Giant gar from directly above the Cretaceous-Palaeogene boundary suggests healthy freshwater ecosystems existed within thousands of years of the asteroid impact

Abstract

The Cretaceous-Palaeogene (K-Pg) mass extinction was responsible for the destruction of global ecosystems and loss of approximately three-quarters of species diversity 66 million years ago. Large-bodied land vertebrates suffered high extinction rates, whereas small-bodied vertebrates living in freshwater ecosystems were buffered from the worst effects. Here, we report a new species of large-bodied (1.4-1.5 m) gar based on a complete skeleton from the Williston Basin of North America. The new species was recovered 18 cm above the K-Pg boundary, making it one of the oldest articulated vertebrate fossils from the Cenozoic. The presence of this freshwater macropredator approximately 1.5-2.5 thousand years after the asteroid impact suggests the rapid recovery and reassembly of North American freshwater food webs and ecosystems after the mass extinction.

Keywords: Fish; K–Pg; Lepisosteidae; Lilliput effect; gar.

Figure 1.

Anatomy of †Atractosteus grandei sp. nov. Skull in (a) dorsal, (b) ventral and (c) lateral views. Inset shows size compared to a 1.85 m tall man.

Figure 2.

Size and phylogenetic relationships of †Atractosteus grandei sp. nov. (a) Linear regression of HL against SL in a sample of gars, with red star indicating the position on the regression length corresponding to the length of the skull of †A. grandei sp. nov. (b) Time-calibrated maximum clade credibility tree from analysis of the morphological matrix in BEAST 2.6.6. Red line denotes the position of the K–Pg boundary/recovery period. Ma = millions of years.