A new genus of hard ticks in Cretaceous Burmese amber (Acari: Ixodida: Ixodidae). George Poinar, Jr1 & Alex E. Brown2. 1Department of Entomology, Oregon ...
Systematic Parasitology 54: 199–205, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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A new genus of hard ticks in Cretaceous Burmese amber (Acari: Ixodida: Ixodidae) George Poinar, Jr1 & Alex E. Brown2 1 Department 2 629
of Entomology, Oregon State University, Corvallis, OR 97331, USA Euclid Avenue, Berkeley, CA 94708, USA
Accepted for publication 20th September, 2002
Abstract A hard tick larva in Cretaceous Burmese amber is described as Cornupalpatum burmanicum n. g., n. sp. Diagnostic characters include a subcircular body with a marginal groove, 11 festoons, elongate four-segmented palpi with the fourth segment distinct and apical, the absence of an anal groove and eyes, and the presence of claws on palpal segment 3. The last character is unique for all members of the Ixodida, both fossil and extant. Aside from the palpal claws and marginal groove, features of the tick larva closely resemble those of members of the genus Aponomma Neumann 1899, considered one of the most primitive tick lineages today, whose hosts are primarily reptiles.
Introduction Recently, an amber site was re-developed in the Hukawng Valley in Burma and discoveries of primitive insect fossils led researchers to speculate that the deposits are Cretaceous in age (Zherikhin & Ross, 2000; Grimaldi et al., 2002), a conclusion reached by Cockerell some 80 years ago (Cockerell, 1922) (further discussion of the dating of these deposits is presented later in the paper). During an examination of this material, a tick larva belonging to the family Ixodidae was discovered. The fossil tick was determined to belong to an extinct genus and is described below. Fossil hard ticks (Ixodidae) have been described from Tertiary Baltic amber (Weidner, 1964) and reported from Dominican (Lane & Poinar, 1986; Poinar, 1992; Keirans et al., 2002) and Burmese amber. The previous Burmese specimen was identified as belonging to the genus Amblylomma Koch 1844 (Klompen in Grimaldi et al., 2002).
Materials and methods The amber was re-cut and polished in order to better view the specimen. Observations, drawings and photographs were made with a Nikon SMZ-10 stereoscopic microscope and Nikon Optiphot microscope
(with magnifications up to 650×). The amber piece containing the tick (accession number A-10- 260) is rectangular in outline, measuring 10 mm in greatest length, 4 mm in greatest width and 2 mm in greatest depth. Although well preserved, shrinkage from preservation resulted in numerous small cracks on the body surface and some distortions to the appendages. However, the resin cleared the specimen so that certain features on the ventral surface of the basis capituli and idiosoma, such as the anus and sub-coxal large wax glands (sensilla sagittiformia), are visible from the dorsal side (Figure 4). All measurements are in micrometres unless otherwise specified. Ixodida Leach, 1815 Ixodidae Murray, 1877 Cornupalpatum n. g. Diagnosis Body subcircular; with 11 dorsomarginal festoons reaching marginal groove; anal groove and eyes absent; scutum indistinct; palpi and hypostome long; palpi with four segments; fourth segment distinct and apical; third segment bearing ventrolateral claws. Type-species C. burmanicum n. sp.
200 Cornupalpatum burmanicum n. sp.
Second specimen
Description (Figures 1-8)
After this manuscript was written, we discovered a second unengorged ixodid tick larva from the same Burmese deposits (Figure 9). The amber piece containing this specimen (accession number A-10-261) is rectangular in outline, measuring 22 mm in greatest length, 15 mm in greatest width and 4 mm in greatest depth. The degree of preservation was not as good as the holotype; however all characters that could be observed were similar to those of the holotype, including the palpal claws (Figure 9, insert). This specimen is considered conspecific with the holotype and is designated a paratype, to be placed in the same repository as the holotype.
Unengorged larva Idiosoma. Ornamentation and scutum indistinct; body about as long as broad; length (excluding capitulum) 328, greatest width 350; marginal groove extending around posterior half of body; 11 festoons ranging in length from 25-35 and in width from 45- 67; central festoon narrower than others (28 in width); festoons reaching marginal groove; anus located 141 from posterior border; paired large wax glands (sensilla sagittiformia) postero-lateral to coxae l-lll and one pair dorsally on posterolateral margin. Capitulum. Length of basis capituli from palpal insertion to posterior margin of basis 70, width 92; basis subrectangular in shape with cornua weakly developed; posterior margin convex ventrally; palpi cylindrical, 90 in length, with length/greatest width of 4 articles as follows: article 1, 11/13; article 2, 32/23; article 3, 29/18; article 4, 18/13; article 4 distinct and apical with numerous setae; lateroventral surface of article 3 with at least 5 claws, 2 of which are toothed (Figures 3,4,7); dark area in article 3 may represent chemosensory organ; hypostome length 79, width at base 27; dentition unclear; cheliceral sheath barely surpassing digit of chelicerae; mantle shorter and wider than sheath; with some short denticles on distal third of hypostome. Legs. Coxae ll with distinctive inner and outer spurs; coxae 1 and lll unarmed or nearly so; tarsus 1 tapering distally, length 122, greatest width 34; tarsi 2 long and narrow, tapering distally, length 140, greatest width 24; tarsi 3 shorter, length 88, greatest width 32; pretarsus elongate, narrow; claws slender, paired, simple, slightly curved; each with 3-lobed empodium (caruncle); setal-like claw supplement (setate paradactyli) located on outer side of each claw. Type-material: Holotype larva in Burmese amber from the Hukawng Valley deposited in the Poinar amber collection (accession number A-10- 260) maintained at Oregon State University, later to be deposited at the California Academy of Sciences, San Francisco. Etymology: ‘Cornu’ is from the Latin cornu (‘horn’), and ‘palpatum’ is from the Latin verb palpare (‘to touch, stroke or feel’); ‘burmanicum’ refers to the country of origin.
Differential diagnosis The palpal claws of C. burmanicum n. sp. distinguish it from all extant larvae of the Ixodida. Other characters, some of which are diagnostic, include the subcircular body with a marginal groove, 11 festoons, absence of an anal groove and eyes, and elongate foursegmented palpi with the fourth segment distinct and apical.
Discussion The striking feature of C. burmanicum n. sp. is the simple and bifurcate claws on subterminal article 3. These claws are difficult to observe, since the specimen must be carefully orientated to view the ventrolateral surface of the third palpal segment. In the paratype, the claws appear terminal, since the fourth palpal segment is bent to one side (see insert, Figure 9). In the Acari, palpal claws are known only for members of the parasitiform suborders Opilioacarida Johnson 1968 (terminal palptarsal claws), Holothyrida Baker et al., 1958 (two or three-tined subterminal palptarsal claws) and Mesostigmata Baker & Wharton, 1952 (two or three-tined basal palptarsal claws) (Krantz, 1978), all on the fourth segment. It is therefore unlikely that the palpal claws of C. burmanicum can be considered homologous to those of other parasitiform groups. The palpal claws on C. burmanicum may have been used to help secure the tick to its host, or to pierce or tear host tissue such as mucous membranes in preparation for a blood meal. It is not known whether these
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Figures 1-2. Cornupalpatum burmanicum n. sp. (holotype, A-10-260). 1. Dorsal view. Arrows show marginal groove (dorsal); fleche shows anus (ventral). 2. Left tarsus. Arrows show possible Haller’s organ. Scale-bars: 1, 96 µm; 2, 21 µm.
palpal claws represent a basal lineage or are a secondary adaptation to a particular host group. Since the retrose teeth on the hypostome of C. burmanicum appear to be few in number, it is possible that, over time, the evolving hypostome (with larger and additional retrose teeth) replaced the palpal claws as a grasping/holding organ. It would be interesting to know if the nymphs and adults of C. burmanicum retained these palpal claws, since Hoogstraal & Kim (1985) mentioned that evolutionary changes in structure over
time have been slower to occur in immature than in adult ticks. In the Clifford & Anastos (1960) key to larval ticks, C. burmanicum would be accommodated in Ambylomma Koch 1844. However, the above authors did not include Aponomma Neumann 1899 in their study. The key presented by Krantz (1978) separated these two genera on the basis of eyes present (Ambylomma) or absent (Aponomma), which would align C. burmanicum closest to Aponomma. Elongate four-segmented
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Figures 3-6. Cornupalpatum burmanicum n. sp. (holotype, A-10-260). 3. Dorsal view of capitulum showing exposed claws on turned left palpal segment 3 (arrow) and hypostome with denticles. Insert shows right palpal segment 3 (fleches outline claw area on under ventral surface; arrow indicates area of a possible chemosensory organ). 4. Detail of claws on left palpal segment 3. 5. Tip of chelicera showing sheath (S), mantle (M) and digit (D). 6. Distal portion of tarsus 1 showing pretarsus (P), three-lobed empodium (E), claw (C) and claw supplement (S). Scale-bars: 3, 35 µm; 4, 23 µm; 5, 18 µm; 6, 48 µm.
palpi with the fourth segment distinct and apical, as occurs in the fossil and in various Aponomma reptilian parasites (Hoogstraal & Kim, 1985), is considered a primitive character and characteristic of reptile feeders, which Hoogstraal & Kim (1985) believe to be the basic host group for the Ixodidae. The palpal claws on the fossil are in roughly the same position as the ventral palpal spurs reported on
immature stages of members of the subgenus Allophysalis Hoogstraal 1971 of the genus Haemaphysalis Koch 1844 (see Hoogstraal & Kim, 1985). As ticks adapted to bird and mammal hosts, palpal segment 4, in most cases, became a diminutive, ventrally directed appendage located in a subapical protective pit on palpal segment 3 (Hoogstraal & Kim, 1985), es-
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Figures 7-8. Cornupalpatum burmanicum n. sp. (holotype, A-10-260). 7. Dorsal view of capitulum with chelicerae and hypostome. Left palp shows exposed claws on ventral lateral surface of palpal segment 3. Claws are on the lower surface of right palpal segment 3. 8. Combined dorsal and ventral view of idiosoma showing marginal groove, festoons, coxae, anus and large wax glands (sensilla sagittiformia). Dashed line represents minute irregular cracks around anus. Scale-bars: 7, 35 µm; 8, 50 µm.
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Figure 9. Cornupalpatum burmanicum n. sp. (paratype, A-10-261). Dorsal view. Insert shows left palp with palpal claws (arrow). Scale-bar: 118 µm (insert 16 µm).
sentially in the area where the palpal claws occur on C. burmanicum. While only 11 festoons are clearly visible on C. burmanicum, a small notch in the body margin at the point where an additional festoon would be expected and a faint groove on the opposite side in the same area (Figure 8), suggests that ixodid ticks with 13 festoons may have anteceded this fossil clade. Extended dark elliptical areas on the dorsal aspect of tarsi l (Figure 2) could represent the anterior and posterior pits of Haller’s organ, a complex sensory setal field located on the dorsal surface of tarsus 1 in all postembryonic stages of ticks (Krantz, 1978). Dark areas in the terminal area of the third palpal claw in the fossil (Figure 3, insert) may also represent some type of chemosensory organ, although nothing similar in modern ticks has been reported. Variation in the width of the festoons on tick larvae occurs in species of Amblyomma (see Krantz, 1978) and Dermacentor Koch 1844 (with a narrow central festoon similar to that of the fossil) (see Clifford & Anastos, 1960). The present find, together with the larval specimen of Ambylomma in the same deposits (Klompen in Grimaldi et al., 2002), demonstrates that at least two lines of ixodid ticks were well established by the Cretaceous, one of which differed from extant forms
by possessing larvae with palpal claws, possibly an adaptation to a now-extinct line of reptilian hosts.
Dating of amber There are many difficulties involved in dating amber deposits. The first task is to attempt to date the strata in which the amber is located, which is done mainly by examining trace fossils that occur in the same strata as the amber. The second is to determine if the amber deposit is primary (original deposit) or secondary (re-deposited in younger geological formations). The third is to determine if the amber deposit is homogeneous (all from the same plant and age) or if it is heterogeneous (a mixture of two time periods and two plant sources). An example of a heterogeneous deposit is New Jersey amber, much of which has been re-deposited in sandy areas where it occurs not far below the surface. While some of the New Jersey amber is Cretaceous (65-95 mya) with Agathis as a source (Lambert et al., 1990), younger Tertiary amber from the angiosperm, Liquidamber, as well as other unidentified material, also occurs in at least six different localities (Langenheim & Beck, 1968; Grimaldi et al., 1989). Amber from Burma is still being investigated in regards to its exact age. The amber occurs in lignitic seams in sandstone-limestone deposits in the
205 Hukawng Valley in upper Burma. Apparently these lignitic seams extend from the valley up the sides of a mountain where the mine that produced this specimen is located (Jim Davis, personal communication). This amber may be from the same source and time period as the earlier collections of Burmese amber (Chhibber, 1934; Cockerell, 1922). The amber appears homogenous, but additional tests are necessary to determine if the beds contain a mixture of amber from different plant sources and/or ages. Nuclear magnetic resonance (NMR) spectra of amber samples taken from the same locality as the fossil ticks indicated an araucarian (possibly Agathis) source of the amber (Lambert & Wu, unpublished research, 2002). Palynomorphs obtained from the amber beds where the tick pieces originated have been assigned to the Upper Albian (c. 100 mya) (Cruickshank & Ko, 2002). While an Eocene age was originally provided for these deposits (Chhibber, 1934), Cockerell (1922) was the first to suggest they were Cretaceous based on primitive insect types found in the amber, and others have concurred (Zherikhin & Ross, 2000; Grimaldi et al., 2002). For further information on these deposits, see Poinar (1992) and Hlaing (1999).
Acknowledgements Thanks are extended to Jerry Krantz for discussions on tick evolution and reviewing earlier versions of this manuscript and to Roberta Poinar for editorial comments.
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