Page 171 - Introduction to Paleobiology and The Fossil Record

158 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

unpreserved components. Fossil plant These four kinds of circumstantial evidence
stems may be stripped of leaves, but the have been useful in understanding how ancient
leaf bases are still there. A fossil trilobite rodents fed on nuts (Box 6.6), and also how
may preserve limbs and other structures T. rex fed. The biomechanical models of
under the carapace. Bones often show feeding in T. rex (see Box 6.5) tell us a great
muscle scars. In conditions of exceptional deal. The rocks in which T. rex bones are
preservation, of course, skin outlines, found confirm it lived in hot, lowland, for-

muscles, sensory organs and internal ested areas. Associated fossils include numer-
organs may also be preserved. For example, ous species of plant-eating dinosaurs, and
the spectacular fossils from Liaoning in some of these even carry tooth marks likely
China (see p. 463) have confi rmed that the made by T. rex. Tracks of footprints made by
fossil birds had feathers and the mammals T. rex, or a relative, show that it trotted along
had hair, as had been expected, but other steadily, but not fast. A famous 1 m long cop-
fossils showed that all the carnivorous rolite dropped by T. rex contained pulverized
dinosaurs had feathers too. That dramati- bone of ornithischian dinosaurs that had been
cally changes all previous paleobiological corroded to some extent by stomach acids,
interpretations of those dinosaurs because but not entirely destroyed. This suggests
they must have been warm-blooded in a relatively rapid transit of food material
some way. through the gut. The bones themselves have

Box 6.6 Who ate my nuts?

Animal–plant interactions are often beautifully documented. Paleobotanists have identifi ed marks of
chewing, tunneling and munching in leaves, stems and seeds from the Devonian Rhynie Chert (see
p. 489) onwards. Margaret Collinson and Jerry Hooker, experts on fossil plants and mammals,
respectively, from London, spotted possible feeding damage in small nuts they collected in the Eocene
of southern England, and reported in 2000. Some of the tiny seeds of the water plant Stratiotes had
round holes on one side and the internal contents had been removed, leaving a husk (Fig. 6.14a).
Stratiotes, sometimes called the water soldier or water aloe, still grows today in the fens and water-
ways of eastern England, as well as elsewhere in Europe, where it is rooted in the mud or fl oats on
the surface of shallow pools and sends spiky, sword-like leaves up out of the water.
Close study of the holes in the seeds showed that some animal had cut the hole vertical to the
outer surface, and that the cut edges of the hole bore numerous parallel grooves. There were more
grooves around the hole, as if some creature had been grabbing at the seed to hold it fi rm while
cutting the hole. Collinson and Hooker immediately thought of rodents as the seed eaters – rodents
cut straight-sided holes into seeds, and leave parallel grooves formed by their long incisor teeth. The
size of the seeds (4–5 mm long) and the size of the holes and grooves suggested a small rodent with
incisors at most 1 mm wide, clearly smaller than a squirrel. Today, bankvole, woodmouse and dor-
mouse use different gnawing actions for opening nuts so the authors used modern gnawed nuts for
comparison. Of these three, the woodmouse makes the most similar feeding marks (Fig. 6.14b).
After gnawing through the surface to make a small hole it grips the outer surface with its upper
incisors and vertically chisels the walls of the hole with its lower incisors. It then inserts its lower
incisors inside the hole to dig out the kernel.
The Eocene beds of southern England have yielded a variety of rodents, and the two that are the
right size to have gnawed the Stratiotes seeds are two species of the early dormouse Glamys. Eocene
Glamys may have swum to retrieve the seeds, or patrolled the shores of small ponds looking for any
that had been washed up.