Titanichthys

Titanichthys Temporal range: Famennian PreꞒ Ꞓ O S D C P T J K Pg N
Rendered reconstruction of Titanichthys clarkii
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Suborder:	†Brachythoraci
Superfamily:	†Dinichthyloidea
Family:	†Titanichthyidae Dean, 1901
Genus:	†Titanichthys Newberry, 1885
Type species
†Titanichthys agassizi Newberry, 1885
Species
T. agassizi Newberry, 1887 T. clarki Newberry, 1887 T. attenuatus Wright in Claypole, 1893 T. hussakofi Hay, 1930 T. termieri Lehman, 1954 T. ?koslowskii Kulczycki, 1957
Synonyms
Brontichthys Claypole, 1894

Titanichthys is an extinct genus of giant, aberrant marine placoderm from shallow seas of the Late Devonian of Morocco, Eastern North America, and possibly Europe.^[1] Many of the species approached Dunkleosteus in size and build. Unlike its relative, however, the various species of Titanichthys had small, ineffective-looking mouth-plates that lacked a sharp cutting edge. It is assumed that Titanichthys was a filter feeder that used its capacious mouth to swallow or inhale schools of small, anchovy-like fish, or possibly krill-like zooplankton, and that the mouth-plates retained the prey while allowing the water to escape as it closed its mouth. A study has since confirmed this assumption as its jaws are functionally closer to that of filter feeders like baleen whales and basking sharks, and it appears to have developed from benthic durophagists that became pelagic suspension feeders. This would make it the first (known) large-sized vertebrate filter feeder.^[2] Titanichthys was estimated to have reached a length of 7–7.6 m (23–25 ft),^[3][4][5] but Engelman (2023) suggested that Titanichthys was comparable in size to Dunkleosteus, likely measuring about or just over 4.1 metres (13.5 ft) in length.^[6]

Phylogeny

Titanichthys is thought to have been a basal aspinothoracid, closest related to Bungartius and Tafilalichthys.^[7]

	Rhachiosteus pterygiatus Tapinosteus heintzi Trematosteus fontanellus Bruntonichthys multidens Kendrickichthys cavernosus Bullerichthys fascidens Dinichthys herzeri Hadrosteus rapax Aspinothoracida Gorgonichthys clarki Heintzichthys gouldii Selenosteidae Mylostomatidae? Tafilalichthys lavocati Bungartius perissus Titanichthyidae Titanichthys agassizi Titanichthys cf. clarki

Species

The genus shows a great diversity in the Famennian-aged Cleveland Shale, though species are also found in similarly aged strata in Morocco and possibly the Holy Cross Mountains in Poland.^[1]

T. agassizi

This is the type species, from the Cleveland Shale. Its infrognathals are strongly recurved medially, and is elongated with a spatula-like process at the anterior end. The headshield averages about 60 cm (24 in) in length.^[1]

T. attenuatus

This Cleveland Shale species is based on an infragnathal bone more than 36 cm (14 in) in length. May possibly be a synonym of T. agassizi.^[8]

T. clarkii

This Cleveland Shale species has infragnathals that are not as recurved as T. agassizi's. The cranial roof is comparatively narrower and more rounded. It is the largest known species in the genus, and possibly one of the largest Devonian vertebrates known. The head is about 90 cm (35 in) in length.^[8]

Fossil head shield of Titanichthys clarkii

T. hussakofi

This Cleveland Shale species is known from a badly preserved, incomplete infragnathal. It was originally described by Claypole as "Brontichthys clarki" in 1894.^[8] As "Brontichthys" is a junior synonym of Titanichthys, it should not be confused with another, similarly-named arthrodire, Bruntonichthys of Dunkleosteidae.

T. rectus

This Cleveland Shale species has an infragnathal as large as that of T. clarkii, though T. rectus' infragnathal is much straighter, and does not have a spatula-like process on its anterior end.^[8]

T. kozlowskii

This species placement within the genus is in doubt. It is based on incomplete nuchal and central plates found in Upper Famennian-aged marine strata of the Holy Cross Mountains in Poland.^[8]

T. termieri

This species is found in Lower Famennian-aged marine strata of Tafilalet, Southern Morocco. The fossil material of this species strongly suggests it is as large as the Cleveland Shale' T. clarkii.^[8] The average combined length of the head and trunk shields for T. termieri is estimated to be 200 cm (79 in)^[8] When the first fossils of T. termieri were found by geologist Henri Termier, the specimens were originally placed within the genus Gorgonichthys - that is, after Termier was able to convince his colleagues that the bone scraps were of a placoderm, and not a dinosaur.^[9]

References

1. Denison, Robert (1978). Placodermi Volume 2 of Handbook of Paleoichthyology'. Stuttgart New York: Gustav Fischer Verlag. p. 100. ISBN 978-0-89574-027-4.
2. Coatham, Samuel J.; Vinther, Jakob; Rayfield, Emily J.; Klug, Christian (2020). "Was the Devonian placoderm Titanichthys a suspension feeder?". Royal Society Open Science. 7 (5): 200–272. Bibcode:2020RSOS....700272C. doi:10.1098/rsos.200272. PMC 7277245. PMID 32537223.
3. Bulletin 70. Ohio. Division of Geological Survey. 1996. p. 290. ISBN 978-0-931079-05-4. Retrieved 2022-08-28.
4. Charlie Underwood, Martha Richter, Zerina Johanson (2019). Evolution and Development of Fishes. Cambridge University Press. p. 13. ISBN 9781107179448. Retrieved 1 September 2022.
5. Bashford Dean (1895). Fishes, Living and Fossil: An Outline of Their Forms and Probable Relationships. Macmillan and Company. p. 130. Retrieved 2022-08-28.
6. Engelman, Russell K. (2023). "A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)". Diversity. 15 (3). 318. doi:10.3390/d15030318.
7. Boyle, James; Ryan, Michael J. (March 2017). "New information on Titanichthys (Placodermi, Arthrodira) from the Cleveland Shale (Upper Devonian) of Ohio, USA". Journal of Paleontology. 91 (2): 318–336. Bibcode:2017JPal...91..318B. doi:10.1017/jpa.2016.136. ISSN 0022-3360. S2CID 132831650.
8. Denison, Robert (1978). Placodermi Volume 2 of Handbook of Paleoichthyology'. Stuttgart New York: Gustav Fischer Verlag. p. 101. ISBN 978-0-89574-027-4.
9. See Janvier (1998) p.323 for details.

Bibliography

• Janvier, Philippe (1998): Early Vertebrates. Oxford University Press, Oxford, New York. ISBN 0-19-854047-7

Further reading

• James Boyle and Michael J. Ryan (2018) "New information on Titanichthys (Placodermi, Arthrodira) from the Cleveland Shale (Upper Devonian) of Ohio, USA"
• Long, John A. (1996): The Rise of Fishes: 500 Million Years of Evolution. Johns Hopkins University Press, Baltimore. ISBN 0-8018-5438-5