Stenocybus is still not a juvenile Sinophoneus

A recent paper by Liu (2013) proposed that three small skull specimens (Fig. 1), including one formerly considered the holotype of Stenocybus, are really just juvenile versions of the much larger anteosaurian dinocephalian, Sinophoneus. This idea was put forth earlier by Kammerer (2011). To support this hypothesis Liu reported the following synapomorphies he said were shared by these four specimens.

From the abstract 
“Sinophoneus yumenensis and Stenocybus acidentatus are the only dinocephalians from China, and the latter taxon has been proposed to be a junior synonym of the former. Here I confirm this synonymy on the grounds that the differences between the two putative taxa are due to ontogenetic variation.  Sinophoneus yumenensis differs from all other anteosaurs in having premaxillary dorsal processes that are separated by relatively long nasal anteromedial processes, and vomers without raised, elongated edges; from all other anteosaurs except Archaeosyodon praeventor in having distinct frontal posterolateral processes, and a wide intertemporal region formed partly by long posterior processes of the postfrontals that approach the posterior edge of the skull roof; and from Archaeosyodon praeventor in having a well-developed midline ridge on skull roof.”

Figure 1. The holotype of Sinophoneus and four smaller specimens (to scale) one of which was formerly attributed to Stenocybus. Images from Liu 2013. The IGCAGS specimen is the holotype of Stenocybus. The V19117 specimen is actually basal to the tiny dromasaurs. The  V18120 specimen is actually basal to dicynodonts and kin. The IVPP V18119 specimen nests between Sinophoneus and Deuterosaurus. They do alike. There are parts that are difficult to score.

Figure 1. The holotype of Sinophoneus and four smaller specimens (to scale) one of which was formerly attributed to Stenocybus. Images from Liu 2013. The IGCAGS specimen is the holotype of Stenocybus. The V19117 specimen is actually basal to the tiny dromasaurs. The V18120 specimen is actually basal to dicynodonts and kin. The IVPP V18119 specimen nests between Sinophoneus and Deuterosaurus. They do alike. There are parts that are difficult to score.

A phylogenetic analysis by Liu (2013) nested Sinophoneus as the most basal anteosaurid. The purported juveniles were not analyzed separately.

Figure 2. The three specimens of Stenocybus nest in three different nodes, all far from Sinophoneus and its smaller sister IVPP V18119.

Figure 2. The three specimens of Stenocybus nest in three different nodes, all far from Sinophoneus and its smaller sister IVPP V18119.

Well, you know what that means… Somebody has to do it and here it is (Fig. 2).

Three specimens, including the holotype of Stenocybus (the IGCAGS specimen) nested several nodes away from Sinophoneus. The Stenocybus holotype still nests at the base of the Anomodontia (Figs. 2, 3), as we noted earlier. Specimens V18117 and V18120 nest at the bases of the two major subclasses within the Anomodontia. One leads to dicynodonts and their ancestors (Fig. 3). The other leads to dromasaurs and their kin.

So it looks like China is where anomodont radiation had its genesis. Or at least this was a refuge for this taxa.

Then the fourth small specimen:
IVPP V18119 nests between Sinophoneus and Deuterosaurus. So, yes, it could be a juvenile Sinophoneus! Then again, it could be a transitional taxon. Only one step is added when the two Sinophoneus nest together as a clade.

Why small specimens considered juveniles?
It’s probably just human nature that juvenile-looking taxa are considered juveniles and therefore are not include in phylogenetic studies. This has to stop. The proof of relationships comes from  phylogenetic analysis, not from a cold reading.

We’ve seen this before
Taxon exclusion by assumption is a problem we found earlier in pterosaurs. Virtually all analyses of the Pterosauria exclude the tiny pterosaurs under the presumption that they, too, were juveniles. That hypothesis has been falsified in phylogenetic analysis here that includes tiny pterosaurs, and, like here, they turned out to be key taxa in evolutionary sequences.

Figure 3. The Anomodontia with al three Stenocybus specimens at the bases of the major clades.

Figure 3. Click to enlarge. The Anomodontia with all three Stenocybus specimens at the bases of the major clades. Note the distinct morphologies of the three skulls. Note also the transitional nature of the two IVPP specimens at the bases of their clades.

Now, about those synapomorphies…
Liu’s (2013) analysis compared the large Sinophoneus only to other anteosaurs, but a larger gamut analysis (Fig. 2) nests three of them far outside the anteosaurs, at the base of the Anomodontia.  I can’t remark on the presence or absence of a nasal separating the premaxillary ascending processes, nor the presence or absence of a midline ridge on sister taxa as most of my data is in lateral view and based on drawings.

Sure three of the four new small skulls look similar to Sinophoneus, but they look more like and nest closer to basal therapsids in the anomodont clade. Unfortunately, neither Kammerer (2011) nor Liu (2013) considered these possibilities by including the small skulls in  larger gamut studies.

References
Kammerer CF 2011. ‘Systematics of the Anteosauria (Therapsida: Dinocephalia)’, Journal of Systematic Palaeontology, 9: 2, 261—304, First published on: 13 December 2010 (iFirst) To link to this Article: DOI: 10.1080/14772019.2010.492645\
Liu J 2013. Osteology, ontogeny, and phylogenetic position of Sinophoneus yumenensis (Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China, Journal of Vertebrate Paleontology, 33:6, 1394-1407, DOI:10.1080/02724634.2013.781505

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11 thoughts on “Stenocybus is still not a juvenile Sinophoneus

  1. For the last time! You can’t test whether something is a juvenile by a simple phylogenetic analysis! We know this becasue such tests have been done on modern animals, where we obviously know what is a juvenile of what, and they do not come out together. Its not about the number of taxa included, it is about the chages in characters througout ontogeny!

    That is why the juveniles were not just stuck into the analysis: because it would have produced the wrong result. Including the latest stage in ontogeny only is not an ommission, it is doing things properly. Yes, ontogenetic serieses can be included in phylogenetic analyses, but it involves a thorough re-evaluation of characters and a evaluation of ontogenetic trends. Read Fink & Zelditch (1995) for one example of how phylogenetic analysis of ontogenetic serieses can be done. It is not just sticking the thing into a character list

    This isn’t the first time I and many others have posted on this issue, and yet you persist in ignoring it. You wonder why no one takes your ideas seriously, and yet when they try and give you advice on the phylogenetic principles which you have clearly made no effort to study, they are either shot down or ignored. This is just one more example of your “phylogenetic analysis is always guarenteed to give you the right answer” mindset. You think phylogenetic analysis is easy, but It is a complicated and controvertial branch of palaeontology which requires considerable research into the pitfalls surrounding it, not just a “let’s wack this specimen into a character list and see where it comes out” way of thinking.

    • I”m beginning to suspect you’re not actually reading posts any more, just trotting out the same stock answer.

      Where did I close the door for discussion? I said that this method is not appropriate. That is not closing the door, it is a suggestion to use a better method. Such as description of the skulls with an emphasis on how ontogeny changes osteology and characters through known growth series and then comparing this to the putitive growth seires (as both Kammerer and Liu did), or maybe even morphometric analysis of known growth serieses and incorporation into a phylogenetic scheme (as the paper I cited did).

      This is why I question whether you read my post beyond a cursory glance. You did not, in your reply, address any of the issues I raised about your method, you merely asked me to repeat the experiment. That would be pointless: my objection is with the method! If your method is wrong (and I explained why it is in my post), what will repeating it accomplish? If I come up with a different result to you, my result will be no better than yours.

      This is where the scientist in me lies: I believe in examining and perfecting the method BEFORE using it and making assertions (or at least, if the perfect method does not exist, acknowledging the limitations of the method).

  2. Neil, I do read your posts. Question for you: How is it that two of the specimens are perfect transitional taxa in another part of the tree? Note that one of the small skulls did nest with Stenocybus.

    Here’s a solution: Send me references to verifiable juveniles (perhaps in the nest) of a therapsid and I will run the test in your stead.

  3. If you read them, don’t keep doing things that people who know how these methods work tell you, with reasons, are wrong! Many have pointed out the issues of trying to prove relationships of different ontogenetic serieses with phylogenic analysis to you. They have provided the scientific reasoning and evidence supporting this (i provide a few more references below) Unless you can provide a counter argument to their reasoning, to keep doing such analyses is to demonstrate either that you don’t understand what you are doing, or that you just want to use the method that gives you the answrer you want, quality of the method be dammed. Both of those would negate any scientific merit of this blog.

    Phylogenetic testing of juvenile to adult relationships just doesn’t work- juvenile analysis shows different relationships to adult ones. We know this through emipical testing of MODERN species where we know what is a juvenile of what!!! (Wiens, Bonnett & Chippendale 2005 – Ontogeny Discombobulates Phylogeny: Paedomorphosis and Higher-Level Salamander Relationships; See also Manabe & Humphries 1993:Coding Polymorphic Data: Examples from Allozymes and Ontogeny ; for more discussion on problems with Ontogeny and phylogeny, see Rieppel 1993, Krauss 1988, Gould 1977)

    As for your question; I think the two speciemns you identify as Sinophoneus nest together since they are the closest in their ontogenetic stage (its probably not a coincidence that they are the two largest). The other (‘Stenocybus’) skulls are of a more similar ontogenetic stage, and so plot close to eachother. But their ontogenetic stage is very different to the Sinophoneus skulls: they arebug eyed, short faced, small temproal fenestra-eda and laterally compressed tooth-ed with a shorter postcanine region of the snout, all of which would be expected much earlier in the ontogenetic history of a species.

    As for the therapsid juveniles, I have a few examples below (although I’m not entirely sure how you’re hoping for a nest, given that such things are virtually never preserved in the terrestrial realm, even in the very recent fossil record, so how you’re hoping for one in the Permian…). The one example of basal synapsids in (probably) a nest is Heleosaurus (which you don’t think is a Synapsid).

    However, what are you hoping to achieve by this? Are you hoping to prove that juveniles show the same relationships as adults? As empirical testing (above shows, this just isn’t the case.

    Juveniles

    Botha Brink & Modesto 2009 Anatomy and relationships of the Middle Permian varanopid Heleosaurus scholtzi based on a social aggregation from the Karoo Basin of South Africa

    ABDALA and GIANNINI – GOMPHODONT CYNODONTS OF THE CHAN˜ ARES FORMATION: THE ANALYSIS OF AN ONTOGENETIC SEQUENCE

    Kammerer et al. Ontogeny in the Malagasy Traversodontid Dadadon isaloi and a Reconsideration of its Phylogenetic Relationships

    Marcelo R. Sánchez-Villagra. Developmental palaeontology in synapsids: the fossil record of ontogeny in mammals and their closest relatives

  4. Heleosaurus is a type of synapsid, of a branch that resulted in diapsids, according to the large reptile tree. Thank you for the literature. I have the Heleosaurus paper and will look for the others. I’ll let you know the results. Thanks for your efforts. I should mention, your phrase, “would be expected” sets up a bias. I don’t enter data with a bias. I let the tree recover what it does. If you blame me for what the data does, then there’s a problem here. And by the way, we’ve seen allometry and isometry in various reptile clades. And we’ve seen tadpoles metamorphosize, so anything can happen. It’s our job to find out the patterns and exceptions.

  5. “would be expected”
    I put it badly, what I perhaps should have said is that in observed taxa in the neontological realm (where we know juvenile relationships) and palaeontology these characters have been shown to correlate with early ontogeny. I don’t think it is at all unreasonable to see thes characters elsewhere and infer early ontogeny. In fact I think it is “find out the patterns and exceptions” and then applying them (as you suggest in your final sentance). And that is what Kammerer and Liu did. and it is a much better way of doing things than phylogenetic analysis.

    Your last couple of sentances nicely demonstrate how bad an idea trying to prove adult-juvenile relationships with phylogenetic analysis is. As you say, tadpoles metamorphose. Say you have a dead tadpole and want to know what it is. Put it in a morphological analysis with some frogs, do you think it will plot with the adult? no, of course it won’t as it’s morphology is completely different. “I let the tree recover what it does” is not looking like a great idea in this case. You have to prove the ontogenetic sequence in other ways; by looking at the morphological changes that are consistant throughout tadpole ontogeny, and apply it to our dead tadpole.

    That is what Kammerer and Liu did with Stenocybus. The looked at consistently observed changes in the synapsid “tadpole” to adult transitions, applied it to Stenocybus and came up with an adult. What you’r edoing is putting a synapsid tadpole into a phylogeny and hoping it will plot with the frog. And I know synapsids don’t go through as much change as frogs, but the changes are still significant, as we can see in modern mammals. This is what I meant by “would be expected”

  6. I think you can change, “would be expected,” to “we hypothesize” and get the meaning intended. You have to have a hypothesis you are testing – i.e. something you are expecting to observe – before you can “do science”.

  7. Expectations based on tested patterns are one thing. Expectations based on nothing more than tradition and extended analogies are another. Today’s post (Nov. 15, 2013) tested those and your hypotheses and found them falsified. So far, no where do we find the elongated and wider muzzle Liu and you need to link the smaller specimens to the larger Sinophoneus.

    • “Expectations based on tested patterns are one thing. Expectations based on nothing more than tradition and extended analogies are another.”
      If they are both testable then no, there isn’t a difference. That’s why I study many of the topics I do; people have long assumed something to be true. Sometimes it is, sometimes it isn’t. If it is unsupported in rigorous scientific testing then it doesn’t matter how firmly people believe it (e.g. Coelophysis cannibalism). If the evidence is flimsy then it doesn’t matter how long the pattern has held if the “tests” are based on bad data; rigorous tests will expose those flaws. Rigorous testing generally doesn’t happen overnight.

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