Analysis of dental morphology in over 600 stratigraphically controlled specimens of tarsier-like primates from early Eocene strata in Bighorn Basin, Wyoming, provides important new data for understanding the tempo and mode of evolution in primates

Rose, Kenneth D

Bown, Thomas M

English

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University of Nebraska - Lincoln 
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USGS Staff -- Published Research US Geological Survey 
1984 
Gradual phyletic evolution at the generic level in early Eocene 
omomyid primates 
Kenneth D. Rose 
Johns Hopkins University, kdrose@jhmi.edu 
Thomas M. Bown 
US Geological Survey 
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Rose, Kenneth D. and Bown, Thomas M., "Gradual phyletic evolution at the generic level in early Eocene 
omomyid primates" (1984). USGS Staff -- Published Research. 204. 
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TO NATURE NATURE VOL. 309 17 MAY 1984 
Table 1 Results of depth tracking for four specimens of Nautilus 
Mean day Mean night 
Dates of deptht deptht 
Name Sex observation Time (m) (m) 
Yellow M 24-30 June 1983 152 290 153 
Blue F 4-15 July 1983 266 329 260 
Green M 26-27 June 1983 34 44 1 321 
Red F 7-15JuIy 1983 32 120 87 
* Hours under observation. 
t Derived from daytime and nighttime depth figures, with a maximum 
of two readings during any single hour being included. In the case of 
Yellow the mean depth figures were computed by integrating the depth 
curves. 
on this southwestern horizontal movement was vertical move- 
ment, which was accomplished by inshore and offshore motion. 
Because of the steepness of the Palauan reefs, very short 
horizontal distances resulted in large vertical displacements. The 
Blue animal, followed for the longest period, travelled a total 
of 16 km along the reef front during the 10-day observation 
period. Horizontal movements of a similar magnitude have been 
observed previously for longer time periods in this population 
of Nautiluss. 
The depths at which Nautilus were found, as computed from 
the ultrasonic emissions, were compared with the bottom depth 
recorded nine times using a fathometer. The two depths differed 
significantly in only two cases, both involving the Blue transmit- 
ter. On 7 October 1983 Blue was followed for about 6 h as it 
ascended from 250 m depth to 150 m. At the end of this period 
the animal resettled to the bottom, after having travelled -1 km 
horizontal distance. Although Nautilus appear to  move mainly 
on the bottom, there does seem to be some movement within 
the water column. 
We thank James McKibben for construction of the transmit- 
ters. This work was carried out a t  the Marine Mariculture 
Demonstration Center, Palau. Mr Tosh Paulis helped with boat 
acquisition. This work was supported by NSF grant PCM 
8202891. 
Received 19 September; accepted 13 February 1984. 
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Kansas Press, 1964). 
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4. Mutvei, H. & Regmcnt, R. Palcontology 16, 623436. 
5.  Denron, E. & Gilpin-Brown, J. Adv mar. Biol. 11, 197-268 (1973). 
6. Ward, P. Paleobiology 6, 32-43 (1980). 
7. Ward, P. Paleobiology 5, 415422  (1979). 
8. Sausders. W. B. & Spinosa. C. Science 204, 1199-1201 (1979). 
Gradual phyletic evolution 
at the generic level 
in early Eocene omomyid primates 
Kenneth D. Rose 
Department of Cell Biology and Anatomy, Johns Hopkins University 
School of Mediclne, Baltimore, Maryland 21205, USA 
Thomas M. Bown 
Paleontology-Stratigraphy Branch, US Geological Survey, Denver, 
Colorado 80225. USA 
Analysis of dental morphology in over 600 stratigraphically 
controlled specimens of tarsier-like primates from early Eocene 
strata in thi~ighorn Basin, wyomibg, provides impoknt new 
data for understanding the tempo and mode of evolution in 
primates. Here we describe two evolutionarv transitions at the 
generic level in separate lineages of the f a m h  Omomyidae. In 
both lines transtonnation occurred not only continuously (rather 
than by abrupt appearance of new morphologies followed by 
stasis), but also in mosaic fashion, with greater variation in 
certain characters preceding a shift to another character state. 
In one lineage this resulted in a significant change in dental 
adaptation. These data support a gradual model of dental evol- 
ution and are inconsistent with the punctuated equilibria model. 
Together with other reported cases, the data suggest that 
gradualism is much more prevalent than proponents of punctu- 
ated equilibria have argued. 
The early Eocene sequence of the Willwood Formation in 
the Bighorn Basin, Wyoming, is more than 700 m thick, spans 
about 4 Myr and is among the richest areas for fossil vertebrates 
in the world. Because of excellent stratigraphical control, 
samples from these deposits constitute some of the most impor- 
tant data for studies of mammalian evol~ t ion ' - '~ ,  including the 
largest and most diverse collection of omomyid primates known 
from any basin. This collection is now several times larger than 
the largest sample studied by previous workers, and nearly all 
specimens are tied into measured stratigraphical sections. 
The omomyid samples have been assigned to at least six 
species in as many as six genera: Teilhardina arnericana, 
Tetonoides tenuiculus, Tetonius homunculus, Pseudotetonius 
ambiguus, Absarokius abbotti and Omomys v e ~ ~ e r t i n u s ~ * ' ~ - ~ ~ ,  
and several undescribed species (Fig. 1). The systematics of 
these fossils is still under study, and it is clear that previous 
understanding of most of them was very incomplete. Our studies 
indicate that all of these species are valid, but it is debatable 
how many genera are represented. Here we provide evidence 
for the transitions between Tetonius homunculus and 
Pseudotetonius ambiguus and between Teil. arnericana and 
Tetonoides tenuiculus. Detailed justification will be provided 
elsewhere for recognition of Teil. americana and P, ambiguus, 
the validity of both of which has been questioned20-22, but for 
this report, the taxonomy of the fossils is of less consequence 
than the evolutionary patterns they show. 
All omomyids from the Bighorn Basin are conservative in 
molar morphology, differing consistently only in absolute size 
or relative breadth. Figure 1 shows that the molars separate to 
some extent on size alone. Teilhardina and Tetonoides are about 
the same size and are significantly smaller than Tetonius or 
Pseudotetonius, whereas the latter and Omomys are slightly 
smaller than Tetonius, and Absarokius is somewhat larger than 
Tetonius. Even so, the latter four taxa overlap substantially in 
molar size. To distinguish between them, differences in crown 
morphology, size and configuration of antemolar teeth are more 
important than molar size. Within each size group (Fig. l),  
different morphologies are recognized under the specific names 
listed above, and our studies demonstrate that each comes from 
a restricted stratigraphical interval. Precise stratigraphical 
documentation has, therefore, been indispensable in determin- 
ing relationships between species. 
In the lineage from Tetonius homunculus to P. ambiguus, the 
anterior dentition evolved dramatically, while the molars and 
the last lower premolar (P,) remained conservative. Here we 
apply the name Tetonius homunculus to the most primitive 
specimens (see also ref. 19), which have a relatively large, 
two-rooted P,, a very small, one-rooted P2, a moderate sized 
canine and second incisor (I,), and an enlarged medial incisor 
(I,). All such specimens (stage 1 in Fig. 2) are confined to the 
180-190 m interval of the Willwood Formation in the principal 
study area (central and southern Bighorn Basin). Tetonius first 
appears at  about 65 m but its anterior dentition is unknown 
below 180 m. Not all specimens in this lineage possess P,; but 
from the stratigraphy it became clear that P, was lost after stage 
1, beginning a trend toward progressive compaction and reduc- 
tion of anterior teeth, except for I, which became larger with 
time. The name Tetonius ambiguus was first applied to a speci- 
men showing extreme compression of the anterior dentition", 
but with increasing knowledge of variation in samples allocated 
to  Tetonius, Tetonius ambiguus was transferred to a new genus, 
P~eudotetonius'~. P  ambiguus, here shown to be the end point 
of the lineage, is characterized by a much reduced P3 with one 
NATURE VOL. 309 17 MAY 1984 LElERS TO NATURE 251 
Fig. 1 Stratigraphical distributions of 
omomyid primates in the central and 
souther Bighorn Basin (Elk Creek, Fifteen- 
mile Creek and Sand Creek sections). 
Abscissa show the natural logarithm of 
crown area (mm2) of the first lower molar; 
the ordinate represents the stratigraphical 
level in Willwood Formation. Some points 
represent more than one individual. Names 
are placed near clusters of specimens that 
can be referred on morphological grounds 
to the species listed in the text and points 
situated stratigraphically between them rep- 
resent evolutionary intermediates. Points 
a-d denote individuals belonging to unde- 
scribed taxa. Some taxa overlap consider- 
ably in size range of M, , but their means may 
differ: for example, mean area of M, in P. 
ambiguus is less than in Tetonius homun- 
culus and both are smaller than the mean 
for A. abbotti. Plots for other teeth show a 
similar pattern except that those based on 
P, and M2 show greater separation between 
Tetonius homunculus and P. ambiguus, and 
that based on P, segregates A. abbotti more 
from other samples. 
root or coalesced roots, absence of P2, diminutive canine and 
12, and much enlarged I, (stages 4 and 5 in Fig. 2). The dentary 
anterior to P4 is much shorter than in Tetonius homunculus. 
This morphology occurs in the 350-390 m interval in the study 
area, at the top of which P. ambiguus apparently became extinct 
(coincidin with an extinction-immigration event termed bio- b horizon B ). Intervening strata have revealed morphologically 
intermediate specimens that. record a gradual transition from 
Tetonius homunculus to P. ambiguus (Fig. 2) .  
Of particular interest is the mosaic pattern of change. Modi- 
fications that characterize Pseudotetonius did not appear 
synchronously, and certain characters (for example, P3 root 
configuration) were more variable during periods of change. P2 
disappeared between stages 1 and 2; P3 gradually diminished 
in size throughout the sequence while its two roots became 
closely appressed and merged into one from stages 2 to 5 ;  the 
canine and I2 became gradually smaller up-section; and I, 
enlarged, principally in stages 3 to 5. There was also a slight 
reduction in mean lengths of P4 and the lower molars in stages 
3-5. The sum of changes during this transition reflect an adaptive 
Stage 2 
265-290 rn 1 Tetonius . .-. homunculus . . . . . - .. 
Stage 1 
180-190 m 
P3 length/P4 length 
Fig. 2 Evolution of the anterior lower dentition in the Tetonius homunculus-P. ambiguus lineage from the central and southern Bighorn 
Basin. Stages in the transition are arbitrarily delimited by slight morphological differences and/or intervals with little or no data, and each is 
a composite dentition (M2-, omitted) based on all known material from the indicated interval. Shaded parts are reconstructed from root size 
and known structure in other stages. The stratigraphical distribution of certain character states is shown on the left; numbers of individuals 
are indicated except where data points represent single specimens. 
252 LETTERS TO NATURE NATURE VOL. 309 17 MAY 1984 
rnefoconrd 
Telono~des tenuiculus 
DPC 1317 180 - 190 m 
YPM 30728 
USGS 478 
YPM 30727 
Fig. 3 Transformation of lower fourth premolar (P,) in the Teil. 
americana-Tetonoides tenuiculus lineage. Left, computer-gener- 
ated digitized lingual profiles, standardized to the same length so 
as to indicate only structural differences. Note the progressive 
enlargement and elevation of the metaconid and the elongation 
of the paraconid in successively higher strata. Right, camera lucida 
tracings, at constant magnification, of the back of the P4 trigonid, 
showing the increase in size and height of the metaconid as well 
as increase in absolute breadth. Profiles for Teil. americana and 
Tetonoides tenuiculus are means computed from only complete, 
unworn specimens; other profiles depict individual specimens. 
Other known specimens from these levels conform to the mor- 
phologies shown. 
shift to  shorter-jawed omomyids with enhanced emphasis of the 
anterior grasping teeth and declining importance of the teeth 
just behind them. 
Also found is a gradual transition from Teil. americana t o  
Tetonoides tenuiculus, best documented in the morphology of 
the posterior lower premolars (P3-,). Teil. americana is the 
oldest and most conservative North American o m ~ m ~ i d ' ~ ~ ~ ~  
and, as in European Teilhardina belgica [clearly its congener 
(K.D.R., T.M.B. and M. Godinot, in preparation)], the P, and 
P4 are relatively high-crowned, pointed and bear small, low 
conids, which are more pronounced on P,; the cheek teeth are  
not basally inflated. These features occur only in the lowest 
50  m (25-50 m interval) of the study area. Tetonoides tenuiculus 
differs from Teilhardina chiefly in having relatively broader and 
lower cheek teeth and a more molariform P4, best illustrated 
by the higher, more salient paraconid and metaconid. Specimens 
in which this morphology is fully developed come from the 
180-190 m interval in the study area. Fossils from intervening 
strata are  intermediate between the two morphologies and 
become progressively more like Tetonoides up-section, the 
cheek teeth increasing in relative breadth and the paraconid 
and metaconid increasing in prominence with time (Fig. 3). At  
n o  level in the section is there an obvious morphological shift 
(punctuation); rather, change appears to  be continuous and 
gradual. Tetonoides tenuiculus was short-lived in the Bighorn 
Basin (but a few stratigraphically higher specimens may be 
related t o  it: Fig. la-c), althou h the genus is known from 25,zP younger rocks in other basins . 
Both of the phyletic transitions described here are  also recor- 
ded in samples from the Clark's Fork Basin, 100 km north of 
the study area. Those samples show the same sequence of 
changes in both lineages as observed in the study area, thus 
providing independent confirmation of the patterns reported 
here. 
The tempo and mode of evolutionary change continue to  be 
among the most actively debated issues in evolutionary biology, 
with particular attention currently focused on punctuational and 
gradual models of . The most convincing 
evidence for gradual evolution in fossil mammals has been 
advanced by Gingerich and but these studies 
concentrate primarily on changes in molar size, and advocates 
of the punctuated equilibria model largely discount 
The transitions in two lineages of omomyid primates detailed 
here involve a mosaic of continuously changing features that 
document the gradual evolution of new morphological types of 
generic rank. Together with Gingerich's examples and other 
detailed cases of gradual e v o l u t i ~ n ~ ~ - ~ ~ ,  our data suggest that 
phyletic gradualism is not only more common than some would 
admit but also capable of producing significant adaptive modifi- 
cations. 
For access to specimens and casts used in this study we thank 
D. Baird, R. T. Bakker, M. R. Dawson, R. J. Emry, P. D. 
Gingerich, M. Godinot, F. A. Jenkins Jr,  J. A. Lillegraven, L. 
D. Martin, M. C. McKenna, G.  E. Meyer, J. H. Ostrom, D. E. 
Savage, C. R. Schaff and E. L. Simons. We thank A. C. Walker 
and S. B. Walker for guidance with computer analyses; and P. 
D. Gingerich, D. W. Krause and A. C. Walker for suggestions. 
We acknowledge support of this research from the American 
Philosophical Society (Penrose 9269), National Geographic 
Society (2366-81), and NSF (BSR-8215099) to  K.D.R. 
Rece~ved 28 November 1983; accepted 23 February 1984 
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Gradual phyletic evolution at the generic level in early Eocene omomyid primates

Keller, Sebastian: Rezension zu: Detlev Mares; Dieter Schott (Hg.): Das Jahr 1913 - Aufbrüche und Krisenwahrnehmungen am Vorabend des Ersten Weltkriegs (= Histoire, Bd. 65). Bielefeld 2014. Das Jahr 1913 ist das letzte Friedensjahr, bevor - einer erfüllten Sehnsucht gleich - der große Krieg über Europa einbricht und später ganze Nationen in Chaos und Verderben stürzt. In diesem Satz wird deutlich, auf was das Jahr 1913 im öffentlichen Geschichtsbild herunter gebrochen wird: Es ist der Voraben..

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Gradual phyletic evolution at the generic level in early Eocene omomyid primates

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