The evolution of teeth got pushed back farther in time, thanks to analysis of a placoderm fossil.
According to Science Magazine’s Science Shot, “Ancient Jaws Had Real Teeth.” Live Science headlined, “Evolution’s Bite: Ancient Armored Fish Was Toothy, Too.” The best graphics are on PhysOrg’s coverage, “Looking for the evolutionary origins of our pretty smile.”
The artist’s rendition of this shark-like fish’s smile is anything but pretty. Neither is the evolutionary implication, stated on Science Shot: “The evolutionary origin of teeth and jaws has long been shrouded in mystery, but the new findings reveal that even the earliest jawed vertebrates had choppers.”
Placoderms supposedly lived between 360–420 million years ago, far earlier than expected for vertebrate teeth. The placoderm teeth had no roots, and grew out of the jawbone, but otherwise were clearly adapted for big bites. What it means is that jaws had teeth from the beginning; teeth were not a later addition.
“It has long been thought that the first jawed vertebrates were gummy — [they had] jaws without teeth, capturing prey by suction-feeding,” researcher Philip Donoghue, a paleontologist at the University of Bristol in England, told LiveScience.
But even though Donoghue claimed this study “solves the debate on the origin of teeth,” it would seem more challenging to explain the origin of both jaws and teeth at the same time. Live Science said, “This discovery that the earliest jawed vertebrates were toothy suggests teeth evolved along with or soon after jaws did.”
According to the paper in Nature, the authors believe jaws came first, then teeth, but their conclusion fails to explain what mutations could have led to neat rows of functional teeth in the first place (for details, see quote below).
This fish looks perfectly adapted for the life it lived. Evolution adds nothing but storytelling from a naturalistic, millions-of-years worldview. With its gummy jaws but no bite, evolution is parasitic on real science.
From Ruecklin et al, “Development of teeth and jaws in the earliest jawed vertebrates,” Nature, doi:10.1038/nature11555, published online 17 Oct 2012.
Our evidence indicates that teeth are present even in the earliest jawed vertebrates and that within the phylogenetic context of placoderm paraphyly they can be identified as homologous to the teeth of crown gnathostomes. This contrasts with the hypothesis that teeth were absent from the earliest jawed vertebrates, evolved convergently through cooption of oral and pharyngeal denticles. Indeed, our tomographic analyses show that the putative tooth-like pattern of placoderm pharyngeal denticle replacement bears no resemblance to that of their teeth, except in superficial morphology. Thus, the hypothesis of a distinct evolutionary origin of teeth and dermal denticles can be rejected, as jawless stem-gnathostomes have been shown to lack homologous dental patterning and the assertion of a fundamental embryological distinction between external and oral denticles has been refuted. Ultimately, teeth and other oral and pharyngeal denticles must be derived through the extension of the odontogenic capacity of the external dermis to the internal dermis and endoderm. However, tooth– and jaw-structure and development is evidently less integrated within the placoderm grade of early jawed-vertebrate evolution than in derived osteichthyans in which teeth, tooth development and jaw structure are intimately interwoven, as part of the process of site-specific tooth replacement. Upper and lower dental ossifications occur in placoderms, but there is no clear homologue of the osteichthyan dentary or coronoid. However, the axial ossification of the infragnathal can be compared to the inner dental arcade of early osteichthyans based on its location relative to the underlying Meckel’s cartilage, overlying dental ossification and lateral muscle attachment. Compagopiscis and other placoderms evidence an early stage in jawed vertebrate evolution in which the components of the mandible were fewer and more obviously distinct than they are in osteichthyan evolutionary and developmental model organisms. Some processes associated with these more derived taxa, such as tooth resorption (as a necessary precursor to tooth replacement), are absent in placoderms. This stepwise acquisition reflects the fact that character complexes like the gnathostome jaw have been assembled over a protracted episode of evolutionary history and so the modular construction of the mandible, for example, reflects the disparate evolutionary origins of its component modules.