Science - USA (2020-04-10)

SCIENCE sciencemag.org

CREDITS: (GRAPHIC) A. KITTERMAN/

SCIENCE

; (PHOTO) CYRIL RUOSO/MINDEN PICTURES

S outh American land mammal age,

which preceded the mammal age,

during which primates appeared.

However, the discovery of primates

(Perupithecus and at least one other

form) much earlier in the Santa Rosa

fauna appeared to bring the two

events closer together in time ( 2 ).

Although the dispersing genera

are not yet identified, new discover-

ies are revealing closer representa-

tives of both groups on the South

American and African continents.

C aviomorph rodents of late Middle

Eocene age ( 3 ) demonstrate a dis-

persal from one continent to the

other at least ~41 million years ago.

As for primates, not only was P eru-

pithecus recognized to be relatively

similar to some late Eocene African

relatives, but Seiffert et al. show that

their Ucayalipithecus fossil is ex-

tremely close to similar well-dated

fossils from African relatives. This

similarity provides a relatively nar-

row time window for the dispersal

of the Ucayalipithecus primate or its

ancestor (35 to 32 million years ago).

The morphology of the newly dis-

covered Ucayalipithecus fossil leaves

no doubt that it is a parapithecid, a

distinct family, unique among pri-

mates, that until now was known to

have existed only in Egypt, Libya, and

Tanzania. Thus, it is likely that the

parapithecid and the ancestor of the

other Santa Rosa primates came from

the same dispersal event. Hence, pale-

ontologists now have convincing evi-

dence for two distinct dispersals, one

for rodents and one for primates, each

separated by 10 million years or more.

These dispersals raise many in-

triguing issues for further research.

Concerning primate dispersals out of

Africa, there is a strong contrast be-

tween the two sides of the continent.

Dispersals to M adagascar crossed

much shorter distances; however, because

of unfavorable currents, such crossings were

also rare. Yet 2 years ago, scientists showed

that, on the eastern side of Africa, two differ-

ent lemur lineages crossed over to Madagas-

car ( 4 ). So why did two types of anthropoids

cross over on one side and two types of le-

murs on the other? A possible explanation is

size. During the Eocene in Africa, a nthropoids

were small and some strepsirrhine primates

were large, whereas later, during the Oligo-

cene, anthropoids became larger. A large size

is a serious obstacle to surviving several days

of rafting. However, there were also some

small strepsirrhines in the Eocene that might

have been carried along westward.

If several dispersals of mammals took

place, other animals and plants should fol-

low the same patterns—for example, the

trees that gave rise to the natural rafts.

Plant dispersals are tracked through dated

phylogenetic analyses. Molecular phylog-

enies of a woody plant family ( 5 ) and of

gecko lizards ( 6 ) provide hypotheses of

such dispersals. When the fossil record

indicates the absence of a family in North

America, the case for dispersal becomes

stronger, as for a mphisbaenids, a group

of fossorial lizards ( 7 ). When fossils pro-

vide the primary evidence, the scenario

becomes even more convincing, as for the

primate reported here, rodents, and prob-

ably also birds with weak flight

capabilities ( 8 ).

After crossing an ocean, species

face serious challenges in order to

survive and flourish in their new

environment. As Seiffert et al. note,

these e arly anthropoids must have

been remarkably adaptable to

harsh conditions to have survived

the crossing. Furthermore, they

succeeded in invading a new ter-

ritory; the environment was not

empty, and the early anthropoids

settled more than 4000 km away

from their landing area. Yet, de-

spite this impressive performance,

parapithecids did not manage to

survive for long and diversify. This

is even more surprising consider-

ing that parapithecids were spe-

cialized for hard-object feeding,

and one of the present-day sub-

families of South American mon-

keys, the P itheciinae (sakis and

ouakaris), is also adapted to feed-

ing on hard fruits and seeds. Were

these resources already present at

the time of crossing over, or were

there changes in the composition

of South American tropical forests?

These forests were established by

the Paleocene (66 to 56 million years

ago) and were not disturbed by

warming episodes. In contrast, they

experienced high diversification

rates during these episodes ( 9 ). An

exciting research avenue concerns

the composition of these forests, in

which rodents and primates play

an important role in seed dispersal

( 10 ). A better record of fossil fruits

and seeds in South America should

provide critical information on both

forest composition and plant disper-

sal—two important aspects of these

tropical forests, which are the most

diverse on Earth. j

REFERENCES AND NOTES

1. E. R. Seiffert et al., Science 368 , 194 (2020).


2. M. Bond et al., Nature 520 , 538 (2015).


3. P.-O. Antoine et al., Proc. R. Soc. London Ser. B 279 ,
   1319 (2012).


4. G. F. Gunnell et al., Nat. Commun. 9 , 3193 (2018).


5. L. Bardon et al., Bot. J. Linn. Soc. 171 , 19 (2013).


6. T. Gamble et al., J. Evol. Biol. 24 , 231 (2011).


7. N. Vidal, A. Azvolinsky, C. Cruaud, S. B. Hedges, Biol. Lett.
   4 , 115 (2008).


8. G. Mayr, H. Alvarenga, C. Mourer-Chauviré,
   Naturwissenschaften 98 , 961 (2011).


9. C. Jaramillo, A. Cárdenas, Annu. Rev. Earth Planet. Sci.
   41 , 741 (2013).


10. P.-M. Forget et al., in Seed Dispersal, A. J. Dennis et al.,
    Eds. (CAB International, 2 007), pp. 5–36.


11. M. L. Augé, S. Brizuela , Palaeobio. Palaeoenv. 1 0. 1 0 0 7/
    s12549-019-00414-2 (2020).
    1 0.1126/science.abb4107

NECC

SEC

00 10001000

kmkm

To Europe

?

AFRO-ARABIA

SOUTH

AMERICA

South American rain forests, like this one in Amazonian Perú, are among the

most diverse tropical forests on Earth. Some of its components came from

Africa during the Tertiary period.

10 APRIL 2020 • VOL 368 ISSUE 6487 137

Rafting route

A Ucayalipithecus monkey or its ancestor sailed from West Africa to

South America on the south equatorial paleocurrent (SEC). Recent data

( 11 ) suggest that teiid lizards crossed over from South America on the

north equatorial countercurrent (NECC), eventually arriving in Eocene

Europe. Continental positions are from the Oligocene.