But 24 of the marathon group and 14 of the control group were referred for surgical treatment of lesions that appeared to be basal or squamous cell carcinomas or the precancerous lesions called actinic keratoses.
Several species thought to be basal ornithopods occur in older beds, but there are so few differences between basal ornithopods and even more basal ornithischians that it is unclear exactly where the ornithopod line started.
This tree provides a simple illustration of the fact that the outgroup lineage cannot be assumed to be "basal," "primitive," or "ancestral" to the other species included on the tree.
Arctometatarsalia has been dismantled and is no longer used by most paleontologists, with tyrannosauroids usually considered to be basal coelurosaurs outside Maniraptoriformes.
This configuration is thought to be basal in sharks and may enhance its sensitivity to the minute movements of its prey.
A further molecular study published in 2005 showed the white-bellied and Sanford's sea eagles to be basal to the four fish eagles (the two mentioned above plus the two hitherto untested species of the genus Ichthyophaga).
Most 21st-century analyses have found them to be basal theropods, though they may in fact represent basal saurischians or even be non-dinosaurian, predating the saurischian-ornithischian split.
While the systematics (evolutionary relationships) of nodosaurids have not been firmly established, the genera Sauropelta, Silvisaurus and Pawpawsaurus are sometimes considered to be basal to geologically younger nodosaurids like Panoplosaurus, Edmontonia, and Animantarx.
Others (such as Ezcurra 2010) have found them to be basal to the clade Eusaurischia, that is, closer to the base of the saurischian tree than either true theropods or sauropodomorphs, but not members of either group.
