Size trends in Holarctic anchitherines (Mammalia, Equidae)

1991 ◽  
Vol 65 (1) ◽  
pp. 147-159 ◽  
Author(s):  
Ann Forsten
Keyword(s):  
Climatic Change ◽  
Late Miocene ◽  
North American ◽  
Size Increase

Size increase in European Miocene Anchitherium was described early in the century. Increase in size, particularly of the teeth, was common to the middle and late Miocene Eurasian Anchitherium and North American Hypohippus, including Megahippus, over the whole Holarctic range of these anchitherines. In this paper, size trends are described and interpreted against the background of simultaneous climatic change.

Spatiotemporal palaeodiversity patterns of modern crocodiles (Crocodyliformes: Eusuchia)

2019 ◽  
Vol 189 (2) ◽  
pp. 635-656 ◽  
Author(s):  
Ane De Celis ◽  
Iván Narváez ◽  
Francisco Ortega
Keyword(s):  
South America ◽  
Least Squares ◽  
Late Miocene ◽  
North American ◽  
Fossil Record ◽  
Generalized Least Squares ◽  
Global Scale ◽  
Biotic Factors ◽  
Species Dynamics ◽  
Over Time

Abstract Eusuchia is a crocodyliform clade with a rich and diverse fossil record dating back to the Mesozoic. There are several recent studies that analyse crocodyliform palaeodiversity over time, but none of them focuses exclusively on eusuchians. Thus, we estimated subsampled eusuchian palaeodiversity species dynamics over time not only at a global scale, but also by continents and main crocodylian lineages (Alligatoroidea, Crocodyloidea and Gavialoidea). These estimates reveal complex spatiotemporal palaeodiversity patterns, in which two maxima can be detected: the first during the Palaeocene and the second, which is also the biggest, in the middle-late Miocene. The Palaeocene shift is related to a North American alligatoroid diversification, whereas the middle–late Miocene maximum is related to a diversification of the three main Crocodylia lineages in Gondwanan land masses, but especially in South America. Additionally, a model-based study using generalized least squares was carried out to analyse the relationships between different abiotic and sampling proxies and eusuchian palaeodiversity. The results show that palaeotemperature is the most important factor amongst the analysed proxies, in accordance with previous studies. However, the results suggest that, along with palaeotemperature, other abiotic and/or biotic factors might also be driving eusuchian palaeodiversity dynamics.

scholarly journals Patterns of evolution in North American Neogene mammals

1992 ◽  
Vol 6 ◽  
pp. 146-146
Author(s):  
Louis Jacobs ◽  
Christine Janis
Keyword(s):  
Late Miocene ◽  
North American ◽  
Morphological Changes ◽  
Ground Squirrels ◽  
Deer Mice ◽  
Leg Length ◽  
Vegetational Change ◽  
Late Neogene ◽  
Tree Squirrels

The Neogene of North American represents a time of climatic change from an initially warm, non-arid climate to one with the development of increasing aridity, with warming temperatures through the early part and fluctuating (but basically cooler) temperatures through the later part. This reflects the classic story of a vegetational change from woodland to savanna and eventually to prairie. Note that the transition to true savanna in the Late Miocene was considerably earlier than the first savannas in the Pliocene of the Old World. The evolutionary trends in mammals reflect these climactic and vegetational changes.Some general broad trends are as follows: the replacement of terrestrial and subfossorial moles and geomyid rodents with more specialized fossorial ones; a decrease in the diversity of brachydont rodents and an increase in the diversity of hypsodont ones (including saltatorial forms), and a late Neogene diversification of microtines and deer mice; a decline in the diversity of tree squirrels and terrestrial beavers, and an increase in diversity of ground squirrels and aquatic beavers; the replacement of carnivores belong to more archaic families by more modern types; taxa and an increase in body size, leg length, and hypsodonty in most ungulate taxa, including oreodonts, protoceratids, camelids, antilocaprids, rhinos and equine horses although a couple of taxa show an apparent reversal of these trends: dromomerycids (cervoids) and some anchitherine horses show other morphological changes that suggest progressively more woodland-adapted (rather than savanna-adapted) forms. Tapirs and (to a lesser extent) peccaries seem little affected by the Neogene changes, and persist until the Recent.The Neogene was also punctuated by immigration events (primarily from Asia) and extinctions. The start of the Neogene shows surprisingly little change, with many Paleogene “holdovers”: some new forms appear as either the result of evolution in situ (e.g. equine horses and osteoborine dogs) or as immigrants (e.g. chalicotheres and hemicyonine “dog bears”). The initial major immigrations are during the late Early Miocene, marked by the Asian appearances of true felids (replacing the “false saber-tooths” or nimravids), pecoran ruminants (replacing the hypertragulids), more derived rhinos (replacing the diceratherine rhinos), neomustelids and procyonids. Archaic suoids such as anthracotheres and entelodonts become extinct at this time, and only the more derived ticholeptine oreodonts survive this period. The start of the Middle Miocene is notable for the appearance of proboscideans and deer mice. The Late Miocene sees the decline and eventual disappearance of hedgehogs, archaic carnivores (hemicyonine bears and amphicyonids), most browsing ungulates (oreodonts, protoceratids, many camelids, anchitherine horses, dromomerycids, merycodontine antilocaprids, hornless ruminants, chalicotheres, bunodont gomphotheres), and rhinos. New taxa appearing including ursine bears (immigrants), oversized camels and more derived gomphotheres (in situ evolution). The Pliocene marks a new wave of immigration: microtines, hyenas, true saber-tooths, and cervids come in from Asia; ground sloths (two families appearing in the Late Miocene), glyptodonts, armadillos and capybaras come in from South America. Most mammals that survived the end Miocene extinctions persist, but for many of them (such as horses, camels and antilocaprids) the generic diversity is greatly reduced.

Chronostratigraphy of glaciations and permafrost episodes in the Cordillera of western North America

1994 ◽  
Vol 18 (3) ◽  
pp. 366-395 ◽  
Author(s):  
Stuart A. Harris
Keyword(s):  
North America ◽  
Climatic Change ◽  
Sierra Nevada ◽  
Late Miocene ◽  
Complete Sequence ◽  
Lava Flows ◽  
Radiometric Dating ◽  
Western North America ◽  
Quaternary Period ◽  
Cold Events

Glaciations in the Cordillera of western North America began during the Late Miocene in the St Elias Range and coastal ranges near Anchorage, Alaska. Radiometric dating of the tephra and lava flows intercalated in the succession of older tills, loesses and outwash deposits permits the reconstruction of the probable early glacial sequence along the Cordillera. No one site shows the complete sequence, but the available data suggest synchroneity of the major glacial events throughout the region. The first evidence for cold conditions at low elevations at midlatitudes is from 3.5 Ma BP. By 2.8 Ma, alpine glaciations may have occurred in the Sierra Nevada and ice wedges had formed in bedrock near Fairbanks, Alaska. Three more major glaciations complete with contemporary periglacial and permafrost landforms had occurred by 1.65 Ma, while at least six more major cold events can be recognized during the Quaternary period. Once again, expansion of permafrost conditions occurred during each event and forms an integral part of the evidence for climatic change.

scholarly journals Evolution of the species–rich Cape flora

2004 ◽  
Vol 359 (1450) ◽  
pp. 1623-1632 ◽  
Author(s):  
H. P. Linder ◽  
C. R. Hardy
Keyword(s):  
Phylogenetic Analysis ◽  
Species Diversity ◽  
Climatic Change ◽  
Plant Species ◽  
Late Miocene ◽  
Cape Floristic Region ◽  
The Third ◽  
Modern Species ◽  
Very High ◽  
General Explanation

The Cape Floristic Region (‘fynbos biome’) has very high levels of plant species diversity and endemism. Much of this diversity is concentrated in a relatively small number of clades centered in the region (Cape clades), and these form a vegetation called ‘fynbos’. The general explanation for the origin of this diversity is that much of it evolved in the Pliocene and Late Miocene in response to progressive aridification. We present a phylogenetic analysis of an almost complete species sample of the largest clade of Restionaceae, the third largest Cape clade. This indicates that the radiation of the Restionaceae started between 20 and 42 Myr ago, and since then there were no, or at most gradual, changes in the speciation rate in this clade. For seven other clades, the estimated starting dates for their radiation ranges from 7 to 20 Myr ago. Combining the radiation patterns for these clades shows that ca . 15% of the modern species evolved during the Pleistocene, and almost 40% since the beginning of the Pliocene. We suggest that these clades might have radiated in response to the fynbos vegetation increasing its extent in the Cape as a result of climatic change.

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