abderitid marsupials from the miocene of patagonia; an assessment of form, function, and evolution...

Abderitid Marsupials from Abderitid Marsupials from the Miocene of Patagonia; the Miocene of Patagonia; An Assessment of Form, An Assessment of Form, Function, and EvolutionFunction, and Evolution

E. R. Dumont, S. G. Strait, & R. Friscia. E. R. Dumont, S. G. Strait, & R. Friscia.

J. of Paleont. J. of Paleont. 74(6), 2000 pp. 1161-117274(6), 2000 pp. 1161-1172

Systema Naturae 2000 http://sn2000.taxSystema Naturae 2000 http://sn2000.taxonomy.nl/onomy.nl/

Taxonomy of the Taxonomy of the CaenolestoidaeCaenolestoidae○Class Mammalia

○Subclass Theriiformes ○Legion Cladotheria

○Cohort Marsupialia ○Magnorder Ameridelphia ○Order Paucituberculata ○Superfamily Caenolestoidea

◊ Family Palaeothentidae

◊ Family Abderitidae ¤ Genus Pitheculites

¤ Genus Abderites

Inca Shrew OpossumLestoros Inca

Chilean Shrew OpossumRhyncholestes raphanurus

Primary Goal of the Primary Goal of the ExperimentExperiment○ Description of the abderitids from

Pinturas Formation and the Santa Cruz Formation - What does the P4/m1 blade complex and details of molar morphology tell us about the dietary and feeding adaptations of these animals?

- Were abderitids dietary generalist or specialists? - Given the many new fossils from a long geological

sequence, what can be said about the changes of abderitids overtime?

- In light of recent work on palaeothentid caenolestoids, how do the diversity and relative abundance of abderitids and palaeothentids at these locals compare?

Collection SitesCollection Sites○ Santa Cruz Formation: Monte Observacion

and Monte Leon - Along coast of Santa Cruz providence of Argentina

- Coast alluvial plains deposits- Intermittent pyroclastic ash and gravel from volcanic uplift of the Andes Mountains- Development of some paleosols – lacked maturity

○ Pinturas Formation- Approximately 400 km inland from the Santa Cruz

Formation near Río Pinturas- More pyroclastic sediments- More paleosols - Two large erosional unconformities

○ This table lists the extant species included in this study.

○ Mean body mass and mean area are provided for species used to establish predictive regression equation between mass and tooth size.

Fossils species showed in this study. Sample size and mean were presented where body was reconstructed

The progression of the wear on th left upper and lower shearing blades of A. meridionalis

The progression of wear on left upper and lower shearing blades of Phalanger orientalis

Abderitid Feeding EcologyAbderitid Feeding Ecology○ Abderitid plagiaulacoid shearing

complex is more similar to that of the living Phalanger than to either carpolestids or multituberculates

○ Phalanger species are frugivor-omniovore:◦ Primarily fruits and seeds◦ Also leaves, blossoms, and nectar

Abderitid Diversity, Abderitid Diversity, Abundance, and EvolutionAbundance, and Evolution

○ Pinturas Formation: ◦ A. meridionalis exhibits little change in the tooth area

○ Santa Cruz Formation: ◦ An abrupt increase in lower molar size in Abderites at the base◦ A similar shift in body size just above the base of the formation in association with volance activity

Summary and ConclusionsSummary and Conclusions

○ Caenolestoid marsupials from Santacrucian Land Mammal Age of southern Argentina contained species from 8-1000 g

○ Although modern caenolestoids are faunivores, the Miocene fauna included both frugivores and faunivores, as well as mixed feeders

○ The two main groups of Santacrucian caenolestoids, abderitids and palaeothenids, differ dramatically in species diversity and inferred dietary strategies

Summary and Conclusions.. Summary and Conclusions..

○ All Miocene abderitids can be placed into four species: ◦ Abderites meridionalis◦ Abderites pristinus◦ Pithiculites minimus ◦ Pithiculites chenche

Summary and Conclusions..Summary and Conclusions..○ Abderites

◦ larger of the two groups and primarily frugivorous◦ all possess a well developed, double-bladed P4/m1 shearing complex◦ Based on comparison to Phalanger orientalis with a similar shearing mechanism, allowed initiation of the breakdown of hard or tough food◦ This unique specialization permitted a varied diet allows them to be veiwed as dietary generalists

Summary and Conclusion..Summary and Conclusion..○ Palaeothentids

◦ Consumed a mixture of plant and animal material◦ More specious: exhibited wider range in body mass and encompassed a broader range of dietary strategies◦ Lacked a highly specialized P4/m1 shearing complex◦ Constrained to food designed for their specific molar teeth allows classification for dietary specialists

Summary and ConclusionSummary and Conclusion○ Abderitids generalized morphology,

low species diversity, and stability over time allows classification as a eurytopic lineage

○ Palaeothentids generally exhibited shorter geological ranges with greater species diversity◦ Appear to be strongly affected by local environmental fluctuations◦ These combined allow for classification of stenotopic lineage