LETTER TO THE BOOKSHELF
A letter from David Grimaldi and Michael Engel regarding George Poinar's review of Evolution of the Insects
To the editor:
In the July-August 2006 issue of American Scientist, George Poinar reviewed our recent book, Evolution of the Insects, along with another large volume on the same topic, History of Insects (edited by Alexandr P. Rasnitsyn and Donald L. J. Quicke) ("Retracing the Long Journey of the Insects," July-August 2006). All reviews of our book thus far have been highly complimentary (for example, Bourke, 2005: TREE; Cranston and Gullan, 2005: Evolution 59: 2492-2494; Jarzembowski, 2005: Science 309: 880-881; Moczek, 2006: Evol. & Development 8: 111-112; ), but this is the only negative one, because, as we discuss below, there is little basis for his critique.
The kernel of Poinar's critique is that we failed to "discuss the controversy surrounding the age, interpretation and identification of fossils that were initially announced with much fanfare and bravado." Actually, we took particular effort to discuss controversies, such as reports of ancient DNA from amber (discussed on pages 60–61), different methods of phylogenetic reconstruction (pages 31–33), historical biogeography (pages 625–634), and myriad fossils and phylogenies. Half of Poinar's review focused on three putative "failures" of ours.
The first case with which Poinar takes issue is our reinterpretation of the remains of the oldest known insect, Rhyniognatha hirsti, from the Devonian chert of Rhynie, Scotland, which we had previously published (Engel and Grimaldi, 2004: Nature 427: 627-630). He says we neglected in the book to mention prior interpretations of Rhyniognatha (including one that the mandibles belonged to a springtail), so apparently Poinar never read page 152. In fact, no one ever proposed that Rhyniognatha was a springtail; he is confusing this fossil with one of the most famous arthropod fossils also from the Rhynie chert, Rhyniella praecursor, which is an unambiguous springtail.
His second charge points to the fossil bee, Cretotrigona prisca in Cretaceous New Jersey amber, which had been co-described (Michener and Grimaldi, 1988: Amer. Mus. Novit. 2917) and re-interpreted (Engel, 2000: Amer. Mus. Novit. 3296) by us, but never seen by Poinar. Exact age of the bee within the Late Cretaceous is uncertain but probably latest Cretaceous, though Poinar alludes to it being Tertiary because, he says, New Jersey amber is a chronological "mixed bag." For this he cited Langenheim and Beck (1968: Harvard Bot. Mus. Leaflets 22: 65-120), but never cited the more comprehensive studies that superseded and revised that one (Grimaldi et al., 1987: Amer. Mus. Novit. 2948; Grimaldi et al., 2000: pp. 1-76 In: Grimaldi (ed.) Studies on Fossils in Amber, with Particular Reference to the Cretaceous of New Jersey: Backhuys, Leiden). In fact, the molecular composition of Tertiary fossil sap from the New Jersey Coastal Plain is unique and unmistakable. Unlike fossilized hydrocarbon polymers (a.k.a. amber), the Tertiary material from New Jersey is actually (and incredibly) composed of polymerized styrenes, and any competent amber specialist can tell the difference by just looking at samples.
Poinar's third and last example involves Cretaceous mosquitoes, of which there are two. One of these, Burmaculex antiquus in 100 million-year-old Burmese amber, Poinar disputed as being a mosquito, since it possesses only some of the features of modern mosquitoes. As was published in detail elsewhere (Grimaldi et al., 2002: Amer. Mus. Novit. 3361; Borkent and Grimaldi, 2004: Ann. Ent. Soc. Amer. 97: 882-888) and mentioned in our book (pg. 506), Burmaculex is a stem-group mosquito, an intermediate form between modern mosquitoes and other midges. At one time birds had teeth, horses had toes, snakes had limbs, and mosquitoes had shorter proboscides. This basic concept of stem groups was impressed upon Poinar earlier with respect to Cretaceous ants (Grimaldi and Agosti, 2000: Can. Ent. 132: 691-693), but apparently to no avail. We specifically discussed stem groups on pages 38–40 in Evolution of the Insects, and applied the concept to numerous insect examples throughout the book. To Poinar, Paleoculicis (in 75 myo amber from Canada) is actually the oldest mosquito, an opinion for which he appealed to Vladimir V. Zherikhin, one of the authors of History of Insects. The real reason Zherikhin did not mention Burmaculex in that book is that it was impossible for him to know about it: he died in 2001. The Russian book was published posthumously in 2002, when our first report of the fossil appeared.
Lastly, contrary to Poinar's review, we did not use the term "citizen roach" as a common name for termites; we merely used it once in a whimsical title of our book (page 238) to illustrate the roach ancestry of termites. This may seem a minor point, but it illustrates how the errors, misstatements and untruths in his critique are so consistent and often profound that one must ask if they are actually deliberate. Since Poinar scarcely commented on the other book, History of Insects, published three years prior to ours, it is difficult to see his "review" as anything but a diatribe.
We welcome and appreciate reviews of our work by recognized authorities, as well as informed debate, but when it comes to this particular reviewer Evolution of the Insects stands on its own merits and posterity shall prove a more enlightened and objective judge of our efforts.
David A. Grimaldi
American Museum of Natural History
Michael S. Engel
University of Kansas
Dr. Poinar responds:
While much could be said about the points raised in the rebuttal, I will limit my remarks to the following.
It is surprising that Grimaldi and Engel state, "no one ever proposed that Rhyniognatha was a springtail." Such opinionated statements are counterproductive in science and indicate a lack of knowledge of the literature. If Grimaldi and Engel had read the classic work on fossil terrestrial arthropods edited by Rohdendorf, they would have noted that Martynova placed both Rhyniognatha Tillyard and Rhyniella Hirst and Maulik in the Family Protentomobryidae of the order Collembola (springtails) (Martynova, O. M. 1991. Subclass Apterygota. Primitive wingless insects. pp. 39-45 in Fundamentals of Paleontology (English translation of the 1962 work), Vol. 9, Rohdendorf, B. B. (Editor-in Chief). Smithsonian Institution Libraries and The National Science Foundation, Washington, D.C.).
Regarding the putative mosquito Burmaculex, it might be easier to identify this fossil if the describers were consistent with their interpretation of certain morphological characters. For instance, in the original description by Grimaldi, Engel and Nascimbene in 2002 (American Museum Novitates 3361:1-71), a slender structure with a double bend at its tip was regarded as a "maxillary stylet." When the official description of Burmaculex by Borkent and Grimaldi appeared in 2004 (Annals of the Entomological Society of America 97:882-888), this same structure was referred to as a "labrum." And in Evolution of the Insects, Grimaldi and Engel re-labeled the identical structure as a mandible, even though in the 2004 official description, it is clearly stated "Mandible not visible." Such inconsistencies serve to raise a red flag about both the specimen and the describer's ability to interpret the characters. Also, this feature is quite different from that found in female culicids (Harbach and Kitching. 1998. Systematic Entomology 23: 327-370) and cannot be used as evidence that Burmaculex is a mosquito.
Criticism and debate provide the basis for scientific progress by furnishing alternative interpretations of discoveries and hypotheses. The ultimate goal should be seeking the truth, not winning the argument. Grimaldi and Engel have undoubtedly expressed negative opinions of the works of others many times and should be able to accept criticism of their own studies. One is left to wonder why, if they have received so many "highly complimentary" reviews of their book, they are so concerned with one that is only moderately negative. Just because I personally believe that History of Insects by Rasnitsyn and Quicke is a more comprehensive and better organized treatise than Evolution of the Insects doesn't mean that others will not buy their book, if for no other reason than because it is much cheaper.