Silmalepis is an extinct genus of jawless fish (agnathan) that lived during the Gorstian to Ludfordian stages of the Silurian Period, approximately 427.4 to 423.0 million years ago.
The genus name Silmalepis likely originates from its discovery locality “Silma” and the Greek word “lepis,” meaning “scale.”
Though only fragmentary fossils of Silmalepis have been discovered, they provide essential insights into the diversity of anaspids in the Birkeniiformes order and their scale patterns during the Silurian.
Silmalepis Taxonomy and Classification
- Domain: Eukaryota
- Kingdom: Animalia (Metazoa)
- Subkingdom: Eumetazoa
- Infrakingdom: Bilateria
- Phylum: Chordata
- Subphylum: Vertebrata
- Evolutionary Lineage: Stem-cyclostome (Cyclostomiformes)
- Class: Anaspida
- Order: Birkeniiformes
- Family: Rhyncholepididae
- Genus: Silmalepis
- Species: Silmalepis erinacea
Geological Time and Habitat
- Period: Silurian
- Stratigraphic Range: Gorstian Stage (Ludlow Series) to Ludfordian Stage of the Silurian Period (approximately 427.4–423.0 million years ago)
- Habitat: Silmalepis lived in nutrient-rich, shallow marine environments. These seas provided ideal conditions for the development of early vertebrates, and Silmalepis would have shared its environment with various other jawless fishes, navigating through ancient waters near what is now modern-day Estonia.
Evolutionary Significance
As part of the Anaspida, Silmalepis belongs to a unique group of jawless fishes that diverged early in vertebrate evolution along the Cyclostome lineage.
This evolutionary pathway places Silmalepis closer to modern hagfish and lampreys, setting it apart from jawless vertebrates in the gnathostome lineage. Like other anaspids, Silmalepis developed without the bony armour that other early vertebrates evolved, instead featuring distinct scale patterns.
Physical Characteristics
Silmalepis is estimated to have measured 10-15 cm in length, though its fossils remain fragmentary. It likely had an elongated, streamlined body covered with scales.
The species name erinacea, meaning “hedgehog” in Latin, suggests that its fossil might display a spiny or rough texture. Though details remain speculative, the scale pattern likely played a crucial role in distinguishing Silmalepis from other early jawless fishes.
Silmalepis Synapomorphies
As a vertebrate, Silmalepis shared several fundamental features with other early vertebrates:
- Vertebral Column: Bony or cartilaginous vertebrae surrounding the ancestral notochord and nerve cord, forming the backbone or spine.
- Neurocranium: A cartilaginous or bony brain casing protected its brain.
- Tri-partite Brain: Like other vertebrates, Silmalepis had a brain divided into three distinct lobes: olfactory (smell), optic (sight), and otic (hearing).
Specific to Anaspida, Silmalepis also exhibited:
- Hypocercal Tail: The vertebrae extended into the bottom lobe of the tail, while the fin structure made up the upper part of the caudal fin.
- Body Fins: While details about the body fins of Silmalepis are unclear, some anaspids developed unbroken fins that extended along the entire body.
Intriguing Mysteries Around Silmalepis
As with many anaspids, Silmalepis presents several fascinating evolutionary mysteries. Its fragmentary fossils provide just enough detail to raise questions, particularly about its scale pattern and the potential “spiny” texture that earned it the species name erinacea (Latin for “hedgehog”).
But anaspids like Silmalepis are particularly perplexing because we know they are one of the first Cyclostomes to diverge – according to molecular clock data, as early as the Cambrian. Yet their fossils don’t show up until 100 million years later in the Silurian.
This likely means anaspids didn’t fossilise well, we haven’t looked in the right places yet, or we simply don’t know how to recognise basal members of the clade. Either that or there are still some very big surprises in store about the true story of early vertebrates.
Discovery & Classification
- Discovery Date: 2002
- Discovery Location: Estonia
- Discovering Paleontologist(s): Henning Blom, Tiiu Märss, and Carl Miller
- Naming: The genus Silmalepis likely refers to the locality “Silma” and the Greek word “lepis,” meaning “scale.”
Known Species of Silmalepis
The only known species of Silmalepis is Silmalepis erinacea, named after the Latin word “erinaceus,” meaning “hedgehog,” likely referring to the spiny or rough texture of the fossil.
Behaviour and Ecology
While little is known about the specific behaviour and ecology of Silmalepis, it is presumed to have been a filter feeder or scavenger, similar to other anaspids.
Its elongated body and unique fin structures would have made it a capable swimmer, navigating through shallow marine environments with relative ease. Its scale pattern may have offered additional protection or helped with hydrodynamics.
Fossil Discoveries
The fossils of Silmalepis were discovered in Estonia, dating to the Gorstian and Ludfordian stages of the Silurian Period. While fragmentary, these fossils offer a glimpse into the structure and scale pattern of this early anaspid. The discovery of Silmalepis adds to our understanding of the diversity of early vertebrates in the region during the Silurian.
Scientific Research and Theories
The study of Silmalepis is primarily centred around the work by Blom et al. (2002), which explored the evolutionary significance of birkeniid anaspids from the Silurian and earliest Devonian periods. This research has helped contextualise Silmalepis within the broader evolutionary framework of early vertebrates and their placement within the Cyclostome lineage.
Current Specimen Locations
Specimens of Silmalepis are held in several notable fossil collections, including:
- TalTech fossil collections
Another Curious Aspect of Silmalepis
One of the most intriguing aspects of Silmalepis and other anaspids is their distinct evolutionary trajectory. Unlike the gnathostome-line vertebrates (where true fishes with jaws will emerge from), anaspids did not develop bony armour or plates, instead evolving different body shapes, scale patterns, and fin configurations.
The “hedgehog” name of Silmalepis suggests a unique texture to its scales, which may have provided insight into its specific adaptations to its environment.
Extinction Theories
Silmalepis, like many other anaspids, likely faced extinction due to environmental changes during the Silurian Period. As marine ecosystems shifted, competition from more advanced vertebrates may have contributed to the decline of Silmalepis and its relatives.
It’s notable though that many anaspids survived well into the Devonian.
Interesting Facts & Trivia
- Silmalepis erinacea was named after the “hedgehog,” suggesting a rough or spiny texture to its fossil.
- The genus name Silmalepis likely refers to the locality of Silma, a nod to its Estonian discovery.
- Despite its fragmentary fossils, Silmalepis provides key insights into the diversity of early anaspids in the Silurian.
Additional Resources & References of Silmalepis
- Blom, H., Märss, T., Miller, C. G. (2002). Silurian and earliest Devonian birkeniid anaspids from the Northern Hemisphere. Transactions of the Royal Society of Edinburgh Earth Sciences, 92(3), 263-323. DOI: 10.1017/S0263593300000250
Discover More Cool Anaspids
Silmalepis is part of the Birkeniiformes order of anaspids alongside the likes of Rhyncholepis, Birkenia, Pharyngolepis, Pterygolepis and Lasanius, etc.
Specifically, it’s part of the Rhyncholepididae family, along with more fragmentary genera like Rytidolepis, Schidiosteus, Vesikulepis and Maurylepis that are basically only known from their scales and small fragments.
They might even be cousins of other fragmentary specimens, such as the Tahulalepididae, namely: Tahulalepis and Trimpleylepis.
Museums with Anaspid Collections & Exhibits
- The on-site museum at Miguasha in Canada
- Swedish Museum of Natural History
- Hunterian Museum and Art Gallery at the University of Glasgow
- Natural History Museum Denmark
- Grant Museum of Zoology, London
- The Royal Ontario Museum, Canada
- American Museum of Natural History
- University of California Museum of Paleontology
Documentaries Featuring Anaspida, Related to Rytidolepis
They’re not always 100% accurate because we make new scientific discoveries all the time. But documentaries at least deliver the gist of the information in a fun and engaging way. Just click play, hit full screen and enjoy hours’ worth of awesome documentaries on first animals, right here…
1. Ancient Oceans
2019
Not just about vertebrates, but featuring some of the most awesome ancient fishes. This short documentary about early oceans and extinction events has two episodes and is available through Curiosity Stream here.
2. Life on Our Planet Episode 2
2023
Though not focused on vertebrates specifically, episode 2 of Steven Spielberg’s Netflix documentary, narrated by Morgan Freeman, features a look at early life and the land transition, featuring some vertebrates like Sacabambaspis.
Watch on Netflix here.
3. Animal Armageddon Episode 2
Animal Planet, 2019
It’s hard to track down a good copy of this one, but Animal Armageddon features quite a few vertebrate evolutionary stories, pegged on the major mass extinctions they faced. This one specifically is during the Devonian, the age of fishes (vertebrates).
Also available on Amazon here.
4. Mankind Rising
2012
The 2012 TV movie production of Mankind Rising is a single animated journey from the earliest vertebrates ancestors right through to present-day humans – it’s pretty cool, maybe a bit dated, but still a lot of fun!
5. Walking with Monsters
BBC, 2005
A bit older now and flashing past early animals a bit too quickly, this one in the “Walking With” series is still pretty cool for its Cambrian bits. It’s also available via Amazon.
6. David Attenborough’s Rise of Animals: Triumph of the Vertebrates
BBC, 2013
Although more focused on the evolution of vertebrates, it’s still an awesome documentary to watch. It’s available to purchase from Amazon.
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