It’s a bipedal, but folded specimen
with a skull and neck resting against its own spine (like Langobardisaurus).
The PMUZ T4823 specimen
of Macrocnemus (Peyer 1937; Figs. 1, 2) had such short forelimbs that it foreshadowed one of its more famous fully bipedal relatives, Sharovipteryx (Fig. 3). I even wondered if they were somehow sisters, but the LRT said, ‘no’, they were only convergent.
This specimen is hard to figure out
without unfolding that long neck (Fig. 2). When that happens, using DGS methods, the T4823 specimen starts to make sense. If you’re like me, sometimes the brain just needs to see things in vivo, not as if it was tucked into an eggshell.
The anterior dorsal ribs of the T4832 specimen were also extra long,
perhaps creating a wide, aerodynamic, pancake-like torso, again, as in Sharovipteryx (Fig. 3) or Draco.
Note the five sacrals that helped support this sprawling lepidosaur (according to the LRT) while bipedal.
The pectoral girdle is tiny with small, disc-like coracoids. Thus, the T4832 specimen was not flapping, like Sharovipteryx (Fig. 3).
There was a soft tissue rostral crest. Soft tissue is impressed everywhere else, too.
Like Sharovipteryx, a pair of large hyoids extend neck skin, creating an aerodynamic strake or throat sac.
That is a very slender set of cervicals for such a large skull. Perhaps most of the bone was preserved below the surface. Remember, this is a cast of the destroyed original. In any case, this was a gracile specimen. If like all other Macrocnemus specimens, it had hollow bones, too.
This is not the first time
someone has suggested that Macrocnemus was facultatively bipedal. Nopcsa 1931 and Rieppel 1989 thought so, too.
Saller writes (translated by Google form Italian):
“PIMUZ T4823: cast of the holotype, originally kept at the Civic Museum of Natural History of Milan (Museum Civico de Storia Naturale in Milano) was destroyed during the Second World War. Exemplary in a bad state of conservation, described by Peyer (Peyer, 1937). Includes skull, neck, trunk, parts of the limbs and the front portion of the tail.”
Rieppel (1989) writes:
“T2473: Specimen “Besano III” (Peyer, 1937). The specimen was collected in the “Sciti bituminous” of Besano and turned over to the Museum Civico de Storia Naturale in Milano after its description by Peyer (1937),, where it was destroyed during World War II. A cast of the specimen is preserved in Zurich. The specimen is fragmentary, but includes a well-preserved hind limb.”
A renumbered specimen?
Rieppel (1989) makes no mention of PIMUZ T 4822, T4823, T4833 or T4834, but his description of the well-known specimen, A III/208. is listed first and matches this description, so it is likely renumbered in Saller 2016,
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.
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
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.
Rieppel, O 1989. The Hind Limb of Macrocnemus bassanii (Nopcsa) (Reptilia, Diapsida): Deverlopment and Functional Anatomy. Journal of Vertebrate Paleontology. 9 (4): 373–387.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.
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.
PIMUZ – Palaeontologisches Institut und Museum, University of Zuerich, Zurigo, Switzerland.