Suminia getmanovi: First Arboreal Vertebrates With Grasping Hands and Opposable Thumbs Lived 260 Million Years Ago

The skeleton of the tree-climbing synapsid Suminia getmanov, a 260-million-year-old animal which scientists believe was the first known tree-dweller. The tiny, agile animal predated the arrival of the dinosaurs.

The Department of Geology, Field Museum Public Relations, Chicago on July 28, 2009, released the following press release: "In the Late Paleozoic (260 million years ago), long before dinosaurs dominated the Earth, ancient precursors to mammals took to the trees to feed on leaves and live high above predators that prowled the land, Jörg Fröbisch, PhD, a Field Museum paleontologist has concluded. Elongated fingers, an opposable "thumb," and a grasping tail of Suminia getmanovi demonstrate that this small plant-eating synapsid is the earliest known tree-climbing vertebrate.

"Suminia was relatively small, about 20 inches from its nose to the tip of its tail. The tree-climbing lifestyle of this Paleozoic relative of mammals is particularly important because for the first time in vertebrate evolution it gives access to new food resources high off the ground, and also provides protection from ground-dwelling predators. The evidence for this lifestyle is based on several excellent skulls and more than a dozen exceptionally well preserved, complete skeletons from a single large block of red mudstone that was discovered in central Russia's Kirov region.

"Having so many individual specimens, some of mature individuals and some of youngsters, was helpful in providing a complete picture of the animal's skeletal anatomy, said Fröbisch. "It's relatively rare to find several animals locked on a single block," he said. "We have examples of virtually every bone in their bodies."

"Finding that vertebrates took to trees so early in Earth's evolution was unexpected. "It's a surprise, but it makes sense," Fröbisch said. "It was a new niche for vertebrates. There was food available and they avoided predators on the ground."

"The study also provides the first evidence in the fossil record of food partitioning between small climbing and large ground-dwelling plant-eaters and this happens shortly after the establishment of the modern terrestrial ecosystem with large numbers of plant-eaters supporting few top predators. Earlier terrestrial vertebrate communities did not have this modern hierarchy, but instead were composed of various-sized predators and relatively few plant-eaters, with most of the food resources being provided by insects and aquatic organisms."

Fleshed-out and skeletal restorations of Suminia. From Frobisch and Reisz (2009)

"As the first tree-climbing vertebrate, Suminia had very long fore and hind limbs, with especially long hands and feet," lead author Jorg Frobisch said. Frobisch continued: "In particular, its long fingers, or digits, contributed to these large hands and feet," ... It further had long, strongly-curved claws — terminal phalanges — that helped with clinging onto tree trunks and branches... Non-mammalian synapsids were formerly unofficially known as 'mammal-like reptiles,' but they are actually not at all reptiles, but are more closely related to mammals," Frobisch said, adding that Suminia indeed "is a distant relative of mammals."

Frobisch explained that before the first known tree-dweller emerged, "terrestrial vertebrate communities were composed of various-sized predators and relatively few plant-eaters, with most of the food resources being provided by insects and aquatic organisms."

"So this shift in what food is eaten all of a sudden increases competition for plant food resources, and shortly after this shift, you see Suminia invade this ecological space for the first time," he added.

The hand of Suminia (right) compared to terrestrial anomodonts (mostly toothless herbivores) Galechirus (middle) and Robertia (left). Note the claw-like finger bones and divergent "thumb" of Suminia. From Frobisch and Reisz (2009)

Brian Switeka science writer who focuses on paleontology, evolution, and the history of science provided the following assessment: "The hands of Suminia widely differed from those of terrestrial anomodonts and more closely resembled those of other arboreal vertebrates from various groups and time periods. It appeared that lineages that adopted an arboreal lifestyle evolved similar traits over and over again, these similarities being due to convergent evolution. Comparisons between Suminia and living arboreal vertebrates supported this hypothesis, and Frobisch and Reisz make a very well-supported case that Suminia moved through the trees by clinging and grasping.

Switeka continued: "Why the ancestors of Suminia moved into the trees, however, is another question. The Permian deposits in which Suminia was found is relatively well-sampled. During the time the little synapsid was skittering through the trees the local environment supported a large number of herbivores (about 83% of all the vertebrates present) and a much smaller number of carnivores (about 13% of all the vertebrates present). While it is true that an arboreal lifestyle may have helped keep Suminia out of the jaws of predators, the authors hypothesize that it was competition with other herbivores that might have driven some synapsids into the trees. These plants would have been a resource unexploited by other vertebrates, and this may have allowed for the evolution of Suminia from more terrestrially-adapted ancestors."

Suminia getmanovi