Tiny enigmatic Feralisaurus nests with a giant bizarre sister

Today
another paleo-enigma is confidently nested after those who had direct access to the specimen gave up on it. The authors admitted they didn’t know what they had.

According to the Cavicchini, Zaher and Benton 2020 abstract:
“Phylogenetic analyses, although showing generalized weak support, retrieved Feralisaurus within Neodiapsida or stem-group Lepidosauromorpha: its morphology supports the latter hypothesis.”

The authors gave up because they excluded pertinent taxa.
The authors did not reference the large reptile tree (LRT, 1745+ taxa; subset Fig. 6), which minimizes taxon exclusion. Here, having a quantity of taxa really paid off.

The ‘enigmatic Otter Sandstone diapsid’ from 2017 finally has a name:
Feralisaurus corami (Cavicchini, Zaher and Benton 2020; Coram, Radley and Benton 2017; BRSUG 29950-12; Middle Triassic). Cavicchini, Zaher and Benton 2020 provided µCT scans (Fig. 1) from which a reconstruction was created and scored using DGS (digital graphic segregation). They nested aquatic Feralisaurus between the gliding reptile, Coelurosauravus and basal lepidosaurs + another gliding reptile, Icarosaurus (Fig. 5).

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here.

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here. Shown about 20% larger than life size. Here more cervicals are present, a sternum is present, The tip of the posterior interclavicle is identified along with several skull bones. Creating or attempting to create a reconstruction is the second half of the DGS method and, as you can see, it is so important in understanding all enigmatic specimens.

After DGS, reconstruction and re-scoring in the LRT
(Fig. 6), tiny, flat-headed Feralisaurus nests with the giant, flat-headed macrocnemid tritosaur lepidosaur Dinocephalosaurus. Both are derived from the PIMUZ 2477 specimen of Macrocnemus, nesting apart from the other tested Macrocnemus specimens (Fig. 6).

Figure 6. Dinocephalosaurus skull in situ.

Figure 2. Dinocephalosaurus skull in situ. The maxillary palatal shelf? is not colored here.

The dorsal nares in both Feralisaurus and Dinocephalosaurus
may have emitted stale air as a bubble net to corral fish swimming overhead (Fig. 3), analogous to the feeding strategy of baleen whales. The larger the size, the longer the neck, the greater storage for this stale air. Perhaps that is what drove the transition from tiny Feralisaurus to the much larger Dinocephalosaurus.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 3. Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis.

Coram, Radley and Benton 2017
presented (then nameless) Feralisaurus as a “small diapsid reptile, possibly, pending systematic study, a basal lepidosaur or a protorosaurian.” According to Coram et al. “The Middle Triassic (Anisian) Otter Sandstone was laid down mostly by braided rivers in a desert environment.” 

What was visible to the unaided eye
in the 2017 report suggested a relationship to the basal lepidosaur, Megachirella. The 2020 µCT scans of Feralisaurus data corrected earlier errors. Here (Fig. 4) is the first reconstruction of Feralisaurus based on DGS. The new data nests it with Dinocephalosaurus, despite the great difference in size, the differences in morphology and the niche relocation from braided river in a desert to ocean.

Figure 2. Feralisaurus reconstructed in lateral and dorsal views.

Figure 4. Feralisaurus reconstructed in lateral and dorsal views.

Although Cavicchini, Zaher and Benton 2020 scanned the specimen
those scans were not enough to clarify phylogenetic issues. The authors not only excluded its LRT sister, Dinocephalosaurus, but hundreds of other taxa that would have split basal Reptilia into the new Archosauromorpha and the new Lepidosauromorpha (Fig. 5) as in the LRT. This basal dichotomy following Silvanerpeton in the Viséan (or earlier) is recovered when sufficient pertinent basal taxa are added to a reptile cladogram. Apparently no one wants to add hundreds of taxa when ready-made smaller invalid cladograms are available.

Figure 3. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

Figure 5. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

The Cavicchini, Zaher and Benton 2020 cladogram
shows what happens when you include too few taxa. As in prior analyses of similar deficit, this one (Fig. 5) shuffles members of the new Archosauromorpha and new Lepidosauromorpha. The Cavicchini, Zaher and Benton 2020 cladogram nests the glider Icarosaurus, with the large plant-eating Trilophosaurus. Note how easily rhynchosaurs (Lepidosauromorpha) nest with protorosaurs (Archosauromorpha) here splitting Protorosaurus from Prolacerta. The LRT adds enough taxa to nest rhynchosaurs with rhynchocephalians and Protorosaurus with the other protorosaur, Prolacerta.

Figure 4. Subset of the LRT with the addition of Feralisaurus (yellow).

Figure 6. Subset of the LRT with the addition of Feralisaurus (yellow).

Feralisaurus was a tiny river predator,
smaller than the PIMUZ 2477 Macrocnemus. Dinocephalosaurus was a giant marine predator with a longer neck, shorter limbs and other extreme traits.

Once again, phylogenetic miniaturization
appears to have preceded a novel morphology.

The apparent lack of maxillary bone
in Feralisaurus (perhaps due to taphonomy) continues as a likely antorbital fenestra in Dinocephalosaurus. What was considered a lateral panel of the maxilla could instead be a maxillary palatal shelf showing through the antorbital fenestra. The broad muzzle and genuine flatness of the Feralisaurus skull continues in Dinocephalosaurus.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Bottom line: 
Create reconstructions using DGS. Add taxa. These methods solve problems. Workers traditionally say first-hand observation is essential. This case proves, once again, first-hand observation is not essential. A cladogram as large as the LRT is essential.


References
Caviccnini I, Zaher M and Benton MJ 2020. An enigmatic neodiapsid reptile from the Middle Triassic of England. Journal of Vertebrate Paleontology e1781143 (18 pages)
Coram RA, Radley JD and Benton MJ 2017. The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead. Proceedings of the Geologists’ Association in press. http://dx.doi.org/10.1016/j.pgeola.2017.06.007

http://reptileevolution.com/dinocephalosaurus.htm

https://pterosaurheresies.wordpress.com/2017/07/27/what-is-the-enigmatic-otter-sandstone-middle-triassic-diapsid/

wiki/Feralisaurus
wiki/Dinocephalosaurus

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.