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[dinosaur] Crocodyliform cranial disparity + temnospondyl eye and jaw muscles + cranial fenestration in birds + more

Ben Creisler

Some recent (and not so recent) non-dino papers that may be of interest:

Free pdf:

Eric W. Wilberg (2017)
Investigating patterns of crocodyliform cranial disparity through the Mesozoic and Cenozoic. 
Zoological Journal of the Linnean Society (advance online publication) zlw027
DOI: https://doi.org/10.1093/zoolinnean/zlw027

Crocodyliforms are traditionally considered a morphologically conservative group, retaining a similar body plan and small range of cranial morphologies throughout their evolutionary history. This qualitative assessment ignores many extinct highly divergent groups. Here the author employs geometric morphometric methods to characterize the crania of 131 extant and extinct crocodyliforms and track changes in disparity and morphospace occupation through time (Early Jurassic–Recent). The data were phylogenetically corrected using a novel method based on squared change parsimony. Cranial disparity peaked in the Late Cretaceous followed by a dramatic decline into the earliest Paleogene. This decline matches in neither timing nor magnitude with changes in diversity, and is not directly related to the end-Cretaceous mass extinction. The decline was partly driven by the evacuation of the region of morphospace exemplified by a short, narrow snout – a morphotype never explored by crown-group crocodylians. The Cretaceous peak in range-based disparity metrics is largely driven by the radiation of the bizarre notosuchians and their exclusion from the data set brings Cretaceous disparity closer in-line with Jurassic and Cenozoic levels. However, the peak remains in variance-based metrics, suggesting the high average dissimilarity between forms during this time period is not driven by this clade alone. Modern crocodylian disparity is low relative to Cretaceous levels, but is similar to Jurassic levels.


Holger Petermann and Jacques A. Gauthier (2017)
Osteohistology and sequence of suture fusion reveal complex environmentally influenced growth in the teiid lizard Aspidoscelis tigris—Implications for fossil squamates.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
doi: http://dx.doi.org/10.1016/j.palaeo.2017.02.034


Age and size in Aspidoscelis tigris are not strongly correlated.
Growth in the first two seasons strongly correlates with final size.
Temperature positively influences growth in the first season, precipitation has a negative influence.
Suture fusion correlates with size, not with age.
Sutures and growth record combined allow for accurate life-history reconstruction.


The interaction between an organism and its environment influences its growth and differentiation during ontogeny. For extinct species in particular, the record of this interaction can be accessed through osteohistology. Such studies have, however, historically focused largely on dinosaurs and mammals, leaving the rest of Amniota understudied. Although accounting for nearly 40% of extant amniote diversity, Squamata (hereafter, “lizards” including snakes and amphisbaenians) is conspicuous for lack of osteohistological study. Here, a large-scale osteohistological study of the growth record of 29 individuals of the cnemidophorine teiid lizard Aspidoscelis tigris—Tiger whiptail—sheds light on the growth patterns not only among individuals, but also between populations. We observed that size and age are not tightly coupled in A. tigris. Rather, growth in this lizard may be influenced by genetically determined growth strategies suited to the highly variable arid environments they inhabit, in conjunction with the environment in which individuals hatch. Hatchlings, which exhibit the highest growth rates, have the smallest home ranges and thus habitat variables such as the density of food and competitors could strongly influence final size. However, smaller size seems to favor longevity in A. tigris as the oldest individuals are below the median snout-vent length for the species. Surprisingly, ‘adult’ ontogenetic fusions in the skeleton did not correlate closely with age. Instead, they strongly correlate with size. Although a terminal asymptotic size appears fixed within a narrow size range, the rate at which they achieve it is highly variable. Our study reveals a complex organism-environment interaction governing growth and differentiation in Aspidoscelis tigris, that has potential implications for the interpretation of osteohistological data in fossil taxa.


Florian Witzmann and Ingmar Werneburg (2017)
The palatal interpterygoid vacuities of temnospondyls and the implications for the associated eye- and jaw musculature.
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.23582

A diagnostic feature of temnospondyls is the presence of an open palate with large interpterygoid vacuities, unlike the closed palate of most other early tetrapods, in which the vacuities are either slit-like or completely absent. Attachment sites on neurocranium and palatal bones in temnospondyls allow the reconstruction of a powerful m. retractor bulbi and a large, sheet-like m. levator bulbi that formed the elastic floor of the orbit. This muscle arrangement indicates that temnospondyls were able to retract the eyeballs through the interpterygoid vacuities into the buccal cavity, like extant frogs and salamanders. In contrast, attachment sites on palate and neurocranium suggest a rather sauropsid-like arrangement of these muscles in stem-tetrapods and stem-amniotes. However, the anteriorly enlarged, huge interpterygoid vacuities of long-snouted stereospondyls suggest that eye retraction was not the only function of the vacuities here, since the eye-muscles filled only the posterior part of the vacuities. We propose an association of the vacuities in temnospondyls with a long, preorbital part of the m. adductor mandibulae internus (AMIa). The trochlea-like, anterior edge of the adductor chamber suggests that a tendon of the AMIa was redirected in an anteromedial direction in the preorbital skull and dorsal to the pterygoids. This tendon then unfolded into a wide aponeurosis bearing the flattened AMIa that filled almost the complete interpterygoid vacuities anterior to the orbits. Our muscle reconstructions permit comprehensive insights to the comparative soft tissue anatomy of early tetrapods and provide the basis for a biomechanic analysis of biting performances in the future. 


Free pdf:

Julia A. Schultz, Ulrich Zeller and Zhe-Xi Luo (2017)
Inner ear labyrinth anatomy of monotremes and implications for mammalian inner ear evolution.
Journal of Morphology  278(2): 236–263, 
DOI: 10.1002/jmor.20632

The monophyletic clade Monotremata branches early from the rest of the mammalian crown group in the Jurassic and members of this clade retain many ancestral mammalian traits. Thus, accurate and detailed anatomical descriptions of this group can offer unique insight into the early evolutionary history of Mammalia. In this study, we examine the inner ear anatomy of two extant monotremes, Ornithorhynchus anatinus and Tachyglossus aculeatus, with the primary goals of elucidating the ancestral mammalian ear morphology and resolving inconsistencies found within previous descriptive literature. We use histological serial sections and high-resolution microcomputed tomography (µCT) for correlating soft tissue features of the vestibule and cochlea to the osseous labyrinth endocast. We found that in both monotremes the scala tympani coils to a lesser degree than scala vestibuli and scala media, although all three scalae show an apical coil inside the osseous cochlear tube. The helicotrema (conduit between scala tympani and scala vestibuli) is in subapical position, and the cochlear and lagenar ganglia and their associated nerve fibers are not enclosed by bone. In comparison, in extant therian mammals (i.e., marsupials and placentals) the helicotrema is located at the apex of the osseous cochlear canal, the three scalae coil to the same degree and the cochlear ganglion is enclosed by the primary bony lamina. Whether the lagenar ganglion is lost in therian mammals or integrated into the cochlear ganglion is still debated. The presence of a sensory lagenar macula at the apex of the membranous cochlear duct, innervated by a separate lagenar nerve and ganglion is a plesiomorphic condition of amniotes that monotremes share. A separate osseous lagenar canaliculus for the lagenar nerve, and the coiling of the distended lagenar sac at the end of the cochlear duct are autapomorphies of monotremes. Based on our findings we hypothesize that the ancestral inner ear of stem mammaliaforms is characterized by a straight or slightly curved osseous cochlear canal, a lagenar macula, lagenar nerve fibers separated from a larger bundle of cochlear nerve fibers, the presence of an organ of Corti and an intra-otic cochlear ganglion suspended by membranous connective tissue. Among the major Mesozoic clades of crown mammals, cladotherians and gondwanatherians most likely acquired a fully functioning organ of Corti but lost the sensory lagenar macula, like extant therians. However, Mesozoic spalacotherioids, multituberculates and eutriconodonts likely retained the mammaliaform condition.


Sander W.S. Gussekloo, Michael A. Berthaume, Daniel R. Pulaski, Irene Westbroek, Jan H. Waarsing, Robin Heinen, Ian R. Grosse and Elizabeth R. Dumont (2017)

Functional and evolutionary consequences of cranial fenestration in birds.

Evolution (advance online publication)

DOI: 10.1111/evo.13210



Ostrich-like birds (Palaeognathae) show very little taxonomic diversity while their sister taxon (Neognathae) contains roughly 10000 species. The main anatomical differences between the two taxa are in the crania. Palaeognaths lack an element in the bill called the lateral bar that is present in both ancestral theropods and modern neognaths, have thin zones in the bones of the bill, and robust bony elements on the ventral surface of their crania. Here we use a combination of modelling and developmental experiments to investigate the processes that might have led to these differences. Engineering-based finite element analyses indicate that removing the lateral bars from a neognath increases mechanical stress in the upper bill and the ventral elements of the skull, regions that are either more robust or more flexible in palaeognaths. Surgically removing the lateral bar from neognath hatchlings led to similar changes. These results indicate that the lateral bar is load-bearing and suggest that this function was transferred to other bony elements when it was lost in palaeognaths. It is possible that the loss of the load-bearing lateral bar might have constrained diversification of skull morphology in palaeognaths and thus limited taxonomic diversity within the group.


Raymond R. Rogers, Matthew T. Carrano, Kristina A. Curry Rogers, Magaly Perez & Anik K. Regan (2017)

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana.

Paleobiology (advance online publication)

DOI: https://doi.org/10.1017/pab.2016.37



Vertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.