Gomphos elkema

Overview

This ancient relative resembled a rabbit, but was not quite like rabbits today. Gomphos elkema combined long hind feet, an unfamiliar tail and ancient dental features in one mammalian body. It is fascinating to see the familiar and unfamiliar together.^[3]

Key facts

Its hind feet are described as more than twice as long as its forefeet. These proportions suggest rabbit-like hopping. Its tail, however, differed from the short tail of a modern rabbit, and its molars had roots and distinct cusps.^[3]

Time and place

It offers a glimpse of ancient Asian ecosystems around the transition from the Paleocene to the Eocene, about 55 million years ago. Fossils from Tsagan Khushu in Mongolia and records from the Erlian Basin in Inner Mongolia, China, have been studied separately. Comparing fossils from these two Asian regions broadens our view of where this animal is known.^[1][2][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

Its hindlimbs and feet were longer than its forelimbs, and its body continued into a tail. The jaws and molars retained features unlike those of modern rabbits. Its legs suggest familiar movements, while its teeth reveal features of an ancient lineage.^[3]

Gomphos, the group to which this species belongs, is described as a relatively large early rabbit relative weighing about 2 kg. This is an approximate genus-level size presented in conference studies from 2015 and 2019, not a measurement of every individual of the species elkema.^[9]

Habitat and reproduction

The long hindlimbs and hind feet have been interpreted as structures suited to hopping. Differences in the length contributed by each toe bone can change the movement of the whole body. Gomphos shows that rabbit relatives had rabbit-like locomotion early on.^[3]

Fossil discovery

The Mongolian fossils were collected by joint expeditions of the American Museum of Natural History and the Mongolian Academy of Sciences. Erlian Basin material was reported in 2004, followed in 2005 by research on the relationship between rabbits and rodents. Comparisons in the field and laboratory revealed the importance of this small animal.^[1][2][3]

References

1. Meng et al. (2004), “Gomphos elkema (Glires, Mammalia) from the Erlian Basin,” American Museum Novitates 3425:1–24.
2. Asher et al. (2005), “Stem Lagomorpha and the Antiquity of Glires,” Science 307:1091–1094.
3. American Museum of Natural History, “Rabbit Fossil: Mammal Evolution Amid Dinosaur Extinction.”
4. Meng et al. (2004), “Gomphos elkema (Glires, Mammalia) from the Erlian Basin,” American Museum Novitates 3425:1–24.
5. Asher et al. (2005), “Stem Lagomorpha and the Antiquity of Glires,” Science 307:1091–1094.
6. American Museum of Natural History, “Rabbit Fossil: Mammal Evolution Amid Dinosaur Extinction.”
7. Ding (1979) · A new edentate from the Paleocene of Guandong · Vertebrata PalAsiatica 17:57–64
8. Society of Vertebrate Paleontology — Fossil skeleton of an ancient digging mammal
9. 2019 North American Paleontological Convention — Foot bones of Gomphos and early relatives of rodents and rabbits

Research questions

How closely related are rabbits and rodents? The rabbit-like legs and ancient jaw features of Gomphos provide evidence for studying the early relationship between the two groups. They also show why an evolutionary family tree is difficult to reconstruct from a single feature.^[2][3]

Observation

Compare the lengths of the forefeet and hind feet, then examine the tail and head.^[3]