An ancient, fossilized piscine creature likely relied on apertures atop its cranium for respiration, newly unearthed in remote regions of Australia.
This species boasted a streamlined physique, equipped with formidable dentition and ossified dermal plates, estimated to reach lengths of approximately 40 cm, as delineated in a scholarly article published in the Journal of Vertebrate Paleontology.
"We chanced upon this novel variant of sarcopterygian fish within one of the most secluded fossil deposits across Australia, the Harajica Sandstone Member situated in the Northern Territory, nearly 200km westward of Alice Springs, originating from the Middle-Late Devonian epoch approximately 380 million years ago," remarked co-author John Long, an esteemed authority on fossilized piscine organisms from Flinders University, Australia.
Dubbed Harajicadectes zhumini after its locale of discovery and the ancient Greek term dēktēs signifying "one who bites", this designation also serves as a tribute to Professor Min Zhu of the Chinese Academy of Sciences, whose contributions to the study of early vertebrates have been profound. The holotype of Harajicadectes, discovered in situ in 2016 (an almost intact specimen observed dorsally), a latex impression of the fossil, and an explanatory diagram. Credit: Brian Choo, Flinders University Despite its peculiarity by contemporary piscine standards, the prominent apertures atop its cranium, referred to as spiracles, are not entirely unprecedented in fish.
"These spiracular structures are believed to facilitate aerial respiration, akin to those observed in present-day African bichir fish, which possess analogous structures for drawing in atmospheric oxygen at the water's surface," noted lead author Dr. Brian Choo of the Flinders Palaeontology Lab.
"This trait manifests across multiple lineages of Tetrapodomorphs during the Middle-Late Devonian era."
Tetrapodomorphs represent a clade of vertebrates encompassing tetrapods and their closest piscine relatives. In addition to Harajicadectes from central Australia, substantial spiracles also emerged in Gogonasus from Western Australia and elpistostegalians like Tiktaalik (the nearest kin to tetrapods with limbs). It also surfaces in the unrelated Pickeringius, a ray-finned fish originating from Western Australia, initially documented in 2018," appended Choo.
According to Long, the synchronous emergence of this aerial-breathing adaptation might have coincided with a period of diminished atmospheric oxygen levels during the mid-Devonian epoch.
"The capacity to supplement gill-based respiration with aerial oxygen likely conferred an evolutionary advantage," he posited.
Determining Harajicadectes' precise placement within this piscine assemblage proves challenging, as it appears to have acquired an array of specialized attributes found across disparate branches of Tetrapodomorpha.
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