Reconstruction of Dynamognathus robertsoni
Matthew Inabinett
Unlike most of the palaeontology unearthed by science—which is often tens or even hundreds of millions of years older than Earth, according to creationist dogma—this discovery dates to a mere 5 million years ago. But the problem for creationists isn’t one of degree; it’s one of absolutes. If anything is older than Earth according to their doctrine, then that doctrine is simply wrong. It’s as straightforward as that.
Likewise, if even a single transitional or ancestral form exists, then the creationist insistence that such forms don't exist is demonstrably false.
Curiously, despite failing to grasp that binary logic, creationists continue to convince themselves that if they can cast doubt on even the tiniest detail of evolutionary science—perhaps a small gap in the fossil record or a question about a single species—then the entire edifice of modern biology collapses and “God did it!” triumphs by default, all without the faintest scrap of supporting evidence.
With that essentially childish view of how evidence and reasoning work, it will likely make no difference to their claims that a team of researchers from the Gray Fossil Site & Museum and East Tennessee State University (ETSU) have discovered the fossil of a comparatively large salamander dating back around 5 million years. This find sheds light on the explosive diversification of salamanders in what is now Appalachia some 12 million years ago. Today, Tennessee is home to about 50 species of salamander—roughly one in eight of all living species.
Evolution of salamanders in the Appalachian region: Why Appalachia Is a Salamander HotspotThe scientists have named the new species Dynamognathus robertsoni and published their findings in the journal Historical Biology, and they explain the discovery in lay terms in an ETSU news release:
- Geographic complexity & climate: The Southern Appalachian Mountains’ mosaic of ridges, valleys and isolated plateaus led to population fragmentation and high levels of endemism, with species often confined to single mountains [1].
- Moist, temperate conditions: The region’s humid, wet climate supports lungless salamanders (family Plethodontidae), which rely on moist skin for respiration [2].
Deep Evolutionary Roots
- The Plethodontidae likely originated in Appalachian mountain streams. Over tens of millions of years (since the Jurassic), they radiated extensively across these forests and waterways [2].
- Periods of climatic fluctuation, especially glacial cycles, further isolated populations, promoting rapid speciation within microhabitats [3].
Mechanisms Driving Diversity
- Niche Conservatism
Appalachian Plethodontids tend to retain ancestral climatic preferences. These ecological “niches” have remained largely unchanged, stabilising gene pools and driving speciation over time—especially at mid‑elevations where diversification peaks [4].
- Cryptic & Non‑adaptive Radiation
Many lineages have diversified genetically without notable morphological change (e.g., Plethodon spp.). Molecular studies have revealed numerous cryptic species-genetically distinct but externally similar—within what were thought to be single taxa [5].
- Hybridisation & Diversification
Research indicates that active hybridisation among salamander lineages tends to accelerate diversification, increasing speciation rates while reducing extinction risk [3].
Fossil Evidence Bolsters the Story
- The discovery of Dynamognathus robertsoni (at ~5 Ma) at Gray Fossil Site represents the earliest lungless salamander fossils known in Appalachia, highlighting a longstanding regional lineage [6].
- Other fossils—including early Ambystoma, Desmognathus, Plethodon—indicate that modern Appalachian lineages were already present before the Miocene-Pliocene boundary [7].
Conservation & Evolution Continue Today
- Many Appalachian salamanders are narrow endemics (e.g., Green Salamander, Shenandoah Salamander, Cow Knob Salamander), vulnerable to habitat loss and climate change [8].
- While introgression can fuel new diversity, modern threats—logging, warming climates, water quality decline—pose severe risks to these unique, evolutionarily distinct populations.
Summary
The Appalachian salamander fauna represents a textbook example of how geography, climate, and ecological constraints foster incredible evolutionary diversification. Over tens of millions of years, Appalachian lungless salamanders have radiated into hundreds of species—driven by niche conservatism, glacial isolation, genetic crypticity, and hybrid dynamics—making this region the world’s salamander epicentre.
ETSU scientists uncover massive fossil salamander, shedding light on ancient Appalachia
A giant, strong-jawed salamander once tunneled through ancient Tennessee soil.
And thanks to a fossil unearthed near East Tennessee State University, scientists now better understand how it helped shape Appalachian amphibian diversity.
The giant plethodontid salamander now joins the remarkable roster of fossils from the Gray Fossil Site & Museum.
The findings appeared in the journal Historical Biology, authored by a team of researchers from the Gray Fossil Site & Museum and ETSU: Assistant Collections Manager Davis Gunnin, Director and Professor of Geosciences Dr. Blaine Schubert, Head Curator and Associate Professor of Geosciences Dr. Joshua Samuels, Museum Specialist Keila Bredehoeft and Assistant Collections Manager Shay Maden.
Our researchers are not only uncovering ancient life, they are modeling the kind of collaboration and curiosity that define ETSU. This exciting find underscores the vital role our university plays in preserving and exploring Appalachia’s deep natural history.
Dr. Joe Bidwell, not involved in the research.
Dean of the College of Arts and Sciences
East Tennessee State University
Johnson City, Tennessee, USA.
Today, Southern Appalachian forests are renowned for their diversity and abundance of salamander species, especially lungless salamanders of the family Plethodontidae. Tennessee alone is home to more than 50 different salamanders – one in eight of all living salamander species.
Dusky salamanders, common in Appalachian Mountain streams, likely evolved from burrowing ancestors, relatives of Alabama’s Red Hills salamander, a large, underground-dwelling species with a worm-like body and small limbs. Their explosive diversification began around 12 million years ago, shaping much of the region’s salamander diversity today.
Dynamognathus robertsoni, the powerful, long-extinct salamander recently discovered at the site, had a bite to match its name. Roughly 16 inches long, it ranked among the largest salamanders ever to crawl across the region’s ancient forests.
Finding something that looks like a Red Hills salamander here in East Tennessee was a bit of a surprise. Today they’re only found in a few counties in southern Alabama, and researchers thought of them as a highly specialized dead-end lineage not particularly relevant to the evolution of the dusky salamanders. Discovery of Dynamognathus robertsoni here in Southern Appalachia shows that these types of relatively large, burrowing salamanders were once more widespread in eastern North America and may have had a profound impact on the evolution of Appalachian salamander communities.
[Dynamognathus robertsoni is] the largest plethodontid salamander and one of the largest terrestrial salamanders in the world.
Davis Gunnin, corresponding author
Don Sundquist Center of Excellence in Paleontology
Gray, Tennessee, USA.
Dusky salamanders in the Appalachians today reach only seven inches long at their largest.
Researchers believe predators like this one may have driven the rapid evolution of Appalachian stream-dwelling salamanders, highlighting the region’s key role in salamander diversification.
The warmer climate in Tennessee 5 million years ago, followed by cooling during the Pleistocene Ice Ages, may have restricted large, burrowing salamanders to lower latitudes, like southern Alabama, where the Red Hills salamander lives today.
Joshua X. Samuels, co-author
Don Sundquist Center of Excellence in Paleontology
Gray, Tennessee, USA And Department of Geosciences
East Tennessee State University
Johnson City, Tennessee, USA.
The species name robertsoni honors longtime Gray Fossil Site volunteer Wayne Robertson, who discovered the first specimen of the new salamander and has personally sifted through more than 50 tons of fossil-bearing sediment since 2000.This group of salamanders has unusual cranial anatomy that gives them a strong bite force, so the genus name – Dynamognathus – Greek for ‘powerful jaw,’ is given to highlight the great size and power of the salamander compared to its living relatives.
Shay Maden, co-author
Don Sundquist Center of Excellence in Paleontology
Gray, Tennessee, USA.
From volunteers and students to staff to faculty, the ETSU Gray Fossil Site & Museum is represented by a dynamic team of lifelong learners and is one of the many reasons ETSU is the flagship institution of Appalachia.
The latest salamander publication is a testament to this teamwork and search for answers. When Davis Gunnin, the lead author, began volunteering at the museum as a teenager with an interest in fossil salamanders, I was thrilled, because this region is known for its salamander diversity today, and we know so little about their fossil record. Thus, the possibility of finding something exciting seemed imminent.
Joshua X. Samuels.
ABSTRACTIn addition to the age of this fossil and its seamless fit within the established narrative of salamander evolution in the Appalachians, creationists will also have to overlook a key detail from the paper itself: the researchers had no difficulty reconciling the find with the Theory of Evolution. There was not the slightest indication—despite frequent creationist predictions to the contrary—that the authors were about to abandon evolutionary science in favour of evidence-free creationism. On the contrary, they suggested that the previously unknown existence of a large, predatory, burrowing salamander could have been one of the environmental pressures driving the evolutionary diversification of salamanders in the region at that time.
An extinct desmognathan salamander is described from the Early Pliocene age Gray Fossil Site in Washington County, Tennessee, USA. The new salamander, Dynamognathus robertsoni gen. et sp. nov., is strikingly similar to the living Phaeognathus hubrichti but possesses osteological features lacking in extant Desmognathini. Size estimation based on P. hubrichti and comparison with the largest plethodontids suggests the new taxon may be the longest known plethodontid salamander – estimated SVL 170-177 mm. Morphometric analysis of the desmognathan atlas reveals that shape correlates with body size and ecology, possibly indicating a unique ecology for Dy. robertsoni. However, ecology is closely tied to body size in Desmognathus and an interpretation of novel ecology for Dy. robertsoni could be due to the fossil taxon’s great size. Overall similarity to P. hubrichti might suggest a fossorial ecology for Dy. robertsoni. Co-occurrence of the new genus with other plethodontid fossils suggests that very large desmognathans like Dy. robertsoni are a previously unknown source of predation and competition in prehistoric Appalachian salamander communities. Large desmognathans may have shaped the evolution and characteristic structuring of Desmognathus communities. Discovery of Dy. robertsoni increases the diversity of Appalachian plethodontid communities, highlighting the importance of the region for plethodontid evolution.lsid:zoobank.org:pub:AA37A78C-AF8D-43B5-BCFD-669D13D10689
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