Sacabambaspis

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Sacabambaspis
Temporal range: Dapingian-Sandbian
Sacabambaspis janvieri cast (cropped).jpg
A cast (replica) of a Sacabambaspis janvieri fossil found in Bolivia. Displayed at the American Museum of Natural History, New York.
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Agnatha
Class:† Pteraspidomorpha
Family:† Sacabambaspidae
Genus:† Sacabambaspis
Gagnier, Blieck & Rodrigo, 1986
Type species
† Sacabambaspis janvieri
Gagnier, Blieck & Rodrigo, 1986
Species
  • S. janvieriGagnier, Blieck & Rodrico, 1986

Sacabambaspis is an extinct genus of armored jawless fish which lived in the Ordovician period. Sacabambaspis inhabited shallow waters on the continental margins of the southern supercontinent Gondwana. The most complete specimens were found in Bolivia, while armor fragments are also known from Argentina, Australia, [1] and Oman. [2] Sacabambaspis vaguely resembles a slender tadpole, with an oversized armor-plated head, flat body, and no discernible fins outside of its narrow tail. The eyes are closely spaced and positioned at the very front of the head, akin to car headlamps. [3] [4] It was about 35 cm (13+3⁄4 inches) long in total, including its distinctively thin scaly tail. [3]

Contents

With many well-preserved specimens, Sacabambaspis is the best-known member of Arandaspida, a group of jawless fish only found in the Ordovician of Gondwana. Arandaspids were among the earliest members of the class Pteraspidomorpha, alongside a far more diverse group of jawless fish, the Silurian– Devonian heterostracans. [5]

History

Bolivian specimens

A bonebed of Sacabambaspis fossils, displayed at Musee d'Histoire Naturelle, Paris. Sacabambaspis janvieri many specimens.JPG
A bonebed of Sacabambaspis fossils, displayed at Musée d'Histoire Naturelle, Paris.

Sacabambaspis is named after the village of Sacabamba, Cochabamba Department, Bolivia, where the first fossils of the genus were found. [6] S. janvieri, the type species of the genus, is known from the Anzaldo Formation of Bolivia. [6]

Sacabambaspis janvieri was first described by Gagnier, Blieck & Rodrico (1986), based on a few armor fragments. [6] Further discoveries in the late 1980s and early 1990s greatly expanded the list of specimens. [7] [8] [9] [3] [10] [11] [4] Later studies in the mid-2000s cleared up a few remaining points of ambiguity regarding its armor structure and tail anatomy. [12] [13]

Over 30 specimens have been found in Bolivia, all crammed into a very confined area. Their close arrangement is believed to be the result of a fish kill, probably due a sudden inflow of fresh water and sediments from a large storm. They were found associated with a large number of lingulid brachiopods, also killed at the same time. [14] [15] [16]

Other specimens

Indeterminate specimens (described as "Sacabambaspis sp.") have been found in many countries corresponding to the margin of Gondwana. Young (1997) described fossils of the genus from the Stokes Siltstone and Carmichael Sandstone of Central Australia. [1] Specimens have also been reported from Argentina. [17] [2]

Sansom et al. (2009) described specimens from the Amdeh Formation of Oman on the Arabian Peninsula. The Oman discoveries showed that the fish were present all around the periphery of the ancient continent of Gondwana, and not just in the southern regions as had previously been shown by the findings from South America and Australia. [2] [18]

Internet attention

A Sacabambaspis model created by Elga-Mark Kurik, very similar to her memetic 1995 model on exhibit in Helsinki. The simple tail fin does not factor in newer research by Pradel et al. (2006). Specimen GIT 865-10 (189360).jpg
A Sacabambaspis model created by Elga-Mark Kurik, very similar to her memetic 1995 model on exhibit in Helsinki. The simple tail fin does not factor in newer research by Pradel et al. (2006).

A Sacabambaspis model exhibited at the Natural History Museum of Helsinki in Finland became a source of internet memes and fan art in June 2023, following a viral tweet from August 2022. The Helsinki model of Sacabambaspis (サカバンバスピス) is a particularly popular subject in Japan, where it receives a level of attention akin to yuru-kyara (cute promotional mascots). [19]

The prehistoric fish models on display at the Natural History Museum of Helsinki are the work of Estonian paleontologist Elga-Mark Kurik (1928–2016), who the museum asked to design their 1995 fossil fish exhibit. Kurik was not an artist by trade, and her models were entirely made from scratch. The exhibited models are made of silicone (copied from a sculpted foam template), with added doll eyes purchased at a nearby craft store. [20]

Description

Sacabambaspis averages around 35 cm (13+3⁄4 inches) in total length, with the head shield about 10 cm (4 inches) long and 8 cm (3+1⁄4 inches) wide. [3] [4]

Head shield

Sacabambaspis had a head shield made from a large upper (dorsal) plate that rose to a slight ridge in the midline and a deep curved lower (ventral) plate. This headshield is ornamented with characteristic oak-leaf shaped or tear-drop shaped tubercles. [12] [21] [22] It also had narrow branchial plates which link these two along the sides, and cover the gill area. [21] The eyes were far forward. Between them were possibly two small nostrils surrounded by what is thought to be endoskeletal bone and putative nostrils found at the extreme anterior of the head, one of the diagnostic features of the arandaspids. [21] [22]

The forward-positioned eyes of Sacabambaspis mean that its brain must have been further back in the head. Though this seems normal from our perspective, it may not have been typical in the Paleozoic. Galeaspids, some placoderms, and Eriptychius , for example, had widely-spaced eyes with the brain filling in the entire front of the head. [23]

Body and tail

Life restoration with a thin, specialized tail, reflecting the conclusions of Pradel et al. (2006). Sacabambaspis.jpg
Life restoration with a thin, specialized tail, reflecting the conclusions of Pradel et al. (2006).

Behind the armored head, the rest of the body was covered by much narrower scales, each bearing a line of oak leaf-shaped tubercles similar to those of the head shields. [21] One series of scales forms a ridge down the upper edge of the body, and another ridge of scales extends along most of the lower edge. Strap-like scales converge towards the middle of each flank, forming a chevron (V-shaped) pattern when seen from the side. The lateral lines of the ventral shield extend beyond the head, marking scales on the lower half of the body about 2/3 as far as the tail. [3] [4]

The tail of Sacabambaspis is one of its most distinctive features, though the exact details were debated for many years. [13] Based on the best-preserved specimen, MHNC 1182, Gagnier (1989) reconstructed the tail as a whip-like scaly tube surrounding the spinal cord, with small symmetrical fins at its base. [7] [3] Most subsequent publications placed doubt on this "rat-tail" [3] reconstruction, which was unprecedented among jawless fish. Instead, they argued that its tail was short and leaf-shaped, with the longer string of scales simply misplaced armor from a nearby specimen. [4] [24]

A 2006 study supported Gagnier's original interpretation, recognizing the thin scaly tail as a valid feature of MHNC 1182. [13] The webbing of the tail fin web is supported by extremely thin scales, split into an upper and lower portion, plus a small patch of webbing at the very tip of the tail. The upper fin web was probably the largest in the tail, though there is some room for interpretation considering the tail is strongly twisted in the fossil. The lower fin web may be equivalent to an anal fin. The tail fin of Sacabambaspis, though unique in its details, can broadly be classified as hypocercal. This means that the spinal chord bends down in the tail, with most of the fin webbing above it, like many other extinct and living jawless fish groups. Heterostracans appear to have a more symmetrical tail, though without a clear axis for the spinal chord. [13]

Classification

There were many types of jawless fish in Paleozoic seas, with countless variations on body types and the arrangement of fins, armor, and other organs. [4] [24] Jawless fish are technically known as "agnathans" while extinct armored jawless fish are called "ostracoderms". These terms are purely categorical, paleontologists no longer use them in the context of evolutionary relationships. Some "ostracoderms" are more more closely related to jawed fish (gnathostomes), others closer to living jawless fish (hagfish and lampreys), and others have no close living relatives. [4] [24] [25] [5]

Sacabambaspis is the best-known member of Arandaspida, a group of armored jawless fish endemic to the Ordovician of Gondwana. Arandaspids were closely related to two other groups: the astraspids (from Ordovician Laurentia, the core of modern North America) and heterostracans (Silurian-Devonian, worldwide). All three groups had several traits in common: large dorsal and ventral head shields (or a mosaic of armor in their place), a characteristic set of internal layers in the armor, and no fins apart from the tail fin. Arandaspids, astraspids, and heterostracans are collectively known as pteraspidomorphs. The main physical difference between the rare Ordovician species and the extremely diverse heterostracans is that heterostracans condense their gill openings into only two holes, one on each side of the head. [8] [5]

Pteraspidomorphs are probably a clade, meaning that they are most closely related to each other and not ancestral to any non-pteraspidomorph fish. [25] [5] The most comprehensive study on pteraspidomorph relationships is by Randle et al. (2025). The result of their maximum parsimony analysis is shown below: [5]

Pteraspidomorphi

Paleobiology

Feeding

Although it was jawless, the mouth of Sacabambaspis janvieri was lined with nearly 60 rows of small bony oral plates which were probably movable in order to provide more efficient suction feeding through expansion and contraction of the oral cavity and pharynx. [24] [16]

Sensory system

The fossils of Sacabambaspis show clear evidence of a sensory structure (lateral line system). This is a line of canal pores, within each of which are open nerve endings that can detect slight movements in the water, produced for example by predators. The arrangement of these organs in regular lines allows the fish to detect the direction and distance from which a disturbance in the water is coming. [22]

See also

References

  1. 1 2 Young, G. C. (1997-04-16). "Ordovician microvertebrate remains from the Amadeus Basin, central Australia". Journal of Vertebrate Paleontology. 17 (1): 1–25. Bibcode:1997JVPal..17....1Y. doi:10.1080/02724634.1997.10010948. ISSN   0272-4634.
  2. 1 2 3 Sansom, Ivan J.; Miller, C. Giles; Heward, Alan; Davies, Neil S.; Booth, Graham A.; Fortey, Richard A.; Paris, Florentin (2009). "Ordovician Fish from the Arabian Peninsula". Palaeontology. 52 (2): 337–342. Bibcode:2009Palgy..52..337S. doi: 10.1111/j.1475-4983.2009.00846.x . S2CID   128704925.
  3. 1 2 3 4 5 6 7 Gagnier, Pierre-Yves; Blieck, Alain (1992). "On Sacabambaspis janvieri and the vertebrate diversity in Ordovician seas" (PDF). In Mark-Kurik, Elga (ed.). Fossil fishes as living animals. Academia. Vol. 1. Tallinn: Academy of Sciences of Estonia. pp. 9–20. ISBN   5-7976-0409-4.
  4. 1 2 3 4 5 6 7 Gagnier, Pierre-Yves (1995). "Ordovician Vertebrates and Agnathan phylogeny". Bulletin du Muséum national d'histoire naturelle. 17: 1–37.
  5. 1 2 3 4 5 Randle, Emma; Keating, Joseph N.; Sansom, Robert S. (2025). "A phylogeny for Heterostraci (stem‐gnathostomes)". Papers in Palaeontology. 11 (5). doi: 10.1002/spp2.70030 . ISSN   2056-2799.
  6. 1 2 3 Gagnier, Pierre-Yves; Blieck, Alain R. M.; S., Gabriela Rodrigo (1986). "First Ordovician vertebrate from South America" . Geobios. 19 (5): 629–634. Bibcode:1986Geobi..19..629G. doi:10.1016/S0016-6995(86)80058-4. ISSN   0016-6995.
  7. 1 2 Gagnier, P.-Y. (1989). "The oldest vertebrate: a 470-million-year-old jawless fish, Sacabambaspis janvieri, from the Ordovician of Bolivia". National Geographic Research. 5: 250–253.
  8. 1 2 Blieck, Alain; Elliott, David K.; Gagnier, Pierre-Yves (1991). "Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates". In Chang, M.M.; Liu, Y.H.; Zhang, G.R. (eds.). Early vertebrates and related problems of evolutionary biology. Beijing, China: Science Press. pp. 1–17.
  9. ↑ Gagnier, P.-Y. (1992). "Ordovician vertebrates from Bolivia". Fosiles y facies de Bolivia. I. Vertebrados. Revista Tecnica de YPFB. 12: 371–379.
  10. ↑ Gagnier, P.-Y. (1993). "Sacabambaspis janvieri, Vertébré ordovicien de Bolivie. I: Analyse morphologique". Annales de Paléontologie. 79 (1): 19–69.
  11. ↑ Gagnier, P.-Y. (1993). "Sacabambaspis janvieri, Vertébré ordovicien de Bolivie. II: Analyse phylogénétique". Annales de Paléontologie. 79: 119–166.
  12. 1 2 Sansom, Ivan J; Donoghue, Philip C.J; Albanesi, Guillermo (2005-07-18). "Histology and affinity of the earliest armoured vertebrate". Biology Letters. 1 (4): 446–449. doi:10.1098/rsbl.2005.0349. PMC   1626355 . PMID   17148229.
  13. 1 2 3 4 5 6 Pradel, A.; Sansom, I. J.; Gagnier, P. Y.; Cespedes, R.; Janvier, P. (2006). "The tail of the Ordovician fish Sacabambaspis". Biology Letters. 3 (1): 72–75. doi:10.1098/rsbl.2006.0557. PMC   2373808 . PMID   17443969.
  14. ↑ Gagnier, P. Y.; Blieck, A.; Emig, C. C.; Sempere, T.; Vachard, D.; Vanguestaine, M. (1996-09-01). "New paleontological and geological data on the Ordovician and Silurian of Bolivia" . Journal of South American Earth Sciences. 9 (5): 329–347. doi:10.1016/S0895-9811(96)00018-1. ISSN   0895-9811.
  15. ↑ Davies, Neil S.; Sansom, Ivan J.; Albanesi, Guillermo L.; Cespedes, Ricardo (2007-06-11). "Ichnology, palaeoecology and taphonomy of a Gondwanan early vertebrate habitat: Insights from the Ordovician Anzaldo Formation, Bolivia" . Palaeogeography, Palaeoclimatology, Palaeoecology. 249 (1): 18–35. doi:10.1016/j.palaeo.2007.01.003. ISSN   0031-0182.
  16. 1 2 Monroe, H.M. (30 October 2011). "Arandaspis prionotolepis". Australia: The Land Where Time Began. Retrieved 28 October 2013.
  17. ↑ Albanesi, G.L.; Benedetto, J.L.; Gagnier, P.-Y. (1993). "Sacabambaspis janvieri (Vertebrata) y conodontes del Llandeiliano temprano en la Formacion La Cantera, Precordillera de San Juan, Argentina". Boletin de la Academia Nacional de Ciencias. 60. Córdoba, Argentina: 519–543.
  18. ↑ Miller, George (24 June 2011). "How can something that small appear on TV?". NaturePlus. Archived from the original on 7 October 2018. Retrieved 28 October 2013.
  19. ↑ Amber V (16 June 2023). "470-million-year-old fish Sacabambaspis goes viral in Japan, Among Us dev joins in on fun". Automaton Media. Retrieved 8 February 2024.
  20. ↑ Kukk, Toomas (6 October 2012). "Intervjuu: Kala hakkas lagunema sabast juba aastamiljoneid tagasi". Eesti Loodus. Vol. 63, no. 10. pp. 34–40.
  21. 1 2 3 4 Benton, Michael J. (2005). Vertebrate Palaeontology 3rd Edition. Blackwell Publishing. p. 47. ISBN   978-1-4051-4449-0.
  22. 1 2 3 Samson, Ivan J.; Smith, Moya M.; Smith, Paul M. (2001-02-15). "The Ordovician radiation of vertebrates". In Ahlberg, Per Erik (ed.). Major Events in Early Vertebrate Evolution. CRC Press. pp. 156–171. doi:10.1201/b12434. ISBN   978-1-134-56886-4.
  23. ↑ Dearden, Richard P.; Lanzetti, Agnese; Giles, Sam; Johanson, Zerina; Jones, Andy S.; Lautenschlager, Stephan; Randle, Emma; Sansom, Ivan J. (2023). "The oldest three-dimensionally preserved vertebrate neurocranium". Nature. 621 (7980): 782–787. doi:10.1038/s41586-023-06538-y. ISSN   1476-4687.
  24. 1 2 3 4 Janvier, Philippe (1996). Early vertebrates. Oxford monographs on geology and geophysics. Oxford: Clarendon press. ISBN   978-0-19-854047-2.
  25. 1 2 Keating, Joseph N.; Donoghue, Philip C. J. (2016-03-16). "Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton". Proceedings of the Royal Society B: Biological Sciences. 283 (1826) 20152917. doi:10.1098/rspb.2015.2917. PMC   4810860 . PMID   26962140.
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