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\b[Southern <fossils> have changed the geography, timing and anatomical character of mammaliaform evolution, while exposing how strongly a northern <fossil> record had shaped earlier expectations.] Their importance is not that every southern lineage arose in the south. A dated occurrence establishes presence and a minimum age; an evolutionary origin requires an argument from <phylogenetics> and <biogeography>. Nor do modern continental outlines reproduce the connections of <Gondwana>.
A particularly consequential example is <Ambondro mahabo>, represented by a <jaw> fragment with lower <teeth> from Middle <Jurassic> Madagascar, approximately $167\pm2$ Ma. The <teeth> possess a basined heel associated with the crushing component of <tribosphenic molars>, which combine shearing and crushing in a single occlusal system. Its age extended the then-known record of this dental construction substantially backwards and challenged a simple northern origin inferred from better-sampled northern localities. The material nevertheless consists of a very restricted part of the animal, and the matching upper <dentition> was not directly observed. Assigning the entire skeleton, physiology or reproductive mode from these <teeth> would go beyond the evidence. <A Middle Jurassic mammal from Madagascar by John J. Flynn and others>[Nature 401, pp. 57–60; Ambondro lower jaw, approximately 167 ± 2 million years old]{ref}
The discovery also changed the character of the phylogenetic question. One hypothesis groups several southern forms in <Australosphenida>, associated with the ancestry of <monotremes>, and proposes that a tribosphenic-like construction arose independently of northern <Boreosphenida>, including <therians>. In that interpretation a highly functional <tooth> arrangement is <convergent evolution>, not a unique certificate of therian ancestry. A competing analysis supports a single origin of <tribospheny> and rearranges the relationships of the relevant southern taxa. <Dual origin of tribosphenic mammals by Zhe-Xi Luo and others>[Nature 409, pp. 53–57; alternative placements of southern tribosphenic mammals]{ref} <The evolution of tribospheny and the antiquity of mammalian clades by Michael O. Woodburne and others>[phylogenetic analysis supporting a single origin of tribospheny]{ref} The important lesson is not to declare one historical topology established by the striking <tooth> alone. The choice depends on which cusps and basins are judged instances of <biological homology>, character coding, inclusion of other anatomical regions, and the taxon sample. Nor does a Middle <Jurassic> tribosphenic <tooth> by itself date the split between living <marsupials> and <placental mammals>.
South American <monotreme> material further undermined the equation of present distribution with evolutionary birthplace. Early <Paleocene> <Monotrematum>, approximately 60–65 Ma, has <teeth> with affinities to the <platypus> lineage. Living <monotremes> are restricted to Australasia, but that restriction cannot be projected unchanged into the past. <First discovery of monotremes in South America by Rosendo Pascual and others>[Nature 356, pp. 704–706; Paleocene Monotrematum teeth]{ref} South America, Antarctica and Australia offered changing opportunities for connection, fragmentation and movement. A South American occurrence is compatible with a geographically extensive southern history; it does not uniquely establish the direction of dispersal or prove that <Monotrematum> was the direct ancestor of the living <platypus>. The distinction between a <crown group> and related members of its <stem group> is essential when attaching such <fossils> to divergence-time estimates.
Latest <Cretaceous> Madagascar has contributed more than isolated <tooth> surprises. The cranium of <Vintana>, around 70 Ma, supplied extensive new characters for the formerly tooth-dominated <Gondwanatheria>. Its robust feeding apparatus and unusual cranial combination permit tests of relationships and ecology that were unavailable from a few <teeth>. Yet a mosaic of familiar and unusual features is precisely the situation in which a single apparently diagnostic character can mislead. The placement of <gondwanatherians> therefore needs broad anatomical and taxonomic comparison, including other extinct groups, rather than assignment to a living order by superficial resemblance. <First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism by David W. Krause and others>[Nature 515, pp. 512–517; Vintana cranium and phylogenetic character sampling]{ref}
The approximately 66 Ma skeleton of <Adalatherium> expanded that evidence into the postcranial skeleton. It documents a relatively large, several-kilogram non-therian mammal with an unusual combination of cranial, dental, vertebral and limb features. This contradicts the caricature that all <Mesozoic> <mammaliaforms> were anatomically interchangeable tiny insect-eaters. Madagascar's long isolation provides a plausible context for its evolutionary distinctiveness, but the claim that isolation caused a particular feature remains an explanatory hypothesis. One needs comparative island and continental samples to distinguish an island effect from inherited lineage-specific <anatomy>. <Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity by David W. Krause and others>[Nature 581, pp. 421–427; Adalatherium skeleton and insularity hypothesis]{ref}
Australia's early <Eocene> <Djarthia>, approximately 55 Ma, addresses a different issue: the relationships and movement of <marsupials>. Its ankle material supports a position close to the base of <Australidelphia>, a group containing the living Australian orders and the South American <Microbiotheria>. This is stronger evidence than assuming that every small Australian <jaw> belongs inside a modern Australian family. <Australia's Oldest Marsupial Fossils and their Biogeographical Implications by Robin M. D. Beck and others>[PLoS ONE 3, e1858; Djarthia tarsals and australidelphian relationships]{ref} It is compatible with a history involving South America and Antarctica, but a branching order is not a map of a single migration. An extinct distribution can be extensive, intermediate populations can disappear, and the oldest sampled <fossil> need not occur near the place where a lineage originated. Also, the older and more inclusive <Metatheria> must not be confused with the living marsupial <crown group>.
Together these discoveries change how large-scale history is tested. First, expanding southern sampling can overturn a supposed absence that arose from collecting intensity, exposure of suitable rocks or preservation. <taphonomy> and the concentration of many early records on durable <teeth> must be modelled before comparing continental diversity. Second, new skeletons can change the inferred <phylogenetic tree>, and therefore whether a <tooth> adaptation counts as one origin or several. Third, <fossil calibration> constrains the minimum age of a lineage, with explicit uncertainty in both geological age and phylogenetic assignment. Fourth, <continental drift> changes which dispersal routes were physically plausible. Shared distributions across former <Gondwana> may reflect <vicariance>, later dispersal, or a mixture; the geological separation must be compared with a defensible lineage age rather than used as its automatic explanation.
From the <Jurassic> through the <Palaeogene>, these independent discoveries have cumulatively changed both the anatomical evidence and its interpretation. \b[They reveal a more diverse southern mammaliaform history and force explicit tests of convergence, missing data and geographic sampling, rather than replacing an assumed northern centre with an equally assumed southern centre.]
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