By now most SV-POW! readers will have heard of Leviathan melvillei, the big-toothed Miocene sperm whale that was named in Nature today (Lambert et al. 2010) — if not, see for example the Discover Magazine blog article for the basics.

My first thought was “Wow, that is one awesome animal.”

My second was, “I can’t believe no-one’s used the genus name Leviathan before”.

So I checked for Leviathan on the super-useful Nomenclator Zoologicus, only to find that indeed it seemed to be, if dubiously, preoccupied:

But it’s really not clear what’s being said here: the relevant page from the printed edition says “Levathan Koch [1841], Descr. of Missourium, 1840, 13 (as Leviathan p. 14). — Mamm”.  The use of italics suggests that the NZ editors considered the name as nomenclaturally valid, but the relation between the names Levathan [sic] and Leviathan is not clear.

Looking around a bit more, I found Lindsay (1991) which happens to discuss the specimen in question, and at least some of the publications.  The first page of this article is freely available and says:

The mastodon’s remains had been discovered by Albert Koch in 1840 on the Pomme de Terre River in Benton or Hickory County in Missouri, and possibly parts were from Jefferson County as well.  A skeleton was assembled later that year in Koch’s St. Louis museum and went on display as the Missourium or Missouri Leviathan.  Koch also referred to the specimen as Levathan [sic] Missourii (1841) and Leviathan Missouriensis (1843), by which time he had also given it the name Missourium Theristocaulodon on account of “its enormous sickle shaped tusks”.

[Update, 1st July. It's now apparent that Lindsay (1991) overlooked a passage in the 1841 first edition of Koch's pamphlet in which he established the name Leviathan two years before the 5th edition in which its name was included in the expanded title.  Thanks to Christopher Taylor for pointing this out.]

The first thing to note is of course that Koch was a truly horrible taxonomist.  He proposed three distinct genus names for a single specimen in a space of three years, and as in fact became apparent subsequently, they are all junior synonyms of Mammut, the mastodon.  The second thing to note is that he was a truly horrible palaeobiologist, concluding for spurious reasons that his specimen was an aquatic animal (hence his use of the name of the biblical sea-monster).

But of course the ICZN doesn’t care about taxonomy, far less palaeobiology — only nomenclature.  So the question for us is only this: was the name Leviathan validly published as a scientific name?

I don’t know whether Lindsay addressed this question, as I only have the first page of his article (and if anyone who has access can send me the whole thing I’ll be grateful).  But now that I knew to search for the relevant date, 1843, I was able to find Montagu and Peterson (1944), which contains the answer:

Sometime during 1843 Koch took his collections to Ireland where they, together with the Missourium, were exhibited at Dublin.  Here appeared the “Fifth edition, enlarged,” of his pamphlet together with a new title-page and a completely rewritten and revised text [25].

And note 25 is the full reference:

Description of the Missourium Theristocaulodon (Koch) or Missouri Leviathan (Leviathan Missouriensis,) together with its supposed habits, and the Indian Traditions: also, comparison on the Whale, Crcocodile, and Missourium, with the Leviathan, as described in the 41st Chapter of the Book of Job; by Albert Koch.  Printed by C. Crookes, 87 Chapel Street, Dublin: 28 pp., 8°, 1843.

It seems apparent from the typography here — with the words “Leviathan Missouriensis” being the only words of the title set in italics — that Koch was indeed publishing this as a scientific name.

Just to reiterate: if the name was validly published according to the tenets of the ICZN, then the genus name Leviathan Koch 1843 is nomenclaturally valid even though taxonomically it’s junk, being a junior objective synonym of Levathan Koch 1841 and a junior subjective synonym of Mammut Blumenbach 1799.  And if it’s nomenclaturally valid, then that name is preoccupied, and Lambert et al. will need to propose a replacement name for their awesome whale.

Important disclaimer

All of this is based on glimpses of single pages and suchlike of the various relevant papers: I don’t have the full text of Lindsay (1991) or Montagu and Peterson (1944), and I have never clapped eyes on the crucial Koch (1843) at all.  So it’s perfectly possible that I’ve overlooked something, and the genus Leviathan Koch 1843 was not validly published.  This should definitely by confirmed or denied by someone who has a copy of that publication.

But at the moment, things aren’t looking good for Leviathan Lambert et al. 2010.

References

Cleaning and bleaching is complete!  Here are all the bones of Veronica’s skull [see earlier part one, part two and part three], laid out as they were in life (though of course much more widely separated), all in dorsal view:

On the left, we have the bones of the lower jaw, palate and braincase, with the first three and a half vertebrae at the bottom.  At the top is the mandible, which is intact on the left side but has separate articular, angular and surangular on the right; between the mandibles are the hyoid bones, of which one of the cartilaginous extensions has survived.  Behind those on the midline are the fused vomers, parasphenoid rostrum and braincase, all fused together.  Alongside this element are the palatines and pterygoids, and to the right of those are the midline supporting cartilage and mesethesmoid ossification.  Behind the braincase are the first three and half vertebrae of the neck.

On the right, we have the superficial bones.  Reading down from top to bottom of the midline, we have the premaxilla, nasals, lacrimals, frontals, parietals, and (out towards the sides) squamosals; from top to bottom down the sides we have the premaxilla (again), maxillae (the left one broken in two), the jugals and quadratojugals (which are still fused together on the right) and finally the quadrates.

That’s everything!  My next tasks are:

  • Repair the three broken bones: left maxilla, left posterolateral process of the premaxilla, and left lacrymal.
  • Photograph every individual bone from all six cardinal directions and maybe some interesting oblique angles.
  • Put the skull back together.
  • Photograph the entire skull, including 3d anaglyphs.

Then I think I’ll be done.

Special bonus encouragement

A few articles back, Zach Miller commented:

You lucky bastard! First a monitor lizard, now this? I’ve really GOT to get some kind of deal going with my local zoo. :-)

Lucky?  Nothing to do with it!  One of the points I keep meaning to make in the Things To Make And Do series is how very much this is something anyone can do.  Well, OK, I admit I was super-lucky to score the monitor lizard; but I got the pig’s head by walking into a butcher’s shop and saying “One of your finest pig’s heads, please, my stout yeoman!”.  I got Veronica by googling for “ostrich farm” and emailing the ones in the UK asking whether any of them had any heads to spare. I urge you, and anyone else who loves anatomy, to do the same.

Anyone can do this!  You don’t need qualifications, or even experience; this is how you get experience.  Seriously, I’ve learned ten times more about dinosaur skulls in the last week from playing with Veronica than I did in the last five years of feeling guilty that I never read any head-related papers.

For reasons that seemed good to me at the time, I took my best shot at photographing the right cervical rib from cervical vertebra 3 of my ostrich, Veronica [see earlier Part A, Part B and Part C for context].  I thought you might like to see the result, so here it is:

Third right cervical rib of subadult female ostrich (Struthio camelus), total length 23 mm. (Total length of the rib, I mean, not total length of the ostrich.) Left column: anterior view; middle column, top to bottom: dorsal, medial, ventral and (inverted) lateral views; right column: posterior view.

For some reason, cervical ribs don’t seem to get a lot of love in the literature: the only paper I know that figures them in half-decent detail is Osborn and Mook’s classic (1921) monograph on Camarasaurus, and even there, the job is done in rather a half-hearted fashion.  I’m planning to buck this trend by properly figuring the cervical ribs of the Archbishop when I finally get around to finishing that paper, and I included a sneak preview of the rib that I’ve arbitrarily designated X1 a while back.  It’s instructive to compare that illustration with this one.  In fact, here it is again:

Brachiosauridae incertae sedis NHM R5937, "The Archbishop", cervical rib X1. Preserved portion is 32 cm long. Top row: anterior view (dorsal to left); middle row, left to right: lateral, dorsal, medial and ventral views (all with anterior to top); bottom row: posterior (dorsal to left)

Enjoy!

Update (the next day)

It occurs to me that I should have composed the ostrich-cervical-rib illustration in the same orientation and order as the Archbishop one, for easier comparison.  So that’s what I’ve done below.  Since the Archbishop rib X1 is from the left side, I’ve also flipped the right-sided ostrich rib to match.  Here it is:

Third right cervical rib of subadult female ostrich (Struthio camelus), reversed, total length 23 mm. Top row: anterior view (dorsal to left); middle row, left to right: lateral, dorsal, medial and ventral views (all with anterior to top); bottom row: posterior (dorsal to left)

After the third simmering, Veronica the Ostrich Head started to come apart beautifully — more so than she should have done in one or two places, as it became apparent that her skull, as well as being incompletely fused due to presumed subadult age at time of death, was slightly damaged.  Still, I’ve been able to tease the bones apart nicely, remove pretty much all the remaining soft tissue, and figure out where most bits go, well enough that I think I’ll be able to put her back together once everything’s been cleaned.

[Anyone who's not yet read parts one and two of this ostrich-head series should probably do so before going on to this one -- apart from anything else, the pictures will make more sense that way.]

Here’s my girl as she emerged from the pot (cranium only — the mandible was separate by this point).  What may not be apparent here is just how fragile she was by this stage: I had to hold her snout as well as the main part of the skull to prevent it from falling off.  You can see that it’s skewed a little sideways, rotating clockwise with respect to the rest of the skull so that the posterodorsally oriented midline “tongue” of bone is off to the left (our right), and lies alongside the central bulging bone rather than overlying it as in earlier stages.

The squamosals are still in place at the sides of the back of the skull, but they came away very easily, and cleaned up nicely.

I carefully removed the snout, and was astounded to see how very thin the bones that connect it to the rest of the skull laterally are:

The midline bone here apparently is the fused ascending processes of the premaxillae, despite my having said last time that it probably wasn’t — thanks to Nick Gardner for putting me straight.  but what are the posterolaterally directed spines?  Can they also be processes of the premaxillae?  Or are they the maxillae?  I think the former: read on.

It’s hard to tell in part, of course, because of the horny beak which obscures whatever sutures might be up there at the front of the skull.  I don’t want to remove that, partly for fear of causing damage to the bones but mostly just because it’s nice to keep.  What I’d not appreciated until I started this exercise is that there’s no hard demarcation between beak and soft-tissue, but they grade into each other so that the posteriormost preserved parts of the beak are not horny at all, but rubbery — even stretchy.  It’s hard to know how much of this to remove.  If there’s a Standard Operating Procedure, I don’t know it — anyone?  Maybe I’ll leave the snout in a bug-box and let the dermestids decide.  (Let the Dermestids Decide would be a good title for a debut novel, and its Oscar-winning movie adaptation.)

(Of course this continuous gradation between tissue types is familiar to all of us who’ve ever tried to remove the cartilage from a skeleton: in some cases, like the cartilage caps on long bones, there’s clear bone and clear cartilage, but in other cases it’s not so well-defined.  Think, for example, of the partially ossified but partially cartilaginous breastbone of a chicken — take a look the next time you have a Sunday roast.  This is a real problem in cleaning skeletons.)

Once I’d removed the snout, here’s what remained:

On the midline, half way along the remaining skull (i.e. anteromedial of the orbits) is a very fragile self-contained bony capsule which seems to be full of some kind of soft tissue — maybe fat.  It’s not easy to make out its boundaries in this photo, so here is another that I took of the skull after lifting the capsule out — you can see it in the background.  Does anyone know what the capsule is?  My feeble bird-skull literature isn’t telling me anything about this.

With this capsule gone, it was with me the work of a moment to lift out the two big, spongy, soft-tissue masses from in front of the orbits, which you’ll remember I decided not to attempt last time.  A very good decision that proved.  Having removed them, I found a neat cartilaginous midline structure which I’d like to preserve for the final reconstruction of the skull, but which is already changing shape dramatically as it dries up so I fear I’m going to have to let it go.  Anyway, the bony structure of the remainder of the skull is now much more apparent:

I am guessing that the anteriormost lateral bones are the maxillae, which are a super-weird shape.  As you can see, the left bone is broken: its anterior portion is missing.  Happily, I have this bit, and it’s a perfect fit for the posterior part, so a bit of superglue should fix this problem — but it does emphasise just how insanely delicate many of the skull bones are.

I think the “wing” bones projecting laterally from near the back of the skull must be quadrates: if so, then the bones that project anteriorly from them are quadratojugals, which shade into straight, elongate jugals (you can see the junction in the near side of the photo above) and then connect with the maxillae.

The midline bone, which is surprisingly robust, seems to be made up of fused vomers or somethingat the front, and the parasphenoid rostrum to the rear [thanks to Nick Gardner for this and other corrections].  They’re hard to see in this photo, but there’s also a pair of oddly shaped more-or-less horizontal plates ventrolateral to this midline bone (I think they must be the palatinespterygoids) and two longer, narrower bones anterior to these (which might be the vomers, in which case the fused midline bones are something else? are the palatines).

Once I’d removed all these, I was left with a solid braincase fused together with that midline bone that might be vomersmade up of the parasphenoid rostrum and vomers.  And that, with surprising suddenness, was that.

So here is the complete set of skull bones, laid out in something resembling their order in life: top of the skull at the top of the picture, facing left, with vertebrae to their right; bottom half of the skull (mandible first, then palate) at the bottom of the picture, also facing left.  (Sorry that the contrast is not great: the sun was almost down by the time I took this photo):

When I looked at this, I was reminded of a passage in one of Dave Barry’s old columns, ‘Mister Mediocre’ Restaurants, in which he proposed some surefire business ideas, including a place where you could have your non-functional gadgets permanently destroyed:

The idea there was that consumers would bring their broken electronic devices, such as television sets and VCR’s, to the destruction centers, where trained personnel would whack them (the devices) with sledgehammers. With their devices thus permanently destroyed, consumers would then be free to go out and buy new devices, rather than have to fritter away years of their lives trying to have the old ones repaired at so-called factory service centers, which in fact consist of two men named Lester poking at the insides of broken electronic devices with cheap cigars and going, Lookit all them WIRES in there!

Similarly, I found myself thinking: lookit all them BONES in there!

Happily, help was on the way: Nick Gardner sent me a copy of Maxwell 2009, which has a few useful figures, and from these I was able to take pretty good guesses on the identities of more of the bones.  (That’s why I’ve included more guesswork above than in previous articles in this series.)  So I leave you with an annotated version of the photo above, with my best guess at identifying the bones.  PLEASE MAKE CORRECTIONS IN THE COMMENTS — I will make up a revised version of this annotated photo once they’re all in.  For for now, here it is Here is the initial version, which Nick critiqued in the comments:

And here is the corrected version, so far at least:

Now let’s get those corrections going!

References

  • Maxwell, Erin E.  2009.  Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae).  Zoological Journal of the Linnean Society 156:184-200.

Yesterday, I followed up Veronica‘s second simmering by taking more flesh off the bones, and in doing this I stared to take apart the bones that constitute the skull.  I assume you’re all keen to see pictures, so here she is upside down and in right posteroventrolateral view:

The interesting thing here is that I have removed all the cartilaginous hyoid apparatus, as I suspected last time that I’d end up doing, only to find that part of that apparatus was bony after all: the pair of slender anteromedially oriented bones that you see at the top of the photo.  Here they seem to be directly somewhat ventrally from back to front (i.e. upwards in the photo, since the head is upside down), but comparing with the earlier lateral-view photos of the intact and skinned head, I think that this is post-mortem displacement caused by cooking, and that in life they were more or less in the horizontal plane.

When I removed these bones, I found that their proximal ends were not articulated with other bones, but that they were extended by cartilage rods that continued posteriorly and seem to have been anchored only in soft tissue.  Is that weird?  Or should I have expected it?  It frightens me sometimes how little I know about heads.

You’ll also notice from this photo that I’ve now removed the anterior part of the neck that was attached to the head: as a result, I have a nice bonus set of atlas/axis complex, C3 and the front half of C4 (all pictured below).

Anyway, it was easy to tease away the soft tissue enclosing the mandibular joint and then to remove the bony mandible completely.  This they now do.  The mandible itself is amazingly lighlty built — see the photo at the end of this post, and more to the point the ones in the next post which I’ve not written yet.  Here’s the cranium in ventral view once the mandible was gone and I’d removed some of the skin from the roof of the mouth:

I’m not even going to expose myself to ridicule by attempting to identify any of the bones of the palate — that’s an area that I don’t know at all beyond the fact that there are things called “vomers”, which would make a good name for a race of bad guys in Buffy.  Clearly I need to get hold of a general bird-skull osteology.  Can anyone recommend anything?  Better still, can anyone offer a PDF?

Instead, let’s flip Veronica over and take a look at her top.  After the second simmering, the bones of her skull were very easy to disarticulate, so that’s what I’ve started to do here:

Those two main bones forming the crown of the skull are the frontals.  I assume those are elongate nasals in front of them, reaching down to the lateral edges of the snout (with the maxillae not visible in this view), but I don’t know what that tongue of bone on the midline is, between them: surely it’s too far back to be fused premaxillae?  Someone help me out here.

Anyway, the frontals lifted away cleanly and easily (the right frontal bringing its ?nasal with it, being still slightly attached).  This reveals how huge the eyeballs are (the big, black globes) and how relatively feeble the brain is (the pale brownish yellow lump between them):

It was easy enough to remove and discard the eyeballs and brain, and some surrounding gloop.  The parietal bones that form the back of the skull also came away easily.  At this stage I could have continued to tear the skull down but there are some very delicate bones along the midline and I thought it wiser to simmer again before tackling those.  So here is Veronica, as she was just before going into the pot for the third time, in right dorsolateral view:

It’s easy to make out the three cavities where the eyeballs and brain were.  There’s still a big mass of soft tissue in the middle of the skull, ahead of the eyes and behind the beak, but there’s no safe way to get at it until I’ve removed more of the bones — and those of the snout are very, very delicate.

Finally, here are the bones that I’ve removed from the main cranium (i.e. to get it into the state seen in the previous picture):

Top left (and facing left) is the mandible in dorsal view, and inside it the pair of hyoid bones, oriented as in life.  To the right of those are the ?nasals, then the frontals, then the parietals; outside the frontals are the ?lacrimals that I noted in the first post were coming away from their position in front of the orbit.

The bottom row is of course the vertebrae: atlas in posterior view, and axis, C3 and partial C4 in dorsal view, all facing to the left.

That’s all for now.  More to come.

Please welcome my new best friend, Veronica the ostrich.  Well, Veronica the ostrich head, if you want to be picky.  She arrived yesterday morning, courtesy of the good folks at Ostrichfayre, very well packaged and still frozen and with a convenient little chunk of distal neck still attached.  Here I am with Veronica, having made my way through the packaging:

And here is Veronica herself, in left lateral view, measuring a healthy 24 cm (including that stump of neck, of course, so the prepped skull will be rather shorter):

Yes, of course I only love Veronica for her skull.  The soft-tissue is probably fascinating, too, but I don’t have the time (or the expertise really) to do a proper dissection, so it’s all about getting her naked as quickly as possible.

I started out, as usual, with a couple of hours of gentle simmering to soften all the gloop.  I used the three standard pieces of equipment: a large pot, an easily cleaned ceramic hob, and a very tolerant wife.  Here she is (Veronica, I mean), cooking up nicely:

Once she’d cooled down, it was gratifyingly easy to peel off the skin:

One thing I’d not appreciated about ostriches before I started playing with Veronica is how tiny their beaks are.  Most of the snout is not covered by beak, and the lower jaw in particular has only a few centimeters of keratinous covering.  You can see this more clearly in ventral view:

Here you can see the very slender mandibular bones running along the lateral edges of the lower jaw, with a thin sheet of muscle stretched between them, and that tiny beak only up on the tip of the jaw.

I also noticed that the trachea seems to be positioned asymmetrically, on the right side of the animal: I don’t know whether this was its permanent position in life, or whether it shifted around and simply happened to get cooked into this position.

For the next step, I carefully removed most of that muscular sheet and the trachea (and some of the neck musculature):

Now you can see the cartilaginous hyoid apparatus that anchors the tongue (that anchor-shaped thing).  This is very fragile, and I am frankly not at all optimistic about its chances of making it through the cleaning process.  I’m likely to end up with only the actual bones, so enjoy the hyoid while you can.  (I similarly lost all the hyoid junk from my monitor lizard.  Bummer.  I must remember to show you more of Charlie’s cleaned bones some time.)

I leave you with Veronica’s peeled head in dorsal view:

You can see that there’s more beak on the upper jaw than on the lower.

This kind of photograph is invaluable when it comes to putting the bones together at the end of the cleaning process.  You can see here that the small bones ahead of the orbits (lacrimals?) are pulling away from the main skull bones.  At some stage they’re likely to come away completely, and it’s photos like this one that will show me where to reattach them.

There is a lot of cartilage on this skull, which is likely going to be painful to remove without damaging the bones.  I gave Veronica another bath last night, and I’ll probably start trimming the softened cartilage away this evening.

Further bulletins:

In a comment on the initial Shunosaurus tail-club post, Jaime Headden pointed out the passage in the Spinophorosaurus paper (Remes et al. 2009) that discusses the club of Shunosaurus (as justification for positioning the Spinophorosaurus osteoderms on the end of its tail):

With the holotypic skeleton, two closely associated dermal  ossifications were found originating from contralateral sides  (Fig. 4A–C). These elements have a subcircular base that is  rugose and concave on its medial side, and bear a caudodorsally  projecting bony spike with a rounded tip laterally. Although these  elements were found in the pelvic region under the dislocated  scapula, we regard it as most probable that they were placed on  the distal tail in the living animal for the following reasons: First,  the close association of the contralateral elements indicates they  were originally placed near the (dorsal) midline of the body.  Second, the stiffening of the distal tail by specialized chevrons is  also found in other groups of dinosaurs that exhibit tail armor  [42,43]. Third, osteoderms of similar shape are known from the  closely related basal eusauropod Shunosaurus [26]. In the latter  form, these elements cover the middle part of a tail club formed by  coalesced distal vertebrae; however, the decreasing size of the distal-most caudal vertebrae of Spinophorosaurus indicate that such a  club was not present in this genus. The right osteoderm is slightly  larger and differs in proportions from the left element, indicating  that, as in Shunosaurus [26], originally two pairs of tail spines were  present (Fig. 5).

– Remes et al. (2009:6-8)

And this gives the reference that I needed for the Shunosaurus tail-spikes (as opposed to the club) — reference 26 is Zhang (1988), which, embarrassingly, we’ve featured here on SV-POW! in our first Shunosaurus post.  Evidently I was so focussed on preparapophyses when I looked at that monograph that I completely failed to register the tail-club spikes — but then, which of us can truly say he has not made that mistake?

Anyway, here’s what Zhang has to show us:

And here’s that tail again, this time from the poorly reproduced photographic plate 12, part 1, and in right lateral view:

It’s apparent that this really is the other side of the distal tail (rather than a reversed image of the same side) because the osteoderms are in front of the club vertebrae in the left-lateral figure, but behind them in the right-lateral plate.

It would be great to say more about these, but the English language summary of Zhang’s monograph is understandably brief, constituting six pages of the 90.  What’s not quite so understandable is that neither the diagnosis of the genus Shunosaurus nor that of the species S. lii mentions the tail-club or spikes, which are arguably the most distinctive features.  The “revised diagnosis” on pp. 78-79 does, however — just:

Posterior caudals platycoelous, with small cylindrical centra; neural spines low, rod-like.  In several last caudals swollen ralidly [sic] and forming “tail-mace”; in addition there are two pairs of little caudal spines, being analogous to that of stegosaurs.

Not much to go on, but something.  That’s all, though — there is no further description, and crucially, no indication of whether the tail elements were found articulated or whether the spikes were found isolated and subsequently moved to the end of the tail.  It may be that Remes at al. know something I don’t, of course — they might have a translation of Zhang (1988) — but if not, then it’s amusing to consider that the spikes on the tail of Shunosaurus may or may not be supported by evidence, and that the inference of tail-spikes on Spinophorosaurus might be based on dodgy premises.

The other thing that struck me forcibly, as I looked at the figure and plate above, is that the caudal vertebrae remain fairly complex all the way to the end: they retain distinct and prominent neural spines, unlike the distal caudal vertebrae of diplodocids and brachiosaurs.  I notice that the distal caudals of Spinophorosaurus also seem to be complex, based on fig. 3H-I and also on the skeletal reconstruction that is fig. 5 — both of which we’ve reproduced before, in our old Spinophorosaurus article.

So what’s going on here?  Are Shunosaurus and Spinophorosaurus unusual in having distal caudals that retain complex neural spines?  If so, is this property correlated with the possession of a tail-club and/or spines?  Is it causally related?  Or could it be that this is normal for basal eusauropods, and my ideas of sauropod tails have been too coloured by extreme neosauropodocentricity?  Clearly I ought to go and look at a lot more basal sauropods’ distal tails before publishing this post.  And prosauropods’, theropods’, ornithischians’, pterosaurs’, crocadilians’ and lizards’ distal tails.

As it happens, the one non-neosauropod group of reptiles whose distal tails I do know something about is monitor lizards, thanks to my adventures with the corpse of “Charlie”.  And those caudals do maintain astonishingly detailed structure right to the end of the tail, with even absolutely tiny caudals having distinct processes.  Here are some photographs that show this.

First, one showing all 56 caudal vertebrae (the 1st is half in frame at top right, next to the sacrum; the rest read from left to right on successive rows, like words on a page).

Now here are five representative caudals from different regions on the tail — the last ones from each row in the picture above, as it happens: caudals 1, 10, 21, 30, 42 and 56.  They are in more or less dorsal view, though caudal 1 has fallen forward onto its anterior face.  In this and subsequent pictures, caudal 10 (the second shown) is  for some reason back to front.

Now here are the same vertebrae, in the same order and orientation, but now in left dorsolateral aspect (except caudal 10 which is of course in right dorsolateral):

Finally, here are the three smallest of these vertebrae (numbers 30, 42 and 56) in close-up, again in left dorsolateral view, so you can more easily see how much structure even the distalmost caudal has:

That last caudal is about 2.5 mm long.

(It’s interesting that caudals 30 and 42 have those cute fused chevrons.)

So anyway: we know that caudal vertebrae retain distinct structure all the way down to the tip of the tail in monitor lizards at least some basal eusauropods: could it be that this is the primitive state, and that degenerate caudals are found only in neosauropods and mammals?  Gotta prep out some more animals’ skeletons and find out!

References

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