#varanidae

[herpsandbirds]

Asian Water Monitors (Varanus salvator), hug and kiss very sweetly, family Varanidae, Singapore

OK, well, actually they are fighting.

photograph by Neil Miner

[alphynix]

Saniwa ensidens was a varanid lizard that lived during the Eocene, about 49 million years ago, in what is now Wyoming, USA.

Closely related to monitor lizards, it would have grown to about 2m long (~6'6") and looked very similar to modern forms, with a pointed snout, well-developed limbs, and a proportionally long tail.

But it also had something not seen in any other jawed vertebrate — a total of four eyes.

Many lizards have a single prominent parietal "third eye" on the top of their heads, which are light-sensitive and involved with both regulating circadian rhythms and hormone production for thermoregulation. However, Saniwa ensidens had two of these structures, with one formed from the parapineal gland like in other lizards, and the second positioned behind it formed by the pineal gland. The only other vertebrates with this arrangement are the jawless lampreys, suggesting that Saniwa somehow re-evolved a pineal eye hundreds of millions of years after its distant ancestors had lost it.

It's not clear what this extra eye was used for. It would have increased the pineal complex's sensitivity to blue-wavelength light, and may have been involved in orientation and navigation using polarized light similar to some modern lizards — or possibly magnetoreception-based navigation similar to some modern newts.

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References:

Beltrami, Giulia, et al. "The lizard celestial compass detects linearly polarized light in the blue." Journal of Experimental Biology 215.18 (2012): 3200-3206. https://doi.org/10.1242/jeb.074419

Deutschlander, M. E., S. C. Borland, and J. B. Phillips. "Extraocular magnetic compass in newts." Nature 400.6742 (1999): 324-325. https://doi.org/10.1038/22450

Rieppel, Olivier, and Lance Grande. "The anatomy of the fossil varanid lizard Saniwa ensidens Leidy, 1870, based on a newly discovered complete skeleton." Journal of Paleontology 81.4 (2007): 643-665. https://doi.org/10.1666/pleo0022-3360(2007)081[0643:TAOTFV]2.0.CO;2

Smith, Krister T., et al. "The only known jawed vertebrate with four eyes and the bauplan of the pineal complex." Current Biology 28.7 (2018): 1101-1107. https://doi.org/10.1016/j.cub.2018.02.021

Wikipedia contributors. “Saniwa” Wikipedia, 03 Dec. 2025, https://en.wikipedia.org/wiki/Saniwa

Witmer, Lawrence M. "Paleoneurology: a sight for four eyes." Current Biology 28.7 (2018): R311-R313. https://doi.org/10.1016/j.cub.2018.02.071

[snototter]

A Merten's water monitor (Varanus mertensi) in Northern Australia

by Stephiny Delamare

[saritawolf]

Komodo Dragon (juvenile) (Varanus komodoensis) - (c) SaritaWolf - please do not repost

[uncharismatic-fauna]

Uncharismatic Fact of the Day

Why build your own nest when you can just someone else's? When it comes to laying eggs, female lace monitors seek out a large termite mound, dig a small hole, and lay their eggs inside. The termites then seal up the hole; the eggs remain protected, and the mound is kept at an ideal incubation temperature. As a bonus, the hatchlings get an all-you-can-eat termite buffet when they emerge!

(Image: A lace monitor (Varanus varius) by Richard N Horne)

[morgansram]

Monitor lizard deep in egg yolk X

[have-you-seen-this-animal]

Have you seen the blue-spotted tree monitor (Varanus macraei)?

I have now

Yes, in photos/videos

Yes, irl

I'm not sure

Voting ended onSep 2, 2025

[thebeastsofindia]

Bengal Monitor (Varanus bengalensis), family Varanidae, order Squamata, Kerala, India

Photo by Ummer K