Fossil Insects

Known Latin American fossil insect sites are few, but they have produced considerable material representing several types of fossilization. Most represent relatively recent strata (Cenozoic).

Impressions in sedimentary rock from the Eocene in South America are most significant (Martinez 1982). One of the best known beds is found at Sunchal, Argentina, in the province of Jujuy. Many specimens of weevils and other insects were excavated there by entomologist T. D. A. Cockerell early in this century. The oldest insects from the region are of an unidentified order (Eugeropteron and Geropteron) from middle Carboniferous beds in the Sierra de los Llanos of the province of Rioja, also in Argentina. Other important sites of insect fossils preserved in sedimentary rocks are located in Rio Grande do Sul, Brazil, and at Bajo de Veliz, in the province of San Luis in Argentina (Upper Carboniferous) (Martinez pers. comm.). An enormous thera-phosine spider (Megarachne servinei), measuring 34 centimeters from the chelicerae to the tip of the abdomen and having a leg span of more than 50 centimeters, was discovered in the Bajo de Veliz Formation (Hunicken 1980). The Santana Formation near Ceara, Brazil, has yielded fossils of Lower Cretaceous age (Grimaldi 1990).

Two amber deposits have yielded abundant specimens, although of relatively recent times. Preservation is exceedingly good. The insects were caught in resinous exudates from various trees. The viscous substance later hardened with burial and time and remained clear within so that the most minute structures (hairs, genitalia, mouthparts) can be observed today in perfect detail, even on the smallest mites and midges. Preservation is so perfect in some cases that attempts are being made to recover and replicate fossilized DNA from cells of fungus gnats with large chromosomes (Poinar and Hess 1982).

A famous site of late Oligocene to early Miocene Age is near Simojovel, in the state of Chiapas, Mexico (Hurd et al. 1962). It has been particularly well studied and has produced a wide variety of taxa (various authors 1963, 1971). These deposits were known to early peoples of Central America, and amber pieces with insect inclusions were fashioned into ornaments. The original resin is believed to have been secreted by a leguminous tree of the genus Hymenaea.

Localities in the Dominican Republic have commanded attention in recent years (Baroni-Urbani and Saunders 1982) and are also the source of a thriving "gemstone" industry (Rice 1979, Rice and Rice 1980). The deposits are generally accepted as of about the same age as the Chiapas amber and likewise derived from Hymenaea. The many mines scattered about the country have produced amber fragments with thousands of specimens of more than one hundred families of insects plus spiders and other arachnida (Cokendolpher 1986) and invertebrates (Sanderson and Farr 1960), including the first fossils of gardening ants (Attini, Trachymyrmex, Baroni-Urbani 1980). Wilson (1985) found 37 genera of ants, of which 34 survive in neighboring areas of Latin America.

In the Americas, there are also a number of other known but unexplored amber deposits, for example, in Colombia (Cocker-ell 1923), Brazil (Froes Abreu 1937), and surely other countries (Poinar and Agudelo 1980).

Good preservation is also characteristic of the Quaternary Age remains found in asphalt deposits. Some sites in this category are located in Trinidad (Blair 1927) and at Talara on the northern Peruvian coast (Churcher 1966). Here, because of the stickiness of the tarlike medium and the attractiveness of the surface, which looks like water, asphalt seeps form very efficient small animal traps. The most numerous kinds of insects found as fossils in these deposits are hard-bodied ground beetles, aquatics, and carrion feeders. Aquatic insects are sometimes indicative of the presence of freshwater pools near the asphalt or overlying it. They were entrapped when the water dried up during drought periods. Carrion-feeding species were caught along with the carcasses of vertebrates that died in the black quagmires.

Because of their small size and delicate -ness, insects and their relatives produce good fossils only in fine-grained or homogeneous matrices. The foregoing are of this type. Other modes of fossilization that may be important in Latin America, and which have been scarcely investigated, are permineralization (such as in mineral-charged waters), peat and soft coal encapsulation, cave sediments (Miller 1986), and silicification, especially evident in calcareous nodules. Evidences of feeding, boring, coprolites, and trails should also be common in deposits of plant fossils. Insect remains in association with ancient human remains may also be of considerable archaeological significance (e.g., Warner and Smith 1968).

References

Baroni-Urbani, C. B. 1980. First description of fossil gardening ants. Amber collection Stuttgart and Natural History Museum Basel: Hymenoptera: Formicidae. I: Attini. Stutt. Beitr. Naturk. Ser. B (Geol. Paleon.) 54: 1-13. Baroni-Urbani, C. B., and J. B. Saunders. 1982. The fauna of the Dominican amber: The present state of knowledge. 9th Carib. Geol. Conf. (Santo Domingo, 1980) Trans. 1: 213-223.

Blair, K. G. 1927. Insect remains from oil sands in Trinidad. Entomol. Soc. London Trans. 75: 137-141. Churcher, C. S. 1966. The insect fauna from the Talara tar-seeps, Peru. Can. J. Zool. 44: 985-993.

Cockerell,T. D. A. 1923. Insects in amber from

South America. Araer. J. Sei. 5: 331-333. Cokendolpher, J. C. 1986 (1987). A new species of fossil Pellobunus from Dominican Republic amber (Arachnida: Opiliones: Phalangodi-dae). Carib. J. Sei. 22: 205-211. Froes Abreu, S. 1937. Sobre a ocorréncia de ambur nos arenitos da serie Bahia: Brasil. Inst. Nac. Tech. (Rio de Janeiro) Bol. Inf. 2(4): 8.

Grimaldi, D. A., ed. 1990. Insects from the Santana Formation, Lower Cretaceous, of Brazil. Amer. Mus. Nat. Hist. Bull. 195: 1-191.

Hünicken, M. A. 1980. A giant fossil spider (Megarachne servinei) from Bajo de Veliz. Acad. Nac. Cien. Córdoba, Bol. 53: 317-325. Hurd, Jr., P. D., R. F. Smith, and J. W. Durham. 1962. The fossiliferous amber of Chiapas, Mexico. Ciencia 21(3): 107-118, PI. I—II. Martínez, S. 1982. Catálogo sistemático de los insectos fósiles de América del Sur. Fac. Hum. Cien. (Univ. Rep., Montevideo) Ser. Cien. Tierra, Rev. 1(2): 29-83. Miller, S. E. 1986. Phylum Arthropoda, Class Insecta. In D. W. Steadman, Holocene vertebrate fossils from Isla Floreana, Galápagos. Smithsonian Contrib. Zool. 413: 1-103. Poinar, Jr., G. O., and F. Agudelo. 1980. El ámbar: Oro fósil del nuevo mundo. Americas 32(10): 33-40. Poinar, Jr., G. O., and R. Hess. 1982. Ultra-

structure of 40-million-year-old insect tissue. Science 215: 1241-1242.

Rice, P. C. 1979. Amber of Santo Domingo— mining in the Dominican Republic. Lapidary J. (Nov. 1979): 1804-1810.

Rice, H. E„ and P. C. Rice. 1980. Pepitas de sol antillano. Americas 32 (10): 37-41.

Sanderson, M. W., andT. H. Farr. 1960. Amber with insect and plant inclusions from the Dominican Republic. Science 131: 1313-1314.

Various authors. 1963, 1971. Studies of fossiliferous amber arthropods of Chiapas, Mexico, Pts. 1, II. Univ. Calif. Publ. Entomol. 31: 1-53, pis. 1 —3; 63: i-vi, 1-106, pis. 1-3.

Warner, R. E., and G. E. Smith, Jr. 1968. Boll weevil found in pre-Columbian cotton from Mexico. Science 162(3856): 911-912.

Wilson, E. O. 1985. Invasion and extinction in the West Indian ant fauna: Evidence from the Dominican amber. Science 229(4710): 265-267.

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