Introducing the Paratetrapoda with a new reconstruction of Pholidogaster

With questions arising
about the phylogenetic nesting of the fish-like paratetrapod Colosteus with Osteolepistoday several putative members of the Colosteidae were added to the large reptile tree (LRT, subset Fig. 1). According to Wikipedia, clade members should include Colosteus, Deltaherpeton, Greererpeton and Pholidogaster.

Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

As you can see
(Fig. 1) only one putative member of the Colosteida. Pholidogaster nests with Colosteus. Deltaherpeton nests with Eryops the temnospondyl. Greererpeton nests between temnospondyls and the Neotetrapoda with Ichthyostega at its base.

A new clade
The Paratetrapoda is here defined as Colosteus, Osteolepis, their last common ancestor and all of their descendants. Derived taxa developed tetrapod-like limbs by convergence. The Neotetrapoda is here defined as Ichthyostega, Homo, their last common ancestor and all their descendants. This is the clade that leads to all other tetrapods.

Figure 1. Greererpeton reduced to a blueprint of body parts. Here there may be one extra phalanx on pedal digit 5 and one missing on pedal digit 2 compared to sister taxa. So an alternate is shown with that repair. The skulls at left are juveniles.

Figure 2. Greererpeton reduced to a blueprint of body parts. Here there may be one extra phalanx on pedal digit 5 and one missing on pedal digit 2 compared to sister taxa. So an alternate is shown with that repair. The skulls at left are juveniles.

Greererpeton burkemorani 
(Romer 1969, Smithson 1982, Godfrey 1989; Early Carboniferous, 320 mya; 1.5 m in length). Godfrey thought it nested closer to Proterogyrinus than to Ichthyostega. Here Greererpeton nests between temnospondyls, like Sclerocephalus and Ichthyostega. The skull was flattened with orbits on top of the skull. The lacrimal contacted the naris. The torso included some 41 presacral vertebrae. The pectoral girdle was robust. The limbs were small. The powerful tail was the chief organ of locomotion.

Figure 3. Deltaherpeton skull with colors added.

Figure 3. Deltaherpeton skull with colors added.

Deltaherpeton hiemstrae 
(Bolt JR and Lombard RE 2010; Viséan, Early Carboniferous; Fig. 3) nests with Eryops among the temnospondyls and appears to have a fused nasal/frontal.

Figure 2. Colosteus holotype drawing of the fossil in situ from Hook 1983 compared to the closely related Osteolepis.

Figure 4. Colosteus holotype drawing of the fossil in situ from Hook 1983 compared to the closely related Osteolepis.

Colosteus scutellatus 
(Newberry 1856, Hook 1983; Westphalian, Late Carboniferous, 305 mya; 1m in length; AMNH 6916; Fig. 4) was originally considered a fish (Pygopterus) and renamed by Cope 1869. Here Colosteus nests with Osteolepis and Pholidogaster (Figs. 5, 6) as a paratetrapod convergent with traditional tetrapods. The skull was ovate, the vomers and dentaries had fangs, the fins had transformed to tiny four-fingered limbs. The lacrimal did not reach the external naris. The scales remained large and rhomboid-shaped. Pectoral girdle had not yet evolved an external scapula and coracoid.

Figure 1. Pholidogaster skulls compared to Colosteus and Osteolepis. Panchen reconstruction on left includes a premaxilla that is too wide. At right revised width to fit premaxilla tracing, pectoral girdle and in situ lacrimal and cheek bones.

Figure 5. Pholidogaster skulls compared to Colosteus and Osteolepis. Panchen reconstruction on left includes a premaxilla that is too wide. At right revised width to fit premaxilla tracing, pectoral girdle and in situ lacrimal and cheek bones.

Pholidogaster pisciformis
(Huxley 1862, Panchen 1975; Visean, Early Carboniferous, 340 mya; Figs. 5, 6) was originally considered a labyrindont and an anthracosaur, but here nests with Osteolepis and Colosteus (Fig. 5) among the Paratetrapoda, a clade that developed limbs independent of the Tetrapoda.

The new skull reconstruction (Fig. 5) is narrower than in Panchen 1975 to match the premaxilla and pectoral girdle. The premaxilla carried a lateral fang and the dentary had a corresponding slot for it.

Figure 5. Pholidogaster in situ and with post crania reconstructed based on the Osteolepis bauplan.

Figure 5. Pholidogaster in situ and with post crania reconstructed based on the Osteolepis bauplan. The long straight ribs are actually neural spines that are elevated here. Small bones, like those found in Osteolepis and Eusthenopteron are retained at the bases of unpreserved dorsal and anal fins. The interclavile extends below the jaw. It appears unlikely that this taxon had a neck.

The vertebral column included small bones that were basal to both dorsal fins and anal fin. The long straight unpaired bones once thought to be ribs are here identified as tall slender neural spines. The tail was little different from that found in Osteolepis, including the slight upturn, like a shark’s tail.

The interclavicle and clavicles extended beneath the mandibles. No scapula or coracoid was visible. Those were tiny elements medial to the coracoid and cleithrum. The fingers did not ossify. The pelvis is well ossified with an acetabulum dorsal to the pubis. The hind limb includes metatarsals and a few digits.

The ossified scales that covered the body in Osteolepis and Colosteus are not present here.

Pholdogaster has been known for over 150 years
and if it had only been reconstructed with the present precision I think its fish-like affinities would have been discovered earlier. It’s 150-year-old specific name ‘pisciformis’ points obviously to its fish-like affinities, which were recognized then, but have received less attention in recent studies. It appears unlikely that any paratetrapod had a movable neck.

Remember
we have tetrapods crawling on shore and leaving footprints in the Middle Devonian, millions of years before Acanthostega and Ichthyostega in the latest Devonian. These famous taxa now appear to be conservative relicts retaining fish-like traits, rather than liberal land pioneers inventing tetrapod-like traits.

References
Agassiz L 1843. Recherches Sur Les Poissons Fossiles. Tome I (livr. 18). Imprimerie de Petitpierre, Neuchatel xxxii-188.
Bolt JR and Lombard RE 2010.
 Deltaherpeton hiemstrae, a New Colosteid Tetrapod from the Mississippian of Iowa. Journal of Paleontology. 84 (6): 1135–1151.
Godfrey SJ 1989. The postcranial skeletal anatomy of the Carboniferous tetrapod Greererpeton burkemorani Romer, 1969. Philosophical Transactions of The Royal Society B Biological Sciences 323(1213):75-133.
Hook RW 1983. Colosteus scutellatus (Newberry), a primtiive temnospondyl amphibian from the Middle Pennsylvanian of Linton, Ohio. American Museum Novitates 2770; 1-41.
Huxley TH 1862. On new labyrinthodonts from the Edinburgh Coal-field. Quarterly Journal of the Geological Society London18:291-296.
Panchen AL 1975. A New Genus and Species of Anthracosaur Amphibian from the Lower Carboniferous of Scotland and the Status of Pholidogaster pisciformis Huxley. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 269(900):581-637.
Romer AS 1969. A temnospondylus labyrinthodont from the Lower Carboniferousw. Kirtlandia 6:1-20.
Smithson TR 1982. The cranial morphology of Greererpeton burkemorani Romer (Amphibia: Temnospondyli). Zoological Journal of the Linnean Society 76(1):29-90.

wiki/Greererpeton
wiki/Osteolepis
wiki/Colosteus
wiki/Pholidogaster

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12 thoughts on “Introducing the Paratetrapoda with a new reconstruction of Pholidogaster

  1. You’ve never even read Jason’s and my numerous criticisms of your Colosteus post, have you?

    I won’t repeat them here, except for the fact that the lateral scales of Colosteus are in fact circular. Go read the others.

    The Neotetrapoda is here defined as Ichthyostega

    As I’ve already told you, Neotetrapoda explicitly excludes Ichthyostega. Don’t confuse your readers by changing that.

    The long straight ribs are actually neural spines that are elevated here.

    I laughed when I read that.

    Neural spines aren’t separate ossifications. Ever. They’re outgrowths from the neural arches.

    You know that most fossils are fossils of rotting corpses, right? One of the most common things to happen before fossilization is gas buildup in the decaying gut. When the belly explodes, guess what happens to the ribs. Hint: the intercentra in that same region are preserved in ventral view.

    Small bones, like those found in Osteolepis and Eusthenopteron are retained at the bases of unpreserved dorsal and anal fins.

    These are intercentra.

    The interclavile extends below the chin. It appears unlikely that this taxon had a neck.

    That’s not where the chin is, the chin is the other end of the lower jaw… but anyway, it’s normal for tetrapods to have an interclavicle and clavicles that extend quite some distance between the lower jaws. Most temnospondyls have that, for example.

    If it didn’t have a mobile neck, why is there no trace of extrascapulars, posttemporals, supracleithra, anocleithra, operculars or suboperculars?

    The tail was little different from that found in Osteolepis, including the slight upturn, like a shark’s tail.

    That’s not an upturn, it’s a break in the rock. Romer’s drawings that you reproduce show that very clearly. Even in your “reconstruction” drawing you rendered the area in question as a break!

    No scapula or coracoid was visible. Those were tiny elements medial to the coracoid and cleithrum.

    Look at the specimen drawing again: the whole area is damaged.

    The fingers did not ossify.

    :-D :-D :-D :-D :-D

    That doesn’t actually ever happen. The area where we’d expect the hand to be is not on the slab! Look at that specimen drawing again that you are reproducing here.

    Besides, what I just said about fossils of rotting corpses.

    It’s 150-year-old specific name ‘pisciformes’

    pisciformis – singular, not plural.

    The ossified scales that covered the body in Osteolepis and Colosteus are not present here.

    There’s this V-shaped pattern in the specimen drawing that looks like the usual rows of ventral scales. I’ll check Romer’s paper tomorrow (currently no access to Panchen’s, but soon). Their absence from Romer’s interpretative drawing is just convention; it doesn’t mean the scales weren’t there. Dorsal scales are easily scattered (rotting corpse!) and easily overlooked.

    Conclusion from this and many other posts: you have no clue about anatomy, and you have no clue that you have no clue about anatomy. You remind me of your president.

    • Even in your “reconstruction” drawing you rendered the area in question as a break!

      As a gap, I meant to say.

      These are intercentra.

      Oops! I should have clicked on the picture. One is the proximal end of a rib, the other is the postacetabular (“posterior” as opposed to “dorsal”) process of the left ilium. This is very clear in Romer’s drawing.

    • Easy stuff first:
      I read all your responses. I have a backlog at the moment. Just getting to this one several days after it was posted. As you’ll see, I do agree with some of your remarks. I do not agree with others and reasons are given. You are correct that the day before I look at a taxon for the first time, I know nothing about it, just like you. I soon learn and sometimes I learn that you make mistakes as well, David.

      Wikipedia lists the specific name as ‘pisciformes’, so I repeated the error. Thanks for the update.
      I don’t see the ossified scales on the fossil photo that one sees on photos of Osteolepis and Colosteus. And neither do you. Either way, it doesn’t affect scores.
      I am aware that the vertebral column is exposed in ventral view, which is one reason that the straight dorsal ribs are neural spines bent down by pressure during burial. The anterior ribs are curved. The scattered bones that I interpret as basal to various fins are flat bones that echo the shape of those in Osteolepis, not curved like intercentra and pleurocentra.

      And finally, you put far too much emotion into Science, David. I realize some of your paradigms are breaking down. Scientists make mistakes all the time. It doesn’t mean they ‘have no clue about anatomy.’ Try to avoid blackwashing. Try to avoid insults. You’re much better when you stick with the the data.

      • I don’t see the ossified scales on the fossil photo that one sees on photos of Osteolepis and Colosteus.

        Is there a photo in Panchen (1975)? I don’t have access to that paper right now. There’s no photo in Romer (’64) or obviously Huxley (1862), just drawings that show the scales quite well. The picture at the top of your fig. 5 is the drawing from Huxley (1862); the ventral scales are there, but not very recognizable, because the resolution of your version is so low.

        Either way, it doesn’t affect scores.

        Too bad! I lament the lack of scale characters in Ruta & Coates (2007) in the preprint, and will add some next week. Florian Witzmann published about the phylogenetic signal in them in 2007 and 2013.

        I am aware that the vertebral column is exposed in ventral view

        Not all of it! Just a part.

        which is one reason that the straight dorsal ribs are neural spines bent down by pressure during burial.

        …I’m sorry, that doesn’t make sense. ~:-|

        I realize some of your paradigms are breaking down.

        You act as if fear is the only emotion there is.

        The most powerful emotion, in fact, is fremdschämen – to feel the shame that somebody else ought to feel but, in your case, doesn’t. My paradigms aren’t breaking down – the ones you believe you’re building aren’t even coming up, but you don’t notice, because you don’t know enough anatomy to score your characters, and you don’t know enough anatomy and evolutionary biology and development biology to code your characters. You believe you’re doing everything right, so the trees you get have to be right or at least reasonably close. The sad fact is that you’re hardly doing anything right, and therefore the trees you get are forgettable. By being completely unaware of this and refusing to learn enough to become aware, you embarrass yourself monumentally; that’s the shame I feel for you.

  2. LOL! I finally did it and opened the folder with the descriptions of Mississippian tetrapods. All boldface is mine, all italics are original.

    Huxley 1962, p. 294: “A recent careful study of the fossil […] has convinced me that the fossil is an Amphibian allied to Archegosaurus, though it differs from the latter in […] and in the characters of its dermal armour. It shares with Archegosaurus, however, the peculiarity of having its overlapping scales arranged in double oblique series between the pectoral and pelvic arches only, whence, and on account of its fish-like form, I propose the name of Pholidogaster pisciformis for the genus and species.”

    p. 295: “The ventral armour commences behind these thoracic plates, and forms an oblong sheet of scales, about 4 inches broad and 17 inches long, while each scale may measure half an inch long by ·15 broad. When the scales are well preserved and separately distinguishable, they are seen to be somewhat oat-shapedd, the outer end being much more obtuse in some sales than in others.  The scale is thick, and rises to a sort of ridge in the middle.  The inner end of its outer face is commonly bevelled off, or grooved, so as to receive the outer end of the next scale in front of and internal to it.  The scales are so arranged as to form oblique series, directed inwards and forwards, and mieeting in the middle line.
      Posteriorly (fig. 4) the scales seem to become longer, so as to assume a bar-like character […]”

    p. 296: “DESCRIPTION OF PLATE XI.”
    […]
    Fig. 4. Scales of Pholidogaster, of the natural size.”

    Fig. 4 of plate XI does in fact show immediately recognizable ventral scales.

    Romer 1964, p. 132: “Decomposition appears to have set in to some degree before burial, so that most of the belly wall and its armor of scales, broadly visible the length of the trunk, lies to the (morphological) right side of the column.”

    The description of the scales takes up more than a page on pp. 141 and 142.

    And finally, the ventral scales are shown in Romer’s reconstruction of the skeleton, his plate I B. Plate I A is the specimen drawing you reproduced after taking the head and shoulder girdle out.

    This is thoroughly amusing. :-)

    • Easy partner. Take a chill pill. I took no head and shoulder girdle out. The separate illustrations of skull and torso have been somewhat joined together. Stop cussing or if you need to cuss, send a private email. You’re way to emotional about this. Evidently the scales and their arrangement is very important to you. It is not that important to matrix scoring. Furthermore, you know that all pre-tetrapods had a certain scale structure and pattern that did not continue in derived taxa. I am proposing the hypothesis that this too was convergent in the two lineages that developed limbs.

      • Evidently the scales and their arrangement is very important to you.

        What’s very important to me is that you said this in your post:

        The ossified scales that covered the body in Osteolepis and Colosteus are not present here.

        They aren’t in Romer’s drawing of the rest of the skeleton. That’s a common convention to improve clarity. You didn’t know that and fell for it. There are lots of things you don’t know and fall for, and some of them cause miscodings in your matrix. That’s important to me and, I hope, to you, too.

        On “cussing”, keep in mind that I’m a scientist. I trained long and hard to call a spade a spade rather than some kind of shovel.

    • Scales have been added to the matrix scoring. That eliminates an autapomorphy, which is always great. You say I believe my scores are correct, and yet I confess over and over again that I change scores whenever I see an error. So YOU believe that I believe my scores are all correct. That’s the problem, David.

      • Scales have been added to the matrix scoring.

        Good. Now add the characters listed here to your matrix. It’ll take a while; we can wait.

  3. As a review, here are the traits you referenced:
    the presence of a stapes integrating a portion of the otic capsule as a footplate,
    the specific geometry of the stapes within the spiracular/stapedial canal,
    the nature of the attachments for the jaw adductor musculature,
    three coronoids,
    the absence of a sphenotic joint,
    closure of the buccohypophyseal canal,
    laterally projecting basipterygoid processes contributing to the basicranial joint,
    a parasphenoid that extends posterior to floor the otic region,
    pineal foramen posterior to the orbits,
    loss of the posttemporal/extrascapular bridge between the skull and pectoral girdle,
    absence of opercular and gular bones,
    presence of true digits,
    pentadactyly,
    integration of the radius into the zeugopod,
    a large interclavicle,
    a well-developed pelvis that articulates directly to sacral ribs,
    absence of supraneural bones in the caudal skeleton,
    gastal scalation,
    well-developed pleurocentra and intercentra,

    Some of these traits are already present.
    Problem #1 here is the term ‘colosteids’. The traditional list of colosteids becomes split up in the LRT.
    Problem #2: Several traits are minutia that I will not be able to confirm.
    Problem #3: If Pholidogaster is developing limbs and digits convergently with traditional tetrapods, we’ll find ‘true digits’, a pelvis, etc. in both clades. The same for the absence of opercular and gular bones.
    Problem #4: Colosteus has only four fingers. So pentadactyly is not present here, but the hind limbs are unknown.

    I realize it’s a shock to read that two clades produced limbs and toes, but remember, the LRT also recovered ‘birds’ unrelated to birds and pterosaurs and other clades that had an antorbital fenestra but they are not archosaurs. Convergence is real. Or at least should be considered as a possibility.

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