Browsing by Autor "Bruce J. Shockey"

Now showing 1 - 7 of 7

A new proterotheriid (Mammalia, Litopterna) from the Salla Beds of Bolivia (upper Oligocene): phylogeny and litoptern patellar pit knee locks
(Taylor & Francis, 2022) Bruce J. Shockey; Emily White; Federico Anaya; Andrew J. McGrath
The Salla Beds of Bolivia reveal a rich, late Oligocene (Deseadan, South American Land Mammal “Age”) fauna composed of at least 50 mammalian species. Many taxa (e.g., rodents and typotherian notoungulates) are represented by dozens to hundreds of specimens. Litopterns are much less common but are represented by one macraucheniid and two adianthid species. Until now, only fragmentary postcrania of proterotheriids have been described from Salla. The recent discovery of a maxillary fragment with two molars, examination of previously recovered mandibular fragments, and a phylogenetic analysis, allow us to recognize Promylophis cifellii gen. et sp. nov. It is characterized by small size, absence of a metaconule on M1–2, and lower molars with a short “paracristid” and reduced or absent “paraconid.” Postcranial elements referred to cf. P. cifellii resemble geologically younger (e.g., Miocene) proterotheriids by way of anatomically tridactyl, but functionally monodactyl pes, and distal femora with a supra-trochlear fossa that forms a “patellar pit” that appears to function as a passive stay apparatus for the knee joint. Such a mechanical means of diverting forces from muscle to bone and sinew could save biologically significant amounts of metabolic energy in long-standing animals.
Analysis of function in the absence of extant functional homologues: a case study using mesotheriid notoungulates (Mammalia)
(Cambridge University Press, 2007) Bruce J. Shockey; Darin A. Croft; Federico Anaya
We use two approaches to test hypotheses regarding function in a group of extinct mammals (Family Mesotheriidae, Order Notoungulata) that lack any close extant relatives: a principle-derived paradigm method and empirically derived analog method. Metric and discrete morphological traits of mesotheriid postcranial elements are found to be consistent with the morphology predicted by a modified version of Hildebrand's paradigm for scratch diggers. Ratios of in-force to out-force lever arms based on skeletal elements indicate that the mesotheriids examined had limbs modified for high out-forces (i.e., they were “low geared”), consistent with the digging hypothesis. Other mesotheriid characters, such as cleft ungual phalanges, a curved olecranon, and a highly modified pelvis (with extra vertebrae incorporated into the sacrum and fusion between the ischium and the axial skeleton) are regarded as being functionally significant for digging and also occur in a variety of extant diggers. Analog methods indicate that mesotheriids share numerous traits common to a variety of extant diggers. Principal component analyses of postcranial elements indicate that mesotheriids consistently share morphometric space with larger extant fossorial mammals: aardvark, anteaters, wombats, and badger. Likewise, discriminant function analyses categorized mesotheriids as fossorial, though imperfectly analogous to the extant diggers analyzed. Thus, both theory-driven and empirically derived methods of estimating function in these extinct taxa support a digging hypothesis for the mesotheriids examined. Adaptations for digging in both the forelimb and sacropelvic functional complexes of mesotheriids provide independent support for the fossorial hypothesis.
Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands/Savannas in South America
(Springer Science+Business Media, 2010) Bruce J. Shockey; Federico Anaya
<i>Pyrotherium macfaddeni</i>, sp. nov. (late Oligocene, Bolivia) and the pedal morphology of pyrotheres
(Taylor & Francis, 2004) Bruce J. Shockey; Federico Anaya Daza
ABSTRACT The common pyrothere of Salla, Bolivia (Deseadan, late Oligocene) is described as a new species, Pyrotherium macfaddeni. It is distinguished by its small size (linear dimensions but two-thirds those of Pyrotherium romeroi) and pi-shaped upper premolare. Recovery at Salla of the first known calcaneum of Pyrotherium permits the description and analysis of the proximal tarsus. It is distinctive by the pronounced dorsoventral compression of the calcaneal tuber and similar flattening of the astragalar trochlea, concavity of the ectal facet of the calcaneum, and extreme reduction of contact between the calcaneum and the cuboid. These derived characters were not seen in any other mammal examined except the embrifhopod Arsinoitherium from the Tertiary of Africa. Whether this is due to common ancestry or the unusual mode of locomotion used by these animals (graviportal and plantigrade) remains to be seen. This more complete study of the tarsus of Pyrotherium fails to support the proposed relationship of pyrotheres with the Xenungulata.
Palaeothentid Marsupials of the Salla Beds of Bolivia (Late Oligocene): Two New Species and Insights into the Post-Eocene Radiation of Palaeothentoids
(Springer Science+Business Media, 2015) Ascánio D. Rincón; Bruce J. Shockey; Federico Anaya; Andrés Solórzano
Postcranial osteology and functional morphology of the Litopterna of Salla, Bolivia (Late Oligocene)
(Taylor & Francis, 1999) Bruce J. Shockey
ABSTRACT Postcranial remains of litopterns of Salla, Bolivia are described and discussed in terms of their functional morphology. These elements are not associated with dental remains, but can be confidently referred to the family Macraucheniidae or Proterotheriidae. The macraucheniids (cf. Coniopternium spp.) have transversely stable joints indicating their specialization for parasagittal movements at these articulations (e.g., the humeral-antebrachial, cruxastragalar, and astragalonavicular joints). A profound suprapatellar fossa ("patellar pit") of the femur is interpreted as having provided a place in which the patella could have become lodged, thus locking the knee-joint in the extended position. Facets on the cuboid and astragalus and their articulation in life position indicate that cuboastragular contact was present. This contact was slight, however, and may have occurred only during the loaded part of the locomotor cycle. A partial pes of a proterotheriid represents the first unambiguous evidence of this group at Salla and are the first Deseadan postcranial elements confidently referred to the Proterotheriinae. These elements indicate that the animal was tridactyl, but functionally monodactyl to the same degree as all Santacrucian proterotheriid genera except the "hypermonodactyl" Thoatherium. These litopterns and those to which they were compared record a great diversity of tarsal arrangements, such that simple characterizations of litoptern tarsals as being serial and "inadaptive" are unwarranted.
Postcranial Osteology of Mammals from Salla, Bolivia (Late Oligocene): Form, Function, and Phylogenetic Implications
(2008) Bruce J. Shockey; Federico Anaya