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Re: Monster of Aramberri

B B wrote:

I have been trying to find out some details of a the Pliosaur (Liopleuodon?) from Mexico that has been named in the press as the Monster of Aramberri (forgive me if my spelling is off). As it stands I have found a lot of nonspecific or contradictory facts. Here is what I am wondering:

Have you seen the entry on Richard Forrest's plesiosaur site? http://www.plesiosaur.com/aramberri.htm . I would consider this to be one of the more reliable sources on the web, in the absence of any actual papers on the specimen. There is a link to a pdf of a conference abstract by Dino Frey et al., which appears to be the only published account thus far.

1.) How big is it? (I have read consistantly that the lower jaw was 10 feet long, but the total length reports vary between 16 meters and 25 meters)

They detail a pectoral vertebrae of 22 cm diameter, which (at a guess,) puts it into the 13 - 16 metre range

2.) How complete is it?

not very

3.) Has it been described? If so where can I find a copy of the description?

not yet

4.) I heard that, "This specimen may require a re-evaluation of the size of other pliosaur specimens." Does anyone know specifically what this statement refers to? (do they mean head to body ratio or some other system of body mass estimates?)

I have no idea what that might mean

5.) is it Liopleurodon sp, Liopleurodon Ferox, another pliosaur taxa entirely, or a new taxa?(I have read most often that it is Liopleurodon sp.)

As Richard emphasises, it's unlikely to be Liopleurodon, which is Callovian and according to Leslie Noe monotypic.

6.) Does this have anything to do the the huge Liopleurdon size given in Walking With Dinosaurs?

No - that estimate was based upon;
1. A possibly incorrect re-identification of a large vertebra from the Oxford Clay (Callovian) at the Peterborough Museum, previously identified as a 'cetiosaurid' caudal, as a pliosaur cervical by McHenry, Martill, Cruicksank, and Noe. The vertebra is 24 cm across - which, by comparison with Kronosaurus, gave us an estimate of 15 - 18 metres - _if_ it is pliosaurian...

2. A really huge, robust mandibular symphysis from the Oxford Clay (in the BMNH collection),

3. The incorrect assignment of the Oxford mandibles (which are 'Stretosaurus' macromerus, see below) to Liopleurodon. The size estimate of that animal is about 15 - 16 metres. This lead to..

4. Dave Martill is (or at least, has been in the past) quite comfortable with 'upsizing' maximum size estimates - the logic being, if the specimen you've got is X long, then given that it is unlikely that you've got the biggest individual of that species, you can say that the species grew to Y metres long. It is not a practice I would agree with unless it's late, the bar is full, and the Guinness is good (and it's Dave's round). Anyway, when he was consulting with WWD (and this is according to Darren Naish) used a guess of 15 - 18 metres (which he based upon the three specimens listed above) and gave them a total length for Liopleurodon of 25 metres. There is, however, no evidence for any pliosaur getting to this sort of size.

5. The mass estimate of 150 tonnes was all Tim Haines' - apparently he saw that blue whales are about that size (25 m is a small blue) and then came up with the weight estimate based upon blue whales. However, the estimates for 150 tonne weights in blue whales is baed upon animals larger than 30 metres long. A 25 metre blue would be about 75 tonnes (but there would a large range). Given that pliosaurs are not as bulky as a roqual, a theoretical 25 metre pliosaur would probably be around 50 tonnes. But remember, there is abosutely zero fossil evidence for pliosaurs getting that big. The largest pliosaur based upon anything like complete remains is Kronosaurus boyancensis, which is about the 10 metre mark (the tail's not preserved, so it's hard to be sure, but the snout - hips length is approx 8 metres.) Even if the various fragments from the Middle and Upper Jurassic turn out to be pliosaurs, not of these really suggest anything bigger than 15 - 16 metres long.

7.) Does anyone know what formation or age this specimen is from? (I know it is Late Jurassic, other than that I don't know anything more detailed)

They give the stratigraphy as being the La Casita Fm, which is apparently Kimmeridgian. This takes it well outside the documented range of Liopleurodon, and into the same age as some other biggies, such as Pliosaurus brachyspondylus, 'Stretosaurus' (= Pliosaurus?) macromerus, and Megalneusaurus rex. The first of these is well described, but is not believed to get any bigger than about 8-10 metres. 'Stretosaurus' macromerus is a taxon in need of revision that has had a load of large Kimmeridgean bits and pieces assigned to it, including Owen's 'Pliosaurus grandis' and the famous 3 metre Oxford mandibles. On the basis of the Oxford jaw, it may have reached 15 - 16 metres. Megalneusaurus rex is still(?) under revision by Bob Bakker, but is probably only slightly bigger than Kronosaurus (i.e. up to 12 metres) and may be the same thing as Stretosaurus. I doubt there were three genera of giant pliosaur in the Kimmeridgean, but you never know...

This subject appears to have arisen periodically on this list and the vrtpaleo list. Check out the on-line artcile by Ben Creisler (I don't have the url handy), and see the relavent chapter in Richard Ellis' book. Also (because the vrtplaeo list doesn't have archives), pasted below is a post I made a couple of years ago. Note Leslie's comments on the Oxford jaws. In the meantime, we look forward to a publication on the Aramberri animal.


-- ***************** Colin McHenry School of Environmental and Life Sciences (Geology) University of Newcastle Callaghan NSW 2308 Tel: +61 2 4921 5404 Fax: + 61 2 4921 6925

Colin McHenry & Sarah Johnston
14 Summer Place
Merewether Heights  NSW 2291
+61 2 4963 2340
mob: 0423 081683


-------- Original Message --------

Subject:        Re: Li_o_pleurodon size
Date:   Mon, 28 Oct 2002 22:56:15 +1100
From:   Colin McHenry <cmchenry@westserv.net.au>
To:     <vrtpaleo@usc.edu>

Hello all - finally got around to finishing this message. Apologies for the

Christine Janis wrote;
> I'm showing some of the Walking With Dinosaurs movies to my
>students ---- and need to know something about Lipleurodon (the giant
>plesiosaur). Was it *really* 25 meters long (i.e., bigger than the
>average blue whale)?

And Leslie Noe wrote; >The largest skull is from the Callovian Stage (or just >possibly Oxfordian Stage) Oxford Clay Formation of Peterborough, England >(NHM R3536) and is about 1.5 metres long, suggesting an animal no longer >than 9.5 metres - similar in size to a modern killer whale.

As others have indicated, there is no strong evidence that _Liopleurodon_ (traditionally represented by two described species, _L. ferox_ and _L. pachydeirus_) exceeded 11 metres in overall length. Most of the described material of these two species seems to come from animals of a slightly smaller size - the skull that Leslie refers to is smaller than QM F18827, which is a complete skull of _Kronosaurus queenslandicus_, and has a mid-line length of 1.89 metres. By comparison with _Kronosaurus boyacensis_, the _K. queenslandicus_ skull appears to be from an animal 10.5 - 11 metres long. Most of the _Liopleurodon_ material that I have seen (at Leicester and the NMH) seems to be from animals 8-9 metres long.

An exception to this is a large tooth that Leslie showed me when we were
going through the NMH collections - referable to _L. pachydeirus_, if I
remember correctly. It's about 30cm long (inlcuding the root, which is
about 2/3 of the total length of the tooth. 30 cms is the size of the
largest teeth in QM F18823 (1st and 2nd maxillary teeth), implying that this
specimen of _L. pachydeirus_ reached at least the same skull size as a large
_Kronosaurus_ (because of the slight differences in the proportions of the
rostrum between these two taxa, the _Liopleurodon_ may even have been
slightly larger than the _Kronosaurus_).

>The mandible in the Oxford University Museum (from the slightly younger
>Kimmeridgian Stage, Kimmeridge Clay), attributed to 'Stretosaurus' later
>referred to Liopleurodon is reconstructed at almost 3.0 metres, suggesting
>an animal of perhaps 18 metres (making lots of assumptions). However in my
>humble opinion this specimen cannot be attributed to Liopleurodon, the
>reason for which I am in the process of writing up. This jaw was the basis
>for the 25m length in the BBC's WWD, with the belief that we are unlikely
>to have found the biggest one yet!

Three metres certainly sounds large for a pliosaur skull, but before anyone
gets too excited you need to remember that pliosaur mandibles are much
longer than the skulls to which they belong. Pliosaur skulls are often
reported as mid-line lengths, but the quadrates lie well behind the line of
the occiput, and the retro-articular process of the mandible extends well
behind the quadrate. So, for example, the mandible of QM F18827 is about
2.2 metres long - even though the length (mid-line) of the skull is under
1.9 metres. Assuming that QM F18827 is from an 11 metre pliosaur, and that
the Oxford University Museum specimen would have had the same proportion of
mandible - body length as QM F18827, then you get an estimate of 15 metres
for the Oxford animal. A 15 metre pliosaurid would probably have weighed
20 - 25 tonnes.

However, pliosaurids (such as the Oxford specimen of 'Stretosaurus') and
brachaucheniids (such as _Kronosaurus_) probably did not have similar ratios
of mandible - overall body length. The head of a brachaucheniid is a larger
proportion of body length than in pliosaurids - thus the Oxford animal was
probably nearer to 15.5 - 16 metres in length.

When Leslie and I were first discussing the possibiliity of 15 metre plus
pliosaurs in the Oxford Clay, our (very scratchy) calculations indicated
that the Peterbrough vertebra (if it's not a cetiosaur!) might, at a
stretch, have indicated an animal of 18- 20 metres; and that a very fat 20
metre pliosaur _might_ get up to 50 tonnes in weight. According to Darren
Naish, this length was exaggerated by Dave Martill to 25 metres when he was
consulting for WWD. Apparently, Dave was annoyed that they took the length
estimate they gave him, but instead of believing the weight estimate of 50
tonnes that he supplied they went off and found a wieght estimate of 150
tonnes for a blue whale (which they seem to claim was about the same size).
Richard Ellis and Ryosuke Motani have already pointed out how unreliable
weight estimates of blue whales are, but I seem to recall that the female
blue whale which has sometimes been used to justify a wieght estimate of 150
tonnes for blue whales was more than 30 metres long. As most of you will
know, it takes only a 25% increase in length to obatin a 200% increase in
mass - thus a blue whale that is between 31 and 32 metres long would be
twice as heavy as a blue whale that is 25 metres long. Like Mssrs Naish and
Martill, I doubt that a 25 metre pliosaur would be as heavy as a 25 metre
blue whale.

>However, this does leave some VERY big pliosaurs in both the Oxford and
>Kimmeridge Clays, so for some more exciting size estimates for pliosaurs,
>hopefully based on reasonable assumptions watch this space (more writing in

I agree with Leslie that there is evidence of large pliosaurs in the Oxford
and Kimmeridge Clays. The taxa known from nearly complete remains -
_Liopleurodon ferox_ from the Oxford, _Pliosaurus brachyspondylus_ from the
Kimmeridge don't appear to have got any bigger than 10 metres in length.
However, as I have mentioned, there is a very large isolated tooth -
referred to _L. pachydeirus_ (Lez, please correct me if I'm wrong) from the
Oxford Clay. Similarly, the material of Owen's _Pliosaurus grandis_,
from the Kimmeridge Clay, includes a 30 cm tooth. _P. grandis_ has for
been synonymised into _P. macromerus_ - I look forward to Leslie's opinion
on whether or not this has been correct.

As for that (large) fragment of mandibular symphysis, well, as Leslie and I
pulled it off the shelves at the NMH we said it was big, and it is. It is a
very important specimen, because it shows that either;
1. Liopleurodon-type animals did in fact exceed 15 metres by a comfortable
2. Large Liopleurodon-type animals underwent a late ontogenetic
'megacephaly', as is the case in some crocs. This would be the first time
that this has been observed in a pliosaur.
3. Something else we haven't though of yet...like a normal 8 metre pliosaur
with a grotesquely disproportionate symphysis, like some sort of Pythonesque
spoonbill with sharp, pointy teeth.

Hopefully Leslie will be able to shed some light on this, and the other
large pliosaurian material, before too long.

> I seem to recall at the time of showing some people saying
>that this was a "Hubble telescope" type of error --- i.e., a direct
>translation of feet into meters without actually doing the numerical
>conversion (something that the charming editors of "The Book of Life"
>did to my chapter in that volume!)

I don't know about Hubble - wasn't this the sort of mistake made in
communications between JPL and NASA which killed one of the Mars missions a
couple of years ago? Anyway, I don't think that an error of this sort is
responsible for the exaggerated _Liopleurodon_ dimensions in WWD. There is,
however, an example of something of the sort in connection with White's 1935
account of the MCZ _Kronosaurus_. The following is taken from an account of
my examination of the MCZ mount;

"The last point to make about the skull involved a couple of critical
errors made by White in his 1935 paper which have managed to become firmly
established in the palaeontological and popular literature ever since. He
states that the length of the skull is 3720 mm, and gives the imperial
equivalent of this measurement as 9 ft., 8 in. Now, 9' 8" is a very, very
big skull by anyone's standards - but a 3.7 metre skull is even bigger.
3720 mm is actually 146 inches, or 12' 2"! Nine feet eight inches converts
to 2946 mm (116").

"Now, you might assume that White, working in the U.S., would have been
working in imperial measurements, and just got his conversions stuffed up.
The problem with this is that the skull of the MCZ mount is nothing like 9
feet long. It looks that big in the famous picture with the lady in the red
dress standing beside the skull, but that lady - who just happened to be a
certain Mrs Romer - was apparently rather short. When I measured the skull
in the MCZ mount I got a measurement of 87 inches (7' 3", or 2210 mm) from
the snout to the occiput. The distance from the snout to the back of the
mandible is 103 inches - 8' 7", or 2616 mm. Of course, that doesn't mean
that the actual skull of this specimen was that size; I suspect it was at
least 250 mm shorter."


"If the vertebrate fossil record of Australia tells us anything, it is this;
dinosaurs, bad; plesiosaurs, good."

Colin McHenry
56 Gaskill St
CANOWINDRA, NSW 2804, Australia
Ph: +61 2 6344 2446
Mobile phone: 0428 131 858
email: cmchenry@westserv.net.au

-- ***************** Colin McHenry School of Environmental and Life Sciences (Geology) University of Newcastle Callaghan NSW 2308 Tel: +61 2 4921 5404 Fax: + 61 2 4921 6925

Colin McHenry & Sarah Johnston
14 Summer Place
Merewether Heights NSW 2291
+61 2 4963 2340
mob: 0423 081683