Can a member of the Carnivora have four molars?

Traditionally
four molars are present in many (but not all ) marsupials and in several other clades within Placentalia.

By contrast
only two or three molars are present in all members of the clade Carnivora (Placentalia), like Daphoenus and Protictitherium (Fig 1)…

…with the exception of
the IVPP V12385 specimen attributed to Hapalodectes (Fig 1). It has four molars.

Figure 1. Daphoenus and Protictitherium skulls to scale with the smaller IVPP V12385 specimen, which has four molars, not three. ” data-image-caption=”

Figure 1. Daphoenus and Protictitherium skulls to scale with the smaller IVPP V12385 specimen, which has four molars, not three.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/daphoenus_protictitherium_size.jpg?w=165″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/daphoenus_protictitherium_size.jpg?w=562″ class=”size-full wp-image-86164″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/daphoenus_protictitherium_size.jpg” alt=”Figure 1. Daphoenus and Protictitherium skulls to scale with the smaller IVPP V12385 specimen, which has four molars, not three.” width=”584″ height=”1064″ />

Figure 1. Daphoenus and Protictitherium skulls to scale with the smaller IVPP V12385 specimen, which has four molars, not three.

The most proximal ancestor
of the IVPP specimen that has four molars is Oodectes, the current basalmost placental = the last common ancestor.

Currently this fourth molar appears to be a reversal,
because the IVPP specimen is much smaller than its LRT relatives (Fig 1). This brings up, again, the subject of phylogenetic miniaturization and neotony.

Figure 2. The IVPP V12385 specimen attributed to Hapalodectes has four molars, distinct from related members of the Carnivora. ” data-image-caption=”

Figure 2. The IVPP V12385 specimen attributed to Hapalodectes has four molars, distinct from related members of the Carnivora.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/hapalodectes-v12385.jpg?w=210″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/hapalodectes-v12385.jpg?w=584″ class=”size-full wp-image-86166″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/hapalodectes-v12385.jpg” alt=”Figure 2. The IVPP V12385 specimen attributed to Hapalodectes has four molars, distinct from related members of the Carnivora. ” width=”584″ height=”833″ />

Figure 2. The IVPP V12385 specimen attributed to Hapalodectes has four molars (green), distinct from related members of the Carnivora. Here the premaxilla, jugal, lacrimal, prefrontal and postfrontal have been restored. This affects scoring. Note the small diameter molars, not touching one another in palate view, unlike all other mammals. The molars are in contact in lateral view. Data like this tends to confuse.

?Hapalodectes ?hetangensis
(Ting et al. 2004; 7 cm skull length; Early Eocene 50 mya; IVPP V 12385, Fig 2) was originally considered a tiny mesonychid. Here it nests as a small member of the Carnivora close to Daphoenus and Protictitherium. The premaxilla is largely missing, but likely was transverse in orientation. Those flattened molars and premolars do look like those of Mesonyx, an herbivore basal to hippos.

Daphoenus vetus
(Leidy 1853; Middle Eocene to Middle Miocene, 37-16mya). Like related dogs (genus: Canis) this mid-sized predator dug burrows for offspring nesting and hiding sites.

Protictitherium crassum
(Kretzoi 1938; Koufos and Konidaris 2011; Miocene-Pliocene) is traditionally considered a hyena-like civet, but civets are not related to hyenas. Here Protictitherium nests with Protictis, basal to the anagalids. These two are among the first tree shrews to become terrestrial.

Figure 4. Protictitherium post-crania. ” data-image-caption=”

Figure 4. Protictitherium post-crania.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/protictitherium-anton-art588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/protictitherium-anton-art588.jpg?w=584″ class=”size-full wp-image-86170″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/05/protictitherium-anton-art588.jpg” alt=”Figure 4. Protictitherium post-crania.” width=”584″ height=”288″ />

Figure 3. Protictitherium post-crania.

The post-crania of Protictitherium
(Fig1, 3) provides some clues to the related taxon IVPP V12385 (Figs 1,2 ). The IVPP V5235 specimen also attributed to Hapalodectes shown above is not related. It is basal to marsupial sabertooths.

The take-away:
Play the cards you are dealt. All the cards, not just the teeth. You might try to nest a taxon in a clade with one, two or a dozen traits, but it is better to use all the traits at hand to nest a difficult taxon like this one.

References
Kretzoi M 1938. Die Raubtiere von Gombaszög nebst einer Übersicht der Gesamtfauna. Annales Musei Nationalis Hungarici 31:88–157.
Leidy J 1853. Observations on a collection of fossil Mammalia and Chelonia from the Mauvaises Terres of Nebraska. Proc. Acad. Nat. Sci. Philad., 6: 392–394.
Ting S and Li C 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids. Vertebrata PalAsiatica. 25: 161–186.

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