Suminia, the arboreal anomodont
11:51 am
Skeletal reconstruction of Suminia getmanovi (sue-MIN-ee-a get-mah-NOVE-eye), an arboreal anomodont therapsid from the Late Permian of Russia. Art by Christina Stoppa.
Paleontologists have described the earliest known animal adapted for life in the treetops, according to a paper in the Proceedings of the Royal Society B, released online today. Jörg Fröbisch, of the Field Museum, and Robert Reisz, from the University of Toronto, found several adaptations for arboreality when they examined fossil skeletons of Suminia getmanovi , a small (20 inches/50 cm) herbivore from the Late Permian of Russia.
The most striking features of the skeleton of Suminia are the relatively large hands and feet. Most of their length is taken up by long, slender fingers and toes tipped with strongly curved, laterally (side-to-side) compressed claws, which are similar in proportion and shape to some modern tree-clinging animals, including dermopterans, megabats, and lizards. The first digits on the hands and feet diverge from the remaining four digits as well, and may have been used as opposable ‘thumbs’ as the animal clung to the branches.
Skeleton of Suminia getmanovi, Paleontological Institute (Moscow) specimen number 2212/116 (spec. 1) Photo by Diane Scott.
More subtle features also point toward arboreal habits. The tail of Suminia is relatively long, and the vertebrae show strong processes halfway down its length. These processes could have supported muscles that allowed Suminia to use its tail for balance or, possibly, as a prehensile grasping organ.
Suminia, at 260,000,000 years old, is the first known vertebrate with this degree of arboreal specialization. Fröbisch and Reisz note that the Late Permian Period, and the Kotel’nich locality where Suminia was found, provides some of the earliest evidence for “modern terrestrial ecosystems with large numbers of plant-eaters supporting few top predators.” While large megaherbivores fed on the greenery below, Suminia found a new way to exploit the foliage in the treetops, taking the first known step into a niche that vertebrates would return to several times over the next 260 million years.
Life restoration of Suminia getmanovi by Christina Stoppa.
Lawless teeth
In part because of some very poorly-written articles and headlines, and in part because talking about vertebrate relationships is just plain enjoyable, it seems like a good place to put in a little bit of context regarding exactly what Suminia is related to.
Suminia is a synapsid, a group of vertebrate animals that would eventually (some 50-100 million years after Suminia) give rise to the ancestors of today’s mammals. Although some synapsids have been called “mammal-like reptiles,” (because they certainly laid eggs and might have looked something like lizards) there are no true reptiles in the synapsid group. All true reptiles—turtles, lizards, snakes, crocodiles—even dinosaurs and birds—belong to a completely separate group.
Among the synapsids, Suminia is considered a therapsid, a phrase commonly used to indicate a grade of synapsid development in between the earlier pelycosaur-grade (think Dimetrodon) and the later mammal-grade. (Although, since mammals evolved from therapsids, we’re technically therapsids too, and since therapsids evolved from pelycosaurs, we can all claim that title as well.)
Among the therapsids, Suminia is an early member of the anomodont (“lawless tooth”) lineage. Sometime during the Early/Middle Permian period, the anomodont line split off from the line of therapsids that would, by way of a whole bestiary of gorgonopsians and therocephalians and countless cynodonts, eventually lead to mammals. The closest relatives we (and all other mammals) share with Suminia would have lived before the Late Permian, around 275,000,000 years ago (give or take several million years) .
The anomodonts have no living descendants, but their roster includes the great radiation of dicynodonts that survived the end-Permian extinction, became some of the largest terrestrial herbivores of the Triassic, and might possibly have survived into the Cretaceous if the identification of an Australian fossil is correct.
Placerias hesternus, a Late Triassic anomodont from Arizona. (Illustration by me, for the day job)
Contrary to what you might have read regarding this discovery, dinosaurs did not evolve from synapsids, and while Suminia is a human relative, this potential predator of Suminia is a much closer relation.
- Reference: Fröbisch, J. and Reisz, R. R. 2009. The Late Permian herbivore Suminia and the early evolution of arboreality in terrestrial vertebrate ecosystems. Proc. Royal Soc. B Published online before print July 29, 2009, doi: 10.1098/rspb.2009.0911.
- Web Coverage:
- Press Release [ZIP file]
- BBC News: Fossil is the earliest tree-dweller
- Laelaps: Suminia: Life in the trees 260 million years ago
- The Dragon’s Tales: Oldest Known Arboreal Herbivore Found…IN THE PERMIAN!
Some images and info for this post came from this press release.
