Despite having only fragmentary fossils, we know Rytidolepis is an extinct genus of jawless fish (agnathan) that lived during the Homerian to Gorstian stages of the Silurian Period, approximately 430.5 to 421.3 million years ago.
Its name is derived from the Greek words “rhytis,” meaning “wrinkle,” and “lepis,” meaning “scale,” referencing its wrinkled, scale-like features.
And, even though we don’t know what the entire animal looked like, we have enough evidence to place it in the Birkeniiformes order of anaspida, in the family Rhyncholepididae.
Rytidolepis 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: Rytidolepis
- Species: Rytidolepis quenstedtii
Geological Time and Habitat
- Period: Silurian
- Stratigraphic Range: Homerian Stage (Wenlockian Series) to the Gorstian Stage (Ludlow Series) of the Silurian Period (approximately 430.5–421.3 million years ago)
- Habitat: Rytidolepis lived in nutrient-rich, shallow marine environments, particularly around what is now Estonia. These waters supported a variety of early vertebrates, and Rytidolepis would have been a part of this thriving ecosystem, using its elongated body and fin structures to move through the ancient seas.
Evolutionary Significance
As a member of the Anaspida, Rytidolepis is part of a unique evolutionary group of jawless fishes that diverged early in the vertebrate tree, specifically along the Cyclostome lineage.
What makes anaspids special is their divergence from the gnathostome lineage, which gave rise to jawed vertebrates. This places Rytidolepis closer to modern hagfish and lampreys, as opposed to other jawless fishes like arandaspids and thelodonts. Despite their evolutionary importance, many aspects of Rytidolepis‘s biology remain unknown due to the fragmentary nature of its fossils.
Physical Characteristics
Due to the fragmentary state of Rytidolepis fossils, many of its physical traits are speculative. However, based on related anaspids, Rytidolepis is estimated to have been 10-15 cm in length and featured an elongated, streamlined body.
Its name, derived from the Greek “rhytis” (wrinkle), suggests a wrinkled scale pattern, though the exact structure of its scales and fins is not fully understood.
Rytidolepis Synapomorphies
As a vertebrate, Rytidolepis 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 that protected its brain.
- Tri-partite Brain: Like other vertebrates, Rytidolepis had a brain divided into three distinct lobes: olfactory (smell), optic (sight), and otic (hearing).
Specific to Anaspida, Rytidolepis also exhibited:
- Hypocercal Tail: The vertebral bones extended into the bottom lobe of the tail, while the fin structure formed the upper part of the caudal fin.
- Body Fins: As with other anaspids, it likely possessed unbroken body fins running along its length, though the details are unclear due to the fragmentary fossil record.
Intriguing Mysteries Around Rytidolepis
Rytidolepis represents one of the many enigmatic anaspids that leaves researchers with more questions than answers. The most perplexing mystery surrounding anaspids is their sudden appearance in the Silurian fossil record, despite molecular clock data indicating they should have existed since the Cambrian.
This 100-million-year gap in the fossil record leaves many questions about the early evolution of anaspids like Rytidolepis.
Moreover, the fish-like appearance of early anaspids, including Rytidolepis, is strange given that most of their later relatives, such as Endeiolepis and Euphanerops, had much more eel-like forms typical of the Cyclostome lineage.
Discovery & Classification
- Discovery Date: 1856
- Discovery Location: Saaremaa Island, Estonia
- Discovering Paleontologist(s): Christian Heinrich Pander
- Naming: The genus name Rytidolepis is derived from the Greek words “rhytis,” meaning “wrinkle,” and “lepis,” meaning “scale.”
Known Species of Rytidolepis
The only known species within this genus is Rytidolepis quenstedtii.
- quenstedtii honours Friedrich August Quenstedt, a German geologist and palaeontologist recognised for his work on Jurassic fossils.
Behaviour and Ecology
Though little is known about the specific behaviour and ecology of Rytidolepis, it likely shared many traits with other anaspids, such as a filter-feeding or scavenging lifestyle. Its elongated body and unique fin structures would have made it a swift and agile swimmer, well-adapted to navigating the nutrient-rich, shallow marine waters of Silurian Estonia.
Fossil Discoveries
Rytidolepis is primarily known from fragmentary fossils found on Saaremaa Island, Estonia, dating to the Homerian and Gorstian stages of the Silurian Period. These fragments provide a glimpse into the structure of this early anaspid but leave many unanswered questions about its complete anatomy.
Scientific Research and Theories
Significant research on Rytidolepis includes studies on its environmental context and evolutionary placement.
Notably, the study by Blom et al. (2002) explored the evolutionary significance of Rytidolepis and other birkeniid anaspids from the Silurian and earliest Devonian periods. More recent research has focused on the geochemistry of the fossil sites, providing insights into the palaeoenvironment of Rytidolepis.
Current Specimen Locations
Specimens of Rytidolepis are housed in several notable collections, including:
- TalTech fossil collections
- Paleozoological Collections (PZ), Swedish Museum of Natural History (NRM)
Another Curious Aspect of Rytidolepis
One of the fascinating aspects of anaspids like Rytidolepis is their unique body structure, particularly their lack of bony armour compared to other jawless fish. While many agnathans developed heavy, protective armour, anaspids like Rytidolepis took a different evolutionary route, emphasising flexibility and agility.
Their wrinkled scales and long bodies are strikingly fish-like, but on closer examination, the similarities are superficial. The fins of anaspids evolved independently from the paired fins seen in later gnathostomes, illustrating a remarkable case of convergent evolution.
Extinction Theories
The extinction of Rytidolepis and other anaspids likely coincided with environmental changes during the later stages of the Silurian. As the marine ecosystems shifted, competition from more advanced vertebrates and changing sea levels may have driven Rytidolepis to extinction.
Interesting Facts & Trivia
- Rytidolepis quenstedtii was named in honour of Friedrich August Quenstedt, a prominent palaeontologist.
- Despite its fish-like appearance, Rytidolepis is more closely related to modern hagfish and lampreys than to true fish.
- The fossil record of Rytidolepis is fragmentary, leaving many questions about its full anatomy and behaviour.
Additional Resources & References of Rytidolepis
- Fadel, A., Žigaite, Ž., Blom, H., Perez-Huerta, A., Jeffries, T., Märss, T., Ahlberg, P. E. (2015). Palaeoenvironmental signatures revealed from rare earth element (REE) compositions of vertebrate microremains of the Vesiku Bone Bed (Homerian, Wenlock), Saaremaa Island, Estonia. Estonian Journal of Earth Sciences, 64(1), 36-41. DOI: 10.3176/earth.2015.07
- 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
Rytidolepis 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, Silmalepis, Vesikulepis 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 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.
About PrehistoricLife.co
I aim to have everything as up-to-date as possible and will continually update this post. Please notify me of any necessary updates, information you think should be included, and references or citations needed.
Enjoy the journey of discovery through Earth’s ancient past, geology, big ideas and, of course, awesome prehistoric life.
