Pliocene Frogs from Langebaanweg, Western Cape Province, South Africa

CORE Metadata, citation and similar papers at core.ac.uk Provided by Stellenbosch University SUNScholar Repository News & Views South African Journal of Science 99, March/April 2003 123 ers, are difficult to distinguish from those of the more slender of the Ranidae. How- Pliocene frogs from Langebaanweg, ever, several bones at Langebaanweg (comprising femur, humerus, ilium frag- Western Cape Province, South Africa ment, scapula, and sacrum) indicate either a third, gracile ranid genus or, more likely, a hyperoliid (compare Figs 2e and D. Eduard van Dijk* 2f). A very slender, nearly straight femur with a distinct, but short, posterior proxi- mal ridge is probably hyperoliid. The HE VARSWATER FORMATION AT LANGE- Ranoidea). Both families are present as femora of Pipidae, Bufonidae, Brevicipi- Tbaanweg, Western Cape Province, South fossils at Langebaanweg. tidae and most Ranidae have distinct Africa, is known particularly for its Late In the Pipidae (Fig. 1a), the transverse curvature; a ridge is rare in ranids, except Miocene–Early Pliocene mammalian and processes (diapophyses) are much ex- abundant avian fossils. Amphibian bones the genera of very small size. Bones of from the site are, like the avian bones, notable panded, with parallel lateral edges (rarely frogs of the only genus of the hyloidean for their variety, surpassed in numbers of fam- intact in fossils), and the paired facets family Heleophrynidae in southern ilies and genera by no site in Africa and few (prezygapophyses), which articulate with Africa are mostly similar to those of sites in the world. The bones were transported the presacral vertebrae, have longitudinal the Bufonidae. However, a distinctive by a river system from a variety of habitats and grooves. In the Brevicipitidae (Fig. 1b), the humerus has, proximally, a groove and include those of swimmers, hoppers, leapers, diapophyses are less expanded and have complex ridges seen only in the genus burrowers and probably also climbers and curved lateral edges, and the prezygapo- Heleophryne among African frogs studied torrent-associated climbers/swimmers. The (Fig. 2b). The anterior vertebrae are bones fossil evidence indicates the presence of at physes are flat. Other bones at Lange- least four anuran families and possibly as baanweg confirm the presence of a pipid with good preservation potential which, many as seven genera in six families. frog similar to the aquatic genus Xenopus, if found, could provide definite proof of and a brevicipitid frog similar to the the presence of the Hyperoliidae and/or Rich1 in 1980 wrote: ‘Langebaanweg is by borrowing genus Breviceps. the Heleophrynidae. far the richest pre-Pleistocene avian site The other sacra (those not fused to In both Hyperoliidae and Heleophryni- yet discovered.’ Amphibian bones from urostyles) at Langebaanweg can be dae the cotyles for articulation with the the same site were known to be numerous divided into two groups on the basis of cranium are well separated, whereas they as early as 19722 but were not mentioned the articulation of the sacrum with the are close in Pipidae, Bufonidae, Brevicipi- in a 1976 overview.3 Two decades later, a centrum of the eighth vertebra (presacral): tidae and most ranoids.† In Heleophry- review of southern African anuran fossil in the one group (suborder Neobatrachia, nidae, the first two vertebrae are fused, a 4 sites drew attention to the Langebaan- superfamily Hyloidea), the sacrum has a condition normal only in brevicipitids, weg site, and an examination of sieved socket (procoelous condition, similar to with close cotyles, and Hemisidae, with a material that had been sorted as anuran at that of the other vertebrae), in the other highly characteristic dorsal ridge. In the South African Museum in Cape Town (suborder Neobatrachia, superfamily Hyperoliidae, the neural ridge of the first showed that various taxa were present. A Ranoidea) the sacrum has a boss vertebra usually articulates distinctively poster illustrating this variety was pre- (diplasiocoelous condition, in which the with that of the second. pared in September 1998, when a labora- other vertebrae are procoelous, except An ilium, of which there are several tory and museum were opened at the for the amphicoelous presacral). The specimens, unlike that of any extant Langebaanweg site. An updated version procoelous sacra (Fig. 1c) are mainly or southern African anuran observed of this material may be viewed at entirely those of Bufonidae (toads) and (Fig. 3), is characterized by a strong dorsal http://www.sun.ac.za/zoology. have somewhat expanded diapophyses process at the base of the shaft, but The anuran bones at Langebaanweg are associated with walking and hopping without the crest (ala), which is associated almost invariably isolated elements. with a strong dorsal process in ranids. locomotion.5,6 The diplasiocoelous sacra Fortunately, the sacral bones of southern There are thus at least four anuran (Figs 1d and 1e) are ranoid, with more or African anurans may be diagnostic at families at Langebaanweg: Pipidae, less cylindrical diapophyses usually subordinal, superfamily, family or generic Bufonidae, Brevicipitidae and Ranidae. associated with leaping.5,6 There is much level and are robust enough for many to There are probably two more families variation, however, and at least two survive transport without losing their represented, Hyperoliidae and Heleo- genera are represented — one robust important characteristics. Two types of phrynidae. Taking the reasonable view sacrum (Fig. 1e) falls outside the variation sacral configurations can be distin- that the ilium with the strong basal of any extant South African (and probably guished in the Langebaanweg fossil process is bufonid or brevicipitid, there sub-Saharan also) genus of the Ranidae, fauna: one in which the sacrum is an are probably six families present, with one Hyperoliidae and Rhacophoridae. Two isolated bone, the other where there is fu- additional, ranoid genus, giving a total of ranid genera (family Ranidae) would sion with the urostyle (consisting of seven genera in six families. With more mean that there are, on the basis of sacra united post-sacral vertebral elements). A specimens likely to be revealed in contin- fused sacrum and urostyle occurs in two only, at least five genera in all. The world- uing research, there are only three com- 8 extant African anuran families, the wide review of fossil Salientia of Sanchez includes more than 1200 sites known in Pipidae (suborder Mesobatrachia, super- †The degree of proximity of atlantal cotyles has proved to be family Pipoidea) and the Brevicipitidae 1998, and fewer than 2% of these are a useful criterion at about subfamilial level.8 However, when (suborder Neobatrachia, superfamily Pliocene or older and have five or more Heleophryne was included in an analysis, it was placed in a genera. group with narrowly spaced cotyles (ref. 9, p. 54), although examination of the cotyles of all Heleophryne species indi- *Department of Zoology, University of Stellenbosch, The bones of frogs of the family Hyper- Private Bag X1, Matieland 7602, South Africa. cates that they would be more appropriately placed in the E-mail: [email protected] roliidae, which are mainly climber/leap- widely spaced category illustrated on the same page. 124 South African Journal of Science 99, March/April 2003 News & Views Dates from Sterkfontein indicate greater age for hominids The discoveries made continually over the past half-century in the limestone caves at Sterkfontein, northwest of Johannesburg, give good reason to be- lieve this to be the richest hominid fossil site in the world. In spite of decades of close study, however,it has been impossi- ble to date the fossils directly. Instead, specimen ages have been inferred by comparison with fossils accurately dated elsewhere — such as animal remains and artifacts enveloped in volcanic sediments of known radiometric age in East Africa — and in relation to how the cave system records reversals in the Earth's magnetic field. Researchers at the University of the Witwatersrand and in the United States have now published the first results of a radiometric method that purports to give absolute dates for Sterkfontein.1 The method, which has been tested on cave deposits in Kentucky and Virginia, depends on measuring the ratio of cosmogenic 26Al and 10Be in quartz parti- cles adjacent to the fossils of interest. Knowing the respective rates of radioac- tive decay, and on the assumption that the indicator isotopes of aluminium and beryllium did not accumulate after burial (which means in practice that the samples must be relatively deeply buried and thus shielded from cosmic rays), it is possible to derive the time since burial. Five burial samples were so tested; three adjacent to the nearly complete Little Foot skeleton (designated StW 573), and two from Jacovec Cavern, some 50 metres distant, where hominid and faunal remains, also described in the Science paper, have been newly discovered. On this basis, Granger determined the burial age of the skeleton to be 4.17 ± 0.14 million years (Myr), corresponding to the Lower Pliocene. This is substantially older than the 3.3 Myr first proposed by Figs 1–3. X-ray images of fossil anuran bones from Langebaanweg. 1, Sacra (a, pipid; b, brevicipitid; c, Clarke et al.2 and even more so than the procoelan (bufonid?); d and e, ranoid). 2, Humeri [a, pipid; b, heleophrynid; c, bufonid; d, brevicipitid; e, gracile less than 3 Myr argued last year by Berger ranid; f, hyperoliid(?)]. 3, Ilium with strong basal process. All images were taken with X-rays (25 kV, 7 mA) on 3 Fujicolor ASA 100 film, with standard colour processing. et al. At 4 million years, StW 573 and the Jacovec specimens are of a similar age parable Pliocene or older sites in the rences in ‘E’ Quarry, Langebaanweg, South Africa. to Australopithecus anamensis from East Ann. S. Afr. Mus. 69, 215–247.

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