Review of the Cretaceous avian diversity of Antarctica:a changing scenario for the evolution of early Neornithine birds

The worldwide record of Cretaceous Neornithes and Neornithine-like birds is both controversial and poorly understood.However,in recent years,the Antarctic continent has yielded a substantial number of Maastrichtian avian specimens,contributing significantly to our understanding of the early evolution of this group.Simultaneously,the keen interest and collaborative efforts of various paleornithologists have resulted in a wealth of knowledge,which we have thoroughly reviewed,updated,and discussed in the context of recent discoveries.

Latitudinal pattern of the thermal sensitivity of running speed in the endemic lizard Liolaemus multimaculatus

Physiological performance in lizards may be affected by climate across latitudinal or altitudinal gradients.In the coastal dune barriers in central-eastern Argentina,the annual maximum environmental temperature decreases up to 2℃ from low to high latitudes,while the mean relative humidity of the air decreases from 50%to 25%.Liolaemus multimaculatus,a lizard in the family Liolaemidae,is restricted to these coastal dunes.We investigated the locomotor performance of the species at 6 different sites distributed throughout its range in these dune barriers.We inquired whether locomotor performance metrics were sensitive to the thermal regime attributable to latitude.The thermal performance breadth increased from 7%to 82%with latitude,due to a decrease in its critical thermal minimum of up to 5℃ at higher latitudes.Lizards from high latitude sites showed a thermal optimum,that is,the body temperature at which maximum speed is achieved,up to 4℃lower than that of lizards from the low latitude.At relatively low temperatures,the maximum running speed of high-latitude individuals was faster than that of low-latitude ones.Thermal parameters of locomotor performance were labile,decreasing as a function of latitude.These results show populations of L.multimaculatus adjust thermal physiology to cope with local climatic variations.This suggests that thermal sensitivity responds to the magnitude of latitudinal fluctuations in environmental temperature.

When a general morphology allows many habitat uses

During the last decades the study of functional morphology received more attention incorporating more detailed data corresponding to the internal anatomy that together contribute for a better understanding of the functional basis in locomotion.Here we focus on 2 lizard families,Tropiduridae and Liolaemidae,and use information re­lated to muscle-tendinous and external morphology traits of hind legs.We investigate whether the value of the traits analyzed tend to exhibit a reduced phenotypic variation produced by stabilizing selection,and whether species showing specialization in their habitat use will also exhibit special morphological features related to it.As a result,we identified that evolution of hind limb traits is mainly explained by the Ornstein-Uhlenbeck mod­el,suggesting stabilizing selection.Liolaemids and tropidurids show clear ecomorphological trends in the vari­ables considered,with sand lizards presenting the most specialized morphological traits.Some ecomorphologi­cal trends differ between the 2 lineages,and traits of internal morphology tend to be more flexible than those of external morphology,restricting the ability to identify ecomorphs shared between these 2 lineages.Conservative traits of external morphology likely explain such restriction,as ecomorphs have been historically defined in oth­er lizard clades based on variation of external morphology.

Are the number and size of scales in Liolaemus lizards driven by climate?

Ectothermic vertebrates are sensitive to thermal fluctuations in the environments where they occur.To buffer these fluctuations,ectotherms use different strategies,including the integument,which is a barrier that minimizes temperature exchange between the inner body and the surrounding air.In lizards,this barrier is constituted by keratinized scales of variable size,shape and texture,and its main function is protection,water loss avoidance and thermoregulation.The size of scales in lizards has been proposed to vary in relation to climatic gradients;however,it has also been observed that in some groups of Iguanian lizards it could be related to phylogeny.Thus,here,we studied the area and number of scales(dorsal and ventral)of 60 species of Liolaemus lizards distributed in a broad latitudinal and altitudinal gradient to determine the nature of the variation of the scales with climate,and found that the number and size of scales are related to climatic variables,such as temperature and geographical variables as altitude.The evolutionary process that best explained how these morphological variables evolved was the Ornstein–Uhlenbeck model.The number of scales seemed to be related to common ancestry,whereas dorsal and ventral scale areas seemed to vary as a consequence of ecological traits.In fact,the ventral area is less exposed to climate conditions such as ultraviolet radiation or wind and is,thus,under less pressure to change in response to alterations in external conditions.It is possible that scale ornamentation,such as keels and granulosity,may bring some more information in this regard.