Mammal diversity study fails to reproduce gradual evolution

Goswami et al 2022 reported,
“While molecular data has largely resolved the higher-level topology of placental mammals and there are detailed morphological phylogenies available for many extinct placental clades, there is continuing debate over the positions of some entirely extinct clades within Placentalia.”

Sadly, like many paleontologists nowadays, the authors drank the Kool-Aid. They believed in deep time genomic results even though their cladogram nested mysticetes with odontocetes and elephants as basal placentals. Their ingroup includes members of the clade Creodonta, which the large reptile tree (LRT, 2173 taxa) nest within Marsupialia. The taxon, Monodelphis, (the marsupial wthout a pouch nesting as the proximal outgroup to the Placentalia in the LRT) is not mentioned in the SuppData nor tested in their cladogram.

A wider gamut of taxa in the LRT tells us which taxa are ingroup members and outgroup members. Cherry-picking taxa (all too common in paleontology) does not work as well.

What the LRT recovers:
Placentalia appeared in the Early Jurassic. Taxa remained small, arboreal and nocturnal until the dinosaur extinction event. Glires (including Jurassic Mutituberculata), primates and leptictids all have Mesozoic roots. Almost immediately after the dinosaurs larger descendants appeared and radiated into diurnal and terrestrial taxa. That means throughout the Jurassic and Cretaceous (2/3 of their time on Earth) placentals did not diversify much, contra the Goswami et al hypothesis.

References
Goswami A et al (12 co-authors) 2022. Attenuated evolution of mammals through the Cenozoic. Science 378(6618(:377–383.

Publicity
Santana SE and Grossnickle DM 2022. Bursts in skull evolution weakened with time. Science 378(6618(:355–356.

Santana and Grossnickle 2022 reported,
“Evolutionary biologists generally agree that placental mammals began as small-sized animals that ate insects, and later evolved to become more varied in size and morphology.

That’s not what Goswami et al recovered. Just the opposite.

“Today, the morphologies of placental mammals are incredibly diverse, ranging from the bumblebee bat to the blue whale. There is considerable debate over how the small, insect-eating ancestors of placental mammals gave rise to such incredibly divergent lineages.

That’s what LRT models, subject to confirmation, refutation and/or modification.

“Among the competing hypotheses are varying opinions on the timing and pace of early placental mammal evolution, especially in the context of major environmental changes such as the Cretaceous-Paleogene (K-Pg) mass extinction event 66 million years ago and the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago. On page 377 of this issue, Goswami et al. (4) contribute to this discussion by reconstructing the patterns and possible drivers of placental mammal morphological diversification with a quantitative analysis of skull shape spanning over 70 million years of evolution.”

First start with a suitable outgroup recovered by builiding your own LRT. Then include as many taxa as possible until the evolutionary patterns emerge from the convergent exceptions.