The bizarre caudal neural spines of Tambatitanis amicitiae
August 13, 2014
Today for the first time I saw Saegusa and Ikeda’s (2014) new monograph describing the Japanese titanosauriform Tambatitanis amicitiae. I’ve not yet had a chance to read the paper — well, it’s 65 pages long — but it certainly looks like they’ve done a nice, comprehensive job on a convincing new taxon represented by good material: teeth, braincase, dentary, atlas, and as-yet unprepared fragmentary cervical, fragmentary dorsals, sacral spines, some nice caudals, some ribs and chevrons, and pubis and ilium.
What catches the eye immediately is the bizarre forward-curved neural spines of the anterior caudals:
Saegusa and Ikeda (2104: fig. 8): Tambatitanis amicitiae gen. et sp. nov., holotype (MNHAH D-1029280). A, Cd2–Cd11 in right lateral view. B, Cdx1–Cdx2 in right lateral view.
Here’s the third caudal in detail. (The first is fragmentary, and the second has some minor reconstruction near the tip of the spine which sceptical readers might think is covering up a misconstruction):
Saegusa and Ikeda (2014: fig. 11): Tambatitanis amicitiae gen. et sp. nov., holotype (MNHAH D-1029280). A–F, stereopairs of Cd3. A, right lateral view. B, left lateral view of the neural spine. C, anterior view. D, posterior view. E, dorsal view. F, ventral view. G, CT slices through the neural spine of Cd3, part corresponding to the matrix that filling the internal chamber is removed from the image. Greek letters in B and D indicate the position of CT slices shown in G. Scale bar = 10cm.
And here is the right-lateral view in close-up:
Saegusa and Ikeda (2014: fig. 11): Tambatitanis amicitiae gen. et sp. nov., holotype (MNHAH D-1029280) in right lateral view.
A phylogenetic analysis based on that of D’Emic (2012) recovers the new taxon in a polytomy with the Euhelopus clade that’s going to need a new name pretty soon, since it keeps growing and can’t be called Euhelopodidae for historical reasons: [that should probably be called Euhelopodidae: see discussion in comments]:
Saegusa and Ikeda (2014: fig. 23): Phylogenetic relationships of the titanosauriform sauropod Tambatitanis amicitiae gen. et sp. nov. from the Lower Cretaceous Sasayama Group of Tamba, Hyogo, Japan produced using the matrix of D’Emic (2012) with the addition of Tambatitanis. The final matrix, including 29 taxa and 119 characters, was analyzed in PAUP* 4.0b10. Left side, strict consensus of 81 most parsimonious trees (length = 207; CI = 0.609; RI = 0.8010; RC = 0.489), figures below nodes are decay indices. Right side, 50% majority rule consensus, figures above and below nodes represents the percentage of MPTs in which the node was recovered (only those relationships recovered in over 50% of the MPTs are shown).
Nice to see that new sauropods just keep on rolling out of the ground faster than we can blog about them!
References
- D’Emic, Michael D. 2012. The early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166:624-671.
- Saegusa, Haruo, and Tadahiro Ikeda. 2014. A new titanosauriform sauropod (Dinosauria: Saurischia) from the Lower Cretaceous of Hyogo, Japan. Zootaxa 3848(1):1-66. doi:10.11646/zootaxa.3848.1.1
Sauropod Vertebra Picture of the Week 
August 14, 2014 at 1:10 am
I never thought I would be so happy to see more sauropod vertebrae. Very cool!
August 14, 2014 at 8:12 pm
Why can’t it be called Euhelopodidae?
August 14, 2014 at 8:26 pm
Upchurch’s 1995 and 1998 analysis used the name Euhelopodidae for what we’d probably now call Mamenchisauridae — the group of Chinese non-neosauropods, which he found to be monophyletic and including Euhelopus, Mamenchisaurus, Omeisaurus and IIRC Shunosaurus. Since all recent analysis (including Upchurch’s own) now find Euhelopus well outside that clade, as a basal somphospondyl, the original group obviously can’t be called by that name. But the group the Euhelopus now does seem to be part of should not be so called either, because it’s previously been used to mean a different group.
August 17, 2014 at 3:44 pm
That’s not how it works – in other words, it doesn’t matter that Euhelopodidae sensu Upchurch had an utterly different content or meaning vs a ‘new’ version of the group. What matters is that we have a name that has consistently included Euhelopus. Indeed, a phylogenetic definition would merely be ‘all taxa closer to Euhelopus zdanskyi than to [insert external specifiers]’. No big deal. Note that there are huge numbers of other clade names where content has changed substantially over the years (see the recent Tet Zoo articles on passerine bird families), yet the names are still in use since they’ve always been associated with the ‘core’ taxon or taxa (examples: Muscicapidae, Turdidae, Timaliidae).
August 17, 2014 at 4:05 pm
Sure that’s how it works — if you care about making names that people can actually use without getting confused, and not mere legalistic rule-following. Calling the clade (Euhelopus not Saltasaurus) by the name Euhelopodidae would not violate any rules; but it would be a terrible idea.
August 17, 2014 at 8:47 pm
As painful as it may be to consider, this far from the cladistic and taxonomic roots it may just not matter whether the name in use exactly matches the best current data. It is, and will remain whatever new information comes to light, in the right neighborhood, and everybody who cares knows the score. Ultimately it’s just a symbol, and *as always* the reader must supply an interpretation. The default assumption about any symbol must be that any meaning that can be derived from deconstructing its expression is approximate, if not actively misleading. (When necessary, we use it with a sense of irony, as when we mention the Department of Justice.) With names, stability is way more important than the facts.
The number of mentions of D. melanogaster in the literature will be little affected by the late revelation of its nonexistence, and that is a wise collective choice by the communities that make it.
August 17, 2014 at 9:01 pm
If Euhelopodidae already had a widely used phylogenetic definition, we’d stick with it. But it doesn’t, and the need to recognise the clade (Euhelopus not Saltasaurus) has only become apparent in the last couple of years. So we are in a position to pick whatever name we want for that clade. I could pick Vermes or Pachyderma if I wanted, but there would be no value in doing so.
August 18, 2014 at 4:23 am
I’m still a fan of using Euhelopodidae. ICZN rules are too restrictive IMO. The only problem with calling the new group Euhelopodidae is that it may actually be 2 or 3 families.
Daxiatitan looks very close to Euhelopus and should probably be in any proposed Euhelopodidae. But it’s got procelous mid-caudals, which Phuwiangosaurus and Huabeisaurus lack. And then you have the fact that Phuwiangosaurus and Baotianmansaurus have ridiculously tall neural arches and tiny neural spines in the dorsals, something not found in Euhelopus – which shows fused pairs of sacral ribs that are not found in Phuwiangosaurus or Huabeisaurus, which have similar straight, small-ended shoulder blades unlike Euhelopus…. and so forth. And then you have this new animal…. which appears to be mixing the amphiplatyan Phuwiangosaurus model with the crazy upcurve spines found in some saltasaurs.
August 18, 2014 at 8:56 am
This is nothing to do with the ICZN rules — which in any case have nothing to say about clades, only rank-based taxa. It’s about avoiding very avoidable confusion.
As for the composition of a putative Euhelopus-based clade: that would be determined by the adopted phylogenetic definition, as applied to a given phylogenetic hypothesis, e.g. that of D’Emic 2012 …
But …
Looking again at that paper, I see that it does use Euhelopodidae for the clade in question, so this ship has probably sailed anyway. D’Emic writes (643):
It’s not what I would have done; but since it’s now been done, it would be worse to introduce more uncertainty by proposing a new name for the same clade.
(Bizarrely, D’Emic’s definition uses Neuquensaurus rather then the otherwise ubiquitous Saltasaurus as his external anchor. Skimming the paper, I see no justification for that choice. It seems unwise, since any analysis that does not recover Neuquensaurus and Saltasaurus as close relatives might yield surprising combinations of clades, e.g. Titanosaurus within Euhelopodidae. But that seems unlikely to happen.)
August 18, 2014 at 9:05 am
I see as well that Mannion et al. 2013 used the name Euhelopodidae in the sense of D’Emic 2012, so that pretty much nails it down as established usage.
Basically, I was just behind the times — a timely kick to remind me that I really need to keep up with the literature more assiduously!
August 19, 2014 at 2:40 am
Hi Mike, Can I get a pdf of this paper from you? Thanks! Mark Hallett
August 19, 2014 at 8:23 am
It’s in the post!
August 27, 2014 at 9:49 am
Saltasaurus is certainly more widely known by more people but this does not make more ubiquitous (?distribution or localities; ?materials) than Neuquensaurus. I don’t really see D’Emic’s choice of using the latter taxon as an external specifier for Euhelopodidae as a big issue. The type species of Neuquensaurus has been known for about 100 years before Saltasaurus, and both genera have been osetologically described in the literature in similar levels of detail. You said it seems unwise because “any analysis that does not recover Neuquensaurus and Saltasaurus as close relatives might yield surprising combinations of clades, e.g. Titanosaurus within Euhelopodidae” — the same result could happen with Saltasaurus as an external specifier.
If in the uber unlikely event that Titanosaurus ends up inside Euhelopodidae, then so be it – as that’s what the data would be pointing to at the time (the clade name should become a junior synonym of a re-employed Titanosauridae then).