Abstract
The positive correlation between speciation rates and morphological evolution expressed by body size is a macroevolutionary trait of vertebrates. Although taxic diversification and morphological evolution are slow in coelacanths, their fossil record indicates that large and small species coexisted, which calls into question the link between morphological and body size disparities. Here, we describe and reassess fossils of giant coelacanths. Two genera reached up to 5 m long, placing them among the ten largest bony fish that ever lived. The disparity in body size adjusted to taxic diversity is much greater in coelacanths than in ray-finned fishes. Previous studies have shown that rates of speciation and rates of morphological evolution are overall low in this group, and our results indicate that these parameters are decoupled from the disparity in body size in coelacanths. Genomic and physiological characteristics of the extant Latimeria may reflect how the extinct relatives grew to such a large size. These characteristics highlight new evolutionary traits specific to these “living fossils”.
Highlights
Body size is often used as a proxy for analyzing morphological disparity, and this element is one of the main evolutionary traits discussed by biologists and paleontologists in order to decipher macroevolutionary processes
We show that the per genus coefficient of body size variance is higher in coelacanths than in ray-finned fishes. This result calls into question the positive correlation between speciation rates and body size found in most vertebrate lineages, and more generally questions the use of body size as a valid proxy for anatomical disparity[3,4]
The presence of a modern barnacle shell on the fossil (Supplementary Fig. S2A), an evidence of its discovery from a locality situated near the seashore, associated to the general type of preservation of the specimen and to the presence of vaginulinids and epistominids associated with vertebrate fossils are strong indications that this specimen probably comes from the late Callovian “Marnes de Dives”, probably from the well-exposed cliffs of the “Vaches Noires”, Villerssur-Mer, Normandy, F rance[31]
Summary
Body size is often used as a proxy for analyzing morphological disparity, and this element is one of the main evolutionary traits discussed by biologists and paleontologists in order to decipher macroevolutionary processes. Coelacanths form a depauperate group of sarcopterygian fish with only one genus today but with a long evolutionary history These fish are nicknamed "living fossils" because they possess characteristics used by Darwin to characterize this ill-defined concept, in particular "new forms ... We further reassess the Mesozoic fossil record of giant coelacanths and provide a large-scale comparison of body size disparity versus taxic diversity between coelacanths (Actinistia) and ray-finned fishes (Actinopterygii) over the Devonian–Paleocene time interval. We show that the per genus coefficient of body size variance is higher in coelacanths than in ray-finned fishes This result calls into question the positive correlation between speciation rates and body size found in most vertebrate lineages, and more generally questions the use of body size as a valid proxy for anatomical disparity[3,4]
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