A dinosaur called "Galtonia gibbidens" left behind some teeth in the Emigsville area. "Rutiodon" fossils were preserved in York County along the Little Conewago Creek. Also near Emigsville, two metoposaurs were preserved in what is now a copper mine. There are few if any rocks from the ensuing Tertiary period of the Cenozoic era in Pennsylvania's geologic record. However, during the Pleistocene, glaciers covered much of the state. Those areas left uncovered formed a tundra dotted with sedges and willows. One legend told among the Delaware Indians describes the discovery of a fragment of bone left by a monster that had once been killing people near modern Philadelphia in either Pennsylvania or eastern New Jersey. When the hunting party brought the piece of bone back to the village, a wise man encouraged them to set out and find more of the monsters remains. He said that smoking fragments of the bone with tobacco in a small clay spoon could grant wishes like good health for one's children, longevity, or successful hunting. The area where the Delaware hunters supposedly found the ancient bones is the same general region as the earliest dinosaur discoveries in North America. Local dinosaurs include ankylosaurs, "Coelosaurus", "Dryptosaurus", and "Hadrosaurus". Other local reptile fossils include crocodilians and "Tylosaurus". This legend likely predates European contact and may have originated prior to 1500. The bones being burnt in the "clay spoon" is a reference to a primitive kind of clay pipe that the local people had abandoned in favor of a design with a deeper bowl by the 17th century. The general lack of any sign of influence by European culture on the tale is also suggestive of its great antiquity. One of the earliest notable events in Pennsylvania paleontology was the October 5th, 1787 presentation by Caspar Wistar and Timothy Matlack of a probable dinosaur metatarsal discovered in Late Cretaceous rocks near Woodbury Creek in New Jersey as "'a large thigh bone'" to the American Philosophical Society in Philadelphia. During the industrial revolution, Carboniferous-aged coal deposits in Pennsylvania were the sites of serendipitous discoveries of early fossil tetrapod trackways. Such discoveries generally occur when the excavation of coal mines removes the rock underlying the trackway, leaving it exposed on the tunnel's ceiling. Later, during the 1840s, Charles Lyell examined some local purported fossil bird and mammal tracks and found that they were actually petroglyphs left by local indigenous people.