The oldest fossil Myriapods which have been discovered at the present time are two species which have been found in the Old Red Sandstone in Scotland. To realise the antiquity of these Myriapods, it will be worth while recalling the typical fossils found in the Old Red Sandstone, so as to see what the contemporaries of these ancient Myriapods were like. Among the plants there were Algae, Ferns, and Conifers, belonging to the lower divisions of the plant tribe. Among the animals there were Sponges, Corals, Starfish, Worms, Shell-fish, and Fishes, but none of the more highly organised of the animal or vegetable tribe had appeared on the earth. The Myriapods of the Old Red Sandstone, as has been before said, differ considerably from those of the present day, and as we proceed towards the species found in the more recent strata we find them more and more like the ones at present living, till we get to the Polyxenus and other species found in amber, which are hardly to be distinguished from living forms.
The next oldest fossil Myriapods are found in the coal measures, when both the animal and vegetable kingdoms were represented by more numerous and more specialised forms. The fossil fauna of this period is characterised by the number of gigantic Amphibia, many remains of which have been found. The great forests and the abundant vegetation of this time must have been favourable to the existence of our class, and accordingly we find no less than 32 species of fossil Myriapods. Of these most have been found in America, some in Great Britain, and some in Germany. One well-preserved fossil of Xylobius sigillariae was found by Dr. Dawson in America in the stump of a tree in the remains of a fossil forest. The eyes, head, and legs were plainly seen under the microscope. All these fossils belong to the earliest or Palaeozoic period.
Fig. 45.—Palaeocampa anthrax. (After Meek and Worth.) From Mazon Creek, Illinois.
The figure below (Fig. 46) shows a fossil also from the coal formations of Illinois, America, belonging to the family of the Euphoberiidae mentioned further on. It shows a nearer approach to the Julidae of the present time. The limbs, however, were of very curious shape, and may possibly have been adapted to locomotion in water as well as on land, and the small supposed branchiae on the ventral surface shown in Fig. 46, B, may possibly have been an arrangement to render respiration in the water possible.
In the secondary period the Myriapods were scantily represented, or, at any rate, geologists have failed to find their fossils. The class is represented by a single specimen found in the chalk in Greenland. This fossil, which has been included in the Julidae under the name of Julopsis cretacea, may perhaps belong to the Archipolypoda.
Passing on to the Tertiary or Recent period, we find the Myriapods again numerous, and more nearly resembling those living at the present time. They belong mostly to the Chilognatha and Chilopoda. They have been found in the fresh-water gypsum of Provence in France, the brown coal of Germany, and the green river formations of America. Several have been found in amber.
Fig. 46.—Acantherpestes major. (After Meek and Worth.) Mazon Creek, America. A, The whole animal; B, branchiae on the ventral surface.
Fossil Myriapods have been divided into four Orders, two of which coincide with the Orders of living Myriapods; the differences between the fossils and the living Myriapods having been held insufficient to warrant the establishment of a new Order. These two Orders are the Chilopoda and the Diplopoda or Chilognatha (Diplopoda is another name used by some writers for the group which we have hitherto called Chilognatha). The other two Orders have sufficient differences from living forms to render it necessary to include them in separate Orders.