#crocodyliformes

[dinoserious]

kaprosuchus comm!

[alphynix]

Metriorhynchids were a group of fully marine crocodyliforms known from the mid-Jurassic to the early Cretaceous of Europe and the Americas. They were the most aquatic-adapted of all known archosaurs, with streamlined bodies, smooth scaleless skin, small front flippers, larger hind flippers, and shark-like tail flukes. They may also have been endothermic, and might even have given live birth at sea rather than laying eggs.

Rhacheosaurus gracilis here was a metriorhynchid that lived in warm shallow waters around what is now Germany during the late Jurassic, about 150 million years ago. Around 1.5m long (~5'), its long narrow snout lined with delicate pointed teeth suggests it fed on small soft-bodied prey, a niche partitioning specialization that allowed it to coexist with several other metriorhynchid species in the same habitat.

Unlike most other marine reptiles metriorhynchids didn't have particularly retracted nostrils, which may have had a limiting effect on their efficiency as sustained swimmers since higher-set nostrils make it much easier to breathe without having to lift the whole head above the surface. The lack of such an adaptation in this group may be due to their ancestors having a single nasal opening formed entirely within the premaxilla bones at the tip of the snout, uniquely limiting how far it could easily shift backwards – other marine reptiles had nostrils bound by the edges of multiple different bones, giving them much more flexibility to move the openings around.

(By the early Cretaceous a close relative of Rhacheosaurus did actually evolve nostrils bound by both the premaxilla and the maxilla, and appeared to have started more significant retraction, but unfortunately this only happened shortly before the group's extinction.)

Metriorhynchids also had well-developed salt glands in front of their eyes, but the large sinuses that accommodated these glands may have made their skulls ill-suited to deep diving, being more susceptible to serious damage from pressure changes and restricting their swimming to near-surface waters only.

Preserved skin impressions in some metriorhynchid fossils show several unusual "irregularities", including curl shapes, small bumps, and cratering. It's unknown what exactly caused these marks, but they may represent scarring from external parasites such as lampreys and barnacles.

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References:

Andrade, Marco BD, and Mark T. Young. "High diversity of thalattosuchian crocodylians and the niche partition in the Solnhofen Sea." 56th Symposium of Vertebrate Palaeontology and Comparative Anatomy, 2008. https://svpca.org/years/2008_dublin/abstracts.pdf#page=14

Séon, Nicolas, et al. "Thermophysiologies of Jurassic marine crocodylomorphs inferred from the oxygen isotope composition of their tooth apatite." Philosophical Transactions of the Royal Society B 375.1793 (2020): 20190139. https://doi.org/10.1098/rstb.2019.0139

Spindler, Frederik. "Live Birth in a Jurassic Marine Crocodile." Abstracts of the 90th Annual Meeting of the Paläontologische Gesellschaft, 2019. https://www.palaeontologie.geowissenschaften.uni-muenchen.de/pdfs/palges2019_abstracts.pdf#page=141

Spindler, Frederik, et al. "The integument of pelagic crocodylomorphs (Thalattosuchia: Metriorhynchidae)" Palaeontologia Electronica 24.2 (2021): a25. https://doi.org/10.26879/1099

Young, Mark T., et al. "Convergent evolution and possible constraint in the posterodorsal retraction of the external nares in pelagic crocodylomorphs." Zoological Journal of the Linnean Society 189.2 (2020): 494-520. https://doi.org/10.1093/zoolinnean/zlaa021

Young, Mark T., et al. "Skull sinuses precluded extinct crocodile relatives from cetacean-style deep diving as they transitioned from land to sea." Royal Society Open Science 11.10 (2024): 241272. https://doi.org/10.1098/rsos.241272

Wikipedia contributors. “Metriorhynchidae” Wikipedia, 12 Nov. 2024, https://en.wikipedia.org/wiki/Metriorhynchidae

Wikipedia contributors. “Rhacheosaurus” Wikipedia, 02 Dec. 2024, https://en.wikipedia.org/wiki/Rhacheosaurus

[princefluph]

Two Ouranosaurus sit in a body of water to cool off on a hot day as an adolescent Sarcosuchus swims up to investigate the couple. Ouranosaurus has found its way back into my heart as one of my favorite dinosaurs. Their shape is really fun to look at with its rather large humped back and beaked face. Honestly, Paleo Pines probably had something to do with my enjoyment of them.

[stargod]

I made my own drawing prompt list :^P i just love the wonderful world of fucked up prehistoric crocodiles

EDIT: updated to make it easier to read. There are a few mistakes in here i will have to fix later 😅

[1aceinspace]

[paleonativeart]

Day 23: KPG Extinction

During the darkness of cloudy weather, an alligatorid Brachychampsa is struggled to tearing a huge flesh dead alamosaurus after a collapsed itself due high starvation.

[mindblowingscience]

Sci-Show: 5 of the Strangest Prehistoric Crocs

Over the years, scientists have found evidence for a lot of weird prehistoric animals, but some of the strangest have been the crocodyliformes! 

Hosted by: Hank Green

[tsaagan]

Sarcosuchus, National Museum of Natural History, Paris, France