The myth of the shrew-like Mesozoic mammal

According to Wikipedia,
“Maelestes is a prehistoric shrew-like mammal discovered in 1997.”

DiscoverMagazine.com reported,
“This ancient shrew like creature weighed next to nothing and survived the Arctic.”

This trope goes on and on… as everyone knows.

In the LRT shrews,
like Scutisorex (Fig 1), are highly derived placental 2 taxa. Their skulls and teeth are nothing like those of known Mesozoic mammals, which have simple, primitive traits.

Basal placental 2 taxa in the LRT,
like Ptilocercus (Fig 2), are small, yes, but otherwise not very shrew-like. They are tree-shrew like. Is that what authors and journalists mean? If so there are literally bigger problems.

Basal placental 1 taxa
(Fig 3) are ALL larger, civet-like, lemur-like creatures, nothing at all like a shrew in size or morphology. These have been traditionally ignored in paleontology textbooks and abstracts.

So why is the trope
‘shrew-like creature’ used so often by paleontologists and journalists?

It’s easy. It’s a tradition. Nobody questions it.

Another example:

A shrew-like creature that lived 225 million years ago is the oldest mammal ever identified

The above publicity
was based on the description of Brasilodon (Fig 4), which nests far from and ancestral to mammals in the large reptile tree (LRT, 2322 taxa).

On another pair of taxa,
Sweetman, Smith and Martill 2017 reported, “The origin of eutherians remains obscure. “We have no idea where the eutherian mammals originated, or from what — we simply don’t have the fossils,” Sweetman told Live Science.“

No idea? Do the work! Build your own LRT.

From that abstract:
“Eutherian mammals (Placentalia and all mammals phylogenetically closer to placentals than to marsupials) comprise the vast majority of extant Mammalia. Among these there is a phenomenal range of forms and sizes, but the origins of crown group placentals are obscure. They lie within the generally tiny mammals of the Mesozoic, represented for the most part by isolated teeth and jaws, and there is strongly conflicting evidence from phenomic and molecular data as to the date of origin of both Eutheria and Placentalia.”

The LRT resolves all enigma taxa. Phenomic and molecular data too often provide “strongly conflicting evidence’ because molecules are not immutable, perhaps due to long exposure to invading viruses. Thus, too often genes produce untenable results (e.g. a clade of bats+cat+horses).

On the other hand, traits document minute changes and similarities
AND traits can be used to test fossil taxa.

Ditch genes. Use traits.

The reason for building the LRT
is simple curiosity. I wanted to learn which taxa were basal to bats, basal to amniotes, basal to whales, basal to pterosaurs, basal to chordates, AND basal to placentals. Luckily I live in the Internet Age. So I had tools and data unavailable just a few decades ago.

Turns out
the placenta evolved at least twice in mammals, according to the LRT. Academics and text book authors should have discovered and reported this decades ago. That’s their job. That’s what they are trained and paid to do. But they’re busy with more important details like quad-launch pterosaurs  and bat-wing birds.

Professors. Don’t leave phylogenetic analysis to amateurs. Assign a bunch of grad students to build their own LRT so myths like ‘shrew-like Mesozoic mammals’ can go extinct.

References
Sweetman SC, Smith G and Martill DM 2017. Highly derived eutherian mammals from the earliest Cretaceous of southern Britain. Acta Palaeontologica Polonica 62 (4), 2017: 657-665 doi:https://doi.org/10.4202/app.00408.2017

wiki/Maelestes

Publicity
livescience.com/60888-rat-creatures-were-earliest-eutherian-mammal-ancestors

Source: https://pterosaurheresies.wordpress.com/2024/08/30/the-myth-of-the-shrew-like-mesozoic-mammal/