because Jensen put a lot of plaster on the proximal half
> of the bone.

Now, taking plaster off a bone is not going to make it any larger. So
the plastered-up specimen is the best case scenario for the RC femur to
represent a
[gigapod](http://svpow.com/2008/05/20/sv-pow-showdown-sauropods-vs-whales/).
And I know the stated width of 665 mm is the max width of the proximal
end, because I sent Brooks a diagram showing the measurements I was
requesting. The length is a little less than anticipated, and doesn't
quite jibe with the max proximal width--I suspect a little might have
broken off from the distal end where the preservation looks not-so-hot.

Based on those measurements, it looks like Jensen got the scale bar in
Figure 8 in his 1987 paper approximately right--if anything, the scale
bar is a little undersized, but only by 5% or so, which is [actually
pretty good as these things
go](http://svpow.com/2009/04/23/mydd/) (scale bars without measurements
are still dag-nasty evil, though). By overlapping Jensen's photo with
the femur of the *Brachiosaurus altithorax* holotype (FMNH P25107) to
estimate the size of the element when complete, I get a total length of
2.2 meters--~~exactly the same size as~~ about 8% bigger than
the *Brachiosaurus *holotype (actual length 2.03 m). If the Recapture
Creek femur is from a *Camarasaurus*, which I don't think we can rule
out, it was 2 meters long when complete, or 11% longer and 37% more
massive than the big *C. supremus* AMNH 5761--about 35 tonnes or maybe
40 on the outside. So it's a big bone to be sure, but it ~~doesn't
extend~~ only slightly extends the known size range of Morrison
sauropods. (**Updated 2014-05-19**--as I related in the first post, I
somehow got it fixed in my head that the holotype *B.a.* femur was 2.19
m when it is actually 2.03 m.)

So, as before, *caveat estimator* when [working from scaled
illustrations of single partial bones of possibly immense
sauropods](http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/).

Now, here's a weird thing. Let's assume for the sake of this discussion
that the Recapture Creek femur is from a brachiosaur. That gives us
three individual Late Jurassic brachiosaurids--the Recapture Creek
animal, [the *Brachiosaurus altithorax*
holotype](http://svpow.com/2012/05/03/mold-a-rama/), and [the mounted
*Giraffatitan
brancai*](http://svpow.com/2008/11/27/shedloads-of-awesome-part-1-the-humboldt-brachiosaur-remount/)--that
are almost exactly the same size in limb bone dimensions (although
[*B.a.* had a longer
torso](http://svpow.com/2009/09/20/what-a-23-longer-torso-looks-like/)).
But we know that brachiosaurids got bigger, as evidenced by [the XV2
specimen of
*Giraffatitan*](http://svpow.com/2009/03/16/brachiosaurus-both-bigger-and-smaller-than-you-think-incomplete/),
and based on the lack of scapulocoracoid fusion in both FMNH P25107 and
the mounted *Giraffatitan*. So why do we keep finding these (and
smaller) subadults, and so few that were XV2-sized? I know that there
gets to be a preservation bias against immense animals ([it's hard to
bury a 50-tonne animal all in one
go](http://svpow.com/2008/07/24/the-enigmatic-taphonomy-of-sauroposeidon/)),
but I would not think the 13% linear difference between these subadults
and XV2-class adults would be enough to matter. Your thoughts?

**Reference**

[Jensen, J.A. 1987. New brachiosaur material from the Late Jurassic of
Utah and Colorado. Great Basin Naturalist 47(4):
592-608.](https://ojs.lib.byu.edu/wnan/index.php/wnan/article/viewFile/1849/2197)


If you’re just joining us, this post is a follow-up to this one, in which I considered the possible size and identity of the Recapture Creek femur fragment, which “Dinosaur Jim” Jensen (1987: page 604) said was “the largest bone I have ever seen”.  True to his word, Brooks Britt at BYU got back to me with measurements of the Recapture Creek femur fragment in practically no time at all:  Now, taking plaster off a bone is not going to make it any

The Recapture Creek sauropod: the reveal

From Jensen (1987, page 604):

"In 1985 I found the proximal third of an extremely large sauropod femur
(Figs. 8A, 12A) in a uranium miner's front yard in southern Utah.  The
head of this femur is 1.67 m (5'6″) in circumference and was collected
from the Recapture Creek Member of the the Morrison Formation in Utah
near the Arizona border.  It is the largest bone I have ever seen."

Jensen included not one but two figures of this immense shard of
excellence. Here they are:

::: {#attachment_7961 .wp-caption .aligncenter shortcode="caption" style="width: 752px"}
[![Jensen 1987 figure
8](https://svpow.files.wordpress.com/2013/02/jensen-1987-figure-8.jpg?w=742&h=1024){.size-large
.wp-image-7961 aria-describedby="caption-attachment-7961" loading="lazy"
attachment-id="7961"
permalink="http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/jensen-1987-figure-8/"
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image-title="Jensen 1987 figure 8" image-description="" image-caption=""
medium-file="https://svpow.files.wordpress.com/2013/02/jensen-1987-figure-8.jpg?w=218"
large-file="https://svpow.files.wordpress.com/2013/02/jensen-1987-figure-8.jpg?w=546"
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sizes="(max-width: 348px) 100vw, 348px"}](http://svpow.files.wordpress.com/2013/02/jensen-1987-figure-8.jpg)

Jensen 1987, Figure 8
:::

::: {#attachment_7962 .wp-caption .aligncenter shortcode="caption" style="width: 752px"}
[![Jensen 1987, Figure
12](https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=742&h=1024){.size-large
.wp-image-7962 aria-describedby="caption-attachment-7962" loading="lazy"
attachment-id="7962"
permalink="http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/jensen-1987-fig-12/"
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orig-size="542,747" comments-opened="1"
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image-title="Jensen 1987 fig 12" image-description=""
image-caption="Jensen 1987, Figure 12
"
medium-file="https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=218"
large-file="https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=542"
srcset="https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=348 348w, https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=109 109w, https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg?w=218 218w, https://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg 542w"
sizes="(max-width: 348px) 100vw, 348px"}](http://svpow.files.wordpress.com/2013/02/jensen-1987-fig-12.jpg)

Jensen 1987, Figure 12
:::

The specimen was heavily reconstructed, as you can see from the big
wodge of unusually smooth and light-colored material in the photo. So we
can't put much stock in that part of the specimen.

Unfortunately, the only measurement of the specimen that Jensen gives in
the paper is that circumference; there are no straight-line linear
measurements, and the figures both have the dreaded scale bars. Why
dreaded? Check this out:

[![Recapture Creek figs 8 and 12
compared](https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=1024&h=529){.aligncenter
.size-large .wp-image-7959 loading="lazy" attachment-id="7959"
permalink="http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/recapture-creek-figs-8-and-12-compared/"
orig-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg"
orig-size="805,416" comments-opened="1"
image-meta="{\"aperture\":\"0\",\"credit\":\"\",\"camera\":\"\",\"caption\":\"\",\"created_timestamp\":\"0\",\"copyright\":\"\",\"focal_length\":\"0\",\"iso\":\"0\",\"shutter_speed\":\"0\",\"title\":\"\"}"
image-title="Recapture Creek figs 8 and 12 compared"
image-description="" image-caption=""
medium-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=300"
large-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=805"
srcset="https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=480 480w, https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=150 150w, https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=300 300w, https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg?w=768 768w, https://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg 805w"
sizes="(max-width: 480px) 100vw, 480px"}](http://svpow.files.wordpress.com/2013/02/recapture-creek-figs-8-and-12-compared.jpg)As
you can see, when the scale bars are set to the same size, the bones are
way off (the scale bar in the drawing is 50 cm). [This is not an
uncommon problem.](http://svpow.com/2009/04/23/mydd/) I make the Fig 8
version 30% bigger in max mediolateral width of the entire proximal end,
and still 17% bigger in minimum diameter across the femoral head, as
measured from the slight notch on the dorsal surface (on the right in
this view).

Can we figure out which is more accurate based  on the internal evidence
of the paper? For starters, the Fig 12 version is a drawing (1), that
does not match the outline from the photo (2), and the hand-drawn scale
bar (3) does not actually coincide with any landmarks (4), and that's
plenty of reasons for me not to trust it.

What about that circumference Jensen mentioned? Unfortunately, he didn't
say exactly where he took it, just that the head of the femur had a
circumference of 1.67 meters. Is that for the entire proximal end, or
for the anatomical head that fits in the acetabulum, er wot? I'm afraid
the one measurement given in the paper is no help in determining which
of the figures is more accurately scaled.

The obvious thing to do would be to see if this bone is in the BYU
collections, and just measure the damn thing. More on that at the end of
the post.

In the meantime, Jensen said that the shape of the Recapture Creek femur
was most similar to the femur of *Alamosaurus*, or to that of
*Brachiosaurus* among Morrison taxa, and he referred it to
Brachiosauridae. So how does this thing--in either version--compare with
the complete femur of FMNH P25107, the holotype of *Brachiosaurus
altithorax*?

::: {#attachment_7964 .wp-caption .aligncenter shortcode="caption" style="width: 840px"}
[![The Recapture Creek brachiosaur femur fragment compared to the
complete femur of the Brachiosaurus altithorax holotype FMNH
P25107](https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=830&h=1024){.size-large
.wp-image-7964 aria-describedby="caption-attachment-7964" loading="lazy"
attachment-id="7964"
permalink="http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/recapture-creek-boba-comparo/"
orig-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg"
orig-size="709,874" comments-opened="1"
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image-title="Recapture Creek – BOBA comparo" image-description=""
image-caption="The Recapture Creek brachiosaur femur fragment compared to the complete femur of the Brachiosaurus altithorax holotype FMNH P25107
"
medium-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=243"
large-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=709"
srcset="https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=389 389w, https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=122 122w, https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg?w=243 243w, https://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg 709w"
sizes="(max-width: 389px) 100vw, 389px"}](http://svpow.files.wordpress.com/2013/02/recapture-creek-boba-comparo.jpg)

The Recapture Creek femur fragment compared to the complete femur of the
*Brachiosaurus altithorax* holotype FMNH P25107
:::

The first thing to notice is that the drawn outline from Figure 12 is a
*much* better match for the *Brachiosaurus altithorax* femur--enough so
that I wonder if Jensen drew it from the Recapture Creek specimen, or
just traced the *B.a.* proximal femur and scaled it accordingly (or
maybe not accordingly, since the scale bars don't match).

But let's get down to business: how long would the complete femur have
been?

Using the scale bar in the photograph from Figure 8 (on the left in
above image), I get a total femur length of 2.36 meters. ~~Which is
long, but only 7.7% longer than the 2.19-meter femur of FMNH P25107, and
therefore only 25% more massive. So, 35 tonnes to Mike's 28-tonne
*B.a.*, or maybe 45 tonnes to a more liberal 36-tonne *B.a.* Big, yeah,
but not world-shattering.~~ **Update 2014-05-19:** I don't know where I
got the 2.19-meter femur length for *Brachiosaurus altithorax*, but it's
a mistake. So the rest of that paragraph should read: Which is 16%
longer than 2.03-meter femur of FMNH P25107, and therefore 57% more
massive. So, 44 tonnes to Mike's 28-tonne *B.a.*, or maybe 57 tonnes to
a more liberal 36-tonne *B.a.* That's nowhere near the 2.5-meter femur
and estimated 70-tonne mass of the largest *Argentinosaurus*, but it's
pretty darned good for a brachiosaur.

Using the scale bar in the drawing from Figure 12 (on the right in the
above image)--which, remember, is 50 cm, not 1 meter--I get a total
femur length of about 1.9 meters, which is considerably smaller than the
*B.a.* holotype. That is very much at odds with Jensen's description of
it as "the largest bone I have ever seen", and given that we have many
reasons for not trusting the scale bar in the drawing, it is tempting to
just throw it out as erroneous.

So it would seem that unless Jensen got both scale bars too big, the
Recapture Creek brachiosaur was at most only a shade bigger than the
holotype specimen of *Brachiosaurus altithorax*.

But wait--is the Recapture Creek brachiosaur a brachiosaur at all?
Jensen didn't list any characters that pushed him toward a brachiosaurid
ID, and I don't know of any proximal femur characters preserved in the
specimen that would separate *Brachiosaurus* from, say, *Camarasaurus*.
And in fact a camarasaur ID has a lot to recommend it, in that
*Camarasaurus* femora have very offset heads (the ball- or cylinder-like
articular surface at the top end sticks out a big more to engage with
the hip socket--see Figure 12 up near the top of the post), moreso than
in many other Morrison sauropods, and that would make them better
matches for the Recapture Creek femur photo. Here's what the comparo
looks like:

::: {#attachment_7966 .wp-caption .aligncenter shortcode="caption" style="width: 940px"}
[![Recapture Creek - Camarasaurus
comparo](https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=930&h=1024){.size-large
.wp-image-7966 aria-describedby="caption-attachment-7966" loading="lazy"
attachment-id="7966"
permalink="http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/recapture-creek-camarasaurus-comparo/"
orig-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg"
orig-size="709,779" comments-opened="1"
image-meta="{\"aperture\":\"0\",\"credit\":\"\",\"camera\":\"\",\"caption\":\"\",\"created_timestamp\":\"0\",\"copyright\":\"\",\"focal_length\":\"0\",\"iso\":\"0\",\"shutter_speed\":\"0\",\"title\":\"\"}"
image-title="Recapture Creek – Camarasaurus comparo"
image-description="" image-caption=""
medium-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=273"
large-file="https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=709"
srcset="https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=436 436w, https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=137 137w, https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg?w=273 273w, https://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg 709w"
sizes="(max-width: 436px) 100vw, 436px"}](http://svpow.files.wordpress.com/2013/02/recapture-creek-camarasaurus-comparo.jpg)

The Recapture Creek femur fragment compared with a complete femur of
*Camarasaurus*.
:::

I make that a 2.07-meter femur using the photo on the left, and a
1.66-meter femur using the drawing on the right. The one decent femur in
the AMNH 5761 *Camarasaurus supremus* collection is 1.8 meters long, so
these results are surprisingly similar to those for the *B. althithorax*
comparison--the drawing gives a femur length shorter than the largest
known specimens, and the photo gives a length only slightly longer. A
camarasaur with a 2.07 meter femur would be 15% larger than the AMNH *C.
supremus* in linear terms, and  assuming isometric scaling, 1.5 times as
massive--maybe 38 tonnes to AMNH 5761's estimated 25. A big sauropod to
be sure, but not as big as [the largest
apatosaurs](http://svpow.com/2012/04/25/the-giant-oklahoma-apatosaurus-omnh-1670/),
and not nearly as big as the largest titanosaurs.

I have always been surprised that the Recapture Creek femur frag has
attracted so little attention, given that "Dinosaur Jim" himself called
it the biggest bone he had ever seen. But it appears that the lack of
attention is justified--whether it was a brachiosaur or a camarasaur,
and using the most liberal estimates the scale bars allow, it simply
wasn't that big.

**Update about half an hour later:** Okay, maybe I was a little harsh
here. IF the photo scale bar is right, the Recapture Creek femur might
still represent the largest and most massive macronarian from the
Morrison Formation (*Edit:* only if it's a brachiosaur and not a
camarasaur; see [this
comment](http://svpow.com/2013/02/28/how-big-was-the-recapture-creek-sauropod/#comment-28212)),
which is something. I suppose I was particularly underwhelmed because I
was expecting something up in [OMNH
1670](http://svpow.com/2012/04/25/the-giant-oklahoma-apatosaurus-omnh-1670/)-to-*Argentinosaurus*
territory, and so far, this ain't it. I'll be interested to see what the
actual measurements say (read on).

**The Moral of This Story**

So, if it wasn't that big after all, and if no-one has made a stink
about it being big before now, why go to all this trouble? Well, mostly
just to satisfy my own curiosity. If there was a truly gigantic
brachiosaur from the Morrison, it would be relevant to my interests, and
it was past time I crunched the numbers to find out.

But along the way something occurred to me: this should be a cautionary
tale for anyone who gets all wound up about the [possible max size of
*Amphicoelias
fragillimus*](http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/).
As with *A. fragillimus*, for the Recapture Creek critter we have part
of one bone, and at least for this exercise I was working only from
published illustrations with scale bars. And as with *A. fragillimus*,
the choice of a reference taxon is not obvious, and the size estimates
are all over the place, and some of them just aren't that big.

It always amuses me when *A. fragillimus* comes up and people ([well,
trolls](http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/#comment-27932))
accuse us of being [big ole' wet
blankets](http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/#comment-27320)
that just don't want to believe in 200-tonne sauropods. It amuses me
because it's wrong on so many levels. Believe me, when we have our
sauropod fanboy hats on, [we most definitely *do* want to believe in
200-tonne
sauropods](http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/#comment-27470).
That would rock. But when we put our scientist hats on, wanting and
belief go right out the window. We have to take a cold, hard look at the
data, and especially at its limitations.

Oh, the other moral is to go [buy a tape measure, and use
it](http://svpow.com/2009/04/23/mydd/). Sheesh!

**Coda**

As I said above, the obvious thing to do would be to just track down the
bone and measure it. It does still exist, it's in the BYU collections,
and Brooks Britt has kindly offered to send along some measurements when
he gets time. So we should have some real answers before long ([and here
they
are](http://svpow.com/2013/03/03/the-recapture-creek-sauropod-the-reveal/)).
But I wanted to work through this example without them, to illustrate
how much uncertainty creeps in when trying to estimate the size of a big
sauropod from published images of a single partial bone.

**Reference**

[Jensen, J.A. 1987. ~~What I did on my holidays~~New brachiosaur
material from the Late Jurassic of Utah and Colorado. Great Basin
Naturalist 47(4):
592-608.](https://ojs.lib.byu.edu/wnan/index.php/wnan/article/viewFile/1849/2197)

From Jensen (1987, page 604):  “In 1985 I found the proximal third of an extremely large sauropod femur (Figs. 8A, 12A) in a uranium miner’s front yard in southern Utah.  The head of this femur is 1.67 m (5’6″) in circumference and was collected from the Recapture Creek Member of the the Morrison Formation in Utah near the Arizona border.

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