Comments on BIG DEAD FISH etc

["Colin McHenry" <cmchenry@westserv.net.au>]

Dear list,

thanks for those who made comments (all constructive so far!) on the big
'big fish' post last week.  Just to summarise and repond briefly to some of
those..

Firstly, there were some questions about Devonian fishes (yeah, baby!)

>From David Marjanovic
>>It's *Xiphactinus* with only one n.

Funny, I've been reading and writing it as _Xiphanctinus_ for years.  Thank
you for the correction.  Just shows what happens when you read it wrong the
first time.  It's like the shock I got the other day when I realised that HP
Headdon isn't called Jamie....

>>Maybe *Dunkleosteus* had lungs, too... *Bothriolepis* had lungs, and some
new trees get Placodermi and Osteichthyes as sister groups.

I have a few problems with this.  I'm not a great subscriber to the "Extant
Pphylogenetic Bracket" line of reasoning, especially at this taxonomic
level.  Beyond perhaps giving you an idea of what anatomical configurations
you might want to consider in reconstructing the anatomy of a fossil
species, it runs the risk of quickly disappearing off into realms of
fantasy - it certainly should not be used to reconstruct anatomies in the
absence of other evidence. It's problematic enough when used it the level of
the Order (see, for example, the discussion of plesiosaur reproduction in
Darren's post that I referenced in the essay), never mind when used at the
level of the Class ("_Dunkleosteus_ might have had had lungs because some
bony fish have them"?! - perhaps I gaven't understood what you meant).

As far as lungs in _Bothriolepis_ go, I recall that the evidence for this
wasn't that robust (interpretation of some ambiguous stains on a well
preserved specimen), but I can't find the original reference so I may not be
doing it justice.  Anyway, even if _Bothriolepis_ did have an air breathing
organ, that says little about _Dunkleosteus_.  _Bothriolepis_ was  an
antiarch, and was a very different animal to the dinichthyid (spelling?)
arthrodires.  I do seem to recall some discussion about the small arthrodire
_Groenlandaspis_ having lungs, but I can't confirm this 'cos I don't have
the reference to hand.

In any case, there is much more to air breathing in fish than the vagarities
of inheritance.  There are many linneages of air-breathing fish.  Air
breathing teleosts include species of catfish, (_Clarias_), climbing perch
(_Anabas_), tarpon (_Megalops_), swamp eels (_Synbrachus_), mudskippers
(_Periophthalmus_) - more 'primitive' air breathing fishes include the
birchir (_Polypterus_), bowfins (_Amia_), and garpike (_Lepisosteus_) as
well as the true lungfishes.  Thus air breathing in fish is not an rare
habit.  As each of these examples have probably evolved air breathing
independently, they haven't acquired it through a common inheritance.  They
do, however, have much in common ecologically, living either in hot,
tropical rivers (lungfish, birchirs, catfishes, climbing perch, swamp eels),
stagnant lakes (bowfin, garpike), or mangrove swamps (tarpon, mudskippers) -
all environments where dissolved oxygen can become very rare.

Perhaps _Bothriolepis_ and _Groenlandaspis_ might have benefitted from an
auxillary breathing system, as their fossils are often preserved in
freshwater or estuarine sediments.  But _Dunkleosteus_?  To say, by
extension, that it could breathe air is as erroneous as suggesting that
coral trout can breathe air, just because climbing perch can.

>>What about *Titanichthys*, the supposed 23 m arthrodire? Is it a
misinterpreted *Dunkleosteus*?

Christian Kammerer also asked about _Titanichthys_;

>>>Thank you for that very informative piece on big swimmers. However, I
must
take issue with your statement that the time of _Leedsichthys_ was the
only pre-whale time when the largest aquatic vertebrate was not an apex
predator. The arthrodirous placoderms _Homosteus_, _Heterosteus_, and
_Titanichthys_ have long been suggested as filter-feeders, and they
equalled or exceeded _Dunkleosteus_ in size. Also, regarding no
"large" agnathans and acanthodians--you don't think that the largest
psammosteids (as best as I can tell, 1+ m swimming boxes of bone) and
acanthodians (3+ m) broke 100 kg? I know the coelacanth is a bulky fish,
but if it can weigh 100 kg, one would think that the big gyracanthids and
ischnacanthids could have.

This is where my 'knowledge' of arthrodires comes grinding to a stop.  I
have to admit that I am not familiar with _Titanichthys_, _Homosteus_, or
_Heterosteus_, either in terms of their reconstructed size or feeding
ecology.  Can anyone educate me on these?

Regarding _Dunkleosteus_ and the other dinichthyids (_Dinichthys_,
_Gorgonichthys_), I have come across a large range of size estimates (from 4
metres to 9 metres) for these animals.  Does this reflect poor understanding
of fragmentary fossils, or the 'text-bookisation' [[o[of unreliable and
exaggerated estimates (like the ones that give us 9 metre salties and white
sharks - I was amazed, when checking up on some stuff for the big essay, to
still see 9 metres being reported as a maximum length for salt water crocs
and great whites by people who really should know better).  Does anyone know
of good estimates for these species please?

As for the other taxa mentioned, I suppose the large agnathans deserve
mention for being large agnathans, and I would expect that a 3 metre
acanthodian would weigh more than 100kg.  A 3.5 metre carcharhinid shark,
such as _Carcharhinus leucus_ for example, will weigh between 200 and 250kg.

This from from Mike Everhart

>>>Just wanted to mention that Xiphactinus probably grew to 6 m or more.
I'm reasonably sure of that claim since I found a very complete one in
Kansas that turned out to be about 5.2 m (it's now in a museum in Utah):
< http://www.oceansofkansas.com/images2/big-xip6.jpg >
...and there are larger vertebrae found in Arkansas.

You just gotta love that fish!  I'll never forget seeing the fossil of a 4
metre Xiph at Boulder with a 2 metre squid pen stuck in its throat.  That's
the sort of attitude that leaves it's modern namesake's bill stuck in blue
whales and nuclear submarines...

I'll probably turn in my grave over some of those size/weight estimates, but
in the context of the earlier essay I would guesstimate a 6 metre
Xiphactinus as weighing in around 1,500 - 2,000 kgs (i.e., slightly lighter
than a white shark of the same length).

>>>... and the 7 m. length of Cretoxyrhina mantelli is very nearly
correct.. just found one that size in the Smoky Hill Chalk:
< http://www.oceansofkansas.com/BigShark.html >
... if they got larger in North America, they didn't leave any shed
teeth lying around.

Picking up on the thread on the vrtpaleo list a couple of weeks back, about
why the teeth of _Cretoxyrhina_ seem small for a 7 metre white shark, that
reminds me of a question I posed to Noel Kemp (Australian fossil shark guru)
a few years back.  I was wondering why, in the Queensland Lower Cretaceous,
we had evidence of a big (> 5 metres) lamniform from vertebrae, but no big
teeth to go with it.  His response was the pretty obvious "well, maybe they
didn't specialise on big animals.." (D'oh!).  Actually, he was very patient
with me, and even suggested that it the big Lower K lamniforms might have
been chasing plankton.  I never followed it up, but maybe the early
lamniforms were eating smaller fish and squid, and managed to move to the
mega predator niche after the marine reps fell off the twig?  Anyone out
there got anything to add (Mike?).

>>>Mosasaurus hoffmanni is documented at about 17 m.... really huge in my
book, although more of a big snake in body plan... Hainosaurus, a
johnny-come-lately tylosaurine reached 15 m during the Maastrichtian
.....
That's bigger than I had realised...in the context of my essay, that puts it
up into the Basilosaurus territory.  Curiouser and curiouser.

>>>Also, we do have fetal material in mosasaurs (South Dakota) and
mosasauroids (Italy), and I have seen fetal material in a Late
Cretaceous pliosaur (Dolichorhynchops) from the Pierre Shale of Kansas
(in the L.A. Museum of Natural History, but not reported yet).

I hadn't heard of the Dolichorhynchops material.  What's the story with
that?

>>>Can't see a big plesiosaur or mosasaur dragging itself up on land, in
any case.

According to the (very basic) biomechanical arguement I was trying to
develop, I would predict that mosasaurs might not have been able to, but
that plesiosaurs might have been able to!

>>You didn't mention thermo-regulation (failure) as a barrier to large
marine reptiles that do have to crawl up on land to lay eggs... I'd
heard someplace that was probably the reason why Protostega / Archelon
didn't get any larger.... they couldn't dump heat fast enough when out
of the water..... anything to that?

Hadn't heard of it, but I think it's unlikely.  Remember that _Dermochelys_
is capable of foraging in cold water but can nest on equatorial beaches.
Thing is, turtles tend come up onto beaches at night, and it does cool down
a lot then.  A good fleece jacket is advisable for anyone working on nesting
beaches in Queensland, for example, especially if you're at the southern end
of the reef and it's early or late in the season.  The nesting season, BTW,
goes smack through the middle of summer.  I don't think a five tonne turtle
would have any problems with over-heating in the few hours it takes to dig
the nest and lay the eggs - in fact, its increased thermal inertia should
help _prevent_ it from getting too hot.

>>>Any feel for the use of gastroliths as buoyancy control? .... I don't
see it, considering their relatively small mass compared to that of the
animal... more likely just there as grinders....

This follows on from some of Mike Taylor's (no, the other one - currently at
the National Museum of Scotland) work on diving strategies.  As it happens,
Alex Cook and I have something in late stages of prep on gastroliths in
plesiosaurs.  As for what they are _for_, I don't think that that is the
best question.  The issue is, what are the consequences of the use of
gastroliths upon the animal?  The answer is, of course, that gastroliths are
going to have an immediate effect on buoyancy and will in all likelihood
have an effect on digestion as well.  Note that in extant sea-lions and
penguins (which are possible modern ecological analogues for at least some
plesiosaurs) the use of gastroliths seems to correalate better with diving
strategy than with diet.


>From: darren.naish@port.ac.uk <darren.naish@port.ac.uk>
Date: Thursday, 6 June 2002 11:21
Subject: BIG DEAD FISH etc


>_Leedsichthys_: the osteology, affinities etc of this fish are
currently being reviewed by Jeff Liston (Hunterian
Museum). ...
>The 'Sikanni ichthyosaur' (Manabe and Nicholls, in press I
believe) is not a shastasaur (neither in the traditional sense
nor in the sense of it being a cymbospondylid or basal
merriamosaurian) according to Makoto Manabe. The photos
and reconstructions do indicate that it was not unlike
_Cymbospondylus_, _Phantomosaurus_ etc in proportions.


Looking foward to these coming out.  Congratulations to Jeff in particular
for taking on the huge (and often thankless) task of sorting out the big
fish, and for getting somewhere with it.  'On ya, mate.

>Giant pliosaurs (again): Martill and I recently borrowed the
giant vertebrae from Peterborough and have been describing
them. Based on comparisons with near-complete skeletons,
we estimate they belonged to an animal 15-17 m long. Dino
Frey and Marie-Celine Buchy have just submitted an MS on
a similar-sized pliosaur from Mexico. Both of these animals
appear to be pliosaurids s. s. (ie. sensu O'Keefe).

Providing you're not basing that estimate on the 13 metres for _Kronosaurus_
that we used in the 1996 abstract, then that  _does_ sound interesting.  I'm
going to leave the final word on the identity of the Peterborough vertebrae
to others, but I think that size estimates based from the vertebrae are more
reliable than those from scrappy bits of jaw.  The vertebrae probably do
scale pretty well with overall body size, but with the pieces of jaw there
is always the possibility of some wierd allometry assciated with late
ontogeny (as we see in crocs, for example).

>>Size of giant rhinos - _Paraceratherium_ (correct name for
_Baluchitherium_, _Indricotherium_ etc according to Lucas
and Schoch) is no way 30 tons. 10-16 tons is more like it.
See Fortelius, M. & Kappelman, J. 1993. The largest land
mammal ever imagined. _Zool. J. Linn. Soc._ 107, 85-101.
Also estimates by Greg Paul in various of his papers.


That sounds more realistic than the 30 tonnes I got out Doug Palmer's
'Encyclopedia of Dinosaurs and Prehistoric Animals'.  Thanks for the ref.

>>Terrestrial locomotion of giant seals and plesiosaurs: this is
very much on my mind at the moment as Dave and I
actually had a huge row about it the other day (plus Stig and
I have recently been working on monachine pinnipeds and
thus have been looking at _Mirounga_ and kin quite a bit).


There are many things worth have a huge row with Martill about, but I don't
think plesiosaur locomotion is one of them.  Don't get too caught up in it -
I can argue myself around in circles about that topic.  There's as much good
evidence/reasoning for as there is against.  At the moment, we might have to
admit that we don't know.

>>>Maybe< if _Mirounga_ wasn't around we might doubt it's
ability to move on land, but not necessarily. Unlike
plesiosaurs, elephant seals still have an intact sacrum and
sacroiliac contact, and also flexible, distally well-muscled
forelimbs with a mobile elbow and foldable fingers. I think
the conclusion from a fossil one would be: it probably could
move on land, but it would have been one hell of an effort.
This is not different from what some people say about
plesiosaurs, even though plesiosaurs lack such features and
are arguably more committed to an aquatic lifestyle.


Okay, I was trying to make a point about over-emphasising our prejudices
when it comes to biomechanical reconstructions of extinct body-plans, but I
take your point.  Anyway, i'm gald that you're having a good look at these
seals, they're amazing animals and well worth the effort.

>>And given that harem-based polygany, marked sexual size
dimorphism, terrestrial moulting and terrestrial pupping are
all ubiquitous throughout pinnipeds, the hypothetical
absence of monachines or even all phocids from the extant
fauna would not stop us from thinking that _Mirounga_
could move on land in an imaginary world where this
animal was only known as a fossil (BTW, it's been
suggested that pinnipeds cannot become fully aquatic
because of the above constraints).


Ah, the tangled web of cause and effect...And without wanting to get bogged
down in this, but you're in a catch 22 with some of these (admittedly very
important) factors...you only know that they are ubiquitous in pinnipeds
because phocids are extant.  Moulting and pupping don't leave much of an
anatomical signature.  Harem-based polygamy is not the only strategy used by
seals (even elephant seals play around with this; gamma males that can't
establish territories on the pupping beaches _do_ mate with females in the
water when the females are moving to/from the beaches), and mating
strategies can vary markedly with subtle differences in ecology, evidence
for which is unlikely to be preserved in the fossil record.  And look me in
the eye and tell me that you wouln't assign fossils of male and female
_Mirounga_ to different species...

If you were going to try to establish that our hypothetically extinct
monachine _did_ in fact come onto the land, the best way to do this (short
of indisputable tracks) is through rigorous biomechanical analysis of its
locomotor capabilities.  And even then, that is only telling you what it was
capable of doing, not what it _did_ do.

It is the same (unfortunately) for plesiosaurs.  If we were to establish
that, biomechanically, even the large ones were capable of coming up the
beach (which I suspect they might have been), that doesn't mean that they
actually did.  The only way to settle the plesiosaur reproduction debate is
to find direct evidence either way - which I'm reasonably confident will
happen, as long as we keep looking.  Dave's arguement of egg laying based on
absence of pregnant female plesiosaurs _is_ cobblers, however. Just because
we are very fortunate in having an ichthyosaur pupping ground preserved as a
lagerstaten (i.e. Holzmaden) doesn't mean that any animals not caught in the
act of reproducting there didn't reproduce.

>>Self-beaching in cetaceans: best known for killer whales,
but not unique to this species - there is one population of
_Tursiops_ that also self-beaches and belugas are known to
stay motionless in water less than 30 cm deep after
intentional and unintentional stranding. _Inia_ is
anecdotally reported with the ability to cross emergent sand
bars.


I was aware of the belugas (I just forgot); didn't know about the _Tursiops_
or the _Inia_.  Any refs?

>>Laying eggs in water: Colin points out that some snake-
necked turtles do this. Apparently laying shelled eggs in
water is not such a problem as traditionally thought. A
must-read on this is... Skulan, J. 2000. Has the importance
of the amniote egg been overstated? _Zool. J. Linn. Soc._
130, 235-261.


Wasn't aware of this one, either - thanks again.

Finally, Colin, I would have loved to do a presentation with
you at SVPCA 2002. Sadly the deadline for submissions
was some weeks ago.



Colin McHenry
56 Gaskill St
CANOWINDRA,  NSW 2804,  Australia
Ph: +61 2 6344 1009
Mobile phone: 0428 131 858
email: cmchenry@westserv.net.au