Revised age estimates for the later faunas of Egypt and Oman

Erik R. Seiffert*

Department of Earth Sciences and Museum of Natural History, University of Oxford, Parks Road, Oxford OX1 3PW, United Kingdom

Communicated by Elwyn L. Simons, Duke University, Durham, NC, January 30, 2006 (received for review January 3, 2006) The of northern Egypt has produced available from the Formation itself is the magnetostratigraphy Afro-Arabia’s primary record of Paleogene mammalian evolution, developed by Kappelman et al. (17) (Fig. 1A), but there remain including the world’s most complete remains of early anthropoid multiple possible correlations of that magnetostratigraphy to the . Recent studies of Fayum have assumed that geomagnetic polarity time scale (GPTS). the Jebel Qatrani Formation contains a significant compo- The Jebel Qatrani Formation is divided into upper and lower nent (Ϸ150 of 340 m), and that most taxa from that succession are sequences (15), with the boundary between these units being the between 35.4 and 33.3 million years old (Ma), i.e., latest Eocene to 4- to 10-m-thick cliff-forming ‘‘Barite Sandstone’’ that uncon- earliest in age. Reanalysis of the chronological evidence formably overlies the upper red sandstone of the lower sequence. shared by later Paleogene strata exposed in Egypt and Oman Rasmussen et al. (16) suggested that the approximate position of (Taqah and Thaytiniti areas, Dhofar Province) reveals that this the EOB is probably marked by this unconformity, and this hypothesis is no longer tenable. Revised correlation of the Fayum interpretation was consistent with Kappelman et al.’s (17) pre- and Dhofar magnetostratigraphies indicates that (i) only the low- ferred correlation of the Jebel Qatrani magnetostratigraphy to est 48 m of the Jebel Qatrani Formation are likely to be Eocene in the GPTS, which placed all of the major mammal localities age; (ii) the youngest Fayum anthropoids, including well known between magnetic polarity Chrons C15r and C13n (i.e., between such as zeuxis and phiomense, 35.4 and 33.3 Ma) (Fig. 2A). Numerous subsequent publications are probably between 30.2 and 29.5 Ma, Ϸ3–4 Ma younger than have accepted the ages of major vertebrate localities previously thought; (iii) oligopithecid anthropoids did not go required by this correlation (18–21). Placement of the EOB at extinct at the Eocene–Oligocene boundary but rather persisted for the division between the upper and lower sequences is not only at least another 2.5 Ma; (iv) propliopithecid anthropoids first convenient but could also have implications for response appear in the Fayum area at Ϸ31.5 Ma, long after the Eocene– Oligocene boundary; and (v) the youngest Fayum mammals may be to early Oligocene ; part of Rasmussen et al.’s (16) only Ϸ1 Ma older than the 28- to 27-Ma mammals from Chilga, justification for their suggested placement of the EOB was a Ethiopia, and not 4–5 Ma older, as previously thought. Whatever perceived ‘‘break’’ in the anthropoid primate faunas at about the gap exists in the Oligocene record of Afro-Arabian mammal evo- level of the Barite Sandstone, just above which specialized lution is now limited primarily to a poorly sampled 27- to 23-Ma propliopithecid catarrhines and parapithecine parapithecids window in the latest Oligocene. make their first appearance. The morphological and dietary adaptations differentiating these taxa from their relatives in the anthropoid ͉ Eocene ͉ Fayum ͉ Oligocene lower sequence have been interpreted as possible responses to global cooling in the earliest Oligocene (22). he later Paleogene Jebel Qatrani Formation, which is The most productive later Paleogene Afro-Arabian mammal Tbroadly exposed north of Birket Qarun in the Fayum De- localities outside of the Fayum area are found in the Dhofar pression, Egypt, has produced Afro-Arabia’s primary record of Province of Oman, where restricted exposures of the Ashawq late Eocene and early Oligocene mammalian evolution. The Formation in the Taqah and Thaytiniti areas have produced succession is particularly well known for its diverse anthropoid mammalian assemblages that are very similar to those from the primate fauna (1–5) and is increasingly notable for its record of Jebel Qatrani Formation (23–30). Importantly, the mammals early strepsirrhine primate evolution (6–10). Members of the from the Ashawq Formation occur in stratigraphic sections that endemic afrotherian mammal orders Hyracoidea, Embrith- preserve marine invertebrates (nummulitid and lepidocycline opoda, Proboscidea, Sirenia, Macroscelidea, Afrosoricida, and foraminifera) that allow for age estimates independent of the Ptolemaiida are also represented, along with hyaenodontid mammals themselves. Magnetostratigraphic sampling in the creodonts and immigrant hystricognathous , chiropter- Taqah and Thaytiniti sections helps to further constrain the ages ans, anthracotheriid artiodactyls, and (11). of these mammal-bearing strata (Fig. 1 B and C) (24, 25, 29). The The position of the Eocene–Oligocene boundary [(EOB), Omani mammals thus hold great promise for helping to reveal Ϸ33.9 million years old (Ma) (12)] in the Fayum area has been the most probable correlation of the Jebel Qatrani magne- a matter of consistent debate over the course of the last century, tostratigraphy to the current GPTS, but as yet there has been no and at various times it has been suggested that the Jebel Qatrani attempt to draw the available magnetostratigraphic and bios- Formation is either entirely Eocene in age (13), entirely Oligo- tratigraphic data from the Fayum and Dhofar areas into an cene in age (14, 15), or composed of both late Eocene and early internally consistent biochronostratigraphic hypothesis. The Oligocene sediments (16, 17). Biostratigraphic information bear- present study provides such a synthesis, and reveals that the ing on the age of the Formation is limited, because its vertebrate Jebel Qatrani Formation is likely to be almost entirely Oligocene fauna is highly endemic, and the succession lacks biostratigraphi- in age. cally useful marine invertebrates. The Widan el-Faras basalt, which unconformably caps the Formation, is the only stratum in the Fayum area that has produced radioisotopic dates, but the Conflict of interest statement: No conflicts declared. 40 39 40 39 argon͞ argon ( Ar͞ Ar) estimate of Ϸ23.6 Ma for the lowest Abbreviations: EOB, Eocene–Oligocene boundary; GPTS, geomagnetic polarity time scale; flow of that basalt (17) is many millions of years younger than all Ma, million years old; kyr, thousand years. previous estimates for the age of the youngest Jebel Qatrani *E-mail: [email protected]. vertebrates. The most useful chronological evidence currently © 2006 by The National Academy of Sciences of the USA

5000–5005 ͉ PNAS ͉ March 28, 2006 ͉ vol. 103 ͉ no. 13 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0600689103 Downloaded by guest on September 27, 2021 Fig. 1. Magnetostratigraphic and nonmammalian biostratigraphic data from the Jebel Qatrani Formation, Egypt, and the Ashawq Formation, Oman. (A) Magnetostratigraphy of the Jebel Qatrani, Qasr el-Sagha, and upper Birket Qarun Formations, modified from Kappelman et al. (17) and Seiffert et al. (19). The stratigraphic positions of major fossil mammal localities (A, B, E, G, I, M, V, and L-41) are marked by horizontal gray bars. (B) Magnetostratigraphy of the Taqah section, modified from Roger et al. (29), with first occurrences of key foraminifera. The Taqah fossil mammal locality is marked by a horizontal gray bar. (C) Magnetostratigraphy of the Thaytiniti section, modified from Thomas et al. (24), with labeling as in B. VGP, virtual geomagnetic pole.

Results 2). Thus it remains possible that E. dilatata’s first appearance Magnetostratigraphic and Nonmammalian Biostratigraphic Evidence along the southern margins of the Arabian Peninsula occurs in from the Ashawq Formation. A maximum age for the Taqah the very latest stages of the long reversed polarity Chron C12r (Fig. 2). The Taqah mammals occur at the top of a long zone of

mammal locality is constrained by stratigraphically lower occur- EVOLUTION rences of the benthic foraminifera Nummulites fichteli (an early reversed magnetic polarity, stratigraphically above the first Oligocene index fossil) and Eulepidina dilatata (29) (Fig. 1B). In appearance of both N. fichteli and E. dilatata in the Shizar southern European basins, the first cooccurrence of N. fichteli Member (Fig. 1B), and taken together, these stratigraphic and the lepidocyclines Eulepidina and Nephrolepidina occurs in relationships suggest a placement in the very latest part of Chron the shallow benthic foraminiferal biozonation 22A (SB22A) of 12r (Ͻ31.5 Ma) (Fig. 2C). The normal polarity zone at the base Cahuzac and Poignant (31), who correlate the base of SB22A of the Taqah magnetostratigraphy would then be Chron C13n. with the base of Berggren et al.’s (32) planktonic foraminiferal The only other option, favored by Roger et al. (29), would be to zone P20, which extends into Chron 11r of the GPTS (30.63– place the Taqah mammal locality in Chron C11r (30.63–30.22 30.22 Ma). Correlation of the benthic and planktonic forami- Ma), but because the Taqah section of the Shizar Formation is niferal records from this time period has proven to be quite likely to contain a considerable amount of time in only a Ϸ50-m difficult, however, and Roger et al. (29) have argued that the first section, the extensive zone of reversed magnetic polarity above appearance of Eulepidina in the Indo-Pacific region would be the Ϸ28-m level in the densely sampled section at Taqah is close to the disappearance of ‘‘Globorotalia’’ ampliapertura, but unlikely to represent a zone as brief [Ϸ410 thousand years (kyr)] after the disappearance of Pseudohastigerina, two events that as Chron C11r. The Roger et al. (29) correlation must also be define the older planktonic foraminiferal zone P19, which considered unlikely, because it requires that the extensive Ϸ2.15- extends well into Chron 12r (to Ϸ32 Ma) on Berggren et al.’s (32) Ma-long Chron C12r intervene between the Taqah and Thayt- revised time scale and the Geological Time Scale 2004 (12) (Fig. initi mammals but nevertheless be completely unsampled in the

Seiffert PNAS ͉ March 28, 2006 ͉ vol. 103 ͉ no. 13 ͉ 5001 Downloaded by guest on September 27, 2021 Fig. 2. Mismatch in the age correlation of the Fayum and Dhofar mammal localities based on different types of data.

magnetostratigraphies from both areas, even though much 31.5 and 33.7–33.3 Ma, respectively. Kappelman et al.’s (17) shorter normal (C13n, Ϸ470 kyr; C12n, Ϸ490 kyr) and reversed preferred correlation of the Jebel Qatrani magnetostratigraphy (C11r, Ϸ410 kyr) zones are densely sampled in one area or the to the GPTS places all of the major mammal localities in that other. Regardless, the age difference between Roger et al.’s (29) Formation between Chron 13n and Chron 15r and requires that placement of the Taqah mammal locality and that proposed here the youngest primate-bearing quarries (I and M) would be no less is potentially Ͻ500 kyr, and the most important point is that the than 33.3 Ma, whereas the oldest (L-41) is no older than 35.4 Ma Taqah mammals, based on combined magnetostratigraphic and (Fig. 1A). This correlation would imply that the Taqah mammals invertebrate biostratigraphic constraints, are unlikely to be older are Ϸ2 Ma younger than the youngest primate-bearing Jebel than 31.5 Ma and are potentially as young as 30.22 Ma. Qatrani quarries (I and M), whereas Thaytiniti would be of The age of the Thaytiniti mammal locality is less well con- approximately the same age as quarries I and M. strained by biostratigraphic data. The locality must be early The mammalian biostratigraphic evidence from the Fayum Oligocene in age, based on the occurrence of N. fichteli (24) and and Dhofar localities is completely inconsistent with this sce- is at least slightly older than Taqah, given its occurrence near the nario. Although many of the mammals from Taqah and Thay- base of the Shizar Member in a zone of normal magnetic polarity tiniti remain undescribed, available evidence strongly suggests (24) (Fig. 1C). If, as suggested here, the Taqah mammals are that both Omani localities are older than quarries I and M and most likely to fall within the Ͻ31.5-Ma part of Chron 12r, then probably intermediate in age between the oldest localities of the the only possible placement of Thaytiniti is in Chron 13n, the Jebel Qatrani upper sequence (quarries G and V, a few meters only older zone of normal polarity in the early Oligocene. If this above the Barite Sandstone) and the oldest productive locality is the case, then the Thaytiniti mammals are no older than Ϸ33.7 from the lower sequence (quarry L-41) (Fig. 2B). Thus far, the Ma. This correlation is consistent with the interpretation of only taxa from the Fayum and Dhofar areas that can be directly Roger et al. (29) and Thomas et al. (25), based on the biostrati- compared are anthropoid primates and hyracoids; the Taqah graphic and magnetostratigraphic data available to them. A less and Thaytiniti assemblages should be of great use in this plausible alternative correlation would place the Thaytiniti regard but are, as yet, largely undescribed. mammals in Chron C12n (Ϸ30.6–31.1 Ma) and would require According to the faunal list of Thomas et al. (25), two the Taqah mammal layer to be correlated with Chron C11r. For mammalian species, the hyracoid Thyrohyrax meyeri and the additional discussion of the Dhofar magnetostratigraphies, see propliopithecid anthropoid Moeripithecus markgrafi, are shared Supporting Text, which is published as supporting information on by the Jebel Qatrani and Taqah faunas. In Oman, T. meyeri is the PNAS web site. found at Taqah, and ‘‘cf. T. meyeri’’ is found at Thaytiniti; in Egypt, T. meyeri is found only at quarry L-41 (33). Another Comparison of Chronological Data Shared by the Fayum and Dhofar hyracoid from Thaytiniti has been described as cf. Saghatherium Localities. The magnetostratigraphic and nonmammalian bios- bowni; like T. meyeri, S. bowni occurs only at quarry L-41 (33), tratigraphic evidence summarized above suggests that the ages of and the Saghatherium does not occur at all in the Jebel the Taqah and Thaytiniti mammal localities are probably Ϸ31.0– Qatrani’s upper sequence. The propliopithecid from Taqah,

5002 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0600689103 Seiffert Downloaded by guest on September 27, 2021 Fig. 3. Revised correlation of the mammal localities from Egypt and Oman. (A) Correlation of the Fayum, Taqah, and Thaytiniti magnetostratigraphies to the GPTS. Major, moderate, and minor unconformities in the Fayum section are marked by black lines on the right side of the Fayum magnetostratigraphic column. (B and C) Phylogenetic relationships of later Paleogene anthropoid primates, based on the Adams consensus tree published by Seiffert et al. (19), plotted against the revised age correlation (B) and the age correlation preferred by Kappelman et al. (17) (C). Broken lines indicate uncertainty in the temporal placement of species; minimum species’ durations are arbitrarily figured as being Ϸ1 Ma. The provenance of M. markgrafi, Parapithecus fraasi, and Propliopithecus haeckeli is unknown. The temporal position of the Taqah anthropoids in C is that previously proposed by Rasmussen et al. (16) and Rasmussen (18). The position of the EOB is marked by a gray line and the letters ‘‘EOB.’’

described by Thomas et al. (26) as M. markgrafi, is perhaps better suggests a correlation with some part of the Jebel Qatrani lower placed in Propliopithecus ankeli, which occurs only at the Jebel sequence. Qatrani quarry V (34). Thomas et al. (26) argued that the There is clearly a profound mismatch between the mammalian propliopithecid specimens from Taqah and quarry V likely biostratigraphic data and the currently accepted correlation of represent members of the same species but opted to place all of the Fayum magnetostratigraphy with the GPTS. Given Kappel- this material (aside from the P. ankeli holotype) into the man et al.’s (17) preferred magnetostratigraphic correlation, the hypodigm of M. markgrafi, a species that was recovered from the Fayum occurrence of P. ankeli would predate that from Taqah Ͼ Jebel Qatrani Formation early in the last century (35) but by 2 million years, the youngest documented Fayum oligo- Ϸ unfortunately is represented only by m1–2 and is of unknown pithecid (Oligopithecus savagei from quarry E) would be 3 provenance in the succession. A recent phylogenetic analysis (19) million years older than the Taqah species, and Fayum records suggests that the Taqah propliopithecid is not M. markgrafi. of stem strepsirrhines and the hyracoid T. meyeri would be Two other biostratigraphically important aspects of the Taqah between 3.5 and 4 Ma older than those from Taqah. The fact that primate assemblages are evident. First is the presence of a Taqah appears to combine taxa from localities distributed EVOLUTION throughout the lower 165 m of the Jebel Qatrani Formation is primitive propliopithecid and a parapithecine parapithecid (‘‘cf. problematic, but the mammalian correlation becomes irrecon- Apidium’’), both of which are entirely restricted to the Jebel cilable if Taqah is, in fact, at least 2 million years younger than Qatrani’s upper sequence, occurring alongside a diverse group of the youngest Jebel Qatrani quarries. oligopithecids (27), which are the most common anthropoids of the Jebel Qatrani lower sequence. This pattern, although not A New Correlation of the Fayum Magnetostratigraphy to the GPTS. based on shared species, strongly suggests that the Taqah The age of the Taqah mammals is constrained by marine mammals are as old as or older than the oldest quarries of the invertebrates that can be correlated across numerous areas Jebel Qatrani upper sequence. On this basis, Rasmussen et al. exposed throughout the Tethyan region and is highly unlikely to (16) argued that the Taqah mammal locality is intermediate in be any older than the latest part of Chron C12r (ϽϷ31.5 Ma). age between quarry V (Ϸ165-m level) and quarries A and B The Jebel Qatrani Formation has no such biostratigraphic (Ϸ62-m level). Second, Taqah has also produced remains of the constraints, and the only 40Ar͞39Ar radioisotopic age constraint stem strepsirrhine primates Omanodon and Shizarodon (28), (from the Widan el-Faras basalt) is much younger (Ϸ23.6 Ma) which are closely related to ‘‘’’ milleri from quarry than the suggested age of the Taqah mammals, so the correlation L-41 (6). There are no undoubted records of Strepsirrhini (stem of the Fayum magnetostratigraphy to the GPTS can and should or crown) above the 48-m level in the Jebel Qatrani Formation, be shifted to resolve the mismatch between the magnetostrati- so the occurrence of these stem strepsirrhines at Taqah again graphic and mammalian biostratigraphic data from the Fayum

Seiffert PNAS ͉ March 28, 2006 ͉ vol. 103 ͉ no. 13 ͉ 5003 Downloaded by guest on September 27, 2021 and Dhofar areas. The correlation of the Fayum magnetostratig- sampled for the Fayum magnetostratigraphy, but the first sam- raphy to the GPTS proposed here (Fig. 3) hinges on the strong pled level above this lacuna is of normal polarity and is thus probability that the Taqah locality, based on its mammalian consistent with the placement of the EOB suggested here. fauna, is of approximately the same age as or older than the Jebel Rasmussen et al.’s (16) recommended placement of the EOB Qatrani quarries G and V (16, 18, 25, 26, 36) (Fig. 2B). It is one around the position of the Barite Sandstone is less likely on these of three alternative correlations that were rejected by Kappel- magnetostratigraphic grounds, because samples from the 20 m of man et al. (17) and is more similar to the correlation proposed sediment overlying that unconformity are all of reversed and not by Gingerich (14), although available data are not consistent normal polarity, as would be expected if erosion and the with his suggestion that the EOB is marked by the unconform- subsequent resumption of deposition occurred within Chron able contact of the Jebel Qatrani and Qasr el-Sagha Formations C13n. The placement of the EOB proposed here gains additional (see below). This is now the only correlation that can accom- support from the observation that the net loss of sediment from modate all of the available magnetostraphic and biostratigraphic the unconformity just above L-41 is likely to have been consid- (both invertebrate and mammalian) data from the Jebel Qatrani, erably greater than the amount eroded before the onset of Barite Taqah, and Thaytiniti sections, and the associated age estimates Sandstone deposition (T. M. Bown, personal communication). for Fayum quarries have important implications for our under- Regardless of whether the EOB is tied directly to the 48-m standing of the timing of later Eocene and early Oligocene level unconformity, the new magnetostratigraphic correlation anthropoid and nonanthropoid mammalian evolution in Afro- requires that almost two-thirds of the lower sequence of the Jebel Arabia. Qatrani Formation is early Oligocene, and not late Eocene, in age as previously thought. The sediments at quarries A and B are Discussion of uncertain position relative to the EOB, but the younger Overall, the most dramatic change to current understanding of Quarry E, which has produced remains of the anthropoids O. later Paleogene mammalian evolution in Africa is the recogni- savagei and Qatrania wingi, is now best placed near the bottom tion of a much greater span of time between the oldest and of Chron C12r and would thus be unambiguously early Oligocene youngest quarries of the Jebel Qatrani Formation. Whereas (perhaps Ϸ33 Ma) in age. Propliopithecids do not appear in the under Kappelman et al.’s (17) preferred correlation, a maximum Jebel Qatrani Formation until the upper part of Chron C12r, of only Ϸ2.15 Ma separated quarries L-41 from quarries I and M, probably later than Ϸ31.5 Ma. Because the propliopithecids given the correlation proposed here, these localities are sepa- from quarries G and V could be almost 1.5 Ma younger than the rated by at least 3.5 Ma, and well known anthropoid species such next-oldest anthropoids in the Formation (from quarry E), their as Aegyptopithecus zeuxis and Apidium phiomense are between first appearance was not necessarily a sudden event, and can no 30.2 and 29.5 Ma in age, at least 3 million years younger than longer be directly tied to earliest Oligocene cooling, given the previously thought (Fig. 3). Taking into account the recently Ϸ2.5-Ma gap between the EOB and their first appearance. The discovered Ϸ37-Ma locality BQ-2 (19, 37), the Fayum faunas absence of more primitive catarrhines that are intermediate in now document almost 8 million years of primate evolution. between oligopithecids and propliopithecids may Recognition of a late component in the upper part of simply be due to sampling and͞or sedimentary gaps between the the Jebel Qatrani Formation is consistent with Kappelman et Ϸ90- and Ϸ165-m levels of the Formation. The new correlation al.’s (17) conclusion that the whole-rock 40K-40Ar date of 31.0 Ϯ also indicates that the of oligopithecids cannot be tied 1.0 Ma obtained by Fleagle et al. (38) for the lowest flow of the to the EOB, although local extinction of strepsirrhines in the Widan el-Faras basalt is inaccurate, possibly due to potassium Fayum area could be, because there are no undoubted records loss, low potassium values, or inaccurate atmospheric correction. of that group above the 48-m-level unconformity. As has already The ages proposed here for the youngest Fayum mammals are been noted by Rasmussen et al. (16), there are no major shifts consistent with all other radioisotopic dates that have been or in the nonprimate mammalian fauna of the Jebel obtained from the Widan el-Faras basalt (17, 39). Qatrani Formation that could be linked to climate change at the The new correlation does not change the age of locality BQ-2 EOB. Other long-term trends, such as increasing selenodonty from the estimate of Ϸ37 Ma proposed by Seiffert et al. (19), but and lophodonty in some hyracoid lineages and increased body quarry L-41 must shift from Chron C15r (35.4–35.0 Ma) into size and bunodonty among anthropoids, could nevertheless Chron C13r (34.8–33.7 Ma). Because Chron C13r crosses the represent delayed adaptive reactions to environmental changes EOB, an earliest Oligocene age for L-41 cannot be rejected associated with early Oligocene cooling. based on the magnetostratigraphy alone, but a latest Eocene age The revised ages for Fayum quarries also have implications for seems more likely based on sequence stratigraphic evidence. The the timing of crown anthropoid origins. All specialists agree that earliest Oligocene was marked by a sudden onset of Antarctic the oldest definitive crown anthropoids occur in the Jebel glaciation and a worldwide drop in sea level, and it has been Qatrani Formation, but there is ongoing debate surrounding argued that this time period was likely marked by net erosion in whether oligopithecids or propliopithecids are the oldest known near-shore continental settings (13, 14, 16). Previously, Rasmus- stem catarrhines (19, 42). Regardless, it should be noted that sen et al. (16) argued that the Barite Sandstone–upper red both groups’ first appearance is later than previously thought. sandstone unconformity was the most likely position for the The oldest oligopithecid, Catopithecus browni, should now be EOB, but pointed out that another possible EOB unconformity considered latest Eocene (or, less likely, for the reasons enu- is present just above L-41. This latter position is precisely where merated above, earliest Oligocene) in age or Ϸ34.8–33.9 Ma. the EOB unconformity would be expected given the correlation This is not a major shift from the previous estimate of 35.4–35.0 proposed here. Importantly, the major benthic foraminiferal Ma. The implications are much more dramatic if Kay et al. (42) ␦18O excursion associated with the rapid development of the are correct in arguing that propliopithecids are the oldest known Antarctic ice sheet (40) and global sea-level fall is now known to stem catarrhines and crown anthropoids, for their first appear- have reached its maximum extent within the early part of Chron ance is now likely to be Ϸ31.0–31.5, at least 2 Ma later than C13n (41). If the EOB is marked by an unconformity in the Jebel previously thought. Recent multigene molecular estimates for Qatrani Formation, then the sediments overlying the unconfor- the origin of crown Anthropoidea extend back to the middle mity should (barring a prolonged Ϸ470-kyr period of erosion or Eocene, around 44 Ma (43). nondeposition spanning beyond Chron C13n into Chron C12r) A much younger age for many of the Jebel Qatrani mammal be of normal polarity. The 20 m of sediment above L-41 localities helps to make sense of other faunal patterns docu- (including those at the quarry A-B level) have not yet been mented in the later Paleogene of Afro-Arabia. For instance, the

5004 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0600689103 Seiffert Downloaded by guest on September 27, 2021 recently described late Oligocene paenungulates (hyracoids, ena to changes in global climate cannot be made until the fossil embrithopods, and proboscideans) from Chilga, Ethiopia, bear mammals of interest can be confidently situated on the global great overall similarity to the paenungulates from the Jebel time scale. Unfortunately, the ages of many important Paleogene Qatrani Formation despite having been radioisotopically and Afro-Arabian mammal faunas, such as those from Chambi (48) magnetostratigraphically tied to Chron C9n (Ϸ28–27 Ma) (44). in and the Hammadu du Dra region of (49), Indeed, as noted by Sanders et al. (ref. 45, p. 386), the similarity remain very poorly constrained, and this problem continues to between the Chilga and Fayum mammals ‘‘is remarkable in light hinder our understanding of early mammalian evolution in of their tremendous differences in geological time, distance, and Africa. However, the precise dating of the Chilga mammal elevation.’’ However, the great temporal gap that was thought to localities (44) and the recent discovery of a middle Eocene separate these faunas largely disappears under the magne- mammal fauna in Morocco (Aznag) that can be dated to tostratigraphic correlation proposed here. Quarries such as I and 45.8–43.6 Ma based on associated foraminifera (50) represent M are probably only Ϸ2 Ma older than the Chilga localities (and major improvements to this situation. Placement of the Fayum not Ϸ5.5 Ma older, as previously thought), and the very youngest and Dhofar mammals into an internally consistent biochronos- localities in the Jebel Qatrani Formation might be Ͻ1 Ma older tratigraphic framework represents another major advance of the than the oldest mammals from the Chilga region. Therefore, the utmost importance, for this revised chronology will inform all unique proboscidean groups documented at Chilga, such as future analyses of the taxa from these, the richest of all Paleo- deinotheriids and gomphotheriids, probably did not appear gene Afro-Arabian mammal localities. suddenly in the short amount of time separating the Fayum and Chilga beds but rather are missing from the Fayum area for This study derives from collaborative research currently being carried out environmental reasons. This hypothesis is consistent with phy- in the Fayum area with E. L. Simons, Y. Attia, and P. Chatrath. Our project has been facilitated by S. Sousa, K. Soliman, and the staff of the logenetic analyses that imply a long ghost lineage for deinoth- Egyptian Mineral Resources Authority and the Egyptian Geological eriids in Afro-Arabia (46, 47). Museum. T. Bown, J. Fleagle, and J. Rossie provided useful comments. Meaningful inferences about evolutionary patterns in the Funding for the Fayum project has been provided by the National mammalian fossil record and the possible links of such phenom- Science Foundation, the Leakey Foundation, and Gordon Getty.

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