Probing the proboscidea: Lessons from the past.

The field of paleoneurology emerged as an independ-ent discipline in the early years of the twentieth centuryand was directed at systematically analyzing the brainsof fossil species within an evolutionary framework. Thepioneer of this effort was Tilly (Johanna Gabrielle Ottilie)Edinger (1897–1967), a German-born vertebrate paleon-tologist, who combined her interests in both paleontol-ogy and comparative neuroanatomy to add a newdimension to evolutionary studies of the brain (Buch-holtz and Seyfarth, 1999, 2001). Her father, LudwigEdinger (1855–1917), was a prominent and pioneeringcomparative neuroanatomist and served as an editorialboard member of the Journal of Comparative Neurology(JCN) beginning with its eighth volume (Herrick, 1954).The 25th volume of JCN was dedicated to LudwigEdinger in honor of his 60th birthday (April 13, 1915),and his brain was the object of study for a 1950 JCNreport (Riese and Goldstein, 1950).Paleoneurologists generally depend on endocasts tostudy the external features of brains because brains them-selves do not fossilize (Edinger, 1927). Endocasts aremade by creating a cast of the interior surface of the skullto reveal external features that left impressions on thebones. Natural endocasts occur when the cranial cavity ofa deceased animal is filled with sediment that is solidifiedby calciferous solutions (Kochetkova, 1978). Prior to the1920s, endocasts had been documented for a variety ofspecies, but these existed as independent observationsthat were purely descriptive. Tilly Edinger compiled allaccounts of natural brain casts that were distributedthroughout the paleontology literature and compiled theminto one volume (Edinger, 1929). Edinger’s unique contri-bution to the study of brain evolution was to add a“longitudinal” view wherein changes in patterns and struc-ture could be reconstructed through evolutionary time(Edinger, 1949). This is in contrast to the necessarily“horizontal”’ comparisons that are made when studyingneuroanatomical features of extant species. She appliedher methods to well-represented fossil sequences, includ-ing those of reptiles (Edinger, 1955b), amphibians (Romerand Edinger, 1942), bats (Edinger, 1926), cetaceans(Edinger, 1955a), and sirenians (Edinger, 1933, 1948),among others. Through her work, Edinger discountedsome prevalent ideas of her time, including the notion thatan increase in brain size was necessary for a species toavoid extinction (Edinger, 1962), and she also developed aconcept of mosaic evolution, that changes in one func-tional system, in this case the central nervous system,were independent of changes in other systems, includingthe postcranial skeleton (Edinger, 1958). Edinger changedour approaches and understanding of comparative neurol-ogy by providing the important additional element of evolu-tionary time with recognition of the sequence of changesthat led to modern species.JCN has had a tradition of presenting the findingsfrom paleoneurological research, including one articlefrom Tilly Edinger (Romer and Edinger, 1942). Theearliest endocast articles in JCN were reporting featuresof the brains of early cetaceans, the archeocetes (Fig.1; Elliot Smith, 1903), and fossil fish, amphibian, andreptile species (Case, 1921, 1928; Moodie, 1915a,b,1920). In the same years, many studies on the endo-cranial and brain anatomy of fossil mammals, includinga hominin, in comparison with their extant relatives(Black, 1915, 1920; Dempster, 1935; Moodie, 1922)were published in JCN, as well as, in more recent years,some of the earliest evolutionary interpretations ofstructure in the context of systems neuroscience in thepioneering work of Leonard Radinsky (Radinsky, 1968),which recently culminated in a review of olfaction inthe evolution of the mammalian cerebral cortex (Roweand Shepherd, 2015).Although natural endocasts are rare, it is almostunheard of to have a naturally preserved brain (i.e., mum-mified) with external and internal structures maintained(but see Papageorgopoulou et al., 2010, for an accountof a remarkably preserved human brain). Our Journal is