Evolution What the Fossils Say and Why it Matters

198 Evolution? The Fossils Say YES!

shows both stasis and gradual evolution, but the conclusion is clear: these trilobites were not
instantaneously created but keep changing through time. Other groups of trilobites show
additional subtle changes through time, such as more complex eyes, increased size, more
complicated tail segment (pygidium), and the development of spines (Eldredge 1977; Fortey
and Owens 1990). Most of these examples are not gradual like those documented by Sheldon
but show punctuation and stasis—and yet, contrary to creationists’ misconceptions, they do
change through time, so they are good examples of evolution (just not gradual evolution).
I could go on and on with many more examples such as these, but for space reasons,
I will move on to the next topic. I recommend reading about some of the many examples
documented in Hallam (1977), Boardman et al. (1987), McNamara (1990), Clarkson (1998),
and Prothero (2013a) if you are interested in further documentation.

What About Macroevolution?

There is no need to apologize any longer for the poverty of the fossil record. In some

ways it has become almost unmanageably rich, and discovery is out-pacing integra-

tion: the growing number of species of Foraminifera that remain undescribed in the

cabinets of the oil companies probably is of the order of thousands; and while most

other organic groups are not so fully collected the ratio of added finds to palaeon-

tologists studying them is constantly expanding. But what remains to be discovered is

likely to be of less and less radical importance in revealing major novelties, more and

more of detailed infilling of fossil series whose outlines are known. The main phyla, in

so far as they are represented by fossils, now have a long and full history that is made

three-dimensional by a repeatedly cladal phylogeny. The gaps are being closed not only

by major annectant forms, the “missing links” that Darwin so deplored. . . . Together,

the discovery of new fossil forms, the filling out of the details of bioserial change, the

interpretation of biofacies, the adoption of new techniques both in fossil morphology

FIGURE 8.12. Evolutionary trends in numerous trilobite lineages from the Ordovician beds of central Wales.
Most lineages show a gradual increase in the number of rib segments in the thorax through the different time
intervals of the Ordovician. (After Sheldon 1987; copyright the Nature Publishing Group)

43

24

47

11

18

11

11

19

5

6

6

4

27 (M)

19

70

640

54

852

73

41

23 (M)

4

x

17

10

4

6

1

x

8

1 2

(^2112)
8
22
(^21)
33
17
(^1213)
(^21)
43
176
525
178
237
27
1
14
(^21131)
25
Gracilis
Shales
LQ
PH
EP
TC
NL
WL
BG
Teretiusculus Shales
Nileids
Bergamia
Cnemidopyge Platycalymene Ogyglocarella Nobiliasaphus
Whittardolithus
Ogyginus
Number of ribs
0 1 23 4 5 65 6 7 8 6 7 8 6 7 8 9 11 12 13 9 10 11 1213141516
Llanvirm
General youngling direction