Fossil Voles

48

CHANGES IN BIRD POPULATION OF SUFFOLK

SOME INCREASE (P.M. AND W.V.) : Cormorant, Wood-pigeon (as w.v.), Spotted Redshank, Lesser Black-backed Gull.

FLUCTUATION : Lapwing (decrease followed by increase), Stone Curlew (increase followed by decrease).

DECREASE

(BREEDING

BIRDS)

: Common Tern, Little Tern,

Corncrake.

MARKED DECREASE (P.M. AND W.V.)

: Bean Goose, Golden Plover,

Dotterel.

SOME DECREASE (P.M. AND W.V.)

: Brent Goose, Grey Plover.

A. C. C.

HERVEY.

FOSSIL VOLES MESSRS. P. and D. Long have sent to the Ipswich Museum another interesting collection of mammalian remains from the Norwich Crag at Covehithe and Easton Bavents. From Covehithe are an upper incisor of a relatively large vole, 5 tail bones of some small mammal and 17 molar teeth, all of some species or other of the extinct vole Mimomys. Some are of M. pliocaenicus, recorded before from Easton Bavents (Trans. S.N.S. Vol. VIII Pt. III, 1953, p. 155) but there are two teeth, a second and a third upper molar, from a much smaller but indefinable species. There is also an interesting second right upper molar of a juvenile animal, probably M. pliocaenicus : the cheek teeth of this species grow roots when adult, the Covehithe tooth (Fig. 2, 2A) has not yet grown roots, though the pulp cavities have closed, while the crown (Fig. 2) is but slightly worn and does not as yet show the enamel pattern characteristic of the adult tooth (Fig. 1). The modern water vole (Arvicola) is descended from Mimomys but its teeth remain rootless throughout life : Fig. 3, 3A, show the same tooth in a water vole. M. pliocaenicus is one of the earlier species of this genus, its teeth forming roots (Fig. 1A) when adult: in the later species the cheek teeth develop roots very late in life and though Fig. 2A does in fact show the side view of the tooth of a young animal of one of the earlier species it is very similar to the same aspect of an adult tooth of one of the later. Figs. 1A, 2A and 3A therefore show the development of the high crowned rootless tooth of Arvicola from the rooted tooth of an early Mimomys.

49

FOSSIL VOLES

The Easton Bavents material consists of 2 lower and 2 upper incisors of a vole larger than a Bank Vole and smaller than a Water Vole and four molar teeth of Mimomys. There is also what appears to be the canine tooth of some small carnivore about the size of a weasel. The cheek teeth consist of a first upper and first lower molar of M. pliocaenicus and the same two teeth of a smaller species. The small first lower molar has somewhat shallow re-entrant angles so that the outer and inner triangles tend to run into each other. The third upper molar from Covehithe referred to above has similarly shallow re-entrants and confluent triangles. In both these two teeth the roots are well developed but broken. The small first upper molar from Easton Bavents has two roots : in M. pliocaenicus this tooth has three, so at least two species are represented.

C.

f x

S

3

Fvg

3 mm Fig. 1

1a

Crown and outer side of right m 2 of M. pliocaenicus (adult).

Fig 2.

2a

Same aspects of right m a of M. pliocaenicus (juvenile from

Fig. 3

3a

Same aspects of right m 5 of Amcola

Covehithe). (recent: about f scale).