Fossilized rod and cone cells the kinds that help people see in color and detail have been discovered for the first time in a 300millionyearold fossil specimen of a fish called Acanthodes
bridgei, according to a scientific study recently published in Nature Communications journal.
New research on Acanthodes bronni, a fish from the Paleozoic era, sheds light on the evolution of the earliest jawed vertebrates and offers a new glimpse of the last common ancestor before the split between the earliest sharks and the first bony fishes - the lineage that would eventually include human beings.
Unexpectedly, Acanthodes turns out to be the best view we have of conditions in the last common ancestor of bony fishes and sharks," said Michael Coates, PhD, professor of organismal biology and anatomy at the University of Chicago and senior author of the study.
But armed with new data on what the earliest sharks and bony fishes looked like, Coates and colleagues re-examined fossils of Acanthodes bronni, the best-preserved acanthodian species.
This has been suggested for the columnar cacti Carnegiea gigantea and Stenocereus thurberi (Parker, 1993; Pierson & Turner, 1998), the barrel cacti Echinocactus polycephalus, Ferocactus acanthodes, and F.
This type of interaction has also been documented between the barrel cactus Ferocactus acanthodes and the perennial bunchgrass Hilaria rigida (Franco & Nobel, 1989), between Opuntia leptocaulis and the shrub Larrea tridentata (Yeaton, 1978), and between O.
Nobel (1988) estimated that the water requirement for reproduction represented only 6% of the stem water at time of flowering in Ferocactus acanthodes
(a barrel cactus), which generally occurs during the seasonal drought in spring.
The other braincase, from a species called Acanthodes, dates to a hundred million years after the Acanthodian group came into existence, casting most of this period of the group's evolution into shadow.
The ancient creature has distinct features of a shark-swirling rows of teeth and a short snout, for instance-and looked little like the early bony fish suggested by the Acanthodes braincase.
triglochidiatus Echinomastus erectrocentrus Ferocactus 1 acanthodes
A scanning electron microscopy of scales Acanthodes
Most seedlings of the boojum (Idria columnaris), a species restricted to Baja California, are found under shrubs (Humphrey, 1974), and seedlings of several other succulent species common in the Sonoran Desert, including Agave deserti and Ferocactus acanthodes
, are associated with nurse plants (Franco & Nobel, 1988, 1989; Jordan & Nobel, 1979, 1981).