Jamaican fossil crabs
Stephen K Donovan (The Netherlands) and Joe SH Collins (UK)
Decapod crustaceans (crabs) are among the most attractive of fossils. Yet, the beautifully preserved specimens seen in museum displays and dealers’ catalogues are in stark contrast with the usual haul of the collector, that is, scraps, commonly claws or (more rarely) bits of carapace, which we all find in (mainly) Cretaceous and Cenozoic sedimentary rocks. However, these bits and pieces represent most of the fossil record of crabs and, as such, are of importance to the systematist and anyone with an interest in aspects such as taphonomy and palaeoecology. Just as it is possible to identify a shark from a tooth or a cidaroid echinoid from a spine, so a crab claw can commonly provide data that permits its identification to the level of genus or species (Collins, 1999).
The present authors, in collaboration with Roger Portell of the Florida Museum of Natural History at the University of Florida in Gainesville, have been collecting and studying the fossil crabs of Jamaica (and the wider Antilles) for over 20 years. Until the 1990s, reports of fossil crabs from the island were limited to a few fragmented specimens and rare, well-preserved carapaces (some retaining claws) or the isolated claws of mud shrimps (=Callianassa sensu lato), which were collected mainly from the Upper Cretaceous and Eocene by visiting geologists as an aside to their own research.
They were sent to the British Museum (Natural History) for description. These early records were reviewed and augmented by Morris (1993), who undertook the sorting and description of a new collection of (mainly) minute fragments of carapaces and claws from recently washed residues from the Late Pleistocene Falmouth Formation (see below).
Most notable among the early twentieth century collectors in the Antilles was the wealthy English amateur Charles Taylor Trechmann (1884-1964), who undertook fieldwork in the Antilles every winter between the two world wars (Donovan, 2003, 2010). Trechmann’s principal research interests in the Antilles were the systematics of fossil Cretaceous and Cenozoic molluscs (for example, Trechmann, 1923, 1924), stratigraphy (for example, Trechmann, 1934), and tectonics (for example, Trechmann, 1955), but he fulfilled the praiseworthy role of a collector for experts on other fossil groups in the UK. It was in this way that Thomas Henry Withers (1883-1953) of the British Museum (Natural History) in London (Stearn, 1998, pp. 239-240) came to be involved in describing fossil crabs from Jamaica (Withers, 1922, 1924a, 1927), and crabs and barnacles from the wider Antilles (for example, Withers, 1924b, 1926a, b). However, we are unaware that he ever visited the region.
This article is not intended to be a field guide to the crab localities, but, rather, a brief illustration of the diversity and beauty of Jamaican fossil decapods. By diversity, we refer to both form and mode of preservation. For the collector considering a Jamaican holiday, a field guide to the principal crab localities already exists (Donovan, 2011) and is available online at http://www.caribjsci.org. (All papers published in Caribbean Journal of Science are available free on this site, including a number of others by the present authors.) We supplement a collection of images of Jamaican fossil crabs, arranged in stratigraphic order, with discussions of preservation, palaeoecology, associations and the history of research.
Jamaican Cretaceous crabs
The oldest rocks in the island are Early Cretaceous (Valanginian or older; Robinson, 1994, fig. 6.4), but the known record of Jamaican fossil crabs is somewhat younger, that is, Late Cretaceous (Campanian and Maastrichtian). There are only two nominal species from this interval, both collected by geologists from northeast England and described by Withers. Carcineretes woolacotti Withers (Fig. 1), was first collected by Dr David Woolacott (1872-1924), reader in geology at Armstrong College, University of Durham. It is a portunid, that is, a member of the group that includes modern swimming crabs (note the rear leg enlarged as a paddle in Fig. 1).
However, Morris (1993, p. 116) explained that this development in early members of the group, like C. woolacotti, was for digging. Cretacoranina trechmanni (Withers), similarly named after its collector, is a raninid, a group that includes modern frog crabs. This taxon has a more elongate, more distally tapered carapace and lanceolate fifth limbs than C. woolacotti, and is more obviously a burrower, well adapted for digging backwards into a sedimentary substrate.
However, this part of the record of Jamaican fossil crabs is almost certainly incompletely known. Nobody has actively pursued fossil crabs in these Late Cretaceous strata since the 1920s, in part because of the difficulty of the terrain and the intractability of the limestones. All records pertain to more or less complete specimens (Figs. 1 and 2) and no new nominal taxa have been added since 1927. The record of fragmentary material in these rocks is waiting to be exploited, although Morris (1993, p. 120) added two further raninids in open nomenclature, Parecrocarcinus? sp and Necrocarcinus sp.
Jamaican Paleogene crabs
Similar comments, regarding how poorly known they remain, might be made about the fossil crabs of the Jamaican Paleogene. One species is known from the Paleocene, about ten from the Eocene (mainly from the highly fossiliferous Yellow Limestone Group) and none from the Oligocene (Figs. 3 and 4).
The Paleocene (Danian) species is based on a single, allochthonous carapace preserved on the sole of a turbiditic sandstone (Fig. 3D to F). The unique holotype of Trechmannius circularis Collins & Donovan is the first crab from the mainly siliciclastic succession of the Lower Paleocene – Lower Eocene Richmond Formation (Donovan, 2011, locality Pa1), which outcrops extensively in eastern Jamaica.
Trechmannius circularis presumably lived in shallower water, but was collected from the sole of a turbidite bed deposited in deeper water and is presumed allochthonous. It is the second and oldest known fossil dynomenid crab to be described from the Caribbean. In having three, well-developed transverse grooves, Trechmannius is strongly reminiscent of, for example, some species in the largely Cretaceous genus Palaeodromites A Milne Edwards and, more particularly, to the Albian-Cenomanian genus Trachynotocarcinus Wright & Collins.
Jamaican Eocene crabs are mainly described from the Yellow Limestone Group (mid Early to mid Middle Eocene), although rare fragments are known from the slightly younger (late Middle Eocene) Swanswick Formation of the White Limestone Group (see below). Nominal decapods from the Chapelton Formation of the Yellow Limestone Group (Donovan, 2011, localities Eo1 and Eo2) were described by Withers (1924a), based on Trechmann’s collections from 1922 and 1923. These included three nominal species of mud shrimp, “Callianassa” trechmanni Withers, “Callianassa” subplana Withers and “Callianassa” gigantea Withers (Fig. 3).
These are preserved solely as parts (=propodi) of claws, the callianassid exoskeleton being otherwise poorly mineralised. They are the most widely distributed decapod fragments in the Cenozoic of the Antilles, but their detailed classification is commonly difficult, due to the lack of morphological features shown by these fossils and the tendency towards development of heterochelae, that is, the claws of one individual are of different sizes. This happens in both sexes.
Callianassids belong to the decapod Infraorder Thalassinidea. Most other decapods discussed above and below belong either to the hermit crabs (from the Infraorder Anomura) or the true crabs (from the Infraorder Brachyura). Four brachyuran species are known from the Chapelton Formation. One is a portunid, which is an example of the swimming crabs already mentioned above and named Callinectes jamaicensis Withers, but known only from a single propodus. A shore crab, Varuna? sp, is similarly known only from a single fragment of limb. A mud crab, Xanthilites? rathbunae Withers, is known from a poorly preserved carapace and attributed propodi. To these, Morris (1993) added Eriosachila bartholomaeensis (Rathbun). A description of a chela fragment attributed to this species is in preparation by JSHC and Roger Portell.
The mid-Cenozoic White Limestone Group is the most widely exposed lithological unit of Jamaica, occurring in outcrop over half the surface area of that island (Robinson, 1994), ranging from the mid Middle Eocene to Middle or Upper Miocene. However, it has been a difficult unit for macropalaeontologists to exploit, because the well-lithified, case-hardened limestones give up their fossils only grudgingly (Donovan, 2004). Like many other taxa, the fossil decapod crustaceans of this unit have been difficult to collect. Morris (1993) noted only “Callianassa” sp from the Paleogene part of the White Limestone Group and indeterminate crab fragments from the Eocene Swanswick Formation, White Limestone Group. A single fragment referred to “Callianassa” sp (Fig. 4G and H) remains the best known decapod from the Swanswick Formation, a unit that has otherwise yielded, for example, many hundreds of fossil echinoids.
Ocalina haldixoni Collins & Donovan (Fig. 4A-C) is known from a single carapace from northeast Jamaica (Donovan, 2011, locality Eo4). It is from the upper Middle or Upper Eocene part of the Montpelier Formation, White Limestone Group, although details of the locality are uncertain. It has a relatively smooth dorsal surface and is the only crab carapace known from the pre-Miocene of the White Limestone Group.
What is surprising is the lack of any Oligocene fossil arthropods, including crabs, from the island. Most invertebrate groups show a decline in diversity following extinctions close to the Eocene/Oligocene boundary (for example, echinoids; Donovan et al., 2007). Yet, the Late Oligocene limestones of the Brown’s Town area were collected in detail by the late Hal Dixon in the early 1990s, an investigation that yielded taxa hitherto unknown from this part of the Jamaican fossil record, such as ophiuroid vertebral ossicles and ribs of dugongs. If there were crabs in these rocks, Hal would have recognised them, as he did with more than one crab locality in the island’s Neogene (for example, Collins et al., 1997; Donovan & Dixon, 1998). What is certain is that the known Paleogene diversity will be improved upon with detailed collection from Trechmann’s and other sites in the Eocene of the Yellow Limestone Group. Crab claws may be widespread in this unit (for example, Donovan et al., 1990, p. 662) and they are waiting for discovery and detailed study.
Jamaican Neogene crabs
If the decapods of the Cretaceous and Paleogene of Jamaica seem few and far between, it should be remembered that, until the 1990s, those species described by Withers were the only fossil crabs known from the island. Yet now, those of the Neogene (particularly the Pleistocene) are the best known and most diverse in the Antilles (for a more detailed review, see Collins et al., 2009c).
The coral-associated crab fauna of the Lower Miocene of the Montpelier Formation, White Limestone Group, at Duncans Quarry (Donovan, 2011, locality Mi1) is comprised of 16 species in 14 genera. More species of fossil crabs are known from this one site than from the rest of the White Limestone Group in total, which represents about 40Ma of limestone deposition. Three of the genera from Duncans Quarry, Actaeops, Pseudoachelous and Duncania, were new when described by Portell & Collins (2004).
Five genera, Daira, Dynomene, Teleophrys, Chlorodiella and Trapezia, are extant taxa that were recorded from the fossil record of the Caribbean for the first time. With the exception of Teleophrys, all are present in the Upper Miocene coral-associated deposits of Europe and similar Middle Miocene beds from Japan, from where Leptodius, also represented in the Montpelier Formation, has also been described. Trapezia spp. are commensal with seriatoporid (=pocilloporid) corals, which (with the exception of Madracis) no longer occur in Caribbean waters (Portell & Collins, 2004, p. 121).
Only three extant genera, Micropanope, Panopeus and Mithrax, have previously been recorded in younger deposits from Jamaica – the last is also known from the Pleistocene Coral Rock of Barbados (Collins & Morris, 1976). The commonest species in the Montpelier Formation is the dairid Daira vulgaris Portell & Collins, which is well represented by numerous carapaces of various sizes, and isolated elements of chelae that are attributed to this fossil species. The genus includes two Recent species.
However, apart from Duncans Quarry, crustaceans remain poorly known from the Miocene of Jamaica. Only two species have been reported from the younger Miocene and from the Upper Miocene August Town Formation in southeast Jamaica (Collins et al., 2010). These sparse remains include poorly preserved propodi of the ubiquitous mud shrimp, “Callianassa” sp, and the anterior part of the carapace of Mithraculus sp aff. Mithraculus coryphe (Herbst) (Fig. 5). The latter occurrence considerably extended the stratigraphic occurrence of the genus in the Antillean region down into the Miocene.
Crabs from the Plio-Pleistocene of Jamaica have been described mainly from four formations: the Upper Pliocene Bowden shell bed of the Bowden Formation, and the Pleistocene Manchioneal (including the Old Pera beds), Port Morant and Falmouth formations, which have, between them, yielded about 70 species. There is also an undescribed collection of crab carapaces and appendages from the Upper Pliocene Hopegate Formation (Roger Portell, research in progress). However, the present total of known species from these deposits is a little more than half the number of living decapod species (130) recorded from the island. Undoubtedly, there is more collecting to be done.
Twenty-eight taxa are recognised (mostly from dactyli and fixed fingers) from the Bowden shell bed (Collins & Portell, 1998; Donovan, 2011, locality Pl1), picked from bulk samples. Of these, nine genera persist from the Miocene, but no species coincide. With but two exceptions, much of this fauna represents the earliest known specific appearance of extant Caribbean crabs. Only two species, Neocallianassa sp and Micropanope aff. spinipes (A Milne Edwards), are in common with the Upper Pleistocene Falmouth Formation. Mithrax sp and, tentatively, Petrochirus bahamensis (Herbst), Calappa springeri, Persephona punctata punctata, Eurytium limosum and Panopeus herbstii are fully recorded from the Port Morant Formation.
The Port Morant Formation (Collins et al., 1997, 2009b; Collins & Donovan, 1998, 2012; Donovan, 2011, localities Qu3, Qu4; see also Fig. 6), which has produced some carapace remains, has only one species, Panopeus herbstii, in common with the Falmouth Formation. This species provides one of those rare instances of a carapace that has been associated, however tentatively, with a taxon recorded as fossilised chelae (that is, the pincer-like organs terminating certain limbs of some arthropods).
An extinct callianassid, Neocallichirus peraensis Collins et al., has affinities with extant Neocallichirus grandimana (Gibbes). A partial carapace of Hepatus praecox Collins et al. has characters in common with the Atlantic form, Hepatus pubibundus (Herbst), and with Hepatus kossmani Neuman, its Pacific analogue, while a fixed finger assigned to Callianectes cf. toxodes Ordway was considered by Collins et al. (1997) more closely to resemble Callinectes bocourti A Milne Edwards, its Caribbean analogue. Also absent from present day Jamaican waters is Raninoides louisianensis Rathbun, now restricted to the Gulf of Mexico. Two extant species, the hermit crab Petrochirus bahamensis and the box crab Calappa springeri (Fig. 6A, H and I), which are relatively common in the Port Morant Formation, are also tentatively recorded from the Bowden shell bed.
The first mention of crabs from the Early Pleistocene Manchioneal Formation (Morris, 1993) was of an “indeterminate fragment” and a “galatheid fragment”. To this meagre sample, Collins et al. (2001) added the description of Euphylax fortispinosus from the Old Pera beds of this formation (Donovan, 2011, locality Qu1), a unit that has otherwise failed to produce crab remains. It is the youngest known fossil member of the genus. At present, Euphylax is confined to the Pacific coast of tropical Central America and the eastern tropical Pacific.
The Late Pleistocene Falmouth Formation is best exposed in the Discovery Bay area of the central north coast of Jamaica. It has yielded a diverse fossil fauna, preserved in a variety of reef-related palaeoenvironments. The Falmouth Formation occurs mainly as hard, well-indurated limestones, but some localities are only weakly lithified and are susceptible to bulk sampling in the field and picking under a microscope. The best studied site, on the east side of Rio Bueno Harbour (Donovan, 2011, locality Qu2), has yielded a diverse fauna of small and fragmentary crab remains, mainly claws, but also rare carapaces. Morris (1993) identified the remains of 14 genera from this site, all known from the modern marine biota. Roger Portell has subsequently made a large collection with many additional species awaiting documentation.
The large land crab, Cardisoma guanhumi Latreille (Fig. 6F and G), was recorded from the Port Morant Formation of Jamaica by Collins & Donovan (1998). However, the only instance of this essentially land crab occurring in a terrestrial deposit in Jamaica, a (Late?) Pleistocene fissure fill, was reported from eastern Jamaica by Donovan & Dixon (1998; Donovan, 2011, locality Qu5). A Late Pleistocene land crab, Sesarma primigenium Collins et al., 2009a, was described from the Western Cement Company Cave in south-western Jamaica (Fig. 6). A similar species was also recognised from the Late Pleistocene Red Hills Road Cave in eastern central Jamaica (Donovan, 2011, locality Qu6). A recent study (Baalbergen, 2011) added a new collection of specimens from the latter site to Sesarma sp cf. S. cookei Hartnoll, which is an extant Jamaican species.
We thank Phil Crabb, formerly of the Photographic Unit of the Natural History Museum, London, for providing the many excellent images we have used in Figs. 4 to 7.
Box crab: The box crabs, also known as shame-faced crabs (family Calappidae), have a box-shaped carapace and conceal their anterior (‘face’) behind their chelae, hence their two common names.
Callianassid: The mud shrimps (family Callianassidae) are burrowers whose principal calcification in the exoskeleton is in the chelae. They are rarely preserved complete, but their chelae may be locally abundant.
Carapace: The carapace is the ‘shell’ (=exoskeleton) of a crab, protecting the dorsal and lateral parts of the ventral surface. In most families, it is well calcified and easily fossilised.
Chelae (sing., chelae): The enlarged anterior-most pair of legs of a decapod crustacean, modified as pinching claws.
Cheliped: A cheliped is the a joint of the anterior limbs that directly supports a chela.
Dactylus (pl., dactyli): The first segment of a limb of the thorax, that is, its termination.
Dynomenid: The family Dynomenidae a group of crabs that preferentially inhabit corals.
Fixed finger: The lower part of the pinching claw, rigidly attached to the chela.
Hermit crab: The hermit crabs (family Paguridae) are a group with a poorly mineralised carapace that live attached to the insides of discarded gastropod shells. Their fossil record is mainly based on the well-mineralised chelae.
Mud shrimp: see callianassid.
Portunid: The family Portunidae includes the swimming crabs, which have the posterior-most pair of legs modified as flattened paddles.
Propodus (pl., propodi): The second segment of a limb of the thorax, that is, the segment that supports the dactylus.
Raninid: The family Raninidae are called frog-crabs because of their appearance.
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