The ancient life of the Atlantic border of North America was also becoming known through the work of the pioneer verte.rate palaeontologists Thomas Jefferson (1743-1826), Richard Harlan (1796-1843), Jeffries Wyman (1814-1874) and Joseph Leidy (1823-1891).
The master works of Joseph Leidy began with the first-fruits of western exploration in 1847 and extended through a series of grand memoirs, culminating in 1874.
Leidy adhered strictly to Cuvier's exact descriptive methods, and while an evolutionist and recognizing clearly the genetic relationships of the horses and other groups, he never indulged in speculation.
Discoveries in North America by Leidy, Cope and Marsh, and the ensuing phylogenies gave enormous prestige to palaeontology.
Leidy on the evidence of imperfect materials, and other remains now known to belong to the same type were subsequently described as Cosoryx, to which Blastomeryx seems to be allied..