The origin of shrews illustrated

‘Housekeeping’ at the root
of the placental tree is moving several taxa into the Marsupialia in the large reptile tree (LRT, 2121 taxa). Among the moving taxa are Caenolestes and Rhyncholestes (Fig 1) which now nest with Early Cretaceous Acristotherium. Earlier these two shrew opossums were nested with convergently similar placental shrews like Scutisorex and Uropeltis (Fig 1). A new understanding of premolars and molars is at the core of these several changes.

Figure 1. Several shrew and shrew opossum taxa tested in the LRT. Numbers at left are incisor counts. Smaller size numbers indicate premolar and molar number.

Another tiny, furry taxon, Late Jurassic Henkeltotherium
(Fig 2) moved next to mouse-sized Early Cretaceous Eomaia (Fig 3) after rescoring in the LRT. The position of the eyeball was moved back, closer to the squamosal. This alone changed several proportional scores. A loose tooth was re-identified as a canine, rather than an incisor.

Figure 2. Henkelotherium with minor corrections resulting in a new nesting with Eomaia. This is a tiny taxon shown here at 1.6x actual size. So it was half the size of a mouse.

These are the sort of changes
that are essential elements of the current round of LRT ‘housekeeping’.

Figure 3. Eomaia in situ, as originally reconstructed, as reconstructed here. Mouse-sized Eomaia is shown full scale at 72 dpi monitors.

All for now.
Work continues. Corrections keep improving the LRT.

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