Introduction

From the last third of the 20th century, local researchers worked to gather information, study the history and analyze the extent of the knowledge about the mammals of Mexico. These contributions include some that deal with this subject in general terms (^{Ramírez-Pulido and Britton 1981}; ^{Ramírez-Pulido and Mudespacher 1987}; ^{Leon-Paniagua 1989}; ^{Villa-Ramirez and Cervantes 2003}; ^{Arroyo-Cabrales et al. 2005}, ²⁰¹⁴; ^{Ríos-Muñoz et al. 2014}; ^{Sánchez-Cordero et al. 2014}), others addressed the subject from the point of view of scientific collections (^{Espinoza et al. 2006}; ^{Ramírez-Pulido and González-Ruiz 2006}; ^{Retana 2006}), literature reviews (^{Guevara-Chumacero et al. 2001}), by geographical regions (^{Ramírez-Pulido et al. 2016}; ^{Zaragoza-Quintana et al. 2016}) or focusing on particular taxonomic groups such as squirrels (^{Ramos-Lara and Koprowski 2014}) and carnivores (^{Perez-Irineo and Santos-Moreno 2011}, ²⁰¹³), also from the standpoint of descriptions of new taxa (^{Ramírez-Pulido and Britton 1981}) or from the history of the Mexican Association of Mammalogy (^{Briones-Salas et al. 2014}; ^{Lorenzo and Hernandez-Betancourt 2014a}), as well as from the influence and participation of foreign researchers (^{Lopez-Medellin and Medellin 2016}).

These contributions delineate with a high degree of certainty the history and current status of Mexican mammalogy; nonetheless, many gaps in the knowledge of this zoological group still remain, leaving many areas of opportunity to address the missing information. However, the increase in the number of researchers and research institutions result in a significant volume of scientific publications encompassing a broad range of research fields and specialties. Consequently, the analysis of the information available is a task that surpasses the individual capacity and demands teamwork, not always easy to achieve.

Despite the wealth of information, a task still pending is the quantification of the references that support the knowledge about mammals. To this end, we used the bibliography on Mexican mammals gathered during more than 40 years for two major objectives: document the geographical distribution at the state level, and complete the synonymy of the mammals of Mexico, for which the corresponding information in its simplest form is concentrated in seven books (^{Ramírez-Pulido et al. 1982}; ¹⁹⁸³; ¹⁹⁸⁶; ²⁰⁰⁰; ^{in press}; ^{Ramírez-Pulido and Castro-Campillo 1990}; ¹⁹⁹⁴), as well as the information produced in the last few years and not yet published. The review of this accumulated information have led to the publication of several papers (e. g. ^{Ramirez-Pulido et al. 2014}; ²⁰¹⁶); however, we have not analyzed the production rate through time, the source of articles, journals and books, nor the issues related to some of the references.

The analysis of the publications of ^{Guevara-Chumacero et al. (2001)} reveals, among other things, that the study subjects have become diversified and the number of works has increased. These conclusions were based on the analysis of 2,129 literature references that yielded a more comprehensive and in-depth approximation, and contribute a better understanding about the history of the mammals of Mexico. The aim of this work is to assess the information derived from the review of 6,732 literature references, to contribute to the understanding of the development and broaden the knowledge of the mammals of Mexico, from the historical and prospective points of view.

Materials and Methods

A database was built with all the literature references related to the mammals of Mexico. Initially, only works dealing with taxonomy and systematics were considered, when these documented the examination of specimens from Mexican sites, irrespective of the group studied. We soon realized that this approach was rather narrow and decided to add those publications that, without reporting the examination of specimens, referred to taxa whose geographical distribution reaches Mexico and its inclusion was mandatory for a better knowledge of the group. However, this lead to a significant increase in the volume of information; with time, a greater amount of publications were added regardless of the language, topic, author and source of the publication, provided the study focused on taxa with geographical distribution in Mexico. This database lists the author, year of publication, title, journal or editorial, volume number, pages, exact date of publication, classification according to book, chapter or journal; although there are publications that, strictly speaking, do not match any group, these have been entered nonetheless as journals for being serial publications. In the case of studies published in journals, the country of origin and the topics addressed were also entered. This literature database includes only journals, books and book chapters; thesis, congress proceedings and technical reports were excluded.

Despite the fact that this work is based on the review of the publications related to Mexican mammals dated from 1648 to 2016, although the 2016 references are not yet complete in spite of the effort to keep the database up to date, there is information beyond our reach for various reasons: the diversification and multiplication of sources of information, especially as regards the number of journals, the topics addressed, and the number of works published per year. We occasionally learn of works published addressing topics related to mammalogy a couple of years after publication.

In some books and serial publications, the year of publication differs from the year of the series; to avoid confusion, we used the date of print, which is also the date of dissemination. This same principle was followed for articles, book chapters, and even journals with outdated publication or articles published after the corresponding number. For managing the information, our analysis covers all published works assuming that they all have the same value, regardless of the topic addressed or its size in number of pages.

Results

A total of 7,727 publications were reviewed, including journals, books and book chapters. Of these, 995 were excluded; although important for the taxonomic history of some species, these only deal with the synonymy of the Mexican mammals (Ramírez-Pulido et al. in litt.). Accordingly, the number of publications included in this analysis was reduced to 6,732, the oldest being those of ^{Marcgraf de Liebstad (1648)} and ^{Hernandez (1651)}. The first mentions Sylvilagus brasiliensis and Eira barbara; the second is the first formal register of Mexican mammals after the graphical representation in pre-Hispanic codices. From these publications and until 1755, one work was published every 20 years, so this information was not included in our analysis. In the 19th century, the academic production was modest and showed slight variations. Nonetheless, in the late 19th century and early 20th century two institutions played a key role in the knowledge of the mammals of Mexico: the British Museum of Natural History, which led to the publication of the Encyclopedia of Natural History of Mexico and Central America (Biology Centrali-Americana), printed in 5 volumes between 1879 and 1888; and the U.S. Bureau of Biological Survey. It is from the involvement of European and North-American naturalists that the production increased significantly, although two events considerably slowed down the production at that time, the Mexican Revolution and the World War I. In the decade of 1930 an upturn was observed, which did not reach the levels observed at the end of 1900 (Figure 1). Again, the World War II had an impact in a variety of socioeconomic aspects at the global level, and mammalogy was no exception, which resulted in another significant decline in the number of published works (Figure 1).

Figure 1 Publications related to the mammals of Mexico from 1756 until the end of 2016. a) Difference of published works, bars above and below the line indicate increase or decrease of the number of works; asterisks indicate extreme values that differ from the average by more than one standard deviation. b) Number of published works and their relationship with the political and social events that influence the academic production (top: historic events in Mexico; down: in the World). 

After World War II the world experienced a complex situation for political and ideological reasons, plagued with key events, but nonetheless their effects reached mammalogical production. This epoch witnessed a trend towards a rise in the number of works, with no significant changes, and it is until the decade of 1990 that a noticeable increase was observed, which continued until the end of 2016.

In spite of the historical fluctuations in the production of works, the 6,732 references contributing to the knowledge of the terrestrial mammals of Mexico have accumulated over a little more than 360 years; of these, 81.2 % (n = 5,467) were published in 702 journals from 45 countries. Of the rest, 9.1 % (n = 610) are book chapters, and 9.7 % (n = 655) specialized books. All references were physically reviewed at least once. Exceptions are seven old publications from the 18th and 19th centuries that could not be located and, hence, were excluded from this study (Appendix I).

Source and situation of journals. Of the 702 journals, 86.3 % (n = 606) are published in the United States of America, Mexico, Germany, United Kingdom, France, Brazil, Italy, Russia, Canada, Argentina and The Netherlands; other 34 countries represent a mere 13.7 % (n = 96), with a number of journals that range between 1 and 8 per country (Table 1). In particular, 41.5 % comes from the United States of America (n = 291), 12.8 % (n = 90) from Mexico, followed by Germany (n = 56; 8.0 %), United Kingdom (n = 51; 7.3 %), France (n = 38; 5.4 %), Brazil (n = 19; 2.7%), and Italy, Russia, Canada, Argentina and The Netherlands (n = 64; 9.1 %).

The U.S. journals have published the largest number of articles on Mexican mammals (61.5 %, n = 3,360), with 60 % concentrated in nine journals and the remaining 40 % in 282. The papers published in Mexican journals (n = 1,012) are found in 90 journals, but the majority is concentrated in just a few, with 81 % of articles published in only eight Mexican journals. In general, the results reveal that a few magazines concentrate most of the works of interest for our objectives; accordingly, 61.5 % (n = 3.363) of the references were published in 27 journals, while the remaining 38.5% (n = 2.104), in 675 (Figure 2).

Figure 2 Trend in the number of articles per journals that were published on the mammals of Mexico from 1648 to 2016. 

The 27 most important journals in terms of the number of articles published come from the United States of America, Mexico, Germany, United Kingdom and France, averaging 127.5 articles per journal during the study period, with a minimum of 34 articles in Mammalia (France) and a maximum of 644 in the Journal of Mammalogy (USA). The most important US journals are the Journal of Mammalogy, Proceedings of the Biological Society of Washington, Mammalian Species, The Southwestern Naturalist, Bulletin of the American Museum of Natural History, American Museum Novitates, University of Kansas Publications Museum of Natural History, Proceedings of the Academy of Natural Sciences of Philadelphia, Occasional Papers The Museum of Texas Tech University, Proceedings of the United States National Museum and North American Fauna (Figure 3); taken together, these 11 journals concentrate 2,123 (64.3%) references.

Figure 3 The 27 most important journals that have published works related to the mammals of Mexico, which altogether account for 61.5 % (n = 3,363) of the articles published in journals. The following journals are included: * Anales del Instituto de Biología, Anales de Instituto de Biología, Serie Zoología y Revista Mexicana de Biodiversidad; ** Acta Zoológica Mexicana y Acta Zoológica Mexicana (nueva serie); *** Occasional Papers of the Museum of Natural History, University of Kansas y University of Kansas Publications, Museum of Natural History. 

Among the Mexican journals, those worth highlighting include Anales del Instituto de Biología of the National Autonomous University of Mexico, founded in 1930 and transformed into Anales del Instituto de Biología, Serie Zoología from 1967 to 2004, to become Revista Mexicana de Biodiversidad in 2005, a journal that has published 265 works. Acta Zoologica Mexicana, created in 1955, accumulates 175 studies; Revista Mexicana de Mastozoología, whose volume one number one was launched in 1995, includes 119 works; and Therya, the most recent journal of those reviewed, launched its volume one in 2010 and has published 121 papers. Other journals, although involving a smaller number of articles, are nonetheless important for the historical role they have played, such as La Naturaleza, Revista de la Sociedad Mexicana de Historia Natural, Anales de la Escuela Nacional de Ciencias Biológicas, Vertebrata Mexicana and Ciencia México (Figure 3), which jointly contributed with 847 works.

Many journals are either short-lived or do not publish on Mexican mammals over long periods of time. The mean active publication period is only 3.7 years; only 54 of them (7.5 %) have lasted more than 10 years and, of these, just nine lasted more than 50 years. The 27 important journals for the number of accumulated works (Figure 3) also include the most long-lasting ones, with an average duration of 84 years for US journals, such as Proceedings of the Biological Society of Washington, Bulletin of the American Museum of Natural History, and Proceedings of the Academy of Natural Sciences of Philadelphia, which have been active for over 130 years and are still being published. Exceptions are the University of Kansas Publications Museum of Natural History, which has adopted a new name, and Proceedings of the United States National Museum, which is no longer printed.

The most important Mexican journals (Figure 3) have been active for an average of 44 years, although not continuously in all cases. One of them is no longer circulating (La Naturaleza), others were short-lived (Vertebrata Mexicana), and yet others are published intermittently (Revista de la Sociedad Mexicana de Historia Natural and Anales de la Escuela Nacional de Ciencias Biológicas).

The number of journals is on the rise, from a single one in 1683 up to 149 in 2016. However, this trend has not been constant through time: in the 19th century, the increase rate was two journals per year; in the 20th century, 9.4; and in the 21th century, 14.6 (Figure 4). The number of papers in each journal also increased with time, from one in 1683 to four works per journal in 2016; however, this number peaked in 1900 to 1910 with 5.4 works per journal per year, even surpassing the current rate.

Figure 4 Increase in the number of journals and articles by journal published from 1756 to 2016. DE = Standard deviation. 

The importance of the impact factor (IF) in our field, associated with the academic and personal economic reward, is evident when the production over the past 25 years is reviewed, a period when 2,144 works were published in 338 different journals; more than half of these (62 %, n = 1,334) appeared in indexed journals with an IF ranging from 13.2 to 0.101. Another relevant data for this period is that 75 % (n = 1.608) of all works were carried out by Mexican colleagues, and 52 % of these (n = 828) were published in indexed journals.

In a first approximation, the average IF for Mexican mammalogy is high, 1.47. However, this value does not strictly represent the reality of this field, since a more detailed analysis reveals that of the 828 published, only 143 (13 %) appear in journals with an IF above 2.0, while 685 (87 %) are included in journals an IF varying from 1.9 to 0.101 and, within this range, the majority (n = 631) were published in journals whose FI is less than 0.590.

Discussion

History of production. The knowledge on the mammals of Mexico has been built throughout a little more than 360 years. It started formally with the book of ^{Marcgraf de Liebstad (1648)} that mentions the name Eira ilya, used by ^{Hamilton-Smith (1842)} to replace [Mustela] barbara, currently known as Eira barbara (^{Linnaeus, 1758}). However, the work by ^{Hernandez (1651)} could be considered as the beginning of the study of mammals of Mexico, because it contains the first list of Mexican mammals. On the other hand, the first record of a specimen from Mexico was mentioned by reporting the name Canis nigrirostris (= Urocyon cinereoargenteus nigrirostris) from Real de Arriba (= Temascaltepec, Estado de México), and 1850 is frequently mentioned as the date of description (^{Hall and Kelson 1959:861}), when in reality the article was read in the Academy in 1827 and published in 1830.

In this way, from 1648 until the end of 2016 a total of 6,732 references have accumulated, surpassing those on ornithology, which totalled 5,500 studies as of 2008 (^{Navarro-Siguenza et al. 2008}), making mammalogy the discipline most studied in Mexico, at least within the field of vertebrate zoology. Until the end of 2016 we recorded 367 years of publications, where the dedication of many researchers and their contributions, especially from the first third of the 19th century, allows to gain a first insight, not comprehensive yet, about the Mexican mammalogy. This overview has been summarized in previous works (^{Ramírez-Pulido and Britton 1981}; ^{Ramírez-Pulido and Mudespacher 1987}; ^{Leon-Paniagua 1989}; ^{Guevara-Chumacero et al. 2001}; ^{Arroyo-Cabrales et al. 2005}; ^{Ramírez-Pulido and González-Ruiz 2006}). However, the production is far from being constant, let alone homogeneous in numerical terms; on the contrary, it fluctuates through time, dramatically at times (Figure 1). As a general trend, since the 17th century the number of works rose steadily until the late 19th century and early 20th century, to show a vertiginous boost in the last third of the 20th century, particularly from 1990 on.

The most important events that affected the production rate of these contributions are closely related to social, political and economic events that influence the development of mammalogy in Mexico. Wars are apparently one of the key drivers that negatively affected academic production, a situation confirmed by the finding that the production rate decreased during wars and increased again when these ended (Figure 1). Particularly during the Mexican Revolution and the World Wars I and II, the production of scientific work (^{Bernal 1960}; ^{Guevara-Chumacero et al. 2001}), the description of new taxa (^{Ramírez-Pulido and Britton 1981}; ^{Ramírez-Pulido and Mudespacher 1987}), and the development of scientific collections (^{Ramírez-Pulido and González-Ruiz 2006}) slowed down. It is understandable that during the war the expeditions were suspended, the economic resources were reallocated to other priorities or persons changed their activity, albeit on a temporary basis. A clear example is shown by US researchers that participated in these wars and postponed their academic activity; examples are Harold E. Anthony, Remington Kellogg and Edward A. Goldman, who served during World War I (^{Sterling 1991}; ^{Layne and Hoffmann 1994}), while Emmet T. Hooper, James S. Findley and Rollin H. Baker, who were recruited in World War II (^{Layne and Hoffmann 1994}; ^{Phillips et al. 2009}), just to mention a few researchers with an important participation in the study of the mammals of Mexico. After World War II, J. Knox Jones, Jr. and Elmer C. Birney were in active service in various parts of the world (^{Findley et al. 1996}; ^{Genoways et al. 2000}). In addition, the only time that the American Association of Mammalogy has cancelled its congresses was during World War II in 1943 and 1944 (^{Gill and Wozencraft 1994}), although the journal of this association (Journal of Mammalogy) did not ceased publication (^{Verts and Birney 1994}). In the particular case of Mexico, after the Mexican Revolution the state policy supported basic education, which explains the lack of support to higher education and science for decades (^{Perez-Tamayo 2005}). The collapse of the production during these three wars was so great that it recovered until the decade of the 1960: before the Mexican Revolution, in early 1900, an average of 37 works were published per year, with a maximum of 52, a figure that was reached again until the late 1960s when an average of 42 works were published per year.

We used the Cold War period to name a period of history in our analysis (1950 to 1989), characterized by a relatively constant production rate (Figure 1). The effects of Cold War on academic production are not unknown, but also true is that during this period, even when the growth was slow, it did exceed the production of the previous years; it contributed with 18.8 % of the total number of publications over the 39 years it lasted. Important investigations were conducted during this period, including most monographs state and many taxonomic revisions. Also, important researchers participated at the time, known for the top quality of their works on Mexican mammals, including George G. Goodwin, Emmet T. Hooper, Rollin H. Baker, Walter W. Dalquest, William B. Davis, E. Raymond Hall, Philip Hershkovitz, Robert S. Hoffmann, J. Konx Jones Jr., Sidney Anderson and Charles O. Handley Jr., just to mention some of the most productive personalities of the time, all of them from the U.S. In Mexico, some mastozoologists that were similarly important for their productivity were Bernardo Villa Ramírez and Ticul Alvarez, the helminthologist Eduardo Caballero y Caballero, and the entomologist Alfredo Barrera Marin.

From the historical point of view, there are periods characterized by a substantial increase in the knowledge of the mammals of Mexico. The first occurred between 1835 and 1840 (Figure 1), and is important for the shift in the approach to observe nature after the publication of the Sytema Naturae, Lamarck’s revolutionary ideas, the discussions of Georges Cuvier and Geoffroy Saint-Hilaire (^{Hoffmeister and Sterling 1994}), the ideological changes and the growing interest in natural sciences worldwide (^{de Gortari 1963}; ^{Guevara-Fefer 2002}). Before and during that period, the European governments sent trade or exploration vessels that included a naturalist as a crew member, with Darwin and the Beagle being the best example (^{Baker 1991}; ^{Hoffmeister and Sterling 1994}). A number of publications resulted from these exploration trips, including those by the French Alcide d’Orbigny, François Louis Paul Gervais, Isidore and Étienne Geoffroy St-Hilaire; the Swiss Henri de Saussure; the English George Robert Waterhouse; and the German Heinrich Gottlieb Ludwig Reichenbach and Eberhard August Wilhelm von Zimmermann.

In the U.S., the Civil War was followed by a period of rapid expansion of scientific development that involved government agencies and educational institutions, including the creation of scientific societies (^{Kevles et al. 1980}). There were two points of peak production, the first led mainly by the English John Edward Gray and the German Wilhelm Peters, who jointly published more than 50 % of the works of the time (1865-1875; Figure 1). Meanwhile in Mexico, scientific interest grew with the creation of the Mexican Society of Natural History in 1868, and subsequently of the Geographical Exploratory Commission (^{Guevara-Fefer 2002}; ^{Ramírez-Pulido and González-Ruiz 2006}; ^{Navarro-Sigüenza et al. 2008}), it was then that the French naturalist Alfredo Dugès performed the first work on mammalogy published in the first issue of the journal La Naturaleza (^{Dugès 1869}). Years later, in a period of U.S. Intellectual effervescence (1885-1905; Figure 1), students were trained in modern biology (^{Hoffmeister and Sterling 1994}) and the U.S. government created the Department of Agriculture in 1862, followed by the Division of Economic Ornithology and Mammalogy, which would become the U. S. Biological Survey in 1905, having its most productive phase during 1890 and 1910 (^{Schmidly and Tydeman 2016}). This and other U.S. institutions conducted many expeditions to Mexico (^{Ramírez-Pulido and González-Ruiz 2006}) and contributed a large number of Mexican mammal specimens to U.S. collections (^{Lopez-Wilchis 2006}; ^{Ramírez-Pulido and González-Ruiz 2006}), which largely served from 1885 to 1905 for primarily taxonomic studies. This was the time when the highest number of publications per year was observed (Figure 4). The journals worth mentioning for the number of works published at that time are: Proceedings of the Biological Society of Washington, Bulletin of the American Museum of Natural History, Proceedings of the Academy of Natural Sciences of Philadelphia, Proceedings of the United States National Museum, North American Fauna, The American Naturalist, Field Columbian Museum Zoological Series. The researcher with the greatest production in this period was Clinton Hart Merriam, which in addition described the highest number of taxa (^{Ramírez-Pulido and Britton 1981}) and was the architect of journals such as the Journal of Mammalogy and North American Fauna (^{Hoffmeister and Sterling 1994}; ^{Gardner 2016}) that are still published to date. Other prominent researchers for their productivity at that time are Joel Asaph Allen, Outram Bangs, Gerrit Smith Miller, Edgar Alexander Mearns, Daniel Giraud Elliot, Samuel Nicholson Rhoads. For its part, the European that published a significant number of works is Oldfield Thomas with 107 works in just two journals, Annals and Magazine of Natural History (90) and the Proceedings of the Zoological Society of London (17).

Together, Clinton Hart Merriam, Joel Asaph Allen and Oldfield Thomas published 40 % of the works of this period, most of their publications being descriptions of species based on specimens collected from multiple expeditions to Mexico. Merriam’s publications come from specimens collected by the U.S. Biological Survey, while Allen’s are based on collections by J. H. Batty, A. C. Buller, A. W. Anthony and F. M. Chapman; Oldfield Thomas’s were based on specimens collected in expeditions all over the world funded by him and his wife , especially to America (^{Hill 1990}).

The latest and most conspicuous change took place at the beginning of the 1990s, when an exponential increase in the number of publications was observed. To appreciate this change, in the 1980s an average of 47.4 works were published per year, lower than in previous decades, but from the 1990s this number increased to 70.3 to reach the maximum of 139 in 2014. To give an idea, in the past 25 years a total of 2,722 works were published, accounting for more than 40 % of the number published in the past 342 years (n = 4,010). This unprecedented growth is the result of social, economic and technological changes at a global scale at the end of the Cold War with the fall of the Berlin Wall in 1989, an event that we take as a reference rather than as a consequence. This is a transition period characterized by global economic prosperity, paralleled by significant scientific and technological advances.

In this period, universities and research centers grow and evolve; the number of researchers increases; the funding for research, although austere, is remarkable (^{Ramírez-Pulido and González-Ruiz 2006}), partly due to the interest in the conservation of the natural resources that propelled not only to mammalogy, but other branches of biology as well (^{Navarro-Siguenza et al. 2008}). The Sistema Nacional de Investigadores (National System of Researchers, SNI) was created in 1984, supplying economic funds for researchers according the category and level granted by this organization; for their part, universities and research centers approved grants and incentives for their researchers based on productivity. The SNI was key not only for stimulating researchers, but also involved a shift in the state policy to invigorate scientific research institutions (^{Perez-Tamayo 2005}; ^{Peterson et al. 2016}). The Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (National Commission for the Knowledge and Use of Biodiversity, CONABIO) was born in 1992 and Zoology received strong economic support for specific projects; in addition, catalogs and biological collections became modernized technologically, among many other supports.

The above conditions were supplemented with the scientific and technological development that allowed for a better communication and data analysis. The production and purchase of personal computers boosted, with the global expansion of environmentally friendly platforms such as Windows and Word, the massive use of the Internet and e-mail. Although many of these technologies were already known since the 1980s, it is in the 1990s when their use became extensive; in fact, ^{Birney and Choate (1994)} mention their amazement about the “electronic age” when they wrote their book with a word processor and they exchanged messages from Kansas to Minnesota, which arrived in seconds. After the 1990s there was a technological development on a larger scale. These advances facilitated office, laboratory and fieldwork, for example, with the new programs available for personal computers, ranging from statistics, Geographic Information Systems, to those that assist in solving complex phylogenies. In the laboratory, these advances involve new equipment ranging from digital calipers to complex DNA sequencing equipment; in the field, multiple remote sensing devices and camera traps, just to mention a few of the technologies that contribute to a faster, more efficient and more diverse work.

It is worth noting that any historical account of this type is necessarily incomplete, because in a global and historical context the contributing factors are varied and complex, and detailed explanations make it difficult to predict the likely progression. However, an exponential growth is observed until 2016 with no apparent asymptote that reduces scientific production (Figure 4). However production may stabilize in the next few years, precisely for the same reasons that led to their increase from the 1990s. While technological development will continue in vertiginous growth, the places for new researchers are increasingly limited; in fact, most universities and research centers increase its human resources only marginally and, in many cases, the academic staff is aging and, consequently, production is likely to slow down and, in the best of cases, will yield production rates similar to the current levels. On the other hand, post-graduate students that largely stimulate the interest to publish will be restrained by the local economic conditions and by the lecturing activities that researchers also undertake. The history of the studies on the mammals of Mexico reveals that the sources of employment and financing are factors that promote growth (^{Ramírez-Pulido and González-Ruiz 2006}), but in our view, when these components are eliminated, without aiming to raise an apocalyptic vision, the development that has taken place up to date will likely slow down.

Dissemination of knowledge. The small works involving just a few pages are usually published in journals, being the ones that stand out for their quantity and, at the same time, supporting a large part of the knowledge of the Mexican mammals. Articles are produced with increasing frequency from a number of factors, including personal convenience and interest, tradition, speed of transmission of knowledge; for being short as opposed to books, articles require relatively less work and time to get published. Although the dissemination of results by means of articles in journals is common practice since the middle of the 17th century (^{Kronick 1962}, ^{Shank 1962}) and has played a key role in the communication of science (^{Moskovkin and Serkina 2016}), this was not always the case. At that time, short communications were not fully accepted by the majority of academics; as a result, the author compiled his/her scattered contributions and edited them in book format, a common practice within societies and academies (^{Kronick 1962}, ^{Shank 1962}), which ultimately led to the genesis of journals. The oldest work we spotted in a journal was published in 1683 in Philosophical Magazine, which is one of the oldest in the world; it mentions the case of a peccary of Mexico, and we assume this refers to Dicotyles tajacu (^{Tyson 1683}). In the 18th and 19th centuries no clear distinction existed between journal, book chapter and book; sometimes books were edited a separate chapters, so in many cases the date of publication is difficult or impossible to assign, as in the case of ^{Cuvier (1820}; ¹⁸²³⁾ and ^{Alston (1879-1882)}. In addition, at that time, the difference between author and editors was not always clear; even today, the authorship of parts or whole books are wrongly attributed to the editor.

According to our analysis, up to 1820 the common practice was to disseminate information mostly through books; afterwards, the communication through articles and magazines were the dominant communication practice, with a considerable increase in the number of journals from that date. This increase is closely related to the multiplication of researchers and the urgency to report their findings, but at the same time the advancement of science brought a greater specialization; consequently, the old journals of general coverage, were divided into different scientific fields and new journals were created, mostly specialized in particular disciplines (^{Moskovkin and Serkina 2016}).

In the history of the Mexican mammalogy, the growth in the number of journals has been modest relative to the general trend, but the overall increase has been accentuated over the past 25 years (Figure 4), a period when 240 journals were created (33 % of the total). The specialized journals created after 1990 such as Acta Chiropterologica, Zootaxa, Mastozoologia Neotropical, Revista Mexicana de Mastozoología and Therya are good examples of recent journals.

Some 21 % (n = 148) journals have been published for a long time, and the majority are dissemination media of renown scientific societies, museums or universities that have been edited and distributed printed materials for more than 40 years. However, a few have remained without changes in name and subject, and most of them were forced to become modernized, adopting the new strategies of editorial standards; reception and arbitration of manuscripts; publication modalities, from printed to digital formats; frequency, with some increasing the issue of numbers per year; some changed the name to another more understandable, more general or in English, as the case of Zeitschrift für Säugetierkunde that changed to Mammalian Biology, Great Basin Naturalist to Western North American Naturalist, The Annals and Magazine of Natural History to the Journal of Natural History, Systematic Zoology who became Systematic Biology, or the Revista de Biología Tropical that was renamed as International Journal of Tropical Biology and Conservation, just to name a few; in addition, many were associated with commercial publishers (e. g. Elsevier, Springer).

However, the reality of many journals, both in Mexico and abroad, is complicated and not always continued, as some are short-living while others ultimately succumbed over time. More than 23 % (n = 165) no longer publish on mammals of Mexico, and most are no longer printed. There are many examples of this type of journals; some worth mentioning for their high productivity are University of Kansas Publications Museum of Natural History, Proceedings of the United States National Museum, Field Museum of Natural History Zoological Series, Archiv für Naturgeschichte (1912-1923), Isis von Oken (1817-1848), Abhandlungen der Königlichen Preussischen Akademie der Wissenschaften zu Berlin (1804-1900), Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin (1856-1881).

In Mexico, several journals have become extinct, some of significant historical value for the number of works published: as La Naturaleza (1869-1912), Anales del Museo Nacional de México (1877-1908), Memorias y Revista de la Sociedad Científica “Antonio Alzate” (1890-1931) and the Boletín de la Dirección de Estudios Biológicos (1916-1931). ^{Guevara-Chumacero et al. (2001)} mention that 13 Mexican journals ceased publication in 1995; four others did so at a later date, such as the Revista de la Sociedad Mexicana de Historia Natural (1938-2005?), Anales de la Escuela Nacional de Ciencias Biológicas (1939-2000?), Zoología Informa (1987-2005?) and Vertebrata Mexicana (1996-2012?).

^{Laborde (2009)} gives solid arguments for some of the reasons behind the extinction of journals; one of these -- and the most important one-- is the current lack of interest of national researchers to publish their results non-indexed journals that, according to common thinking, have with poor international visibility, particularly as regards taxonomic work. Another reason is the high cost of printing, even if editing involved a few copies and the distribution was undertaken through electronic means. In other cases, the disappearance is likely due to reasons that not exclusively economic, such as the disappearance of funding institution, the lack of attention and/or interest of the editor, because these have not been adapted to the new digital technologies, and for failure to meet the national or international index standards. Currently and in view of a global scientific communication system, journals have assummed an uncontrolled race in search of “quality”, where the strong journals get even stronger and the weaker become even more vulnerable (^{Moskovkin and Serkina 2016}). Under this principle, journal managers should develop a number of strategies to maintain the form and substance, obtain the necessary support to ensure rigorously the periodicity of publication, increase the number of articles, incorporate the citation index, improve design quality, have proofreading and secretarial support in place, but, above all, manage the impact factor and everything needed to ensure the continuity of the journal.

Impact of Journals. The Impact Factor (IF) by Thomson Reuters is one of the most widely applied bibliometric indicators in assessment processes both of scientific journals (^{Michan and Llorente-Bousquets 2010}), as in the academic staff, institutions and disciplines, although the latter has led to severe criticism in various articles around the world (see ^{Laborde 2009}); Thomson Reuters, ISI’s owner (for its acronym in English: Institute for Scientific Information) has proposed to use the IF with discretion (^{Thomson Scientific 2015}); however, as this practice has permeated so deep in evaluation exercises in our field, it is likely to remain for a long time.

The Mexican mammalogy has obtained a high FI score in the past 25 years. This is explained because works are published not only in journals specialized in mammalogy or any of the various branches of zoology, but dissemination is also made in journals of related areas that have achieved a higher average FI, such as ecology (FI > 2.5) and conservation (FI > 1.8; ^{Thomson Scientific 2015}). Although the mean IF is high, most works (76.2 %) are published in journals with a low IF, below 0.590. It is well known that the basic research disciplines such as zoology generally have a low IF just for being basic, rasing little general or global interest (^{Krell 2000}). At the same time, the average citation life is short, the recovery and dynamics of citations are comparatively low relative to high-impact or applied disciplines such as oncology, immunology and molecular biology (^{Laborde 2009}). This situation has led to proposals that raise the need to set different standards to assess basic research disciplines, such as the ones mentioned above, and for high-impact areas or specialized fields (^{Krell 2000}).

In spite of the high productivity of mammalogy in Mexico, it is likely that the impact of the discipline and of national journals, measured with the Impact Factor, does not significantly increase in the coming years. We cannot ignore that journals that publish in Spanish are less favored in the number of citations relative to English-language journals; there is a marked preference to cite the works published in foreign journals of countries like the U.S. and Europe, in contrast to those published in Latin American countries. On the other hand, mammalogy as a discipline of zoology has less impact than other areas such as ecology, conservation, and biogeography, among others, because most studies on mammals have a local or regional and importance, reaching global interest occasionally (^{Seglen 1997}; ^{Krell 2000}; ^{Shubert 2012}), as well as a widespread trend in most national researchers to prefer to publish their best contributions in international journals (^{Laborde 2009}). Unfortunately, none of these criteria addresses the scientific quality of the articles, journals or the discipline.

Influence of scientific societies. It has been mentioned that 61.5 % of the knowledge of Mexican mammals comes from 27 journals that stand out not only for the amount of works relating to mammalogy, but also because they are those with the greater permanence. These journals are published under the auspices of scientific societies, universities, museums of natural history, research centers and a minority are private. It is precisely scientific societies that have participated overwhelmingly in the knowledge of the Mexican mammalogy with over 60 % of all reviewed works (Figure 3).

The U.S. societies that have made the greatest contribution to the study of the mammals of Mexico are the American Society of Mammalogists founded in 1919, with a long tradition in Mexico (^{Birney and Choate 1994}) through two journals (Journal of Mammalogy and Mammalian Species); the Southwestern Association of Naturalists, created in 1953 and its journal, The Southwestern Naturalist, published since 1956; and the Biological Society of Washington with a long history since 1880 and with prominent members such as C. Hart Merriam and Wilfred H. Osgood (^{Aldrich 1980}), with its journal Proceedings of the Biological Society of Washington published since 1882.

In Mexico, societies have promoted the biological knowledge and gave a great impetus to the publication of works (^{Llorente-Bousquets et al. 2008}). Specialized organizations include the Asociación Mexicana de Mastozoología (Mexican Association of Mammalogy) that, in addition to the organization of congresses and grant of awards to stimulate and promote the knowledge of the mammals of Mexico (^{Lorenzo and Hernandez-Betancourt 2014}b; ^{Sanchez Herrera 2014}), has published three journals: Zacatuche, published for a few years (1987-1989); Revista Mexicana de Mastozoología (1995-2010) which was issued annually and convened a large number of researchers, institutions and subjects; the journal Therya was launched in 2010, being the youngest of all of the journals analyzed and has become the most productive of all in recent years (2010-2016), including foreign magazines, with 121 articles specifically focused of the mammals of Mexico, although its scope is broader the contribution of works conducted in Central and South America is considered.

The history of other journals has been strikingly different, for instance, the “Antonio Alzate” Scientific Society founded in 1884, which published the Memorias y Revista de la Sociedad Científica “Antonio Alzate” whose issue number 1 appeared in 1890 and the last issue was published in 1921. Only seven of all the works published in this journal regarded mammals, but are worth mentioning for the personalities that authored them, including Alfredo Dugès and Alfonso L. Herrera.

The history of other societies is full of twists and turns, for instance the Mexican Society of Natural History and its journals La Naturaleza and Revista de la Sociedad Mexicana de Historia Natural, whose history has been widely documented (^{Beltrán 1948}; ^{Gio-Argáez and Rivas-Lechuga 1993}; ^{Saldaña and Azuela 1994}, ^{Rosas-Becerril 2012}; ^{Ramírez-Pulido and González-Ruiz 2006}; Armendariz et al. in press), included detailed accounts of their history and contribution to science, published works, topics covered, as well as their evolution. The Society was created on 29 August 1868 and one of the first tasks to undertake was the creation of an information instrument through the journal La Naturaleza, which published 11 volumes including a total of 690 articles, 22 on mammals. Worth mentioning is the participation of Mexican naturalists like Alfredo Dugés, Alfonso Herrera and Manuel M. Villada, the painter José María Velasco who made remarkable contributions, as well as distinguished foreigners such as Joel A. Allen, Elliot Coues and Frederick Sumichrast. The Revista de la Sociedad Mexicana de Historia Natural was published uninterruptedly for 65 years; in spite of this, after 2005 its fate is uncertain, with various factors playing against, including fading interest and, perhaps most importantly, the lack of funding. The Society, characterized by maintaining the scientific tradition in Mexico, is one of the few such organizations that have managed to reach our days and be considered as one of the oldest in Latin America, even more than the Spanish Royal Society of Natural History, founded in 1871.