Trilobites had 3 additional eyes

[JBkansas]

Trilobites were thought to be the only arthropods without median eyes. Turns out we just weren't looking hard enough:

 

https://phys.org/news/2023-03-eyes-trilobites.amp

 

The 3 additional eyes are marked by the white arrows in L below (only visible due to damage to the glabella which normally covers them):

Edited March 21, 2023 by JBkansas

[Ludwigia]

I'd be curious to hear what @piranha has to say about this.

[rocket]

a third eye, incredible..., never heard or read about. Why not...

 

wait what @piranha says, thanks for sharing this really interesting info

 

 

e.g. Published from a researcher of Cologne, main city for Carneval. Hope it is not a costume 

[piranha]

Another excellent paper from Schoenemann and Clarkson: the leading experts on all things ocular concerning trilobites.

 

The Nature Scientific Reports paper was posted earlier this month with an additional supplemental pdf: LINK

 

 

***More eye-opening fun facts:

 

Agnostus had ventral eyes and it has been suggested that the hypostomal maculae of polymerid trilobites may have also had a light-sensing function.

 

 

"Agnostus pisiformis lacks dorsal eyes and was long thought to be blind. However, it does have ventral and probably light sensitive eye structures associated with the hypostome in later ontogentic stages (Müller and Walossek, 1987; Walossek and Müller, 1990). Thus, it was probably able to see while the shields were gaping, though not as well as many polymerid trilobites with their dorsal compound eyes."

 

Eriksson, M.E., Horn, E. 2017
Agnostus pisiformis - A Half a Billion-Year Old Pea-Shaped Enigma.
Earth-Science Reviews, 173:65-76  PDF LINK

 

Müller, K.J., Walossek, D. 1987
Morphology, Ontogeny, and Life Habit of Agnostus pisiformis from the Upper Cambrian of Sweden.
Fossils and Strata, 19:1-124  PDF LINK

[JBkansas]

32 minutes ago, piranha said:

Eriksson, M.E., Horn, E. 2017
Agnostus pisiformis - A Half a Billion-Year Old Pea-Shaped Enigma.
Earth-Science Reviews, 173:65-76  PDF LINK

Love the reconstruction:

 

[piranha]

Some additional info from the Treatise on Invertebrate Paleontology: Trilobita Part O 1959:

 

MACULAE

Maculae are absent in the hypostomata of many trilobites, whereas in others they consist of a pair of smooth rounded or elongate protuberances visible on the lateral or posterolateral areas of the median body (Fig. 68 ). In a few species the outer surface of the maculae is reticulate or bears closely set, regularly arranged tubercles resembling the lenses of the dorsal eyes. Usually only a small portion of the macular surface is reticulate or faceted, the remainder being smooth. Usually only a small portion of the macular surface is reticulate or faceted, the remainder being smooth. The significance of the maculae and of their reticulate or faceted surface, is still a matter of subjective interpretation. LINDSTRÖM (1901), HANSTRØM (1926), and HUPÉ (1953) regard the maculae as true ventral eyes, whereas other paleontologists such as RAYMOND (1920), STØRMER (1949), and WHITTINGTON & EVITT (1953) prefer to regard them as places of muscle attachment. 

 

The probability that the maculae represent places of muscle attachment seems rather small. This is indicated by several features: (1) the mineralized integument of the maculae is much thinner than that of the remainder of the hypostoma, as pointed out by LINDSTRÖM and amply verified by WHITTINGTON & EVITT (1953) on silicified material: (2) the places of muscle attachment in the cephala of trilobites lacking apodemes invariably have a smooth surface, differing markedly in this respect from maculae with a reticulate or faceted surface; and (3) in some species of trilobites having the hypostoma firmly welded to the rostral plate (as Holmia kjerulfi, Redlichia noetlingi, Paradoxides davidis, Fieldaspis furcata) smooth maculae are well developed. In the last-named trilobites it is evident that, if the maculae represent places of muscle attachment, the muscles would function as for movements of the hypostoma alone. They may have been expansor muscles of the stomach, attached to the ventral wall of the subglabellar proventriculum, but it seems strange that such powerful muscles (judging by the size of the maculae) should have been needed to produce slight expansion of the soft-tissued stomach.

 

The available evidence seems to favor the view that the maculae had a visual function. This is especially true for the reticulate and faceted maculae present in such genera as Scutellum, Lichas, and Illaenus. The smooth maculae seem best regarded as "degenerate" ventral eyes that have lost their lenses. Sections normal to the surface of the maculae show that in those of "reticulate" type the macula consists of numerous prismatic bodies very similar to the prismatic lenses of the dorsal holochroal eyes. According to LINDSTRÖM this is true of the maculae observed in several asaphids and in some species of Illaenus. The "faceted" maculae show an aggregate of "globular" lenses resembling biconvex lenses of the dorsal eyes. These are especially well developed in some species of Scutellum and Lichas (Fig. 68B-F). The presence of ventral eyes in some trilobites would certainly not constitute a unique feature among the Arthropoda, as similar organs are known among the Chelicerata and Myriapoda (HANSTRØM, 1926).

 

 

Moore, R.C. (ed.) 1959
Treatise on Invertebrate Paleontology. Part O. Arthopoda 1. Trilobita.
Geological Society of America and University of Kansas Press: 560 pp.