Paleocene mammals (and the origin of bats) – svp abstracts 2013

Updated Sept 30, 2016 with the shifting of Protictis to the Carnivora.

This is the abstract and analysis
that nested the scansorial Paleocene mammal, Chriacus, with bats (Fig. 1), matching the earlier analysis covered here.

Halliday, Upchurch and Gosswami 2013 wrote: “The Palaeocene is arguably the most important interval in mammalian evolution. Prior to the Cretaceous-Palaeogene (K-Pg) extinction, the mammal fauna is largely, though not exclusively, restricted to the scansorial or terrestrial insectivore niche; afterwards, there is a broad diversity of large herbivores, large carnivores, and later gliders, flyers and aquatic forms quickly evolved. The majority of the taxa known from the Palaeocene, however, belong to ‘wastebasket’ taxa or clades of unknown affinity – these include cimolestids, pantodonts, and the “condylarths”. Only Rodentia, Carnivora and possibly Primates have well supported Palaeocene members. Clarifying the relationships of Palaeocene mammals is thus essential for any reliable macroevolutionary study into the early phases of placental mammal evolution. 

“Here we present the results of an extensive cladistic study of fossil mammals, focusing on Laurasiatheria and possible laurasiatheres, with 130 taxa coded for 681 dental, cranial and postcranial characters. Preliminary analyses in TNT resulted in 2448 trees of length 6474 steps when constraining Afrotheria as a monophyletic group. A strict consensus after pruning the seven least stable taxa yields highly resolved relationships for the enigmatic Palaeocene mammals, including the majority of the “condylarth” groups. Relationships between extant taxa are largely upheld, although miacid and viverravid carnivorans are not recovered as monophyletic, and Eulipotyphla is not recovered. “Condylarths” are found to be polyphyletic, as expected, with apheliscids and pleuraspidotheres falling closest to Artiodactyla, and phenacodontids closest to Perissodactyla. Arctocyonids are reconstructed as a paraphyletic lineage leading to miacid carnivorans, while periptychids lie at the base of a clade containing the majority of the non-euungulate Laurasiatheria. Cimolestids lie on the eutherian stem and are separate from Pantodonta. One novel result is the placement of Leptictida as sister taxon to Afrotheria. With the exception of the leptictid Gypsonictops, all Cretaceous taxa are resolved as stem Eutheria, supporting a Palaeocene origin for the majority of placental orders. 

“There is much debate over the role of the K-Pg extinction in the origin of the placental mammal orders. This phylogenetic analysis will provide a useful basis for many future studies of major evolutionary patterns in early crown placental mammals.”

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

I am told that this presentation recovered Chriacus as the sister to fossil bats. That matches results recovered here two years ago with Protictis intervening. Unfortunately no post-crania has been described for Protictis.

The lack of wings in outgroup taxa is really no problem when you have teeth, ribs, etc. to work with in a data matrix. After all, the complete suite of traits is what determines sisterhood.

Figure 2. Known bat ancestors to scale. Click to enlarge.

Figure 2. Known bat ancestors to scale. Click to enlarge.

It’s good to get confirmation of the nesting of Chriacus with bats. We looked at the origin of bats earlier here.

References
Halliday T, Upchurch P and Goswami A 2013. A phylogenetic analysis of palaeocene mammals. Journal of Vertebrate Paleontology abstracts 2013.

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