Earlier in six prior posts we looked at some new basal amniotes revealed by phylogenetic bracketing and phylogenetic analysis. Data was gleaned by DGS, Digital Graphic Segregation, a technique that is currently used by a few paleontologists and should be used more often by more of them as you’ll see in the present demonstration.
DGS – Digital Graphic Segregation
has been getting a bad rap for a long time. Here, once again, I was able to find more bones than did prior workers not using DGS. Instead they examined these basal amniotes first hand and created tracings or sketches in their own manner, often without great precision and too often leaving out bones that were indeed present (Fig. 1).
Here’s a good chance to judge the results for yourself.
If this is voodoo, if this is useless, ignore it. If you think it has value, embrace it. Click here to see a rollover image of Gephyrostegus watsoni, both in situ and with bones colorized. The original image was 600 dpi. The presentation on the web is at 72 dpi. Even so you’ll have trouble seeing everything. Sometimes it takes awhile. I can only share my results and encourage you to experiment on your own.
is a crushed Westphalian (310 mya) amniote currently considered to be an anamniote juvenile of Gephyrostegus bohemicus. It was traced by Brough and Brough (1967) and Carroll (1970, Fig. 1). Brough and Brough determined that it was sufficiently distinct from the holotype of G. bohemicus to erect a new species. Carroll did not recognized those differences and so considered it a juvenile lacking carpals and tarsals, having a large skull with short rostrum and other traditional juvenile traits. Klembara et al. (2014) agreed.
DGS found more bones than firsthand observation and enabled a precise reconstruction (Fig. 3). Tracing the bones in color enables one to lift those bones, as they are, to create a more accurate reconstruction while minimizing handwork that could introduce error.
Phylogenetic analysis nests G. watsoni with Eldeceeon (Fig. 4), not with G. bohemicus. So this specimen is not a juvenile and it needs a new generic name. DGS was key to recovering the data found here. If you take a look at the specimen with colorized bones, you’ll soon realize that the several layers would leave a pencil and a prism in the dust. On the computer monitor tracing becomes simpler pulling bones out of the chaos on the matrix layer by layer.
And here’s a second example
Eldeceeon is a Viséan amniote known from another crushed skeleton (Fig. 4). Here I was able to find more bones than in prior tracings (Fig. 5) and create a more accurate reconstruction (Fig. 6) than created by prior workers (Fig. 7).
Note that drawings of bones often unlabeled, don’t tell the whole story. By colorizing each bone and using the same color for the left and right counterparts the chaos is reduced and reconstructions can be created with ease.
These two Eldeceeon specimens (Fig. 6) nest together, but would clearly be distinct genera if they lived in the modern world. This also means that if you use the skull of one on the body of the other, you will create a chimaera, which only leads to phylogenetic trouble. See the family tree of basal amniotes here. See basal amniotes to scale here.
Data from the literature
While we all have to rely on specimen drawings and reconstructions, that’s not always a good idea, as this little exercise demonstrates. After DGS I have more confidence that the reconstruction is more accurate.
The upshot is
with DGS I was able to more accurately nest these taxa on this side of the anamniote/amnote transition and shed new light on this important stage in the evolution of amniotes/reptiles, including you and me. Making discoveries like this is richly rewarding. The extra effort used to create DGS is definitely worth the extra effort.
this demonstration puts an end to the bad rap that DGS has been getting.
And a big hello
to all the paleontologists in Berlin attending the SVP convention there.
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165.
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Smithson TR 1994. Eldeceeon rolfei, a new reptiliomorph from the Viséan of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (3-4): 377–382.