This started with
a fuzzy photo of a complete fossil Macrocnemus specimen, PMR T2472 (Fig 1).
Figure 1. Skull of the T2472 specimen attributed to Macrocnemus with higher resolution. Earlier mistakes (below) are corrected here. Epipterygoids are displaced to the orbit and anterior orbit region.
Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.
Many specimens attributed to Macrocnemus
are known, each one a little different phylogenetically. Reports of a ‘juvenile’ Macrocnemus refer to the phylogenetically basalmost and smallest of the known specimens, the one closest to its outgroup taxon, the tritosaur lepidosaur, Huehuecuetzpalli.
It’s good to remind yourself
before reading the reference titles, that Macrocnemus and kin are not protorosaurs (= prolacertiforms), nor are they archosauriforms. Even I made the same mistake (Peters 2000b) in my more naive days before the LRT recovered Macrocnemus and kin as tritosaur lepidosaurs in Peters 2007.
From this rather ordinary taxon arises
such diverse and exotic taxa as Dinocephalosaurus, Sharovipteryx, a variety of Tanystropheus, several Langobardisaurus, Longisquama and pterosaurs. Peters 2007 reported, “The basal lizard, Huehuecuetzpalli is the most primitive taxon in this newly revealed third squamate clade between Iguania and Scleroglossa. Two branches arise from it. Jesairosaurus is basal to the Drepanosauridae. Three distinct specimens of Macrocnemus give rise to the Tanystropheidae,the Langobardisaurinae and to the Fenestrasauria respectively.” Jesairosaurus and Drepanosauridae are now basal lepidosauriformes.
References
Li C, Zhao L-J and Wang L-T 2007. A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
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 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.
The Pterosaur Heresies 