Nothing is known of the pterosaur ancestor,
Cosesaurus aviceps (Figs. 1, 2), except an exquisite mold that preserves an impression of its bones and soft tissue — along with the softest of soft tissue: a jellyfish also impressed into the matrix (the blob in Fig. 1), and a few trapped air bubbles.
Mold fossils are interesting.
Shadows and highlights are the only data. By rotating the light and viewing angle some bones appear and others disappear. So, you need to see such fossils from several angles.
I reexamined a photo of the pelvis and sacral vertebrae of Cosesaurus. I suspected the pubis and ilium were actually deeper than I previously thought. That hunch paid off (Figs. 3, 4) as DGS tracings showed edges of the pubis and ischium peeking out from both sides of other overlapping bones, sometimes rotated from their original positions.
When both pelves matched
that confirmed the new interpretations.
These new reconstructions and orientations
also more closely match both ancestral and descendant taxa (Fig. 5). These corrections are but a few of the over 100,000 corrections made during the last ten years. The LRT is getting better and better with every improvement like this.
(Ellenberger and DeVillalta 1974; Ladinian, upper Middle Triassic ~230 mya, ~16cm long), was originally considered an ancestor of birds, then a juvenile Macrocnemus (Sanz and López-Martinez 1984) and finally an ancestor of pterosaurs (Peters 2000a, b; 2009).
Here Cosesaurus was derived from a sister to Huehuecuetzpalli and, more proximally, BES SC 111. Cosesaurus was a basal fenestrasaur that phylogenetically preceded Sharovipteryx, Longsiquama and pterosaurs. This is a hypothesis that pterosaur workers with PhDs have avoided for the last twenty years. For reasons only they know, other paleo workers have preferred to report, “We don’t know where pterosaurs came from” or “pterosaurs are the closest relatives of dinosaurs.” Those who make their living from delivering traditional lectures and selling traditional textbooks have been suppressing this information.
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.
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
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.