The elephant shrews, or sengis (Order Macroscelidea, Infraclass Eutheria) are rat-sized African mammals named for their long, tapered, and flexible snout, or proboscis (Encyclopaedia Britannica). They comprise around 20 living species in six genera.
The following phylogenetic time tree is taken from the phylogenetic tree proposed by Tabuce (2018), which is one of the few available in the relatively recent literature:
The following phylogenetic time tree is taken from the phylogenetic tree proposed by Tabuce (2018), which is one of the few available in the relatively recent literature:
Figure 1. Time tree of the stem-Macroscelidea
The oldest known member of the stem-Macroscelidea is Chambius kasserinensis, described from Late Paleocene to Early Eocene (Late Ypresian - Early Lutetian) sediments at the CBI-1 Djebel Chambi locality, on the Kasserine Plateau, Tunisia (Tabuce, 2018; Heritage et al, 2021). Unfortunately, no images of this species or any of the other fossils in the stem group are available.
The oldest known crown-group macroscelidean is Oligorhynchocyon songwensis (belonging to the stem-Rhynchocyoninae), described from the Late Oligocene Songwe Member of the Nsungwe Formation at Site TZ-01S in the Mbeya Region, southwestern Tanzania (Heritage et al, 2021; Stevens et al, 2022). Again, no public-domain images are available.
Taking into account the ghost lineage of 4.1 million years on the macroscelidean stem line (see Figure 1), the stem group of the Macroscelidea must have appeared very late in the Paleocene, which implies a stem-to-crown transition of at least 30 million years, from Late Paleocene to Late Oligocene time.
The oldest known crown-group macroscelidean is Oligorhynchocyon songwensis (belonging to the stem-Rhynchocyoninae), described from the Late Oligocene Songwe Member of the Nsungwe Formation at Site TZ-01S in the Mbeya Region, southwestern Tanzania (Heritage et al, 2021; Stevens et al, 2022). Again, no public-domain images are available.
Taking into account the ghost lineage of 4.1 million years on the macroscelidean stem line (see Figure 1), the stem group of the Macroscelidea must have appeared very late in the Paleocene, which implies a stem-to-crown transition of at least 30 million years, from Late Paleocene to Late Oligocene time.
References
D’Agostino, J. (2014). Insectivores (Insectivora, Macroscelidea, Scandentia). Fowler’s Zoo and Wild Animal Medicine; Elsevier Health Sciences, 8, 275-281.
Heritage, S., Seiffert, E. R., & Borths, M. R. (2021). Recommended fossil calibrators for time-scaled molecular phylogenies of Afrotheria. Afrotherian Conservation 17 https://www. afrotheria. net/newsletter. php.
Springer, M. S., Murphy, W. J., Eizirik, E., Madsen, O., Scally, M., Douady, C. J., ... & O'Brien, S. J. (2007). A molecular classification for the living orders of placental mammals and the phylogenetic placement of primates. Primate origins: adaptations and evolution, 1-28.
Stevens, N. J., O’Connor, P. M., Mtelela, C., & Roberts, E. M. (2022). Macroscelideans (Myohyracinae and Rhynchocyoninae) from the late Oligocene Nsungwe formation of the Rukwa Rift Basin, southwestern Tanzania. Historical Biology, 34(4), 604-610.
Tabuce, R. (2018). New remains of Chambius kasserinensis from the Eocene of Tunisia and evaluation of proposed affinities for Macroscelidea (Mammalia, Afrotheria). Historical Biology, 30(1-2), 251-266.
Heritage, S., Seiffert, E. R., & Borths, M. R. (2021). Recommended fossil calibrators for time-scaled molecular phylogenies of Afrotheria. Afrotherian Conservation 17 https://www. afrotheria. net/newsletter. php.
Springer, M. S., Murphy, W. J., Eizirik, E., Madsen, O., Scally, M., Douady, C. J., ... & O'Brien, S. J. (2007). A molecular classification for the living orders of placental mammals and the phylogenetic placement of primates. Primate origins: adaptations and evolution, 1-28.
Stevens, N. J., O’Connor, P. M., Mtelela, C., & Roberts, E. M. (2022). Macroscelideans (Myohyracinae and Rhynchocyoninae) from the late Oligocene Nsungwe formation of the Rukwa Rift Basin, southwestern Tanzania. Historical Biology, 34(4), 604-610.
Tabuce, R. (2018). New remains of Chambius kasserinensis from the Eocene of Tunisia and evaluation of proposed affinities for Macroscelidea (Mammalia, Afrotheria). Historical Biology, 30(1-2), 251-266.
Image credit – stem-Macroscelidea
- Header (round-eared sengi: Macroscelides flavicaudatus): John P. Dumbacher, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons