Macrocnemus bassanii (Nopcsa 1931) Ladinian, Middle Triassic ~220mya, is known from several specimens ranging in size and varying in morphology. Romer (1970) considered Macrocnemus a lepidosaur. Carroll (1988) placed it with Protorosaurus and Prolacerta, which is where most current workers consider it, but that would be an error. Here, following a larger phylogenetic analysis, Macrocnemus is derived from a sister to the basal lizard, Huehuecuetzpalli. The smallest Macrocnemus, BES SC 111, is also the most primitive. Larger species are considered below. As in Huehuecuetzpalli, this clade practices isometric growth, so all morphological differences are indeed valid traits, not signs of immaturity within a single genus or species.

T4822 Distinct from BES SC 111 and ~ 25% larger overall, specimen T4822 had a skull with a more gracile temple. The upper temporal fenestrae were not open to the occipital plane. The cervicals were shorter and more robust. The pubis was narrower proximally. Pedal digit III was longer than IV and pedal digit V was shorter relative to metatarsal IV. This specimen nested at the base of Tanytrachelos+ Langobardisaurus and Tanystropheus.

All known specimens of Macrocnemus had a relatively short pedal digit five, so they are distinct from all other huehuecuetzpalians. However, several characters appear to bridge gaps between Huehuecuetzpalli and Cosesaurus. Strangely, many of the nested descendants of Macrocnemus retained or regained the elongated digit V. This is a mystery that needs more data and more study.

T4823 is a small, poorly preserved Macrocnemus with short forelimbs and 5 sacrals indicating yet another bipedal configuration, convergent with Sharovipteryx.

T2472 was nearly twice as long as T4822. The rostrum was longer and the posterior cranium iwas depressed. The palatal reconstruction offered here is narrower than illustrated by Kuhn-Schnyder (1962) due to the narrowness of the maxilla and premaxilla. The mandible was more gracile. The anterior teeth were larger than the others. The cervical count increased to ten. The posterior ribs demonstrated that the torso and tail base were wider than deep because the stuck out laterally.

Likely less able to clamber in the trees due to its size, this taxon may have preferred the ground or sea, especially considering the apparently terrestrial characters of its sister taxon, Macrocnemus fuyuanensis (below).

Macrocnemus fuyuanensis (Li, Zhao and Wang 2007; Middle Triassic, < 1 m in length; GMPKU P3001), was the only Macronemus not considered conspecific by its authors. Distinct from T2472, M. fuyuanensis had a coracoid with a concave posterior margin (as in Cosesaurus), only eight cervical vertebrae and an ischium with a flared distal margin.

The Tritosauria ("third lizards") is a new squamate clade, now all extinct. It flourished in the Triassic, but was reduced to only the Pterosauria during the Jurassic and Cretaceous.

Tanystropheidae and Fenestrasauria (including Pterosauria) were successively derived from Huehuecuetzpalli and Lacertulus.

At right is a small subset of the large reptile family tree.

In addition the large pterosaur tree includes more pterosaurs.

Kuhn-Schnyder E 1962. Ein weiterer Schädel von Macrocnemus bassanii Nopcsa aus der anisischen Stufe der Trias des Monte San Giorgio (Kt. Tessin, Schweiz). Palaeontologische Zeitschrift 36:110-133.

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.

Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

Scheyer TM, Wang W, Li C, Miedema F and Spiekman SNF 2020. Osteological re-description of Macrocnemus fuyuanensis (Archosauromorpha, Tanystropheidae) from the Middle Triassic of China. Vertebrata PalAsiatica. DOI: 10.19615/j.cnki.1000-3118.200525

Wang et al (6 co-authors) 2023. A new long-necked archosauromorph from the Guanling Formation (Anisian, Middle Triassic) of southwestern China and its implications for neck evolution in tanystropheids. Anatomical Record (Hoboken) 2023. doi: 10.1002/ar.25216. Online ahead of print.

wiki/Gracicollum
wiki/Macrocnemus