Four camera-type eyes in the earliest vertebrates from the Cambrian Period

Lei et al 2026 re-interpteted former nasal capsules
in Cambrian Haikouichthys as twin, close-set pineal eyes with lens and retina medial to larger traditional lateral eyes.

The identification of retinal tissue, along with the eyeball-ish shape, shifted the traditional paradigm from nose to eye. Good job, authors!

“Vertebrate vision is mainly accommodated by a pair of lateral image-forming camera-type eyes and is supplemented in non-mammalian vertebrates by a dorsal pineal complex (pineal and parapineal organs) functioning as photoreceptive and/or endocrine organs.

“The pineal complex shares a common genetic and embryological basis with the lateral eyes, both derived from evaginations during the development of diencephalon. Despite being widely heralded as the ‘third eye’ in crown vertebrates, the nature of the pineal complex and its presumed visual capability in early vertebrates² remain unknown.

“Here we describe two pigmented features situated between the lateral eyes in two species of myllokunmingids, the earliest known fossil vertebrates (approximately 518  million years ago), and interpret these as pineal/parapineal organs.

“In both myllokunmingid species, the pineal complex contains abundant melanin-containing melanosomes identical to those in the retinal pigment epithelium in the lateral eyes, together with a distinctive, regularly ovoid structure interpreted as a lens.

“Our results indicate that the lateral eyes and pineal complex in myllokunmingids probably functioned as camera-type eyes capable of image formation. Thus, we propose that the four camera-type eyes represent an ancestral vertebrate character, corroborating hypotheses about the deep homology between the eyes and pineal complex.”

After an earlier phylogenetic analysis
in the large reptile tree (LRT, 2340 taxa) Cambrian Haikouichthys nested basal to Silurian Kalanaspis + Hemicyclaspis (with close-set tiny dorsal eyes) AND extant sturgeons (with large lateral eyes). All of these taxa have/had a flat ventral surface and a ventral oral cavity, rather than jaws, posterior to a ventral olfactory organ. They also had similar armor plates and a heterocercal tail.

Thus the new interpretation of Haikouicthys with four eyes
provides a novel solution to the phylogenetic split between Kalanaspis + Hemicyclaspis, (which lose or cover up the large lateral eyes) AND extant sturgeons, (which lose or cover up the tiny dorsal eyes).

A former hypothesis imagined a migration of eyeballs between the Silurian taxa and extant sturgeons.

Early Silurian
Thelodus is also related. It had large lateral eyes. If it had tiny dorsal eyes those are obscured in the fossil data presently available.

These taxa are all members of the clade
Acipenseriformes = sturgeons and their kin. Apparently this four-eyed trait is restricted to this clade, not vertebrates or chordates in general. See the LRT for details.

References
Let X-T et al (5co-authors) 2026. Four camera-type eyes in the earliest vertebrates from the Cambrian Period. Nature https://www.nature.com/articles/s41586-025-09966-0
Luo H, Hu and Shou 1997. New occurrence of the early Cambrian Chengjiang fauna from Haikou, Kunming, Yunnan province. Acta. Geol. Sin. 71, 97-104.
Shu D-G et al. (8 co-authors) 1999. Lower Cambrian vertebrates from China. Nature 402:42-46.

wiki/Haikouichthys

Acipenseriformes

https://pterosaurheresies.wordpress.com/2023/12/24/early-cambrian-haikouichthys-in-dorsal-view-and-the-naris-migration-problem/

Source: https://pterosaurheresies.wordpress.com/2026/01/29/four-camera-type-eyes-in-the-earliest-vertebrates-from-the-cambrian-period/