A negative view of Cosesaurus

Glad to see this
…someone else has finally taken a good look at my favorite fossil.

Cosesaurus aviceps at close to actual size.

Figure 1. Cosesaurus aviceps at close to actual size. The blob next to it is a jelly fish. No actual bones are preserved. Cosesaurus is nothing but a deep impression faithfully preserving ever aspect of its skeleton down to the finest details. The tail is especially deep, which created the impression, when transferred to 2-D, of emanating feathers. Tomorrow the same image will be presented but flipped 180 degrees.

The one and only Cosesaurus 
is a negative mold (Figs. 1, 2) in matrix so sensitive to impressions that it also preserves a jellyfish (medusa). Here (Fig. 3) the skull of Cosesaurus was photographed by doctoral candidate, now Dr. Franco Saller, in his 2016 thesis on several Macrocnemus specimens.

Figure 1. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Figure 2. Cosesaurus insitu. No bones are present. This is a negative mold (here lit from below to make it appear positive) that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Here
(Fig. 1) Adobe Photoshop software inverts the colors restoring the appearance of Cosesaurus as a positive impression, which makes it easier to interpret. Can you see the wispy cranial pycnofibers forming a crest over the orbit and antorbital fenestra?

Figure 1. GIF animation of Cosesaurus. Two frames, each five seconds long. The golden image is the negative mold in natural light. The blue image restores the appearance of a positive mold.

Figure 3. GIF animation of Cosesaurus. Two frames, each five seconds long. The golden image is the negative mold in natural light. The blue image restores the appearance of a positive mold.

Saller (p.148) wrote (translated from the original Italian):
“At the base of the orbit there is a depression that has been interpreted as a window  antorbital from Ellenberger (1977) and from Peters, which even distinguishes three antidotal windows (Peters, 2000). While the presence of a depression is certain, the conditions of conservation and the difficulty in identifying the sutures among the various elements makes it difficult to propose one of his own reliable interpretation. If it were really an anti-orbital window, this circumstance, together with the poor development of the subnarial process of the premaxillary, they would be elements a support of the hypothesis of an affinity with the pterosaurs. The analysis of the postcranial skeleton offers
however, very little space for this interpretation.”

That’s a rather short and unsupported dismissal, without phylogenetic analysis, for a taxon (Cosesaurus) with prepubes, an elongate ilium, four sacrals, the genesis of a sternal complex, a strap-like scapula, an stem-like coracoid, an attenuated tail, pycnofibers trailing the fore limbs, uropatagia trailing the hind limbs, a pteroid and preaxial carpal and a pedal digit 5.1 as long as a metatarsal, to name just a few traits that link Cosesaurus with pterosaurs.

Figure 2. Ironically, the Saller 2016 freehand reconstruction of Cosesaurus looks more like the pterosaur, Bergamodactylus, than the tracing by Peters of Cosesaurus. Yet Saller does not see the shared traits in Cosesaurus and pterosaurs.

Figure 4. Ironically, the Saller 2016 freehand reconstruction of Cosesaurus looks more like the pterosaur, Bergamodactylus, than the tracing by Peters of Cosesaurus. Yet Saller does not see or test for the shared traits in Cosesaurus and pterosaurs.

Saller presents a freehand reconstruction of the skull of Cosesaurus which I show alongside my own tracing of the skull of Cosesaurus and that of the basalmost pterosaurs, Bergamodactylus (Fig. 4). Ironically, his freehand sketch is more similar to Bergamodactylus than it is to my tracing of Cosesaurus in situ. See how dangerous freehand sketching can be? See how dangerous taxon exclusion can be?

Saller recognizes
the straight shape of the clavicles, long, thin scapulae and coracoids with an expanded articular portion, but fails to mention those are pterosaur traits not found in Macrocnemus. Saller recognizes the long preacetabular process of the ilium and the length of the hand exceeding the length of the forearm with compact metacarpals, but fails to mention those are pterosaur traits not found in Macrocnemus. Saller sees no carpals or distal phalanges on digit 4. Ellenberger and Peters both saw them earlier. Saller reports the tarsus “is not completely preserved,” but fails to mention fewer tarsals is a pterosaur trait not found in Macrocnemus. Saller reports the fifth metatarsal is, “as in the archosauromorpha, much shorter and expanded in a mediolateral direction to form a kind of a hook.” but fails to mention that’s the same shape and size seen in the lepidosaur, Huehuecuetzpalli, a taxon basal to Macrocnemus in the LRT… and also found in basal pterosaurs. Saller continues, “The first phalanx of the fifth finger is elongated and in appearance metapodial as in Tanystropheus, Langobardisaurus and Tanytrachelos,” but fails to mention those are pterosaur traits not found in Macrocnemus.

Among the other traits that Saller didn’t see,
Saller only saw two sacrals, but an elongate ilium can accommodate four.

Sad to see this
…doctoral students, now PhDs with their blinders on. Once again (remember Hone and Benton 2007 2009?), taxon exclusion is the main cause of the problems here. Why does this keep happening when the solution is just so damn simple? Add taxa to see what happens. That’s just good science.

And that’s why this blogpost exists:
To fact check those with their blinders on.

For those interested in a career in paleontology,
be prepared and look for disinformation like this. Sometimes it is not what they say, but what they should say and don’t say. 

References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Kellner AWA 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais da Academia Brasileira de Ciências (2015) 87(2): (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Saller F 2016. Anatomia, paleobiologia e filogenesi di Macrocnemus bassanii Nopcsa 1930 (Reptilia, Protorosauria). Alma Mater Studiorum – Università di Bologna Dottorato di Ricerca in Scienze della Terra Ciclo XXVII 206pp.
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Bergamodactylus
wiki/Cosesaurus

Cosesaurus paper at ResearchGate (not peer-reviewed)

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