[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[dinosaur] Crocodylomorpha evolution and habitat shifts + filling gap between "Tomistominae" and Gavialinae




Ben Creisler
bcreisler@gmail.com


Recent papers:


Free pdf:

Eric W. Wilberg, Alan H. Turner & Christopher A. Brochu (2019)
Evolutionary structure and timing of major habitat shifts in Crocodylomorpha.
Scientific Reports 9, Article number: 514Â
DOI: 10.1038/s41598-018-36795-1
https://www.nature.com/articles/s41598-018-36795-1

Free pdf:
https://www.nature.com/articles/s41598-018-36795-1.pdf


Extant crocodylomorphs are semiaquatic ambush predators largely restricted to freshwater or estuarine environments, but the group is ancestrally terrestrial and inhabited a variety of ecosystems in the past. Despite its rich ecological history, little effort has focused on elucidating the historical pattern of ecological transitions in the group. Traditional views suggested a single shift from terrestrial to aquatic in the Early Jurassic. However, new fossil discoveries and phylogenetic analyses tend to imply a multiple-shift model. Here we estimate ancestral habitats across a comprehensive phylogeny and show at least three independent shifts from terrestrial to aquatic and numerous other habitat transitions. Neosuchians first invade freshwater habitats in the Jurassic, with up to four subsequent shifts into the marine realm. Thalattosuchians first appear in marine habitats in the Early Jurassic. Freshwater semiaquatic mahajangasuchids are derived from otherwise terrestrial notosuchians. Within nearly all marine groups, some species return to freshwater environments. Only twice have crocodylomorphs reverted from aquatic to terrestrial habitats, both within the crown group. All living non-alligatorid crocodylians have a keratinised tongue with salt-excreting glands, but the lack of osteological correlates for these adaptations complicates pinpointing their evolutionary origin or loss. Based on the pattern of transitions to the marine realm, our analysis suggests at least four independent origins of saltwater tolerance in Crocodylomorpha.


====


Masaya Iijima &Â Yoshitsugu Kobayashi (2019)
Mosaic nature in the skeleton of East Asian crocodylians fills the morphological gap between "Tomistominae" and Gavialinae.
Cladistics (advance online publication)
doi:Â https://doi.org/10.1111/cla.12372
https://onlinelibrary.wiley.com/doi/10.1111/cla.12372


Crocodylian systematics has long been confounded by conflicting hypotheses of higher level relationships--although molecular data sets strongly supported the sisterâtaxon relationship of Tomistoma and Gavialis, morphological data sets placed Gavialis as sister to all other living taxa. One of the perceived difficulties in interpreting morphological character evolution on the molecular tree is the extensive character reversal occurring in Gavialinae, the mechanism of which has yet to be explained. Here, we provide evidence of gavialineâspecific atavistic characters from East Asian "tomistomines" Penghusuchus pani and Toyotamaphimeia machikanensis. These taxa exhibit a mosaic assembly of "tomistomine" and gavialine features, which fill the gap between the two longirostrine groups. Although the parsimony analysis of morphological data (69 taxa, 254 characters) still supports the previous morphological hypothesis, the alternative tree that was forced to fit the molecular hypothesis was insignificantly (5/954 steps; 0.52%) longer than the unconstrained tree, suggesting that morphological evolution can also be interpreted on the molecular tree. Although the problem of stratigraphic gaps remains, future studies may be directed to resolving the interrelationships within Gavialoidea, a large longirostrine group of crocodylians, in the molecular tree context.

===



Virus-free. www.avg.com