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:
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:
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:
[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.