We’ve looked at DGS (Digital Graphic Segregation) before here, here and here. Today another example, pulling more data from a published photo of a prehistoric reptile crushed flat on an Early Cretaceous matrix. It’s Eichstaettisaurus gouldi (Evans et al. 2004, Figs. 1-7), a pre-snake, which we looked at yesterday.
Figure 1. The hind limb and skull of Eichstaettisaurus gouldi according to Evans et al. 2004.
DGS is a method of tracing the bones (Figs. 2-6), then using the tracings to reconstruct the animal (Fig. 7). On the other hand, by using traditional methods, Evans et al. (2004) produced conventional tracings (Fig. 1).
Figure 2. Eichstaettisaurus gouldi in sintu and traced in color. Here the tail and other bones are identified.
Overall the specimen (Fig. 2) appears to lack most of its dorsal vertebrae and most of its tail. However, using DGS enables these areas to provide data.
Figure 3. Eichstaettisaurus gouldi pes in situ and traced in color. Compare to figure 1. Impressions count in paleontology, not just bones.
Here (Fig. 3) the foot of E. gouldi is traced using colors for digits. Compare this data to the original tracings of Evans et al. (2014, Fig. 1). All of the elements are similar to those in sister taxa. All PILs (parallel interphalangeal lines) are continuous.
Figure 4. Eichstaettisaurus gouldi skull in situ and colorized in ventral view.
Here (Fig. 4) is the skull in ventral view with elements identified (for mandible and palatal bones see below). Rather than a hyoid, as originally tentatively identified, a supratemporal (St) is positively identified here and there’s another one, too. Elements not originally identified include the prefrontal (Prf), postfrontal (Pof), lacrimal (La), nasal (Na), opisthotic, (Op) and supra occipital (So).
Figure 5. Eichstaettisaurus gouldi mandible in situ traced and colorized.
Here (Fig. 5) the mandible elements are digitally segregated. Here teeth are identified. In figure 1 no teeth are identified, but Evans et al. (2004) do note the presence of teeth in the text.
Figure 6. Eichstaettisaurus gouldi palate in situ and colorized. More elements were found here using DGS than by personal examination of the specimen by the three authors, who should have thought it odd that in ventral view so few palatal elements could be identified ten years ago.
Here (Fig. 6) the palate elements are identified using DGS. They are few and far between. Evans et al. only identified the pterygoids, premaxilla and maxilla.
Figure 7. Eichstaettisaurus schroederi. Previous to 2004, the only known specimen of this genus. Proximal carpals are missing here, as they are missing in Adriosaurus.
Eichstaettisaurus schroederi (Fig. 7) has a more generalized (plesiomorphic) shape. The palate can be partly seen within the orbit, and the elements are more robust than in E. gouldi.
Figure 8. Eichstaettisaurus gouldi. A transitional taxon in the lineage of terrestrial snakes. Here all the parts listed above are added to a reconstruction to ensure fit, both mechanically and phylogenetically. The scapula is assumed to have a soft dorsal extension, as in Varanus. The ribs are more slender than phylogenetic bracketing would indicate, and the coracoids are triangular, the only autapomorphies I’ve found so far. Not sure about neural spines as these are buried in the matrix.
A reconstruction of E. gouldi (Fig. 8) demonstrates the validity of the DGS interpretations as all parts fit both mechanically and phylogenetically. See Varanus, Ardeosaurus, Adriosaurus (Fig. 9) and Pachyrhachis for phylogenetic bracketing. Thus, all the parts are transitional morphologies between varanids and basal snakes. Even the anterior bowing of the radius is found in Adriosaurus.
Figure 8. Various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely. Note the curved radius and long pedal digits as in E. gouldi.
Eichstaettisaurus gouldi is the first taxon in the lineage of snakes to demonstrate an elongate torso and reduced limbs (though not by very much at this point). These become exaggerated in Adriosaurus and Pachyrhachis.
Evans SE, Raia P and Barbera C 2004. New lizards and rhynchocephalians from the Lower Cretaceous of southern Italy. Acta Palaeontologica Polonica 49:393-408.