Modified June 09, 2015 with the addition of clades named by Peters 2000 overlooked by Pritchard et al. 2015.
Pritchard et al. (2015)
report on 3D Tanytrachelos (Fig. 1) individual bones from New Mexico (Late Triassic, Chinle Formation). And I think they’re spot on with regard to bone identification.
The problem comes from their phylogenetic analysis.
From the Pritchard et al. text: “Our analysis incorporated a range of fossil taxa that have traditionally been allied with Tanystropheus and Macrocnemus.” Unfortunately that tradition is ‘bogus’ based on the larger taxon list of the large reptile tree in which macronemids and tanystropheids are lepidosauromorphs, not archosauromorphs. In the Pritchard et al. cladogram (Fig. 2) note the separation of Prolacerta and Protorosaurus to make room for a “by default clade” of tanystropheids that should nest within the Lepidosauromorpha when more taxa are added. This abbreviated taxon list and “by default clade” actually separates the two prorotorosaurs from each other.
of the large reptile tree taxon list (Fig. 3) matched (as closely as possible) to the Pritchard et al taxon list demonstrates the problems with such a short taxon list using these taxa in which archosauromorphs and lepidosauromorphs are shuffled like a deck of cards. And sister taxa do not resemble one another at each color-shift clade. For instance, in figure 2 Macrocnemus does not resemble Mesosuchus and in figure 3 Macrocnemus does not resemble Petrolacosaurus.
Traditions need to be tested
The Pritchard et al. studied relied on a traditional taxon list that was falsified four years ago here. So why did the referees let this manuscript get published? (Answer: tradition, status quo, established paradigm, plus shunning, marginalizing, ignoring the larger gamut study).
The sternum issue
Tanystropheids, like all tritosaurs and most squamates (but not Adirosaurus through snakes because the forelimbs are shrinking), have a sternum not found in protorosaurs and other archosauromorphs. I know I just pulled a “Larry Martin” by noting one and only one trait…
below is the list of all the other traits from the large reptile tree that unambiguously separate tanystropheids (T) from protorosaurs (P). There are 30. Many of these traits extend to other tritosaurs (a subset of the Lepidosauria) and are not found in other archosauromorphs or vice versa.
- ventral naris: T = chiefly mx; P = chiefly pmx
- dorsal nasal shape: T = pmx invasion; P = narrows toward naris
- pmx orientation: T = horizontal; P = down
- naris placement: T = displaced or elongated; P = snout tip
- posterolateral pmx: T = absent; P = narrower than naris
- frontal/parietal suture: T = straight and > than nasal suture; P = not
- frontal shape: T = wider posteriorly; P = not
- frontal posterior process: T = absent; P = present
- postparietals: T = absent; P= present
- tabulars: T = absent; P = present
- friontal/nasal suture: T = anteriorly oriented; P = zigzag
- quadratojugal presence: T = jugal ramus only; P = quadrate ramus only
- squamosal/quadratojugal indent: T = no qj ascending process; P = semicircle
- parietal and frontal fusion: T = both fused; P = no fusion
- pterygoid lateral edge: T = ectopterygoid continues margin laterally; P = sharp angle
- pterygoid shape: T = narrow; P = broad triangular
- procumbent pmx teeth: T = present; P = absent
- posterior mandible shape: T = deeper anteriorly; P = mid rise
- caudal transverse processes: T = absent beyond 8th caudal; P = present beyond
- short lumbar ribs: T = present; P = not short
- second sacral rib: T = not bifurcate; P = bifurcate
- chevron shape: T = parallel to centra; P = descends, distal wider
- anterior caudal spines: T = shorter than centra; P = taller than centra
- sternum: T = present; P = absent
- scapula shape: T = not robust; P = robust
- pubic apron: T = not present; P = present and wide
- tarsus: T = not fenestrated; P = fenestrated
- calcaneal tuber: T = no tuber: P = lateral tuber
- metacarpal 5: T = straighter or twisted: P = hooked
- pedal 3.1 longer than p2.1: T = present; P = not
This reference probably snuck under the radar
Pritchard et al. noted several unnamed clades that were actually named in Peters 2000, some 15 years ago. Further work with the large reptile tree has shown that these clades are all lepidosaurian, not archosaurian or protorosaurian.
Clades named by Peters 2000
Macrocnemus + Characiopoda
Tanystropheidae + Langobardisaurus + Fenestrasauria
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Pritchard AC, Turner AH, Nesbitt SJ, Irmis RB and Smith ND 2015. Late Triassic tanystropheids (Reptilia, Archosauromorpha) from northern New Mexico (Petrified Forest Member, Chinle Formation) and the biogeography, functional morphology, and evolution of Tanystropheidae. Journal of Vertebrate Paleontology 25(2):e911186 (20pp).