Enigmatic Apterodon enters the LRT with marsupial dogs and cats

Updated April 2, 2022
with nearly a hundred more taxa and scoring corrections.

Taxon exclusion problems have followed this genus
for over 100 years. In the large reptile tree (LRT, 1972+ taxa; subset Fig. 4) Apterodon (Fig. 1) nests with the IVPP V 12385 specimen assigned tentatively to Hapalodectes hetangensis (Fig. 2). Apterodon is much larger and the orbit is further forward. It is best known from two 20cm skulls (AMNH 13236 and 13237) and a mandible (AMNH 13241, Fig. 3) from Oligocene deposits in the Fayum Depression of Egypt where small to giant archaeocete whales are found. The related tiny anagalid, Ptolemaia, is also found there.

According to Wikipedia
“Apterodon is an extinct genus of hyaenodontid mammal that lived from the mid Eocene through the Oligocene epoch.”

Perhaps they were following Szalay 1967, who reported, “As is shown in the above presentation and discussion, the undoubted hyaenodontid affinity of Apterodon is confirmed.” In the LRT (Fig 1) Hyaenodon nests in a nearby clade.

Figure 1. Apterodon, Pterodon, Hapalodectes and kin derived from a sister to Thylacinus.
Figure 1. Apterodon, Pterodon, Hapalodectes and kin derived from a sister to Thylacinus. Note the convergence here with placental dogs and cats.

Szalay and all prior workers were slightly wrong, according to the LRT.
Taxon exclusion is the issue here (again). Hyaenodontids are creodont marsupials in the LRT. Szalay followed Van Valen 1965 who erected the clade Deltaheridia within Creodonta within Placentalia, separating these clades from Carnivora, not realizing the marsupial affinities.

Figure 3. Apterodon skull and mandible material. The AMNH 13237 small skull (lateral view) is the same one shown in figure 1 as a diagram.

Szalay 1967 wrote,
“The mere fact that the preglenoid process of Apterodon is large and well developed (point 3) is a feature shared with mesonychids. Instead of viewing one fact out of context, however, we can examine the structures that are in close morphogenetic dependence on one another-in
this case the entire zygomatic portion of the squamosal and its relation to the posterior part of the cranium.”

Ironically,
Szalay 1967 was the first worker to warn others not to “Pull a Larry Martin” when he said, “Instead of viewing one fact out of context”. Then he went ahead and pulled his own Larry Martin when he continued, “however, we can examine… the entire zygomatic portion of the squamosal and its relation to the posterior part of the cranium.”

Don’t list traits. Run your analysis. Let the software do the work. Find a last common ancestor for your clade of interest. Then list traits, noting instances of convergence. Granted, no one in 1967 had this option.

Van Valen 1966 wrote:
“The relationships of Apterodon are questionable.” He mentions that several workers considered Apterodon a mesonychid, then lists several hyaenodontid traits found in Apterodon that are not known in mesonychids, then reverses himself with other traits.

Van Valen 1966 also wrote,
“Ptolemaia has a number of similarities to the Mongolian genus Anagale, of which the most important follow.” In the LRT (Fig. 4) Ptolemaia (also from the Fayum Depressions) is another sister to Apterodon, but Van Valen never made the connection.

According to Wikipedia
“With the exception of the type species, A. gaudryi, all species of Apterodon are known from Africa. Uniquely among hyaenodontids, it was a semiaquatic, fossorial mammal. It possessed strong forelimbs that were well equipped for digging, compared to those of modern badgers, while the tail, torso and hindlimbs show adaptations similar to those of other aquatic mammals like otters and pinnipeds. The dentition was suited to feed on hard-shelled invertebrate prey, such as crustaceans and shellfish. It probably lived along African coastlines.”

Previous workers did not include Apterodon sister taxa in their analyses.
Omitting taxa leads to confusion. The LRT leads to discovery by minimizing taxon exclusion. Other workers minimize discovery by omitting taxa. Don’t follow those who are academically forced to do the bidding of their professorial masters. Don’t follow those who borrow cladograms or create supertrees. Create your own cladogram. Then you’ll have this powerful tool for the rest of your professional career.

Apterodon macrognathus
(Fischer 1880; Eocene to Oligocene; Fig. 1) was considered a member of the Hyaeodontida, a clade within Creodonta, a clade within Marsupialia in the LRT. Here Apterodon nests with the IVPP V 12385 specimen (Fig. 2) assigned tentatively to Hapalodectes hetangensis (above) close to the Delatheroidea. Apterodon is much larger, The orbit is further forward. The teeth extend behind the orbit. What looks like a carnassial is the anterior of four molars. The small, transverse premaxilla has two robust teeth. The mandible (= dentary) has no retroarticular process in one species, a straight process in another. Most specimens are from Egypt. The type genus is from Germany.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation for the earlier hypothesis so I can promote it here.

wiki/Apterodon

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