A newly published study examining the growth rates of Dimetrodon teutonis and Dimetrodon natalis has provided a fresh perspective on a famous, primitive synapsid. Researchers have discovered that the smallest known species of Dimetrodon achieved their diminutive size in contrasting ways. The study provides fresh insights into the lives of these iconic sail-backed predators that roamed the Earth millions of years before the dinosaurs evolved.
The Dimetrodon genus comprises several species. Most of these species grew into large predators more than three metres in length. For example, Dimetrodon grandis measured about 3.2 metres long and weighed approximately 250 kilograms. However, a few species were much smaller. An international team of researchers has now investigated how these animals evolved their reduced body size.
Dimetrodon teutonis – The Smallest Known Dimetrodon Species
The study focused on two species. One is Dimetrodon natalis from North America. The other is Dimetrodon teutonis from the Bromacker fossil site in Germany. This German species is significant because it is the only known Dimetrodon discovered outside North America.
For many years, D. natalis was regarded as the smallest species. However, D. teutonis turned out to be even smaller.
- Dimetrodon natalis – named in 1936 by Romer from earlier work by Cope. It measures about 1.7 metres long with an estimated bodyweight of 38 kilograms*.
- Dimetrodon teutonis – named in 2001 (Berman, Reisz, Martens and Henrici) and measuring around 70 cm in length and weighing approximately 24 kilograms*.
Limb bone midshaft circumference analysis of fossil material used in this research suggests that the individual animals representing D. teutonis had a body weight of 6.3 to 6.8 kilograms. In contrast, the same analysis method provides body weight estimates for the D. natalis individuals between 20.9 and 21.7 kilograms.
To learn more about these animals, the scientists examined the microscopic structure of fossil bones. Bone tissue preserves information about growth rates and development. Therefore, it can reveal important details about the life history of extinct species.
Bone Histology Reveals Different Life Histories
The results have been published in the academic journal “Scientific Reports”. They show that the two species followed contrasting growth strategies. Dimetrodon natalis appears to have grown quickly. However, it stopped growing at an early age. As a result, it reached adulthood while remaining small. In contrast, Dimetrodon teutonis grew much more slowly. It continued developing over a longer period. The researchers suggest that it probably reached sexual maturity later in life.
Bone histology comparison between D. teutonis and D. natalis demonstrates fundamentally different bone microanatomy. The humerus cross section of D. teutonis (left) exhibits thin cortices composed of poorly vascularized parallel-fibered bone. This suggests slow growth and delayed maturity. In contrast, the bone histology of D. natalis (right) shows thick and highly vascularised woven to parallel-fibered bone cortices. Picture credit: Frederik Spindler, PALAEONAVIX.
Picture credit: Frederik Spindler, PALAEONAVIX
Dr Tom Hübner, curator and head of the Bromacker project at the Friedenstein Foundation Gotha, commented:
“This work demonstrates that bone histology can provide direct insights into the palaeobiology of long-extinct animals. Who would have thought that these two small species had such different life histories?”
Different Environments Influenced Growth
According to the research team, environmental conditions played a key role. North American Dimetrodon species lived in humid lowland habitats. These ecosystems contained abundant food resources. In addition, predators were common. Under these conditions, rapid growth would have offered advantages for survival and reproduction.
The Bromacker ecosystem in Germany presented different challenges. Seasonal droughts and limited resources shaped this environment. Fossilised burrows suggest that potential prey animals retreated underground during dry periods. Consequently, slower growth may have helped Dimetrodon teutonis cope with fluctuating food supplies.
Dr Aurore Canoville explained:
“These new findings once again highlight the uniqueness of the Bromacker locality compared with other Early Permian fossil sites. They make Dimetrodon even more fascinating. Long before dinosaurs dominated the Earth, these early synapsids were already responding in remarkably flexible ways to climate, food availability, competition and predation.”
Unique Insights from the Bromacker Fossil Site
Professor Jörg Fröbisch of the Museum für Naturkunde Berlin emphasised the importance of the discovery.
He stated:
“These fascinating results provide an increasingly complete picture of the Bromacker ecosystem and its enormous potential for many decades of future research.”
The study highlights how adaptable these early synapsids were. It also demonstrates the importance of the Bromacker fossil locality. Thanks to discoveries such as these, scientists continue to improve our understanding of life during the Early Permian.
Unique fossil provides information on Bromacker food web: Regurgitated Pellet from a Dimetrodon.
In the paper, the researchers state that the largest known species of Dimetrodon is D. angelensis. It is stated that this species was up to 4.6 metres long and weighed 250 kilograms.
Everything Dinosaur acknowledges the assistance of a media release from the Museum für Naturkunde Berlin in the compilation of this article.
The scientific paper: “Contrasting life history in the diminutive Dimetrodon species from North America and Germany” by Aurore Canoville, Philipp L. Knaus, Lorenzo Marchetti and Jörg Fröbisch published in Scientific Reports.
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