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Hadrosaur tooth wear &Texas ichthyosaur in new Palaeontologia Electronica



From: Ben Creisler
bh480@scn.org

The new November 2011 issue of Palaeontologia Electronica is out with 3
Mesozoic articles that may interest the DML:
http://palaeo-electronica.org/2011_3/index.html

The pdfs are free!

Anthony R. Fiorillo (2011)
Microwear patterns on the teeth of northern high latitude hadrosaurs with
comments on microwear patterns in hadrosaurs as a function of latitude and
seasonal ecological constraints.
Palaeontologia Electronica  14(3) Article Number: 14.3.20A
http://palaeo-electronica.org/2011_3/7_fiorillo/index.html 

Abstract 
Dental microwear studies have value in qualitatively addressing patterns of
food use in both extinct and extant vertebrates. This study has examined
dental microwear patterns on the teeth of Campanian/Maastrichtian
hadrosaurs from northern Alaska to western Texas. The primary parameters
examined were the incidence of pitting and the orientation of linear
features on the occlusal surfaces of the teeth. The results of the
examination have shown similar patterns of tooth wear independent of
geographic location. Thus it may be that hadrosaurs all along western North
America were consuming food items with similar hardness. 

The dominant food consumed by hadrosaurs is considered to be conifers,
although it is unlikely that conifers constituted the entire diet of the
high latitude forms given the constraints imposed by a highly seasonal
annual cycle. Further, given the similarity of food items consumed along
such a large latitudinal gradient, combined with the deciduous nature of
the food items in Alaska, it seems likely that northern hadrosaurs reduced
their metabolic rates during the winter months, in a manner similar to many
modern terrestrial Arctic vertebrates. This reduction in metabolic rate
during the winter months may have been facilitated if these animals were
inertial homeotherms (i.e., of a low surface: mass ratio) or ectotherms
rather than full endotherms. 


==


Thomas L. Adams and Anthony R. Fiorillo (2011)
Platypterygius Huene, 1922 (Ichthyosauria, Ophthalmosauridae) from the Late
Cretaceous of Texas, USA. 
Palaeontologia Electronica  14(3) Article Number: 14.3.19A
http://palaeo-electronica.org/2011_3/1_adams/index.html

A partial ichthyosaur skeleton is described from the Grayson Marl (Late
Cretaceous: Early Cenomanian, ~97 Ma) from Tarrant County, Texas. Prior to
this discovery, the Cretaceous record of Texas ichthyosaurs consisted of
isolated vertebrae. The new specimen consists of a partial disarticulated
skull and postcranial elements including a postfrontal, parietal, quadrate,
angular, surangular, several teeth, and several vertebrae including the
atlas-axis complex, coracoid, and articulated partial forelimb. The
forelimb is diagnostic in having a zeugopodial element anterior to the
radius, rectangular phalanges, and an intermedium that does not make
contact with the humerus allowing referral to Platypterygius von Huene
1922. This occurrence is the youngest of that taxon in Texas and is
consistent with late European occurrences of the genus Platypterygius. 

===
Dale A. Winkler, Louis L. Jacobs, Y. Kobayashi, and Michael J. Polcyn (2011)
CT reconstructions and relationships of the Early Cretaceous tribosphenidan
mammal, Slaughteria eruptens (Trinity Group Texas, USA). 
Palaeontologia Electronica  14(3) Article Number: 14.3.21A
http://palaeo-electronica.org/2011_3/18_winkler/index.html
 
Among the nine taxa of tribosphenidan (boreosphenidan) mammals named from
the Early Cretaceous Trinity Group of Texas and Oklahoma, Slaughteria
eruptens provides unique information about the evolution of tooth
replacement. High-resolution CT scans and SEM imagery elucidate the jaw
anatomy of S. eruptens. Associated upper and lower dentitions from Asian
Cretaceous mammals provide the basis for a statistical model to quantify
the tooth size relationships of the often cited Trinity Group mammals
Pappotherium pattersoni and Holoclemensia texana, which were named based
upon upper molar teeth. Two groups of Trinity mammals are evident based on
lower molar size. Most large teeth are referable to H. texana. The lower m1
of S. eruptens fits neatly into the size range predicted for lower molars
of P. pattersoni, and it shares compatible tooth cusp relationships.
Slaughteria eruptens is regarded most parsimoniously as a junior synonym of
P. pattersoni. Pappotherium pattersoni thus shares the alternate premolar
replacement pattern of more primitive therian mammals and basal eutherians,
but lacks any hint of a submolariform last premolar, as typifies Eutheria.
Other small therian mammal teeth from the Trinity Group should be evaluated
as possible deciduous teeth. 



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