A jaw-dropping fossil cache was found in the Grand Canyon. In a 2023 expedition along the Colorado River, paleontologists led by the University of Cambridge uncovered a trove of soft-bodied Cambrian fossils.
These were found primarily from an oxygen- and nutrient-balanced environment the team calls an evolutionary “Goldilocks zone”. These rare finds include snails, crustaceans, and worms with truly wild feeding gear, preserved in fine-grained mud rocks previously thought unlikely to harbor such treasures. This is the first Cambrian soft-animal fossil colony found within the Grand Canyon. Specifically, this is from the Bright Angel Formation of the Grand Canyon
These fossils date back 507 to 502 million years ago, during the explosive dawn of animal life. Mimicking iconic sites like the Burgess Shale (Canada) and Maotianshan Shale (China), this Grand Canyon discovery revealed soft shell creatures. These are typically invisible in most rock layers, making this a paleontological gold mine.
Molluscan radulae from the Bright Angel biota: (A) Series of shovel-shaped teeth displaying an element of bilateral symmetry. (B) Recurved partial series of shovel-shaped teeth. (C) Partial series of peg-shaped teeth. (D) Partial series showing teeth with marked terminal wear. (E) Detail of boxed area in (D). (F) Partial series of peg-like teeth. (G) Detail of teeth in boxed area in (F) showing low to moderate terminal wear. (H) Partial series of peg-like teeth displaying terminal wear. Image Credit: Giovanni Mussini et al
Strange Creatures with Cutting-Edge Feeding Tools
“This biota preserves probable algal and cyanobacterial photosynthesizers together with a range of functionally sophisticated metazoan consumers: suspension-feeding crustaceans, substrate-scraping molluscs, and morphologically exotic priapulids with complex filament-bearing teeth, convergent on modern microphagous forms”, the researchers wrote in their paper. “The Grand Canyon’s extensive ichnofossil and sedimentological records show that these phylogenetically and functionally derived taxa occupied highly habitable shallow-marine environments.”
These ancient animals show off some of the most complex evolutionary adaptations of their era. The treasure chest contains crustaceans that acted like conveyor belts of brine shrimp. They swept in food with hairy limbs and ground particles with grooved teeth. Also present are snail-like molluscs that scraped algae with tooth belts very similar to today’s garden snails.
But, a new species of worm, named Kraytdraco spectatus (after Star Wars’ krayt dragon from Star Wars) is probably the most exciting discovery for its long-bodied frame and sweeping rows of branching teeth, unlike anything alive today.
Kraytdraco spectatus gen. et sp. nov., proximal (i.e., narrow) pharyngeal tract: (A) Articulated proximal tract showing flaring proximal region and possible tapering distal “funnel.” (B) Detail of boxed area in (A), showing teeth of the flaring region in side view. (C) Detail of boxed area in (A), showing teeth of the flaring region in frontal view and denticles with club-like terminations. (D) Detail of boxed area in (A), showing teeth of the tapering funnel with complex filamentous denticles. (E and F) Introvert hooks with associated cone-like scalids. (G) Proximal teeth from the flaring region showing falcate profile and club-like terminations of denticles. (H) Isolated introvert hook. (I) Detail of boxed area in (H), showing filamentous projections of the basal denticles. (J) Tooth morphotype showing falcate shape. (K and P) Semi-articulated filamentous teeth from the narrow tract. (L) Detail of boxed area in (K) showing teeth in side view, with club-like to laterally branching denticles but already showing a multicuspidate apex (black arrowhead). (M) Tooth intermediate between those of the “flaring” and funnel-like regions, showing bifurcating basal denticles and apical denticles with lateral tuberculate projections. (N) Articulated filamentous teeth from the narrow tract. (O) Detail of boxed area in (N), showing relatively distal teeth with fine side-branches and multicuspidate apex. (P) Semi-articulated proximal teeth. (Q) Articulated funnel-like region of the narrow tract. (R) Tooth from the funnel-like region showing finely branching apical and basal denticles. (S to U) Distal-most teeth of the narrow tract, showing finely branching denticles, broadly equilateral profiles, transverse comb-like striations and multicuspidate prongs. Slide numbers and England Finder coordinates listed in data S1. Scale bars, (A and Q) 100 μm; (B, C, J, M, and R) 20 μm; (D, I, L, and O) 10 μm; (E, F, H, K, N, P, and S) 60 μm; (G) 50 μm; (T) 25 μm; (U) 45 μm. Image Credit: Image Credit: Giovanni Mussini et al
An Evolutionary Petri Dish
Five hundred million years ago, the Grand Canyon was closer to the equator, bathed in nutrient-rich, oxygen-balanced water. These were ideal conditions that allowed life and evolution to experiment.
“If the Cambrian Explosion laid the foundations of modern metazoan adaptive solutions, it is the scaling up of their competitive interactions that may have enforced directional, long-term trends of functional innovation in the Phanerozoic biosphere”.This zone enabled flashy, costly feeding adaptations long before such complexity took root elsewhere. Scientists compare the evolutionary innovation of that time to economic risk-taking when resources are abundant: go bold when things are good.