The exposure by a stroke of the hammer, on the fractured surface of a rock picked up on the beach at Hayburn Wyke (a few miles south of Whitby), of a piece of fern frond which is unmistakably closely allied to the species described by Wallace on Mount Ophir, establishes a link between the Jurassic and the present era and presents a fascinating problem in geographical distribution. These fossil Matonias are known to students of ancient plants as species of the genus Matonidium, a name adopted by a German botanist for specimens apparently identical with those from the Yorkshire coast discovered in slightly younger rocks (Wealden) in North Germany. The same type has been found also in sediments of Wealden age on the Sussex coast. Other leaf-impressions agreeing closely with those of Matonidium have been obtained from the Yorkshire Jurassic rocks and these are assigned to another genus Laccopteris, an extinct member of the family Matonineae. It is not merely in the habit of the fronds and in the shape and venation of the leaflets that these fossil ferns resemble the existing species, but the more important features exhibited by the spore-capsules supply additional evidence. It has already been pointed out that the stems of Matonia are characterised by a type of structure unknown in an identical form in any other recent fern.
A few years ago Prof. Bommer discovered fragments of leaves and stems in Wealden beds a few miles from Brussels sufficiently well preserved to reveal the details of internal organisation. Some of these fossils were found to possess structural features identical with those of the Malayan species of Matonia. A full account of the fossil representatives of the Matonia family would be out of place in a general essay on Links with the Past, but brief reference may be made to some of the data which throw light on the geological history of the family. In strata classed by geologists as Rhaetic, a phase of earth-history between the Triassic and Jurassic eras (see [p. 42]), species of Laccopteris and allied forms have been described from several other countries; from Jurassic and Wealden strata examples of both Laccopteris and Matonia have been found in Germany, Portugal, Belgium, Austria, and elsewhere. From rocks of Cretaceous age, higher in the series than the Wealden strata, well preserved impressions of a Matonidium have been discovered in Moravia. The Matonineae were widely distributed in Europe during the Rhaetic and Jurassic periods, but, so far as we know, the family did not survive in the northern hemisphere beyond the limits of the Cretaceous period. It is noteworthy that, in spite of the preservation of the remains of Jurassic and Cretaceous floras in many extra-European regions, notably in India, South Africa, Australia, China, and Tonkin, no specimens have been found which can with confidence be assigned to the Matonineae. A single fossil has, however, been described from Queensland which may be a piece of a Laccopteris frond.
There is some evidence that ferns very similar to Matonia existed in North America during the Mesozoic period. It would be in the highest degree rash to assume that the Matonineae played no part in the Jurassic vegetation of India, South Africa, and other southern lands, but there can be little doubt that the family was especially characteristic of European floras during a portion of the Mesozoic era. It would seem that subsequent to the Wealden period the ancestors of Matonia dwindled in numbers and their geographical range became much more restricted.
The records of Tertiary rocks have hitherto added nothing to our knowledge of the distribution of the family subsequent to the Cretaceous period. All we can say is that the existing species of Matonia are the last survivors of a family which in the Jurassic period overspread a wide area in Europe and probably extended to the other side of the Atlantic. Exposed to unfavourable climatic conditions and possibly affected by the revolution in the plant world consequent on the appearance of the Flowering Plants, the Matonineae gradually retreated beyond the equator until the two surviving species found a last retreat in the Malayan region.
Fig. 12. Dipteris conjugata Rein. and, in the middle of the upper part of the photograph, a frond of Matonia pectinata R. Brown. Mount Ophir. (Photograph by Mr A. G. Tansley.)