The Squirrel Imitator


Ok, so I get why Oliver Rauhut and crew named their new theropod dinosaur, a purported megalosauroid, Sciurumimus albersdoerferi. It has all the appreciative charm of being cute, fluffy, and the specimen is preserved with its tail up and over it’s head … like a squirrel! [n1] (I will at this point not mention — at all — that the word “sciurumimus” should have been “sciuromimus,” due to correct use of connection vowels in Greek.) I mean, look:

DAWWWWWWWW

On the left, Sciurumimus albersdoerferi, in the undecent act of being dead. On the right, Sciurus carolinensis, looking altogether well and hale. Look at that tail. And you wonder why the names are so similar….

When you get down to the facts of the comparison, the name is obvious. But….

It’s a juvenile. It may be so young, that it is quite possible it is but weeks after having hatched. Maybe not THAT young, but pretty close. And, as I may have mentioned before, problems occur when you go around producing taxonomy for species based on juveniles, because some features that diagnose adults do not appear until well along in age. Moreover, there is the whole question of Juravenator starki:

Juravenator starki, in the scaly buff.

They seem very similar, although Rauhut et al. have done a fairly good gob in telling you why they are different (from the supplemental online material):

[T]he two taxa show numerous differences in anatomical details[:] in the skull of Juravenator, the anterior margin of the antorbital fossa is rectangular, rather than gently rounded, the maxillary fenestra is relatively smaller, the antorbital fossa is smaller, the ventral process of the postorbital is more massive and notably curved, the ventral (quadratojugal) process of the squamosal tapers to a point, and the posterior premaxillary teeth bear serrations, whereas they are more slender and devoid of serrations in Sciurumimus. In the vertebral column, Juravenator differs from Sciurumimus in the following characteristics (in the following all characters listed refer to the situation in Juravenator): cervical epipophyses are small, barely (if at all) overhanging the postzygapophyses; prezygoepipophyseal laminae in the cervical vertebrae are absent; a posterior pleurocoel is present in a midcervical centrum; anterior-most dorsal vertebrae are distinctly elongate; neural spines in the anterior caudal vertebrae are triangular and strongly posteriorly inclined; the posterior caudal vertebrae are relatively more elongate; posterior caudal prezygapophyses are more elongate and are directed anteriorly rather than anterodorsally; distal chevrons are skid-like. In the pectoral girdle and forelimb, the following differences can be established: The scapula is less slender and has a distinctly curved blade; the supraglenoid fossa is triangular, with an acutely angled posterior rim; the internal tuberosity of the humerus is confluent with the proximal humeral articular surface, forming a rectangular edge on the medial side of the proximal humerus; the ulna lacks a proximal expansion and olecranon process; and the shaft of the ulna is more massive than the shaft of radius. In the pelvis and hindlimb, Juravenator differs from Sciurumimus in the lack of an anterior dorsal lip of the ilium (the presence of which represents an autapomorphy of Sciurumimus); the relatively smaller pubic peduncle of the ilium; a more reduced supraacetabular crest, which is confluent posteriorly with the lateral brevis shelf; a pronounced antitrochanteric lip on the ischial peduncle of the ilium; a rectangular rather than undulate posterior end of the postacetabular blade of the ilium; an obturator process on the ischium [erroneously identified as pubis by Chiappe and Göhlich (26)] that is offset from the pubic peduncle; the lack of a distal expansion of the ischial shaft; the short and triangular metatarsal I; a metatarsal IV that is distinctly longer than metatarsal II; and the shorter and more robust metatarsal V.

Thus, they conclude:

These numerous differences strongly indicate that the two animals cannot be referred to the same taxon, despite their similar size and proportions.

Rauhut et al. also make a point of dumping both taxa (as juvenile as they are) into a phylogenetic analysis, and cannot recover them as sister taxa, which one might expect if they are the same species, given how complete they are. They are similar in many respects, but distinct in others — for example, Rauhut et al. argue Sciurumimus albersdoerferi is a megalosauroid, part of the spinosaur-torvosaur-megalosaur lineage, while Juravenator starki is a “compsognath-grade” form (although Andrea Cau has a different opinion, but still can’t get the two together as sister taxa, and as such reinforces the distinctions provided by Rauhut).

No, my problem — and it’s a haughty one — is that one should not have much recourse when encountering even a distinct taxon and then decide to name it. It is quite possible you have a new taxon, but you do not know what it is diagnostically … just what it once what diagnosed by. Theropods change through time, a thing I mention when I talk about Raptorex kriegsteini, leaving them with more diagnostic features as an adult, less as a juvenile. This does not mean that a lot of features to differentiate Sciurumimus albersdoerferi is suddenly reason to name a new form: Indeed, the authors only define THREE features that diagnose the taxon, and two are related to the shapes of neural spines, and another to the anterior edge of the ilium (pg. 11746):

Megalosauroid theropod with the following apomorphic characters: axial neural spine symmetrically “hatchet-shaped” in lateral view; posterior dorsal neural spines with rectangular edge anteriorly and lobe-shaped dorsal expansion posteriorly; anterior margin of ilium with semioval anterior process in its dorsal half.

How are we to not think that vertebral spine shape changes with ontogeny? It changes with relative size of muscle attachment, I would think this would be a point of caution.

But, despite this … nay, in spite of all this, this is one extraordinary fossil. And the exceptional thing is, that unlike the type specimen of Juravenator starki (JME Sch 200), the type specimen of Sciurumimus albersdoerferi (BMMS BK 11) although the same size and from OLDER strata, is clothed in filamentous stage I feathers. Jura, for all his glitz, only has scales preserved. And even though Cau may recover a different position for little Otto (as the specimen is also known), it comes out still at the base of Coelurosauria, while Jura is more derived by several nodes of other, albeit incomplete taxa, and may itself be closer to birds than even tyrannosauroids. To commemorate this fact, so that he may lord it all over you, I drew this — enjoy:

Prissier than the real thing.

[Covered by a CC 3.0 BY-NC-ND license. Please respect it. If you want, you can pay me for a copy by clicking on the link.]

[n1] The name derives from the Greek words σκία (skía, “shadow”) + ούρος (oúros, or -uro, “tail”), and thus provides us with Sciurus. The provided etymology is “Sciurus mimic” (Grk. μίμος – mímos: “mime” or “mimic” or “one who imitates, copies”), or “squirrel imitator,” but can also be read as “shadow-tail imitator.” We can probably assume the authors are aware that the posture of the fossil is opisthotonic, and not a life pose, and that the animal likely may never have held its tail like that.

Rauhut, O. W. M., Foth, C., Tischlinger, H. & Norell, M. A. 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences of the United States of America 109(29):11746-11751.

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13 Responses to The Squirrel Imitator

  1. several things:
    – Sciurus can be derived from the Latin form. Legal, although not pretty.
    – stage I feathers is what they LOOK like. As Foth has shown, you’re likely to get this even for way more derived feathers if you flatten them.

    • It is true that they could be using the messier Latin form for Sciurus, rather than skiouros, but … they explicitly use Greek for mimos, not Latin mimus, so I am presuming Greek straight across. But then wouldn’t the Latin connector in this case would be “sciurimimus”?

      I recall Foth’s paper. I will generalize at this point that they are modified stage I, based on the likely LESS basal Sinosauropteryx prima and general agreement on which stage it has. Then again, we can suggest that all “stage I” identifications for fossil theropods are more ambiguous than we’ve assumed (a fair assumption).

  2. “Jura, for all his glitz, only has scales preserved.”

    Wasn’t a paper published in 2010 that reported the presence of filament-like structures extending across a substantial amount of a Juravenator skeleton?

    • Ah, yes. This had completely slipped by me; I didn’t consider it at all!

      Chiappe, L. M. & Göhlich, U. B. 2010. Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen 258(3):257-296.

      However, they seem to say that there are hints, but no actual traces. Of course, I fully expect there to be filaments, but I sadly do not have the paper to check their data.

  3. “I will generalize at this point that they are modified stage I, based on the likely LESS basal Sinosauropteryx prima and general agreement on which stage it has.”

    Another case of general agreement about fossil feathers that (as with Foth’s paper) was demonstrated to be wrong long ago in important research which was subsequently ignored by all researchers who simply accept the meme that Sinosauropteryx has stage 1 filaments without thinking about it too much.

    Currie & Chen 2001 (which as far as I know is the only non-BAND paper to examine the S. prima integument in detail and actually publish their findings) concluded that “The mixture of thick and thin strands close to the body, the increased presence of thinner strands distally, the fact that the thicker strands are posi- tioned close to the body and are normally oriented at higher angles from the body than more distal strands (Fig. 12g), the presence of areas where many of the finer strands lie adjacent and parallel to each other (even kinking together in a few places), and the tendency of finer filaments to angle away on both sides from thicker structures (Fig. 13a) all suggest a feather-like structure with central shafts and plumulaceous barbs.”

    So, the feathers of S. prima are at least Prum’s stage 3! So why does everyone continue to refer to them as “protofeathers” or stage 1 feathers? It’s not like this is an obscure paper. Sorry if I sound exasperated the the state of the literature on fossil feathers is absolutely atrocious and seems to be plagued by lack of research and plain laziness. Not only do important specimens get barely a sentence mentioning the feathers after pages and pages of detailed osteology, but the papers that do bother to describe feather structure go almost completely ignored by subsequent authors.

    Currie, P.J.; and Chen, P.-j. (2001). “Anatomy of Sinosauropteryx prima from Liaoning, northeastern China”. Canadian Journal of Earth Sciences 38 (1): 705–727.

    • Matt, I agree with you, but…

      The case for stage III is problematic, in that while Currie & Chen suggest that branching is going on, they imply it is basal, plumulaceous fluff. I imply this in the tail of Otto, in which the distal tail feathers are puffing out into a sort of ostrich-like array … but that’s as close as I will go when it comes to close examination by three groups (Chen, Currie, and of course TLS). The latter confers this “branching” to fraying of collagen, but it is irregular. So, I cannot accept stage III identification … yet. Right now, I am anchoring on at least stage I.

  4. “Currie & Chen suggest that branching is going on, they imply it is basal, plumulaceous fluff. ”
    Where do they imply this? “a feather-like structure with central shafts and plumulaceous barbs” and “filaments to angle away on both sides from thicker structures” implies to me, well… a central shaft with barbs along its length. This is what seems to be illustrated in the adjacent figure (13b). Nothing in the description seems to suggest that the barbs are radially attached to a very short rachis (i.e. Prum’s stage 2).

    • I can still agree with your premise (at the least, that the structures were branching), but not with the conclusion (that they were stage III) based also on a reading of Currie and Chen. Perhaps this is because the authors do not isolate structures for examination (because the features are too dense to do so) but also because when illustrated the structures are essentially arrayed in two directions, not the three we might expect for a full plumulaceous structure. For a stage III — as preserved in other Jiufotang specimens, especially as in NGMC 91, aka “Dave” — you should have 1) a central rachis, which should be generally oriented with other large raches and sparser than other structures; 2) an array of thinner, more numerous structures largely aligned cranial to the rachis and more dorsally projecting due to forming a leading vane; and 3) an array of structures more like 2 but oriented caudally instead. What we have preserved are portions of structures that seem to preserve 1 and 2, but in which other long structures are oriented at the distal extent of 1 which parallel those of 2 in broad arrays, but no 3. This is one of the reasong, which I don’t agree with the conclusion of, TLS things they are collagenous instead. The structures do not need to be obviously radially arrayed to be type II (as in Caudipteryx zoui).

      My running hypothesis is that they are at the least stage I with clumping stage II structures, and are aligned taphonomically, with finer features being obliterated by layering of other structures and the fineness of the preserving medium. Note that finer, layered structures are also present in other specimens from this general horizon, so in this case I take it that for NGMC 127586 and 127587, preservation was not as kind to them as it could have been. It is enough for me to at least support the most supported notion (a single rachis) rather than rely on concerning data for less supported ones (vanes and barbs), a conclusion that Xu, Zheng and You (2010) follow:

      From the supplemental online material:
      “Nine major feather morphotypes have been reported and identified in non-avian dinosaurs and Mesozoic birds[26], and only some of these morphotypes can be easily determined to correspond with modern feather types. A lack of correspondence does not, however, necessarily refute a homologous relationship, as discussed above.

      Morphotype 1 is known from the heterodontosaurid Tianyulong[30] and possibly the ceratopsian Psittacosaurus[31], and is characterized by its monofilament structure and relatively great length and rigidity. Morphotype 2 (EBFF) is also monofilamentous but differs from Morphotype 1 in its great width. It is seen in the therizinosauroid Beipiaosaurus[18], a large unnamed tyrannosauroid, and a large compsognathid specimen. Morphotype 3 is a compound structure composed of multiple filaments joined basally. This morphotype is present in the dromaeosaurid Sinornithosaurus[32] and the troodontid Anchiornis[33], and probably also in the compsognathid Sinosauropteryx, the tyrannosauroid Dilong, and Beipiaosaurus.

      18. Xu X., Zheng X.-t. & You H.-l. 2009. A new feather type in a nonavian theropod and the early evolution of feathers. PNAS 106:832-834.
      26. Xu X. & Guo Y. 2009. The origin and early evolution of feathers: insights from recent paleontological and neontological data. Vertebrata Pal Asiatica 47:311-329.
      30. Zheng, X.T. 2009, in press. A heterodontosaurid dinosaur from the Early Cretaceous of China with filamentous integumentary structures. Nature in press.
      [This is now: Zheng X.-t., You H.-l., Xu X. & Dong, Z.-m. 2009. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458:333–336.]
      31. Mayr, G., Peters, D. S., Plodowski, G. & Vogel, O. 2002. Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften 89:361-365.
      32. Xu X., Zhou Z.-h. & Prum, R. O. 2001. Branched integumental structures in Sinornithosaurus and the origin of feathers. Nature 410:200-204.
      33. Hu D.-y., Hou L.-h., Zhang L.-j. & Xu X. 2009. A pre-Archaeopteryx troodontid from China with long feathers on the metatarsus. Nature 461:640-643.”

      So, while the data for stage III is questionable, the data for stage I is secure. Xu interpolates a form of stage I in between that of I and II, but that’s not really an issue. Do I think Sino could have stage III? Sure, but I have to see stronger evidence before I will go full monty on this. Note that I still made the tail plumulaceous for the sake of the art, and I can have this both ways by arguing that the raches are basally vaned, but distally not, a feature seen in modern brush feathers … but that would be cheating for me.

      • “you should have 1) a central rachis, which should be generally oriented with other large raches and sparser than other structures; 2) an array of thinner, more numerous structures largely aligned cranial to the rachis and more dorsally projecting due to forming a leading vane; and 3) an array of structures more like 2 but oriented caudally instead. What we have preserved are portions of structures that seem to preserve 1 and 2, but in which other long structures are oriented at the distal extent of 1 which parallel those of 2 in broad arrays, but no 3.”

        Based on my reading of Prum, a feather with 1 and 2 but not 3 would *still* be stage 3, rather than stage 1 or 2. In Prum’s scheme, Stage 3 is a rachis with barbs (it doesn’t say anything about having barbs on both sides of the rachis, though the idea that you would even be able to see this in the matted feathers of Sino is questionable). Stage 2 is numerus barbs essentially stemming directly from the calamus (no real rachis to speak of) which is not what you agreed above is present in Sino. I’m not saying sino had ratite-like fully formed plumulaceous feathers, just that they cannot be considered stage 2 based on the published evidence.

        • Just realized might be misreading your comment. Are you saying that based on Currie & Chen, it would be possible to conclude that the thicker filaments (~rachides) and thinner filaments (barbs) they report are all stemming from the calamus rather than the barbs from a point somewhere along the length of the thicker filament? I agree that would be one possible interpretation but would be such a novel structure it is not parsimonious to allow for this without further study.

          • Let me put it this way, for the sake of clarity:

            I can infer that the structures in NGMC 127587 are at least stage 1 feathers, bearing a distinct tubular rachis (Currie & Chen); these structures do not distinctly bear branching filaments, and instead there are arrays of two sets of filaments that run parallel to the verebral column which the thicker, central “rachis” corresponds to; if we disregard TLS’ argument about these as collagenous structures, then we infer there are thinner filaments. This is out primary, level 1 inference. It takes a second, less strongly supported inference to indicate that they are branching structures, which would correspond at least to stage II and above, excluding flattened structures of Xu. If we assumed that the structures are branching from the central raches, then we can say that because they tend to be aligned, they form a partial vane (and thus correspond to stage III); this is your argument.

            Where this argument gets tricky, and is where I start putting my doubts on the table, is that only a trailing vane is apparent: there are only parallel-running and posterior-angled perpendicularly-angled structures — there are no vertical-oriented structures as we would assume if there was both a leading and trailing vane present. One solution is that these structures are being influences by taphonomy, and that the leading vane is obscured … in all specimens. This can happen, for example, due to overlap … but given that this is on the body wall or on the thin edge of the tail, projecting outward, the same degree of appearance of the vane as we see in Caudipteryx zoui from the same beds should also be apparent. But we do not.

            Foth argues that the methods of compression obscure details of preservation, and I will accept this. This means we are missing details. Perhaps I am also missing evidence of the leading vanes in these structures, and that they are in actuality at least stage III. I am left with then considering if they can be stage II. The parallel-running fibers hinder this, but may better explain the lack of leading barbs, in such that these are a centralized rachis that is partially developing a vane and is, perhaps, transitional with stages II and III. This would be bizarre, for as Prum and Brush argue, formation of stage III from stage II corresponds to identical development of the leading and trailing vanes as a plane. So what then if the structures are merely stage II? I suggest then that the formation of stage II in the preserving plane is causing the barbs (the thinner filaments) to form parallel-aligned arrays, and that this can cause the appearance we see (I can’t test this, and it doesn’t look like Foth accounted for it by using brush feathers, with that structure).

            I will give NGMC 127587 the benefit of the doubt and suggest it really does have stage III, but would prefer evidence of it before I do. Right now, I am having difficulty finding secure evidence for stage II. This leads me to balance stage I feathers versus collagen, the only other argument proposed, and as I mentioned here, I do not think his argument holds water.

            (I should also mention that there is the possibility that there are two types of filaments involved, a “rachis-like” form, which is sparse, relatively short, and a thinner, “filament” form which is ridiculously long, and this might also achieve the preserved effect. I’m not going to presume this idea is stronger than even a stage II feather argument.)

        • I should note that one specimen, casually referred to Sinosauropteryx prima, that if NGMC 2124, preserves what looks like absolute and clear cases of stage III (shown here from National Geographic‘s page on feathering in dinos). I wish the preservation in the type and paratype were more clear, to this level.

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