Though known only from fragmentary remains, Trimpleylepis represents an extinct genus of Anaspid, a jawless fish (agnathan) on the Cyclostome lineage of vertebrates that lived during the Ludlow stage of the Silurian, approximately 427 to 423 million years ago.
Discovered primarily in the Ohesaare borehole in Estonia, as well as in Britain, Trimpleylepis contributes to our understanding of early vertebrate evolution in the Birkeniiformes order.
In this post, we’ll explore where Trimpleylepis fits in the Tree of Life (taxonomy), when and where it lived, how it became extinct, what its fossils reveal, its unique physical characteristics (synapomorphies), its scientific discovery, ongoing mysteries, and where its fossils are preserved.
Trimpleylepis 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: Tahulalepididae
- Genus: Trimpleylepis
- Species: Trimpleylepis concatenata, Trimpleylepis juncta
Geological Time and Habitat
- Period: Silurian
- Stratigraphic Range: Ludlow Stage of the Silurian Period (approximately 427–423 million years ago)
- Habitat: Trimpleylepis likely inhabited shallow, nutrient-rich marine environments similar to modern coastal areas. These habitats would have been home to various early vertebrates and other marine organisms, supporting complex and dynamic ecosystems.
Evolutionary Significance
As a member of the Anaspida class, and despite its fish-like appearance, Trimpleylepis belongs to the Cyclostome lineage, making it more closely related to modern hagfish and lampreys than to true fish or any jawed vertebrates (gnathostomes), the lineage where we humans and all other land vertebrates come from.
Unlike true fish, Trimpleylepis and other anaspids display body features that make them primitive members of the cyclostome line.
Physical Characteristics
Trimpleylepis must have been relatively small, likely measuring only around 10–15 cm in length. Due to fragmentary remains, many specific details are unknown, but its scale pattern is distinct among anaspids, indicating unique adaptations.
Trimpleylepis Synapomorphies
As an early vertebrate, Trimpleylepis shared several foundational features with other early vertebrates:
- Vertebral Column: Bony or cartilaginous vertebrae around the ancestral notochord and nerve cord, forming a backbone.
- Neurocranium: A protective brain casing made of cartilage or bone.
- Tri-partite Brain: Like other vertebrates, Trimpleylepis had a brain divided into three distinct lobes: olfactory (smell), optic (sight), and otic (hearing).
Specific to Anaspida, Trimpleylepis exhibited:
- Hypocercal Tail: Vertebrae extend into the bottom of the tail, while the fin structure forms the upper lobe.
- Body Fins: Though unconfirmed for Trimpleylepis, many anaspids had long, unbroken fins along the body that are distinct from modern fish fins.
Intriguing Mysteries Around Trimpleylepis
Trimpleylepis raises intriguing questions about early vertebrate evolution. As part of the Cyclostome lineage, it suggests the presence of primitive vertebrates that evolved body structures distinct from those of jawed vertebrates.
Most intriguingly, agnathans like Trimpleylepis, who were once thought to be the precursors to jawed fishes, actually turned out to be Cyclostomes (true jawless fish), which are still vertebrates but much more distantly related to most vertebrates we know today.
What’s more, molecular data studies show that Anaspids like Trimpleylepis should have appeared on Earth in the Cambrian already, diverging even before conodonts. Yet we don’t find evidence of them until the Silurian – 100 million years later.
This embarrassing gap indicates that either: Early members didn’t fossilise, or we just haven’t found them yet (and there is a major discovery out there somewhere), or there’s something wrong with our current understanding of early vertebrate evolution.
Whoever solves that puzzle could be the next rockstar of palaeontology.
Discovery & Classification
- Discovery Date: 2004
- Discovery Location: Ohesaare borehole, Estonia, and Britain
- Discovering Paleontologists: Carl Miller, Tiiu Märss, Henning Blom
- Naming: Trimpleylepis remains fragmentary, and its genus name does not have a specific meaning.
Known Species of Trimpleylepis
Two species within this genus are recognised: Trimpleylepis concatenata, named for a “linked” or “connected” structure, and Trimpleylepis juncta, which also implies connected or joined traits, likely descriptive of morphological features.
Behaviour and Ecology
Though details about its behaviour are limited due to fragmentary evidence, Trimpleylepis likely lived a similar ecological life to other anaspids, possibly feeding through filter-feeding or scavenging strategies, utilising its streamlined body for swimming in nutrient-rich waters.
Fossil Discoveries
The fragmentary fossils of Trimpleylepis were mainly recovered from the Ohesaare borehole in Estonia, with additional fragments found in Britain. These fossils date to the Ludlow Epoch of the Silurian Period, approximately 427 to 423 million years ago.
Scientific Research and Theories
The genus Trimpleylepis has been studied extensively by Carl Miller, Tiiu Märss, and Henning Blom in their work on Late Silurian anaspid fossils from Northern Europe. Their research, particularly the 2004 paper in Acta Universitatis Latviensis, has contributed significantly to our understanding of birkeniid anaspid diversity and distribution.
Current Specimen Locations
Specimens of Trimpleylepis are curated within:
- TalTech fossil collections (Tallinn University of Technology), Estonia
Extinction Theories
Environmental changes during the Silurian likely contributed to the extinction of Trimpleylepis and other anaspids. Rising sea levels, shifts in marine ecosystems, and competition from other vertebrates may have driven its decline.
Interesting Facts & Trivia
- Trimpleylepis concatenata is named for a unique “linked” or “connected” feature in its fossil remains.
- Anaspids like Trimpleylepis display a fish-like body structure but are not closely related to modern fish, showing the variety of evolutionary paths early vertebrates explored.
- The genus offers a rare look into anaspid diversity and distribution across Europe during the Silurian Period.
Additional Resources & References of Trimpleylepis
- Miller, C. G., Märss, T., Blom, H. (2004). New anaspid material from the Late Silurian of Britain and Estonia. Acta Universitatis Latviensis, 679, 46-56.
Discover More Cool Anaspids
Trimpleylepis 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 Tahulalepididae family along with Tahulalepis.
Some close relatives might include the Rhyncholepididae family, with more fragmentary genera like Rytidolepis, Schidiosteus, Vesikulepis, Silmalepis and Maurylepis that are basically only known from their scales and small fragments.
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 Trimpleylepis
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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