Oldest coelacanth, from the Early Devonian of Australia

Abstract

Coelacanths are well-known sarcopterygian (lobe-finned) fishes, which together with lungfishes are the closest extant relatives of land vertebrates (tetrapods). Coelacanths have both living representatives and a rich fossil record, but lack fossils older than the late Middle Devonian (385-390 Myr ago), conflicting with current phylogenies implying coelacanths diverged from other sarcopterygians in the earliest Devonian (410-415 Myr ago). Here, we report the discovery of a new coelacanth from the Early Devonian of Australia (407-409 Myr ago), which fills in the approximately 20 Myr 'ghost range' between previous coelacanth records and the predicted origin of the group. This taxon is based on a single lower jaw bone, the dentary, which is deep and short in form and possesses a dentary sensory pore, otherwise seen in Carboniferous and younger taxa.

Earliest known coelacanth skull extends the range of anatomically modern coelacanths to the Early Devonian

“…The presence of the dentary pore raises the tantalizing possibility that Eoactinistia may be an anatomically modern coelacanth, previously known only from the late Middle Devonian and younger age. However, the unknown phylogenetic position of Eoactinistia and the lack of any other Early Devonian coelacanth fossils make it impossible to weigh this possibility against other possibilities (that is, the dentary pore as an independently derived feature that arose twice among coelacanths, or as a primitive feature that was lost in other Devonian forms but then reappeared in later coelacanths) 17 .…”

“…The early fossil record of coelacanths has been scarce, and opinions differ on which sarcopterygian taxon is the closest sister group of coelacanths 15,16 . So far, the earliest record of the traditionally defined coelacanth group 3,6,7,17 is one isolated dentary (Eoactinistia) from the Early Devonian (late Pragian, ~409 Myr ago) of Australia 17 . Because of its limited morphological features, Eoactinistia cannot be subjected to a phylogenetic analysis and its position within the coelacanths is unknown.…”

Single-male paternity in coelacanths

“…The nearly unchanged morphology of coelacanths for the last 400 mya 4,13 has led to the conclusion that their behaviour, ecology and genetics are very likely unchanged since the Devonian, and several molecular studies have confirmed their slow rate of evolution at the genetic level [14][15][16][17] . However, recent population genetic studies revealed genetic divergence between individuals among and within the field sites and thus a potential for adaptation in L. chalumnae 18,19 .…”

“…As this very first report from South Africa, more than a hundred individuals have been found off the East African Coast, most of them on the Comoros 2,3 . Researchers refer to coelacanths as 'living fossils' because of their nearly unchanged morphology since the late Devonian, approximately 400 mya ago 4 . They are of major scientific interest as they represent a very basal group of the gnathostomes.…”

New parasite in a coprolite of 240 million years, biogeography of fossil coelacanths, and the influence of air pollutants in a coastal area of northeastern Brazil

“…This group of lobe-finned fishes is presently represented by only two species found in the coastline of the Indian Ocean and Indonesia (Holder et al 1999), but in deep time they showed quite some diversity (Johanson et al 2006, Miguel et al 2014. Raphael Miguel (Universidade do Estado do Rio de Janeiro) and colleagues have reviewed the distribution of the extinct coelacanth group called Mawsoniidae.…”