Ancient Human Size Fish Breathed with Lungs

1

Before the dinosaur age, the coelacanth — a hefty, mysterious fish that now breathes with its gills — sported a well-developed lung, a new study finds.

This lung likely helped the fish survive in low-oxygen, shallow waters hundreds of millions of years ago, the researchers said. During the Mesozoic era, more commonly known as the dinosaur age, it’s likely that some species of coelacanth (see-leh-kanth) moved to deeper waters, stopped using their lungs and began relying exclusively on their gills to breathe, the researchers said.

This adaptation to deep water likely helped coelacanths survive the asteroid that slammed into ancient Earth and killed the nonavian dinosaurs, the researchers said. The fish’s gill- and lung-breathing relatives were not as lucky; during the Late Cretaceous period, about 66 million years ago, coelacanths living in shallow waters disappear from the fossil record, they said.

The hulking 6.5-foot-long (2 meters) fish has long baffled scientists. Fossils of the predatory fish date back to the early Devonian period, about 410 million years ago. The fish was thought to have gone extinct after the dinosaur-killing asteroid hit Earth, but living coelacanths were discovered off the coast of South Africa in 1938.

Today, there are two known species of living coelacanths that live in the deep waters near Mozambique and Indonesia. Scientists have collected and preserved entire specimens of these fish (which give birth to live young) over the decades, allowing researchers to study how the fish change from embryos to adulthood.

This image shows 3D reconstructions of the pulmonary complex of Latimeria chalumnae at different ontogenetic stages.
Credit: Brito et al. Nature Communications

View full size image

In the new study, researchers examined the curious lungs of one species of coelacanth (Latimeria chalumnae) at five different stages of growth. They scanned each specimen with X-ray tomography, a method that allows researchers to take multiple X-rays of an object, compile them and create a 3D image.

“Our results demonstrate the presence of a potentially functional, well-developed lung in the earliest known coelacanth embryo,” the researchers wrote in the study. However, as the embryo grows, its lung development slows, and it eventually becomes a vestigial (functionless) organ in the fish, they observed.

Interestingly, adult L. chalumnae have small, hard, flexible plates scattered around their vestigial lungs. It’s possible that these plates are similar to the “calcified lung” of fossil coelacanths, said Paulo Brito, one of the study’s researchers and a professor of zoology at Rio de Janeiro State University in Brazil.

“In fossil coelacanths, these plates surrounding the lung most probably had a function in lung volume regulation, moving over each other to accommodate volumetric changes,” Brito told Live Science in an email. “In extant [living] coelacanths, it represents a rudimentary anatomical structure.”

It’s possible that the lung became less developed as the coelacanth moved to deeper waters, but remnants of it still exist as a vestigial organ, the researchers said. However, as the lung shrank and became useless, a fatty organ that the fish uses for buoyancy control in deep waters grew and took over the space once occupied by the lung.

“Although we cannot know whether the fatty organ ever existed in fossil forms, due to its unique soft-tissue constitution, this organ in Latimeria has a function in buoyancy control,” the researchers said in the study.

Given that the coelacanth has evidence of “calcified lungs” in the fossil record, as well as a developing lung early in its embryonic development, it’s possible that the “lung is a primitive character[istic] in bony fishes,” Brito said. Lungs are also present in most ancient ray-finned fishes (a subclass of boney fishes), lungfishes and living lobe-finned fish (such as the coelacanth), as well as four-legged vertebrates, including amphibians, reptiles, mammals and birds.

Bird Mummy’s Secret Why Raptor Was Force-Fed by Ancient Egyptians

Mummification wasn’t reserved for people in Egypt. The archaeological record is full of examples of cats, dogs, crocodiles and birds that were mummified and used as religious offerings to their corresponding animal gods, a practice that was popular from about 600 B.C. until around A.D. 250, well into the Roman period. Salima Ikram, a professor of Egyptology at the American University in Cairo, has made a living studying these animal mummies, and for her latest research, she examined the ancient remains of a European kestrel from the Iziko Museums of South Africa in Cape Town. [See Photos of Dog Mummies in Ancient Egyptian Catacomb

An X-ray revealed a mouse tail extending from the ancient bird’s stomach up through its esophagus.

Credit: Stellenbosch University, via Salima Ikram

View full size image

New imaging technologies have made it possible to see through mummies without butchering ancient corpses: Ikram and her colleagues used an X-ray computed tomography scanner at Stellenbosch University in South Africa to see the insides of the kestrel in 3D. The images revealed the bird’s stomach was stuffed with bones and teeth from at least two mice —one with its tail inside the raptor’s esophagus —and a partially digested sparrow.

The kestrel’s skeleton showed no signs of trauma. And whereas other bird mummies in Egypt had their gizzards removed or their beaks packed with food after death, this specimen also had no signs of evisceration. The kestrel was likely desiccated with natron (a naturally occurring soda ash) embalmed with resin and wrapped in bandages (in this case, quite haphazardly) with its stomach contents intact.

“We were extraordinarily surprised by the virtual autopsy as we had no expectation of any contents within the kestrel’s body,” Ikram said. “To learn that it choked was amazing.”

Ikram and her colleagues say it’s unlikely the kestrel accidentally or deliberately ate itself to death, as the birds are known to store food when they catch too much for a single meal. Rather, the bird likely had lots of help dying from its captors.

In Egyptian art, images show a variety of animals, from hyenas to geese, being force-fed by people, Ikram told Live Science. But this is the first time archaeologists have identified an animal mummy that died of overeating. The kestrel in the Iziko Museums might also be among the earliest evidence of falconry.

“The fact that wild birds that were not of use for food themselves were tamed and controlled provides an insight into Egyptian religious practices,” Ikram said. “The ability of the Egyptians to tame and control wild bird populations, and the possible use of these creatures in falconry, either as sport or in obtaining small game, is of interest as it documents the evolving relationship between humans and animals.”

The mummy arrived at the Iziko Museums in the early 20th century, but unfortunately the authors of the study don’t know where it came from. Ikram thinks it likely was unearthed in a catacomb or special burial linked with the sun god. Her team is going through the museum archives to try to trace the artifact to a specific geographic area.