Pholidocercus and Alcidedorbignya now together in the LRT
Two traditional fossil placentals
Middle Eocene Pholidocercus (Figs 1, 2) and Early Palaeocene Alcidedorbignya (Figs 3, 4) now unite as primitive marsupials in the large reptile tree (LRT, 2324 taxa). Their last common ancestor (at least for the moment) in the LRT is extant mouse-like Monodelphis domestica.
Figure 1. Only one of the several Messel Pit Pholidocercus specimens. This one has a truncated tail and a halo of soft tissue (pre-spines).
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2019/01/pholidocercus-insitu588.gif?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2019/01/pholidocercus-insitu588.gif?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-35443″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2019/01/pholidocercus-insitu588.gif” alt=”Figure 1. Only one of the several Messel Pit Pholidocercus specimens. This one has a truncated tail and a halo of soft tissue (pre-spines).” width=”584″ height=”377″ />
Figure 1. Only one of the several Messel Pit Pholidocercus specimens. This one has a truncated tail and a halo of soft tissue (pre-spines).
Earlier the LRT overlooked the similarities between these two taxa
due to several scoring errors. Adding the dorsal and ventral views of Pholidocercus (Fig 2) clarified several sutures. The lacrimal (tan) overlapping the jugal (cyan) is a recent insight. The nasal (pink) now extends to mid orbit. Four incisors are shown in ventral view. Only three are visible in lateral view.
Figure 2. Skull of Early Eocene Pholidocercus in three views.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/pholidocercus-skull588.jpg?w=180″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/pholidocercus-skull588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-88814″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/pholidocercus-skull588.jpg” alt=”Figure 2. Skull of Early Eocene Pholidocercus in three views.” width=”584″ height=”972″ />
Figure 2. Skull of Early Eocene Pholidocercus in three views. Compare the retroartcular process of this taxon with that of Alcidedeorbignya in figure 4. That’s what originally raised the eyebrow of suspicion that these two were possibly related.
Pholidocercus hassiacus
(von Koenigswald & Storch 1983; HLMD Me 7577; Middle Eocene) is an extinct sister to Erinaceus. Known from several fossils, Pholidocercus has a long thick tail provided with tall neural spines and deep chevrons. The rostrum is short. Soft tissue is preserved as scales on the head in a helmet-like formation and scales on the tail, a pattern convergent with armadillos.
Figure 3. Alcidedorbignya skeleton in lateral view.
Alcidedorbignya inopinata
(Muizon and Marshall 1992 Muizon et al 2015; MHNC 8372, Early Paleocene, 64 mya; scale bar is 2cm) was originally considered a basal pantodont (Condylartha) close to Pantolambda and the origin of ungulates and digging placentals. The rostrum is curved with a smaller naris. Long hooves are former claws on a semiplantigrade manus.
Figure 3. Alcidedorbignya skull about full scale at 72 dpi screen resolution. Select bones are colorized.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/alcidedorbignya-skull588.jpg?w=294″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/alcidedorbignya-skull588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-88816″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/alcidedorbignya-skull588.jpg” alt=”Figure 3. Alcidedorbignya skull about full scale at 72 dpi screen resolution. Select bones are colorized. ” width=”584″ height=”597″ />
Figure 3. Alcidedorbignya skull about full scale at 72 dpi screen resolution. Select bones are colorized.
If these two taxa are not closely related,
the convergence is worth noting. In the LRT the pantodonts first entered as marsupials, then placentals, now some are marsupials again.
The present scoring program,
Mesquite, permits traits to be scored with more than one score. I’m likely the last to know this. Even so, I’m taking advantage of this option. Like evolution itself scores are no longer restricted to discrete A or B or C or D. Now a transitional AB or CD can be scored. This is especially useful when the nuchal and parasagittal crests are just barely visible rising over an otherwise broad cranium… as well as other such borderline decision traits.
References
deMuizon C, Billet G, Argot C, Ladeveze S and Goussard F 2015. Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology. Geodiversitas 87(4):397-634.
von Koenigswald W and Storch Gh 1983. Pholidocercus hassiacus, ein Amphilermuride aus dem Eozan der “Grube Messel” bei Darmstadt (Mammalia: Lipotyphla). Senchenberg Lethaia 64:447–459.
wiki/Pholidocercus
wiki/Alcidedorbignya
Source: https://pterosaurheresies.wordpress.com/2024/09/18/pholidocercus-and-alcidedorbignya-now-together-in-the-lrt/
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