Earlier we discussed the evolution of the pterosaurian sternal complex beginning with the plesiomorphic basal tritosaur lizard, Huehuecuetzpalli, and continuing through Cosesaurus (Fig. 1). Though flightless, Cosesaurus had all the elements of a pterosaurian sternal complex in place: 1) strap-like scapula; 2) quadrant-shaped coracoid with stem attached to interclavicle anterior to the transverse processes; 3) cruciform interclavicle; 4) transverse clavicles rimming the broad sternum; 5) sternum and interclavicle layered and coincident. In pterosaurs the clavicles extend posteriorly along an initially triangular sternum and in most pterosaurs the coracoid stem straightens out. So it looks like Cosesaurus was flapping, but not flying.
The evolutionary leap from Huehuecuetzpalli to Cosesaurus was great, but not insurmountable. Now we find a transitional taxon between these two to better bridge that gap and provide data on the order of changes. Some surprises and unexpected wonders are here that should open all new chapters on the origin of vertebrate flapping and flight.
Today we reexamine Langobardisaurus tonelloi (Figs. 1-3), a close relative of Cosesaurus, Tanytrachelos and the long-necked giant, Tanystropheus. Langobardisaurus demonstrates a transitional phase in the evolution of the fenestrasaurian/pterosaurian pectoral girdle.
New Interpretations of the Langobardisaurus pectoral elements
Renesto’s tracing of L. tonelloi (Fig. 2) included his interpretations based on what was known of sister taxa at the time, all of which were thought to have a Tanystropheus/Macrocnemus-like pectoral girdle with short broad, elliptical elements. Now Cosesaurus (Fig. 1) offers new possibilities. Here colorized to re-identify the elements (Fig. 2), the original coracoid is now the broad clavicle. The original scapula is now the coracoid. The original rib #10 (on the right) is now the strap-like scapula. Rib #10 (on the left) and the sternum were identified correctly. See below for a reconstruction and comparison.
Distinct from Cosesaurus
The coracoid in L. tonelloi did not develop an elongated stem. Otherwise the Cosesaurus and Langobardisaurus shared many pectoral shapes and arrangements.
In order for the fenestrasaur pectoral girdle to develop, the coracoids had to move anterior to the interclavicle transverse processes. Langobardisaurus gives us that transitional mid-point. Remember the sternal complex was chiefly transverse in orientation while the the scapula/coracoid was largely parasagittal.
Bipedalism Frees up the Forelimbs
How the muscles shifted and why they shifted is still to be determined. A study by Renesto, Dalla Vecchia and Peters (2002) described the bipedal abilities of Langobardisaurus. When the forelimbs rise off the substrate, they are free to do other tasks. There’s the opportunity.
The coracoids do not appear to be locked in place in Langobardisaurus as they were in Cosesaurus, so pterosaur-like, bird-like flapping was not so well developed.
As small insectivores, langobardisaurs and cosesaurs might have made tasty meals for larger predators. If similar in their bipedal abilities to the living lizard, Chlamydosaurus (Fig. 4), then bluff and charge might have been in their repertoire. Lacking expanding neck skin, langobardisaurs and cosesaurs might have charged bipedally frantically waving their forelimbs. This might have also impressed the girl langobardisaurs and if that’s deemed sexy, well, folks, you just get more of the same generation after generation.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.