Organism · Placental mammals
Diacodexis metsiacus
Source time context (not species duration) · ≈ 56–33.9 Ma
Inferred life reconstruction
Diacodexis metsiacus
Overview
The distant history of the relatives of today’s deer and pigs also begins with very small bodies. Diacodexis metsiacus is an early Eocene even-toed ungulate. It reveals one form of an ancient hoofed mammal with slender legs and a small body.[1][2]
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Key facts
Small size did not necessarily mean slow movement. The skeleton of this species has been interpreted as belonging to a fast runner or leaper. Comparisons with the movements of modern rabbits or small deer help us imagine what its long hind legs could do.[1][2]
Time and place
It is known from early Eocene North America, roughly 56–50 million years ago. One jaw specimen at the Smithsonian was collected from the Willwood Formation in present-day Wyoming, USA. Even tiny teeth can mark a time and place.[3][4]
The time range describes source context, not the complete duration of this species.
Size, form and skeleton
This group is characterized by long, slender limbs and hind limbs more developed than the forelimbs. Premolars and molars are preserved in the jaw. Limb proportions and ankle structure are more helpful than large horns for understanding this early even-toed ungulate.[1][3][2]
The mean body mass of Diacodexis metsiacus estimated from dental material was approximately 1.62 kg before warming and approximately 1.37 kg at peak warming. These results compare specimen groups from two periods, showing traces of environmental change even in small bodies.[7]
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Habitat and reproduction
A study of skeletal function proposed a way of life combining running and leaping. The long tail is compared as a structure for maintaining balance during movement. Picture a small body changing direction rapidly on the ground.[1][2]
Fossil discovery
A jaw collected in Wyoming in 1931 remains available for research as a museum specimen. A 1982 study examined the body of an early even-toed ungulate in detail through its skeleton. A name centered on teeth thus became connected to whole-body movement.[1][3]
References
- Rose, K. D. (1982). Skeleton of Diacodexis, Oldest Known Artiodactyl. Science 216(4546):621–623. DOI 10.1126/science.216.4546.621.
- Orliac (2012). The inner ear of Diacodexis, the oldest artiodactyl mammal. Journal of Anatomy. DOI 10.1111/j.1469-7580.2012.01562.x.
- Smithsonian Institution. Diacodexis metsiacus (Cope), USNM V19272.
- ICS geologic time chart2024/12
- Zhou et al. (1992) — Vertebrae and body structure of Pachyaena
- Smithsonian Institution. Diacodexis metsiacus (Cope), USNM V19272.
- D’Ambrosia et al. (2017) — Warming and body-size changes in early mammals
Research questions
What was life like when even-toed ungulates first diversified? CT research on another species in the same genus compared ears and the sense of balance as well. Studying several Diacodexis species together gives a fuller picture of early hoofed animals.[2]
Observation
Look first at the length of the hind legs and the balance provided by the tail, rather than at body size.[1][2]
Related organisms
Pachyaena ossifragaPlacental mammalsFossil record age bounds · ≈ 56–48.1 MaEocene mammals connected through the Willwood Formation
Pachyaena and Diacodexis are linked through the early Eocene Willwood Formation in present-day Wyoming, USA. Follow different evidence, such as studies of postcranial bones and jaw specimens, to compare mammals from the same broad time and region.