Part 1: King and Beck 2020
bring us their views (again), on ‘early mammal relationships‘. Let’s see how they stack up (again) against the validated (thanks to taxon inclusion) results of the large reptile tree (LRT, 1697+ taxa).
From their abstract:
“Many phylogenetic analyses have placed haramiyidans in a clade with multituberculates within crown Mammalia, thus extending the minimum divergence date for the crown group deep into the Triassic. Here, we apply Bayesian tip-dated phylogenetic methods [definition below] to investigate these issues. Tip dating firmly rejects a monophyletic Allotheria (multituberculates and haramiyidans), which are split into three separate clades, a result not found in any previous analysis. Most notably, the Late Triassic Haramiyavia and Thomasia are separate from the Middle Jurassic euharamiyidans.”
Bayesian tip-dated phylogenetic methods = online definition here.
You heard it here first
Earlier (2016) the LRT rejected a monophyletic Allotheria (separating Haramiavia (Fig. 1) and Thomasia), from Megaconus and all the multituberculates (Fig. 2). Haramiavia and Thomasia nest as pre-mammal synapsids (tritylodontids), not far from Pachygenelus. Several dozen nodes away, Megaconus and the multis nest within the placental clade Glires, at a node more highly derived than tree shrews, rodents and rabbits. So far that hypothesis of relationships has not been tested by other workers, despite several invitations to expand their taxon lists.
Figure 1. Haramiyava dentary showing what a more typical stem mammal dentary and teeth look like. Earlier studies linked this clade to multituberculates, but this dentary was cause to reject that association.
According to King and Beck 2020,
“Our analysis places Haramiyavia and Thomasia in a clade with tritylodontids, a result that may be the result of insufficient sampling of non-mammaliaform cynodont characters and taxa, and which we consider in need of further testing (see detailed discussion in the electronic supplementary material).” This confirms relationships first recovered by the LRT.
Figure 2. LRT taxa in the lineage of multituberculates arising from Carpolestes and Paulchoffatia.
The authors continue,
“Our focal dataset was taken from Huttenlocker et al. 2018, which comprises 538 morphological characters scored for 125 mammaliaforms and non-mammaliaform cynodonts.
Unfortunately,
as I mentioned earlier, King and Beck still need to include extant mammals, like montoremes, marsupials, rodents and Daubentonia, rather than rely on fossil taxa exclusively. (See below).
Figure 3. Subset of the LRT focusing on Glires and subclades within.
Part 2: King and Beck 2020 report:
“A second taxon of interest is the eutherian Juramaia (Fig. 4) from the Middle–Late Jurassic Yanliao Biota, which is morphologically very similar to eutherians from the Early Cretaceous Jehol Biota and implies a very early origin for therian mammals. We also test whether the Middle– Late Jurassic age of Juramaia is ‘expected’ given its known morphology by assigning an age prior without hard bounds. Strikingly, this analysis supports an Early Cretaceous age for Juramaia, but similar analyses on 12 other mammaliaforms from the Yanliao Biota return the correct, Jurassic age.”
Figure 4. Juramaia (Late Jurassic, 160 mya) is more completely known and nests between monotremes and therians (marsupials + placentals).
By contrast In the LRT,
Juramaia is a basal protorothere, nesting between Megazostrodon + Sinodelphys and Chaoyangodens, all basal to the extant platypus and echidna in the LRT. Beck and King omit so many key taxa that they do not recover Prototheria, Metatheria and Eutheria.
The same authors publishing on a similar topic in 2019
were reviewed here. The following is one paragraph from that review: King and Beck 2019 bring us a new phylogenetic analysis restricted to Mesozoic mammals. This represents a massive case of taxon exclusion of basal mammals as demonstrated earlier here, because so many basal mammals are still alive! Think of all the tree shrews, arboreal didelphids, and nearly every little creeping taxon in Glires that nest basal to known Mesozoic mammals. You cannot restrict the taxon list to just those extremely rare Mesozoic mammals.
Colleagues: Please use extant mammals in your analyses!
They are guaranteed complete and articulated with soft tissues and gut contents. Figure out your cladogram with as many of these complete specimens as possible. Then… start adding crushed, incomplete and disarticulated fossil taxa. In other words, give yourself a basic education first. Establish a valid tree topology first. Don’t muddle through your studies with questionable traits based on fractured mandibles missing several teeth. As longtime readers know, a valid phylogenetic context is paramount for all further studies.
References
Huttenlocker AK, Grossnickle DM, Kirkland JI, Schultz JA and Luo Z-X 2018. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature 558, 108–112. 8. (doi:10.1038/s41586-018-0126-y);
King B and Beck R 2019. Bayesian Tip-dated Phylogenetics: Topological Effects, Stratigraphic Fit and the Early Evolution of Mammals. PeerJ
doi: http://dx.doi.org/10.1101/533885.
King B and Beck RMD 2020. Tip dating supports novel resolutions of controversial relationships among early mammals. Proceedings of the Royal Society B 287: 20200943. http://dx.doi.org/10.1098/rspb.2020.0943
https://pterosaurheresies.wordpress.com/2019/02/07/taxon-exclusion-mars-mesozoic-mammal-study/
The Pterosaur Heresies 