Palaeontology and caves in Jamaica

Stephen K Donovan (The Netherlands).

Although it has a rock record that only extends back to the Early Cretaceous, the geology of Jamaica is sufficiently diverse to satisfy most appetites (Donovan & Jackson, 2012a, b). It lies within the North Caribbean Plate Boundary Zone and displays a range of geological structures, commonly faults, both ancient and modern. There are about 25 Cretaceous inliers, from small to large, each including a sequence of volcanic and/or sedimentary rocks that are rarely metamorphosed. The half-graben Wagwater Belt in the east, flanking the western margin of the Blue Mountain inlier, is a Paleogene succession of terrestrial red beds, shallow to deep water siliciclastics and volcanics. These older rocks are draped by thick sequences of Eocene and younger rocks, which are mainly sedimentary (Robinson, 1994).

Of the sedimentary rocks, limestones from the Cretaceous to the Quaternary are particularly widespread (Fig. 1), covering about two-thirds of the island’s surface. Although only subaerially exposed for about the last ten million years, these limestones have been strongly karstified under conditions of tropical high temperatures and seasonal extreme precipitation (Donovan, 2002). This has produced widespread, and magnificent, karst topography.

One of the most distinctive karst features of Jamaica is its extensive system of caves. These were documented, splendidly, in Jamaica Underground, a monograph by the late Alan Fincham (1997; Figs. 2 and 3 in this article). This is the standard reference to the caves of Jamaica, with information on over 1,000 caves. It includes many cave surveys, some of which are so extensive that they are figured on fold-out sheets – an expensive rarity in modern publishing.

In this article, I shall introduce the reader to the two Jamaican caves that I know best. Both are recorded in Fincham (1997) (although only one impressed Alan, very obviously). The importance of both is in their palaeontological content. In one of them, the limestone of the walls has yielded a fauna of Eocene marine taxa; the other has a fill of Pleistocene terrestrial animals. Neither has, so far, had all the components of their fauna described.

Wait-a-Bit Cave, parish of Trelawny

The survey of Wait-a-Bit Cave by Miller & Donovan (1996) has a slightly whimsical history. The paper had been submitted, reviewed, revised and resubmitted, and was scheduled for publication. The Press at the University of the West Indies approached Dave Miller and me to act as reviewers of Jamaica Underground, to which we both agreed. Imagine our surprise to find a version of our survey (Fig. 2) of Wait-a-Bit Cave in Fincham’s submitted typescript. That told us who the ‘anonymous’ reviewer had been.

(Adapted from Donovan, 2002, pp. 146-147.) Wait‑a‑Bit Cave (called Lichfield Cave by Fincham) is south of Green Town in the parish of Trelawny, central Jamaica (Fig. 3). It preserves a model cave meander, which shows a range of geomorphological features. Most river caves of Jamaica have streams that disappear into the mid-Cenozoic, White Limestone Group. In contrast, Wait-a-Bit Cave is a short river cave with a sinuous, single conduit passage formed within the Eocene Yellow Limestone Group. It is broadly rectangular in shape, with sub‑vertical walls in rubbly, nodular limestone and a roof span in a massive limestone bed. The rubbly limestones were deposited in a silty shallow marine environment, inhabited by burrowing heart urchins, the giant gastropod Campanile sp and other molluscs (including rare nautiloids), and primitive dugongs that fed on sea grass (Fig. 4). The massive roof beds are coarser grained and have a different fauna, such as furrowing echinoids.

Wait-a-Bit Cave is unusual in being a meander cave; the stream that flows through it has both an entrance and an exit (Fig. 2). There is also a steep side-conduit that is approached across yam fields and is the only dry entrance. The cave sediments vary in grain size from muds to boulders, and include fossils from the Yellow Limestone Group. These sediments are the product of wall and roof collapse, and of alluvial deposition by the meandering stream flowing through the cave. Evidence of both former phreatic and vadose conditions occur as ceiling pockets and speleothems; at present the cave is being modified by breakdown of the nodular limestone due to mechanical weathering and erosion.

Red Hills Road Cave, parish of St Andrew

(Adapted from Donovan et al., 2013.) The site is on the south side of the Red Hills Road (Fig. 5), in the parish of St Andrew, Jamaica, close to Kingston.

The cave is flask‑shaped and exposed in vertical section, with a narrow opening at the top. It was presumably exhumed when the road was built, when most of the extent – and content – was lost. The cave was dissolved into well-lithified limestones of the mid-Tertiary White Limestone Group, and is partially infilled with dripstones, fallen limestone boulders and siliciclastic sediment. The last is probably largely derived from the terra rossa soils that are prevalent in this area, hence the name Red Hills. (Terra rossa are well-drained, reddish, clayey to silty clayey soil with a neutral pH.) Where lithified, the sediment is cemented by calcite.The fill of the Red Hills Road Cave (RHRC) is Late Pleistocene, about 40,000 to 25,000 years old (McFarlane & Blake, 2005).

The fauna of the Wait-a-Bit Cave is Eocene, exposed within the sedimentary beds of the walls of the cave. In contrast, and although the RHRC is dissolved into mid-Cenozoic limestones, it is the fill itself that is notably fossiliferous. It is the most species-rich terrestrial fauna of Pleistocene age from Jamaica. Most notably, it is a rare Antillean example of a deposit that yields terrestrial arthropods.

Land snails (Fig. 6a and m)

The diversity of Pleistocene terrestrial gastropods from RHRC is the richest yet reported from a Jamaican cave with 62 species (Paul & Donovan, 2006), possibly accumulated over a long time period. Jamaica has a highly varied fauna of extant terrestrial gastropods with over 500 species, making it a biodiversity ‘hot spot’ for this group. The RHRC has a particularly low proportion of fossil species known to still live in the immediate vicinity of the cave. Of a total of 80 species recognised, only 30 (37.5%) are common to both the fossil and Recent faunas (Paul & Donovan, 2006, table 2). This suggests a significant migration of snails has occurred in the Red Hills area. These, and other limited records, suggest that the climate was probably wetter when the cave deposits were forming.

Vertebrates (Fig. 6j to l)

Terrestrial tetrapods of the RHRC are only being described slowly, as they are invariably preserved in a state of disarticulation, like a Pleistocene ‘Irish stew’. Amphibians and reptiles await serious study, although lizard mandibles are among the most recognisable of vertebrate remains. Birds have fared only slightly better (Boot et al., 2015), but at least the limb bones of the flightless ibis, Xenicibis xympithecus Olson & Steadman, are easy to recognise (Fig. 6j).

Mammals that have been described in some detail inclued the extant Jamaican hutia, Gecapromys brownii (Fischer) (Fig. 6j), which is known from skulls, jaws and teeth. At the present day, there are about 21 extant species of bat in Jamaica, but only four species are known from the RHRC. Stenoderma rufum Desmarest (Fig. 6k and l), the red fruit bat, is the most common taxon in the cave and is still extant in the more eastern Greater Antilles, but has been extirpated in Jamaica.

Arthropods (Fig. 6b to i)

Macro-arthropods of the RHRC consists of millipedes (four species), isopods (four species), decapods (one species) and insects (four species) (Baalbergen & Donovan, 2013). Most of these taxa are classified in open nomenclature (that is, partly informally), which is a function of the preservation of most of these fossils with a sugary coat of calcite on the external surface. Preservation has favoured those taxa with a small proportion of calcite in their exoskeleton in life, which facilitated inorganic encrustation with calcite post-mortem.

References

Baalbergen, E. & Donovan, S.K. 2013. Terrestrial arthropods from the Late Pleistocene of Jamaica: systematics, palaeoecology and taphonomy. Geological Journal, 48: 628–645.

Boot, A., Donovan, S.K. & Meijer, H.J.M. 2015. Fossil birds of the Late Pleistocene Red Hills Road Cave, Jamaica: appraisal and biodiversity. Cave & Karst Science, 42: 95–103.

Donovan, S.K. 1993. Geological excursion guide 9: Jamaica. Geology Today, 9: 30–34.

Donovan, S.K. 2002. A karst of thousands: Jamaica’s limestone scenery. Geology Today, 18: 143–151. [Erratum. 2003. Geology Today, 18 (for 2002): 174.]

Donovan, S.K., Baalbergen, E., Ouwendijk, M., Paul, C.R.C. & Hoek Ostende, L.W. van den. 2013. Review and prospectus of the Late Pleistocene fauna of the Red Hills Road Cave, Jamaica. Cave and Karst Science, 40: 79–86.

Donovan, S.K. & Blissett, D.J. 1998. Palaeoecology of the giant Eocene gastropod Campanile. Eclogae Geologicae Helvetiae, 91: 453–456.

Donovan, S.K. & Jackson, T.A. 2012a. Jamaica’s geodiversity (Part 1): introduction and some older highlights (Cretaceous to Miocene). Deposits, 31: 8–13.

Donovan, S.K. & Jackson, T.A. 2012b. Jamaica’s geodiversity (Part 2): highlights from the Neogene. Deposits, 32: 14–19.

Donovan, S.K., Portell, R.W., Pickerill, R.K., Robinson, E. & Carter, B.D. 1995. Further Tertiary cephalopods from Jamaica. Journal of Paleontology, 69: 588–590.

Donovan, S.K. & Veltkamp, C.J. 1994. Unusual preservation of late Quaternary millipedes from Jamaica. Lethaia, 27: 355–362.

Fincham, A.G. 1997. Jamaica Underground: The Caves, Sinkholes and Underground Rivers of the Island. Second edition. The Press, University of the West Indies, Kingston.

McFarlane, D.A. & Blake, J. 2005. The late Pleistocene hutias (Geocapromys brownii) of Red Hills Fissure, Jamaica. Geological Journal, 40: 399–404.

Miller, D.J. & Donovan, S.K. 1996. Geomorphology, stratigraphy and palaeontology of Wait‑a‑Bit Cave, central Jamaica. Tertiary Research, 17 (for 1995): 33–49.

Paul, C.R.C. & Donovan, S.K. 2006. Quaternary land snails (Mollusca: Gastropoda) from the Red Hills Road Cave, Jamaica. Bulletin of the Mizunami Fossil Museum, 32 (for 2005): 109–144.

Robinson, E. 1994. Jamaica. In Donovan, S.K. & Jackson, T.A. (eds), Caribbean Geology: An Introduction. University of the West Indies Publishers’ Association, Mona, Jamaica, 111–127.