Restoring Plagiomene (incomplete basal placental)

Wikipedia reports,
Plagiomene multicuspis (Fig. 1; Matthew 1918; MacPhee et al. 1989; YPM VP 030624; Wyoming; Paleocene) is an extinct genus of early flying lemur like mammal from North America that lived during the Paleogene.”

Here
using imagination (Fig. 1) to restore the missing parts, scrappy Plagiomene data turns into a more complete skull. Plagiomene had four small molars and a narrow snout between wide robust cheekbones. Those facts and phylogenetic bracketing suggest forward-pointed eyes sitting atop wide cheekbones for bifocal vision.

Figure 1. What little is known of Plagiomene seems to agree with the North American adapid, Smilodectes, among tested taxa.

Figure 1. What little is known of Plagiomene seems to agree with the North American adapid, Smilodectes, among tested taxa. Plagiomene was not added to the LRT.

Here an attempt at restoring the rest of the skull
(Fig. 1) results in a short-snouted taxon with robust cheekbones, more or less similar to Smilodectes (Fig. 1), which has not four, but only three molars and lived during the middle Eocene. An extremely tall coronoid process requires a similarly tall skull. If valid, Plagiomene would be a basal primate, or basal to Primates + Volantia (where dermopterans are a basal taxa).

Possible outgroups,
such as basal Carnivora and Cheiroptera, do not have a similar mandible or molars.

The basal dermopterans,
Palaechthon
(Fig. 1) and Cynocephalus, both have 4 molars, but do not have a tall coronoid process on the mandible.

Earlier we looked at the evidence for
the clade that includes Smilodectes (Adapidae) nesting at the base of the clade of New World monkeys (Platyrrhini). Plagiomene is also from North America.

The last upper premolar
of Plagiomene extends further toward the midline than the molars do. That is unusual in basal mammals. When I find this trait in another basal mammal palate, I will let you know.


References
MacPhee RDE, Cartmill M and Rose KD 1989. Craniodental morphology and relationships of the supposed Eocene dermopterans Plagiomene (Mammalia). Journal of Vertebrate Paleontology 9(3):329–349.
Matthew WD 1918. A revision of the Lower Eocene Wasatch and Wind River faunas. Part V. Insectivora (Continued), Glires, Edentata. Bulletin of the American Museum of Natural History 38(16):429-483.

wiki/Plagiomene
wiki/Smilodectes

Tweaking Palaechthon (basal Volitantia)

Kay and Cartmill 1977 wrote:
“The Middle Paleocene paromomyid Palaechthon nacimienti has the most primitive cranial anatomy known for any plesiadapoid. In relative size and functional morphology, its molars resemble those of primates and tree shrews known to feed largely on insects. Its orbits were small, laterally directed, and widely separated, and the relative size of its infraorbital foramen shows that it had well-developed facial vibrissae resembling those of extant erinaceids. Its anterior dentition was probably also hedgehog-like. These features suggest that it was a predominantly terrestrial insect-eater, guided largely by tactile, auditory and olfactory sensation in its pursuit of prey. Adaptations to living in trees and feeding on plants probably developed in parallel in more than one lineage descended from the ancestral plesiadapoids. A new genus and species of paromomyid, Talpohenach torrejonius, is erected for material originally identified as Palaechthon.”

This was done in the days before software phylogenetic analysis.
In the large reptile tree nests (LRT, 1413 taxa) Palaechthon as a sister to the dermopterans, like Cynocephalus, both derived from basal Carnivora, like Vulpavus (Fig. 1). All of these taxa are basal to Primates in the LRT.

Palaechthon is known from several partial specimens
combined to make the incomplete skull drawing shown here (Fig. 1).

Figure 1. Palaechthon compared to outgroup, Vulpavus, and sister, Cynocephalus using drawings from Kay and Cartmill 1974. Colors added.

Figure 1. Palaechthon compared to outgroup, Vulpavus, and sister, Cynocephalus using drawings from Kay and Cartmill 1974. Colors added.

Palaechthon nacimienti (Wilson and Szalay 1972) ~4cm skull length, middle Palaeocene, was originally and traditionally considered a basal plesiadapiform (traditionally considered a clade of basal primates). Here derived from a sister to the basal placental and carnivoran, Vulpavus, Palaechthon phylogenetically nests with Cynocephalus, the colugo. The premaxilla is missing and may have been nearly toothless, as in the colugo. Distinct from Vulpavus, but as in Cynocephalus, and the basalmost eutherian, Caluromys, four molars are present in Palaechthon.

Figure 3. Cynocephalus, the flying lemur, shares many traits with Ptilocercus and basal bats.

Figure 2. Cynocephalus, the flying lemur, shares many traits with Ptilocercus and basal bats.

Phylogenetic bracketing
makes Palaechthon an arboreal taxon, possibly with a prehensile tail. Kay and Cartmill 1974 imagined large, rodent-like teeth emerging from the missing premaxilla and missing anterior dentary (Fig. 1). Phylogenetic bracketing indicates just the opposite—tiny anterior teeth, as shown in Vulpavus and Cynocephalus. The auditory bulla was probably small, as indicated by phylogenetic bracketing. The post-dentary part of the skull was probably short, as in Cynocephalus.

Figure 1. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

Figure 3. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

The present ‘tweaking’
benefits from more recent additions to the LRT that provided more clues to the closest relatives of Palaechthon, cementing relationships recovered years earlier. First hand access did not give Kay and Cartmill more insight into the relationships of Palaechthon, a basal member of the clade Volitantia.They presumed from the start that it was a primate ancestor, close to Plesiadapis. Both presumptions have been refuted by the LRT, which tests both basal primates and plesiadapiformes, now nesting within Glires. Based on the appearance of descendant taxa in the Middle Jurassic, Palaechthon had its genesis in the Early Jurassic.


References
Fleagle JG 1988. Primate Adaptation and Evolution. Academic Press: New York
Kaplan M 2012. Primates were always tree-dwellers. Nature. doi:10.1038/nature.2012.11423
Kay RF and Cartmill M 1974. Skull of Palaechthon nacimienti. Nature 252:37–38.
Kay RF and Cartmill M 1977. Cranial Morphology and Adaptation of Palaechthon nacimienti and Other Paromomyidae (Plesiadapoidea, Primates), with a Description of a New Genus and Species. Journal of Human Evolution, Vol. 6, 19-53.
Sloan RE and Van Valen L 1965. Cretaceous mammals from Montana. Science 148:220–227
Van Valen L and Sloan R 1965. The earliest primates. Science. 150(3697): 743–745.
Wible JR, Rougier GW, Novacek MJ and Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.” Nature volume 447: 1003-1006
Wilson RW and Szalay FS 1972. American Museum Novitates 2499:1.

 

Resurrecting the clade ‘Volitantia’ Illiger 1811.

Volitantia
was defined by Illiger 1811 as Chiroptera (bats) + Dermoptera (colugos). Wikipedia authors consider this clade obsolete and polphyletic. The large reptile tree (LRT, 1233 taxa) nests these two taxa together in a monophyletic clade that also includes the pangolins and their closest ancestors (e.g. Zhangheotherium). We looked at their traditionally overlooked relationships a few days earlier here.

Szalay and Lucas 1996 reported, “We find support for the Volitantia in the nature of the shared derived similarities (and phyletically significant differences as well) in the elbow complex, and in Leche’s (1886) suggestion of the synapomorphus and unique presence (in non aquatic mammals) of an interdigital membrane of the hand in bats and colugos. They studied Chriacus and Mixodectes (not yet tested), not pangolins.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Like another clade traditionally considered obsolete,
Enaliosauria, that was resurrected by the LRT, Volitantia is likewise resurrected as a monophyletic clade, but it now includes the Pholidota (pangolins) according to LRT results.

Goodbye ‘Ferae’
The putative clade ‘Ferae‘ (pangolins + carnivorans) is not supported by the LRT because pangolins nest within the Volitantia.

As long-time readers know,
many traditional relationships between placental clades are not supported by the LRT, which continues to document a gradual accumulation of derived traits at every node in nearly full resolution for a wide gamut of tetrapod taxa.

Many arboreal mammals were experimenting with gliding
(e.g. Volaticotherium and  Maiopatagaium), but only one clade, bats, experimented with flapping. This was, perhaps not coincidentally, during the Middle to Late Jurassic (Oxordian, 160 mya). Remember, these membranes were all extensions of the infant nursery found in colugos and other volatantians, not far from the basalmost placental, Monodelphis. It is possible that all basalmost mammals had these membrane extensions and most of their ancestors lost them.

References
Illiger C 1811. Prodromus systematis mammalium et nivium additis terminis zoograhicis utriudque classis. Berlin: C. Salfeld.
Szalay F and Lucas SG 1996. The postcranial morphology of Paleocene Chriacus and Mixodectes and the phylogenetic  relationships of archontan mammals. Bulletin of the New Mexico Museum of Natural History and Science 7: 47 pp.

wiki/Volitantia