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Description

Upon the end of the Ordovician and the episodes of suddenly glacial and interglacial cycles around 443 million years ago most of sea life was devastated, many marine biomes lost a great amount of species (trilobites, brachiopods, conodonts, nautiloids, corals etc.) and those that survived started to recover slowly with the small amount of organisms, but eventually these organisms would thrive and claim the oceans in the new period, the Silurian. This was the third period of the Paleozoic as well the shortest period of the whole era lasting around 24 million years, ending around 419 million years with very minor extinctions and the gradual changes of geography climate and environments. Although of the very small time span, this moment contain some interesting major ecological and anatomical development including the expansion of complex benthos communities formed by bivalves, echinoderms, bryozoans and brachiopods, a huge explosion of varieties of jawless fishes, eurypterids and the eventual colonization of the freshwater environments.

Probably something remarkable were some evolutionary trends, including the eventual appearance, successive rise and high diversification of jawed vertebrates (acanthodians and just at the end of the period first bony fishes) branched from the first placoderms, making this a “prelude” of what would be the Devonian, as well for the first time in Earth’s history , the proliferation of land ecological communities across humid coastal regions these formed by groups of plants fungus and microorganisms and with these the first terrestrial fauna and some of the tallest land organisms of the period.

This period represented a crucial moment for the Arthropod clade and from here many of the common and prominent clades make an appearance, including several different types of Chelicerata, Myriapods (which reached sizes less than 10 cm long) and Insects that would establish in the first coastal terrestrial ecosystems, becoming the first land animals to have colonized this new medium after plants had reached land tens of millions of years ago, most of these very tiny, and meanwhile in the oceans other groups were growing as well in great amount and specially on sizes.

Chelicerata had exploited in diversity and number becoming among the most prominent groups in the oceans as well in the primordial first terrestrial environments, which the quintessential example of these were the Eurypterids having expanded from the few groups that had appeared to a very prolific variety of pelagic swimmers and bottom seabed dwellers, covering a long range of niches being some detritivorous, some filter feeders and others major predators, and coming in different sizes that some of the largest species during this period reached surprising measurements, exceeding the size of an average human being reaching two meters in length, thus being among the largest animals of the period, although is important to remark that these estimations comes from fragmentary specimens compared with smaller and more complete individuals.
Among those big species stands the Carcinosomatoid Carcinosoma punctatum which had a different morphology compared to other giant species of eurypterids which wasn’t streamlined, but very flattened and round and expanded shaped on its mesosoma, most specimens doesn’t reach sizes larger than 1 m but based from large appendages it was estimated to be 2,2 m and probably even longer; On the other side there were the most well known Pterygotids which some of its largest members of the period were Acutiramus bohemicus with 2.2 m.
At the same time during this period Chelicerata not only diversifying those groups that had emerged from the Ordovician, but also forging new types with different anatomical variations different from that of their relatives, this includes the Arachnids being among the first terrestrial animals, as well the first terrestrial major predatory species of this period, although that most of these were small mostly reaching sizes of 8 cm in lengths, there is a remarkable identified specimen to this group from a isolated pedipalp of around 10 cm found in England corresponding to this period being attributed to a scorpion, this is the Brontoscorpio anglicus which based on complete scorpion specimens of the age is calculated to have been around 80 cm long making it (if it is truly a scorpion) one of the biggest non-eurypterid chelicerae as well the biggest arachnid ever.

Trilobite despite having survived the great Ordovician mass extinction, had a severe loss among their numbers, several families perished and there was a considerable reduction in the size of the individuals, unlike the common 40 cm to 70 cm giant individuals that they had proliferated in the seabed of the previous period in the Silurian only a considerable amount of species reached sizes greater than 10 cm with some exceptional species reaching more than 20 cm of length, such as the genus Arctinurus boltoni being around 25 to 30 cm and the genus Brongniartella sp. with a specimen of around 35 cm long.

Some of the current jawless Vertebrates started to diversify exponentially and evolve further of what they did on the Ordovician of the arandaspids and Astraspis not so heavily armored, in the Silurian these informally know as the “Ostracoderms” showed increasing complexity in design from the simple one or two bony plate semi-oval armor of the first groups varying much more in hydrodynamic forms with greater complexity in the form of the scales, although as they still lacked a properly jaw these would still be relegated as bottom detritivorous or free suspension filters feeders.
Heterostracans evolved around the end of the Ordovician, going though the Silurian they would suffer a major explosion of species diversity, some adopting some peculiar armor shell shapes and very varied scales arrangement, most of these were minuscule with less than 10 cm in length, but species like the cyathaspidiform Boothiaspis ovata had a cephalothorax size of 18 cm and a probable total body length of about 30 cm.
Galeaspids were other peculiar clade limited so far to the coast of north east hemisphere of Gondwana which one day would become East Asia, they were characterized by hypertrophied opening above the cranial shield which have been important for smell and respiration, as well a very complex internal cranial anatomy. Similar to Heterostracans they had a variety of head shield shapes with prominent flaps, most of these had small bodies coming around some centimeters long, but some Silurian species such as Hanyangaspis guodingshanensis and Dayongaspis hunanensis were able to reach some 25 to 30 cm.
Osteostracans were formed by species with a simple semi circular cephalothorac shield but compared to others agnathans they seems to have been the most advanced in terms of body morphology and anatomy due to the development of pectoral and dorsal fins as well possessing a complex braincase, and over some part of its head they had variable sensory organs all around the facial shield; they evolved around the middle Silurian as coastal marine dwellers, some not larger than 10 cm with few species reaching sizes of around 20 cm such as Ateleaspis tessellata.

Apart of very armored forms there were others types of armor less forms including the cosmopolitan Thelodonti a bizarre group of jawless fishes, their affinity is a little complicated and is considered that these are polyphyletic, but still, for the members identified in this group were characterized by lacking armor, being mostly covered by a peculiar type of rough spiny scales similar to shark dentricles and with almost the same functionality of these, most of them being found disarticulated. However, complete well preserved specimens have been found that have shown that this group was variable in body shape as many other fishes groups even showing unique morphologies. Most were tiny with size ranges going around less than few centimeters long but there are also peculiar giants, of course some of the biggest are based on fragmentary remains; Eestilepis prominens is one of these, being only the frontal region well preserved in life could have been able to reach 35 cm on length, but this would be surpassed by other; based from a patch of scales scattered in a piece of rocks which belongs to the species Thelodus macintoshi has suggested of a specimen with a size of 60 cm to even 1 meter long making it one of the biggest vertebrates as well jawless fish of the time.

Other clade but with minor prominence were the Anaspids, a group of small vertebrates which lacked armor, their bodies were mostly elongated and covered by a different set of scales and developed well shaped tails, these during this age had some of the biggest specimens Jamoytius kerwoodi which although is half preserved with only the front part, is calculated to have been 30 cm long.

As mentioned at the beginning, vertebrates had achieved great anatomical advances and the most crucial and important has been the development of the true jaw on which we form part of as well most of the current terrestrial and marine vertebrates today, the Gnathostomes.
Although there are some records of the presence of possible jawed vertebrates since the Ordovician these tend to be quite scarce and only formed by isolated scales, is not until the Silurian strata can be found some concrete evidence with some incomplete but still of good quality remains which shown that they were already quite advance, although most of prominent clades that would proliferate in the Devonian would have evolved just at the end of the period, most considered to have been branched from the earliest Placoderms (I will cover about them in the Devonian chart) such as Entelognathus primordialis of around 20 cm, although as mention there were larger species of placoderms like the Antiarch Silurolepis platydorsalis that were able to reach around 50 cm in length.
Acanthodians or informally called “Spiny sharks” were among the first recognizable of these clades to have appeared in the fossil record (probably they branched from early placoderms), having mixed features of cartilaginous and bony fishes although they are assumed to be ancestral to the Chondrichthyes which predates these for some 50 million years, most of these were pretty small not reaching less than 10 cm on length like Nerepisacanthus denisoni.
Osteichthyes or bony fishes evolved around the end of the period showing a great degree of anatomical development including toothed jaws varied different settlings of fins as well a complex group of dermal scales. The most prominent an ancient members of this group belong to the Sarcopterygii clade or “lobe finned fishes” the clade that would give the rise of tetrapoda as well being one of the most prominent groups of bony fishes during the Paleozoic and Mesozoic; at the end of the Silurian the best preserved specimens shown that they were already quite developed in their morphology, and one of these species stands out to be the largest bony vertebrates of the time. Scaled from a single jaw piece Megamastax amblyodus would have had a total length of 1 m long making it the biggest vertebrate of the silurian.

Mollusks were still thriving on many benthonic and pelagic environments, being Cephalopods a major example of such persistence with many nautiloids surviving the mass extinction, although the gigantic Endocerida declined during the end of the previous period becoming extinct at the beginning of the Silurian. Most of the remaining clades even though they diversified, most were minuscule and had shell sizes less than a meter long with some sample reaching shell sizes of around 2 m long, being major members of the Actinocerids as well some Ortocerids, one particular genus Temperoceras were able to reach shell length near 2 m. Bivalves during this period grew up from the minuscule species reaching considerable sizes, such as Pycinodesma giganteum with a shell diameter of around 30 cm, and the very cosmopolitan genus Megalodontid Megalomoidea canadensis which their biggest shell known is around 40 cm in diameter, these are found in large numbers, having formed large sedentary colonies.

Echinoderms in terms of diversity suffered a considerable loss of clades after the Ordovician mass extinction and their evolutionary peak, and even at the end of the period some groups disappeared (like Eocrinoidea), the rest of clades were thriving in different environments, specially crinoids which have grown in numbers across reefs regions alongside the shallow waters across the tropical regions in reef which shared with different varieties of Poriferans as well colonial and solitary Cnidarians, there is one peculiar large species of crinoid characterized by its bulbous part that helped it to anchor in the bottom sea (believed to have been used for flotation) Scyphocrinites elegans, it had a stem size of around 3 m, a calyx height of 10 cm and branches of around 30 cm.

References

- Chlupac, I. (1994). Pterygotid eurypterids (Arthropoda, Chelicerata) in the Silurian and Devonian of Bohemia. Journal of Geosciences, 39(2-3), 147-162.
-Kjellesvig-Waering, E. N. (1972). Brontoscorpio anglicus: a gigantic lower Paleozoic scorpion from central England. Journal of Paleontology, 39-42.
- Turner, S. (1986). Thelodus macintoshi Stetson 1928: The largest known Thelodont (Agnatha: Thelodonti).
-Märss, T., Wilson, M. V., & Thorsteinsson, R. (2002, June). New thelodont (Agnatha) and possible chondrichthyan (Gnathostomata) taxa established in the Silurian and Lower Devonian of the Canadian Arctic Archipelago. In Proceedings of the Estonian Academy of Sciences, Geology (Vol. 51, No. 2, pp. 88-120). Estonian Academy Publishers.
-Ferron, H. G., & Botella, H. (2017). Squamation and ecology of thelodonts. PloS one, 12(2), e0172781.
- Zhao, W. J., & Zhu, M. (2010). Siluro-Devonian vertebrate biostratigraphy and biogeography of China. Palaeoworld, 19(1-2), 4-26.
- Elliott, D. K. (2016). The Boothiaspidinae, a new agnathan subfamily (Heterostraci, Cyathaspididae) from the late Silurian and Early Devonian of the western United States and the Canadian Arctic. Journal of Paleontology, 90(6), 1212-1224.
-Ritchie, A. (1967). Ateleaspis tessellata Traquair, a non-cornuate cephalaspid from the Upper Silurian of Scotland. Zoological Journal of the Linnean Society, 47(311), 69-81.
-Sansom, R. S., Freedman, K. I. M., Gabbott, S. E., Aldridge, R. J., & Purnell, M. A. (2010). Taphonomy and affinity of an enigmatic Silurian vertebrate, Jamoytius kerwoodi White. Palaeontology, 53(6), 1393-1409.
- Burrow, C. J., & Rudkin, D. (2014). Oldest near-complete acanthodian: the first vertebrate from the Silurian Bertie Formation Konservat-Lagerstätte, Ontario. PloS one, 9(8), e104171.
- Zhu, M., Yu, X., Ahlberg, P. E., Choo, B., Lu, J., Qiao, T., & Zhu, Y. A. (2013). A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature, 502(7470), 188-193.
-Zhu, Y. A., Lu, J., & Zhu, M. (2019). Reappraisal of the Silurian placoderm Silurolepis and insights into the dermal neck joint evolution. Royal Society open science, 6(9), 191181.
-Choo, B., Zhu, M., Zhao, W., & Jia, L. (2014). The largest Silurian vertebrate and its palaeoecological implications. Scientific Reports, 4, 5242.
- Pohle, A., & Klug, C. (2018). Body size of orthoconic cephalopods from the late Silurian and Devonian of the Anti‐Atlas (Morocco). Lethaia, 51(1), 126-148.
-Klug, C., De Baets, K., Kröger, B., Bell, M. A., Korn, D., & Payne, J. L. (2015). Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change. Lethaia, 48(2), 267-288.
-Kirk, E. (1927). Pycnodesma, a new molluscan genus from the Silurian of Alaska. Proceedings of the United States National Museum.
- Engelbretsen, M., Farrell, J., Mathieson, D., & Pickett, J. (2000). Giant bivalves from the Silurian Molong Limestone, Central Western NSW.

-Gorzelak, P., Kołbuk, D., Salamon, M. A., Łukowiak, M., Ausich, W. I., & Baumiller, T. K. (2020). Bringing planktonic crinoids back to the bottom: Reassessment of the functional role of scyphocrinoid loboliths. Paleobiology, 46(1), 104-122.

Description

Upon the end of the Ordovician and the episodes of suddenly glacial and interglacial cycles around 443 million years ago most of sea life was devastated, many marine biomes lost a great amount of species (trilobites, brachiopods, conodonts, nautiloids, corals etc.) and those that survived started to recover slowly with the small amount of organisms, but eventually these organisms would thrive and claim the oceans in the new period, the Silurian. This was the third period of the Paleozoic as well the shortest period of the whole era lasting around 24 million years, ending around 419 million years with very minor extinctions and the gradual changes of geography climate and environments. Although of the very small time span, this moment contain some interesting major ecological and anatomical development including the expansion of complex benthos communities formed by bivalves, echinoderms, bryozoans and brachiopods, a huge explosion of varieties of jawless fishes, eurypterids and the eventual colonization of the freshwater environments.

Probably something remarkable were some evolutionary trends, including the eventual appearance, successive rise and high diversification of jawed vertebrates (acanthodians and just at the end of the period first bony fishes) branched from the first placoderms, making this a “prelude” of what would be the Devonian, as well for the first time in Earth’s history , the proliferation of land ecological communities across humid coastal regions these formed by groups of plants fungus and microorganisms and with these the first terrestrial fauna and some of the tallest land organisms of the period.

This period represented a crucial moment for the Arthropod clade and from here many of the common and prominent clades make an appearance, including several different types of Chelicerata, Myriapods (which reached sizes less than 10 cm long) and Insects that would establish in the first coastal terrestrial ecosystems, becoming the first land animals to have colonized this new medium after plants had reached land tens of millions of years ago, most of these very tiny, and meanwhile in the oceans other groups were growing as well in great amount and specially on sizes.

Chelicerata had exploited in diversity and number becoming among the most prominent groups in the oceans as well in the primordial first terrestrial environments, which the quintessential example of these were the Eurypterids having expanded from the few groups that had appeared to a very prolific variety of pelagic swimmers and bottom seabed dwellers, covering a long range of niches being some detritivorous, some filter feeders and others major predators, and coming in different sizes that some of the largest species during this period reached surprising measurements, exceeding the size of an average human being reaching two meters in length, thus being among the largest animals of the period, although is important to remark that these estimations comes from fragmentary specimens compared with smaller and more complete individuals.
Among those big species stands the Carcinosomatoid Carcinosoma punctatum which had a different morphology compared to other giant species of eurypterids which wasn’t streamlined, but very flattened and round and expanded shaped on its mesosoma, most specimens doesn’t reach sizes larger than 1 m but based from large appendages it was estimated to be 2,2 m and probably even longer; On the other side there were the most well known Pterygotids which some of its largest members of the period were Acutiramus bohemicus with 2.2 m.
At the same time during this period Chelicerata not only diversifying those groups that had emerged from the Ordovician, but also forging new types with different anatomical variations different from that of their relatives, this includes the Arachnids being among the first terrestrial animals, as well the first terrestrial major predatory species of this period, although that most of these were small mostly reaching sizes of 8 cm in lengths, there is a remarkable identified specimen to this group from a isolated pedipalp of around 10 cm found in England corresponding to this period being attributed to a scorpion, this is the Brontoscorpio anglicus which based on complete scorpion specimens of the age is calculated to have been around 80 cm long making it (if it is truly a scorpion) one of the biggest non-eurypterid chelicerae as well the biggest arachnid ever.

Trilobite despite having survived the great Ordovician mass extinction, had a severe loss among their numbers, several families perished and there was a considerable reduction in the size of the individuals, unlike the common 40 cm to 70 cm giant individuals that they had proliferated in the seabed of the previous period in the Silurian only a considerable amount of species reached sizes greater than 10 cm with some exceptional species reaching more than 20 cm of length, such as the genus Arctinurus boltoni being around 25 to 30 cm and the genus Brongniartella sp. with a specimen of around 35 cm long.

Some of the current jawless Vertebrates started to diversify exponentially and evolve further of what they did on the Ordovician of the arandaspids and Astraspis not so heavily armored, in the Silurian these informally know as the “Ostracoderms” showed increasing complexity in design from the simple one or two bony plate semi-oval armor of the first groups varying much more in hydrodynamic forms with greater complexity in the form of the scales, although as they still lacked a properly jaw these would still be relegated as bottom detritivorous or free suspension filters feeders.
Heterostracans evolved around the end of the Ordovician, going though the Silurian they would suffer a major explosion of species diversity, some adopting some peculiar armor shell shapes and very varied scales arrangement, most of these were minuscule with less than 10 cm in length, but species like the cyathaspidiform Boothiaspis ovata had a cephalothorax size of 18 cm and a probable total body length of about 30 cm.
Galeaspids were other peculiar clade limited so far to the coast of north east hemisphere of Gondwana which one day would become East Asia, they were characterized by hypertrophied opening above the cranial shield which have been important for smell and respiration, as well a very complex internal cranial anatomy. Similar to Heterostracans they had a variety of head shield shapes with prominent flaps, most of these had small bodies coming around some centimeters long, but some Silurian species such as Hanyangaspis guodingshanensis and Dayongaspis hunanensis were able to reach some 25 to 30 cm.
Osteostracans were formed by species with a simple semi circular cephalothorac shield but compared to others agnathans they seems to have been the most advanced in terms of body morphology and anatomy due to the development of pectoral and dorsal fins as well possessing a complex braincase, and over some part of its head they had variable sensory organs all around the facial shield; they evolved around the middle Silurian as coastal marine dwellers, some not larger than 10 cm with few species reaching sizes of around 20 cm such as Ateleaspis tessellata.

Apart of very armored forms there were others types of armor less forms including the cosmopolitan Thelodonti a bizarre group of jawless fishes, their affinity is a little complicated and is considered that these are polyphyletic, but still, for the members identified in this group were characterized by lacking armor, being mostly covered by a peculiar type of rough spiny scales similar to shark dentricles and with almost the same functionality of these, most of them being found disarticulated. However, complete well preserved specimens have been found that have shown that this group was variable in body shape as many other fishes groups even showing unique morphologies. Most were tiny with size ranges going around less than few centimeters long but there are also peculiar giants, of course some of the biggest are based on fragmentary remains; Eestilepis prominens is one of these, being only the frontal region well preserved in life could have been able to reach 35 cm on length, but this would be surpassed by other; based from a patch of scales scattered in a piece of rocks which belongs to the species Thelodus macintoshi has suggested of a specimen with a size of 60 cm to even 1 meter long making it one of the biggest vertebrates as well jawless fish of the time.

Other clade but with minor prominence were the Anaspids, a group of small vertebrates which lacked armor, their bodies were mostly elongated and covered by a different set of scales and developed well shaped tails, these during this age had some of the biggest specimens Jamoytius kerwoodi which although is half preserved with only the front part, is calculated to have been 30 cm long.

As mentioned at the beginning, vertebrates had achieved great anatomical advances and the most crucial and important has been the development of the true jaw on which we form part of as well most of the current terrestrial and marine vertebrates today, the Gnathostomes.
Although there are some records of the presence of possible jawed vertebrates since the Ordovician these tend to be quite scarce and only formed by isolated scales, is not until the Silurian strata can be found some concrete evidence with some incomplete but still of good quality remains which shown that they were already quite advance, although most of prominent clades that would proliferate in the Devonian would have evolved just at the end of the period, most considered to have been branched from the earliest Placoderms (I will cover about them in the Devonian chart) such as Entelognathus primordialis of around 20 cm, although as mention there were larger species of placoderms like the Antiarch Silurolepis platydorsalis that were able to reach around 50 cm in length.
Acanthodians or informally called “Spiny sharks” were among the first recognizable of these clades to have appeared in the fossil record (probably they branched from early placoderms), having mixed features of cartilaginous and bony fishes although they are assumed to be ancestral to the Chondrichthyes which predates these for some 50 million years, most of these were pretty small not reaching less than 10 cm on length like Nerepisacanthus denisoni.
Osteichthyes or bony fishes evolved around the end of the period showing a great degree of anatomical development including toothed jaws varied different settlings of fins as well a complex group of dermal scales. The most prominent an ancient members of this group belong to the Sarcopterygii clade or “lobe finned fishes” the clade that would give the rise of tetrapoda as well being one of the most prominent groups of bony fishes during the Paleozoic and Mesozoic; at the end of the Silurian the best preserved specimens shown that they were already quite developed in their morphology, and one of these species stands out to be the largest bony vertebrates of the time. Scaled from a single jaw piece Megamastax amblyodus would have had a total length of 1 m long making it the biggest vertebrate of the silurian.

Mollusks were still thriving on many benthonic and pelagic environments, being Cephalopods a major example of such persistence with many nautiloids surviving the mass extinction, although the gigantic Endocerida declined during the end of the previous period becoming extinct at the beginning of the Silurian. Most of the remaining clades even though they diversified, most were minuscule and had shell sizes less than a meter long with some sample reaching shell sizes of around 2 m long, being major members of the Actinocerids as well some Ortocerids, one particular genus Temperoceras were able to reach shell length near 2 m. Bivalves during this period grew up from the minuscule species reaching considerable sizes, such as Pycinodesma giganteum with a shell diameter of around 30 cm, and the very cosmopolitan genus Megalodontid Megalomoidea canadensis which their biggest shell known is around 40 cm in diameter, these are found in large numbers, having formed large sedentary colonies.

Echinoderms in terms of diversity suffered a considerable loss of clades after the Ordovician mass extinction and their evolutionary peak, and even at the end of the period some groups disappeared (like Eocrinoidea), the rest of clades were thriving in different environments, specially crinoids which have grown in numbers across reefs regions alongside the shallow waters across the tropical regions in reef which shared with different varieties of Poriferans as well colonial and solitary Cnidarians, there is one peculiar large species of crinoid characterized by its bulbous part that helped it to anchor in the bottom sea (believed to have been used for flotation) Scyphocrinites elegans, it had a stem size of around 3 m, a calyx height of 10 cm and branches of around 30 cm.

References

- Chlupac, I. (1994). Pterygotid eurypterids (Arthropoda, Chelicerata) in the Silurian and Devonian of Bohemia. Journal of Geosciences, 39(2-3), 147-162.
-Kjellesvig-Waering, E. N. (1972). Brontoscorpio anglicus: a gigantic lower Paleozoic scorpion from central England. Journal of Paleontology, 39-42.
- Turner, S. (1986). Thelodus macintoshi Stetson 1928: The largest known Thelodont (Agnatha: Thelodonti).
-Märss, T., Wilson, M. V., & Thorsteinsson, R. (2002, June). New thelodont (Agnatha) and possible chondrichthyan (Gnathostomata) taxa established in the Silurian and Lower Devonian of the Canadian Arctic Archipelago. In Proceedings of the Estonian Academy of Sciences, Geology (Vol. 51, No. 2, pp. 88-120). Estonian Academy Publishers.
-Ferron, H. G., & Botella, H. (2017). Squamation and ecology of thelodonts. PloS one, 12(2), e0172781.
- Zhao, W. J., & Zhu, M. (2010). Siluro-Devonian vertebrate biostratigraphy and biogeography of China. Palaeoworld, 19(1-2), 4-26.
- Elliott, D. K. (2016). The Boothiaspidinae, a new agnathan subfamily (Heterostraci, Cyathaspididae) from the late Silurian and Early Devonian of the western United States and the Canadian Arctic. Journal of Paleontology, 90(6), 1212-1224.
-Ritchie, A. (1967). Ateleaspis tessellata Traquair, a non-cornuate cephalaspid from the Upper Silurian of Scotland. Zoological Journal of the Linnean Society, 47(311), 69-81.
-Sansom, R. S., Freedman, K. I. M., Gabbott, S. E., Aldridge, R. J., & Purnell, M. A. (2010). Taphonomy and affinity of an enigmatic Silurian vertebrate, Jamoytius kerwoodi White. Palaeontology, 53(6), 1393-1409.
- Burrow, C. J., & Rudkin, D. (2014). Oldest near-complete acanthodian: the first vertebrate from the Silurian Bertie Formation Konservat-Lagerstätte, Ontario. PloS one, 9(8), e104171.
- Zhu, M., Yu, X., Ahlberg, P. E., Choo, B., Lu, J., Qiao, T., & Zhu, Y. A. (2013). A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature, 502(7470), 188-193.
-Zhu, Y. A., Lu, J., & Zhu, M. (2019). Reappraisal of the Silurian placoderm Silurolepis and insights into the dermal neck joint evolution. Royal Society open science, 6(9), 191181.
-Choo, B., Zhu, M., Zhao, W., & Jia, L. (2014). The largest Silurian vertebrate and its palaeoecological implications. Scientific Reports, 4, 5242.
- Pohle, A., & Klug, C. (2018). Body size of orthoconic cephalopods from the late Silurian and Devonian of the Anti‐Atlas (Morocco). Lethaia, 51(1), 126-148.
-Klug, C., De Baets, K., Kröger, B., Bell, M. A., Korn, D., & Payne, J. L. (2015). Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change. Lethaia, 48(2), 267-288.
-Kirk, E. (1927). Pycnodesma, a new molluscan genus from the Silurian of Alaska. Proceedings of the United States National Museum.
- Engelbretsen, M., Farrell, J., Mathieson, D., & Pickett, J. (2000). Giant bivalves from the Silurian Molong Limestone, Central Western NSW.

-Gorzelak, P., Kołbuk, D., Salamon, M. A., Łukowiak, M., Ausich, W. I., & Baumiller, T. K. (2020). Bringing planktonic crinoids back to the bottom: Reassessment of the functional role of scyphocrinoid loboliths. Paleobiology, 46(1), 104-122.