chordata – Nix Illustration

Haikouichthys

Haikouichthys ercaicunensis was one of the earliest known vertebrates, living in what is now southwestern China during the Cambrian, around 518 million years ago.

About 2.5cm long (~1″), it had a streamlined body with a long fin along its back and tail. It lacked limbs and jaws, but it did have a flexible “upper lip” that could potentially have been used to manipulate food particles, either engulfing them on the seafloor or stirring them up into the water for filter-feeding.

And a recent study revealed a big surprise — it had four eyes! Along with its already-known large sideways-facing pair of eyes, it also had another smaller upwards-facing pair in the middle of its face, giving it a much wider field of vision and the ability to watch out for predators from multiple angles at once.

The extra pair of eyes may be the evolutionary precursors to the pineal complex in later vertebrates — represented in modern forms by the pineal gland and the parietal eye.

Eons Roundup 13

I haven’t posted any PBS Eons commissions here for quite a while, so let’s catch up a bit of the backlog:

An illustration of the extinct mammal Repenomamus robustus. It's a low-slung, stocky, badger-like animal with a thick tail, depicted as colored brown and white. It's shown baring a mouth full of pointed teeth. — *Repenomamus robustus*

An illustration of the extinct mammal Repenomamus giganticus. It's a low-slung, stocky, badger-like animal with a thick tail, depicted as colored yellow-brown and dark brown. It's shown walking with its head held down as if stalking something. — *Repenomamus robustus*

The Cretaceous mammals Repenomamus robustus and Repenomamus giganticus, from “When Mammals Only Went Out At Night”
https://www.youtube.com/watch?v=JqZONKXWPfw

An illustration of a decaying carcass of the extinct whale Borealodon. Its skin is tattered and torn as if scavengers have been picking at it, and part of its lower jaw bone is exposed. — *Borealodon osedax* (carcass)

A carcass of the whale Borealodon, from “How Ancient Whales May Have Changed the Deep Ocean”
https://www.youtube.com/watch?v=1vb00-gcdtA

An illustration of the extinct early vertebrate Haikouichthys. It's a small eel-like animal with large eyes, a circular mouth, and seven gill slits. It's depicted as pale blue colored, and it's swimming in dark blue water. — *Haikouichthys ercaicunensis*

An illustration of the extinct early vertebrate Myllokunmingia. It's a small eel-like animal with fairly large eyes, a circular mouth, and six gill slits. It's depicted as pale green colored, and it's swimming in dark blue water. — *Haikouichthys ercaicunensis*

And the early vertebrates Haikouichthys and Myllokunmingia, from “Why Sour May Be The Oldest Taste”
https://www.youtube.com/watch?v=XXgd_cNZSvk

Spectember 2021 – Dimorphic Tunicates

As we come to the end of the month, here’s another #Spectember concept from an anonymous submission:

Cambrian Explosion Month #16: Phylum Chordata – Vertebrata

Vertebrates are by far the most numerous and diverse group of chordates today, with over 65,000 known species including fish, amphibians, reptiles, birds, and mammals. Genetic studies show that they’re closely related to the weird bag-like tunicates, and their shared common ancestor was probably something lancelet-like.

And the earliest true vertebrates would have looked something like Haikouichthys ercaicunensis.

Cambrian Explosion Month #15: Phylum Chordata – Early Forms & Tunicates

Chordates are one of the most diverse animal phyla, ranging from tiny lancelets to sac-like tunicates to all fish and tetrapods. They share a common deuterostome ancestor with echinoderms and hemichordates, probably diverging from them sometime in the Ediacaran Period, and are characterized by having specific anatomical features at some point during their life cycle – a notochord, a dorsal nerve cord, pharyngeal slits, a post-anal tail, and an endostyle.

The earliest chordates were all small soft-bodied animals with no mineralized tissues, so their fossil record is poor aside from rare locations with exceptional preservation. But one of the best known examples is Pikaia gracilens from the Canadian Burgess Shale fossil deposits (~508 million years ago).

Myllokunmingia

Myllokunmingia, from the Early Cambrian of China (~530 mya).

Just under 3cm long (or just over 1″), this tiny animal seems to have been a very close relative of the true vertebrates – almost a vertebrate itself but not quite there yet. A single known fossil specimen shows evidence of a cartilage skull and skeletal elements, five or six gill pouches, a large sail-like dorsal fin, and paired finfolds on its underside.