Tiny rabbit ancestor learned to hop in Jurassic trees
When did rabbits learn to hop?
In the large reptile tree (LRT, 2048 taxa, subset Fig 1) and elsewhere, rabbits, like Oryctolagus (Fig 2), nest within the clade Glires, the gnawing clade. Specifically the rabbit clade split prior to rodents and after shrews, like Desmana, Fig 2) and these after tree shrews, like Tupaia (Fig 2). Rabbits traditionally nest alongside pikas (Ochotona), but the tiny Jurassic climber, Henkelotherium (Fig 1) is closer and known from a complete skeleton. Eocene Gomphos was originally described as ‘the earliest and most complete ancestor to modern rabbits.’
Of course, evolution is seamless, so it’s up to the lumpers and splitters, the systematists and taxonomists, to determine how taxa divide and are defined.
The LRT nests Cretaceous Zalambdalestes
(Fig. 1) and extant Solenodon (Fig. 2) in a clade proximal to the rabbit clade. Based on the chronology of the late Jurassic pre-rabbit, Henkelotherium (Fig 2), that rabbit-solenodon split occurred in the Middle to Late Jurassic, under the watchful gaze of giant dinosaurs.
Based on phylogenetic bracketing
(Fig 1) the cold-adapted pika (Fig. 5) lost its tail convergent with rabbits, which retain a short fluffy tail. The pika shares a diet of short ground plants, mosses and lichens whether by convergence or homology. The single extant genus, Ochotona has a world-wide distribution from the Rocky Mountains to the Himalayas. That radiation might have resulted from migration during the time of Pangaea, or later, crossing Beringia.
Less than half the size of a pika,
Henkelotherium guimarotae (Krebs 1991; Late Jurassic 150 mya) was traditionally considered a eupantothere (replaced by the clade name Dryolestida). Like its rabbit sisters, the manus was small and the pes had short metarsals combine with long digits with sharp claws. That changes in rabbits where the pedal digits are shorter and the metatarsals are longer. The lumbar region was long and flexible all taxa going back to the tree shrew, Tupaia and its ancestors, the adapid primate, Notharctus, and extant basal palcental, Nasua, the coatimundi. Like these jungle tree hoppers, Henkelotherium fossils were found in ‘Jurassic jungle’ strata.
Phylogenetic bracketing and comparative anatomy indicate
rabbits first learned to hop when they were small, arboreal and squirrel-like in the Jurassic. Tree kangaroos and terrestrial kangaroos followed the same convergent path. So did primates in 1953 according to this YouTube video:
Phylogenetic miniaturization strikes again!
Solendon and pikas do not hop. Rabbits do. Henkelotherium was a phylogenetically miniaturized taxon and, like so many other phylogenetially miniaturized taxa, tiny Henkelotherium evolved new skills and traits, like hopping between tree branches, later inherited by larger extant descendants, the rabbits, that refined those skills and traits.
References
Krebs B 1991. Skelett von Henkelotherium guimarotae gen. et sp. nov. (Eupantotheria, Mammalia) aus dem Oberen Jura von Portugal. Berl Geowiss Abh A.: 133:1–110.
Jäger KRK, Lu Z-K and Martin T 2019. Postcranial skeleton of Henkelotherium guimarotae (Cladotheria, Mammalia) and locomotor adaptation. Journal of Mammalian Evolution https://doi.org/10.1007/s10914-018-09457-2
wiki/Glires
wiki/Zalambdalestes
wiki/Henkelotherium
wiki/Oryctolagus
wiki/Gomphos
American Museum of Natural History/Gomphos
wiki/Pika
wired.com/2015/03/creature-feature-10-fun-facts-solenodon/
livescience.com/2381-fossil-oldest-rabbit-relative.html
amnh.org/research/science-news/2006/earliest-rabbit-fossil-found-suggests-modern-mammal-group-emerged-as-dinosaurs-faced-extinction
Source: https://pterosaurheresies.wordpress.com/2022/02/27/tiny-rabbit-ancestor-learned-to-hop-in-jurassic-trees/
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