The Ichthyosaur Thread

Adam Khor

And sight, but we already knew that.

http://news.sciencemag.org/paleontology/2015/06/ghost-image-shows-how-ichthyosaur-ruled-seas

Apparently they were quite deaf, tho.

Adam Khor

http://www.sci-news.com/paleontology/sclerocormus-parviceps-ancient-ichthyosaur-like-reptile-03888.html

Adam Khor

Very interesting find as ichthyosaurs in general are rare by the lower Cretaceous. The find also suggests these ichthyosaurs were breeding in shallow, inland seas:
https://www.sciencedirect.com/science/article/pii/S0195667117304494

Capt'n Midnight

https://phys.org/news/2018-04-prehistoric-reptile-pregnant-octuplets.html

Capt'n Midnight

Big sea reptile- as big as a whale:




Ancient sea reptile was one of the largest animals ever

''We were mind blown to think that a sea creature the size of a blue whale was swimming off the English coast about 200 million years ago.''

Adam Khor

Amazing discovery! 
Just to give you all some background, the largest sea reptile known until now was the ichthyosaur Shastasaurus sikanniensis, at around 21 meters long. That is as big as some of the largest modern day whales, and much larger than the largest known pliosaurs (Pliosaurus and Kronosaurus at about 9-10 meters, probably). The 25 meter Liopleurodon made famous by Walking with Dinosaurs was a hypothetical creature, based on very fragmentary remains; something like it is not beyond the realm of possibility, but there's no good evidence thus far. Some mosasaurs may have been longer than Pliosaurus and Kronosaurus but were not particularly massive, with a considerable part of their length corresponding to the tail.

The newly discovered ichthyosaurs (apparently there's more than one) would be considerably larger than any other marine reptile including Shastasaurus sikanniensis, making them the largest marine reptiles known, by far, being estimated at 26-27 meters long, that is in the same range as the fin whale and the blue whale today. 

jaxxx

There's finally a contender that could potentially knock the blue whale off its top spot as largest known animal to have ever lived. Well even if it does, at least old bluey still outranks all known sauropods.

It's only now that I've seen your comparison picture Adam but just looking at how a great white compares to a blue whale, I've just realised that megaladon was more than half the size of a blue whale. I've never actually compared it to a whale before now. Goddamn great whites scare the bejaysus out of me enough, let alone megaladons! This is why I'm glad I can't swim :pac:

Adam Khor

Indeed, C. megalodon was a true monster! 

When I was a kid, many books claimed the whale shark (largest fish nowadays) could reach 21 meters long. More recent sources usually say 12 meters, if anything. Still, a 12 meter long whale shark is only slightly smaller than modern estimates for C. megalodon, and the same size as other, earlier "megatoothed sharks" such as Otodus.  

Behold the whale shark, and imagine it with bigger teeth! 

Adam Khor

Relevant to the thread:
http://blogs.plos.org/paleocomm/2018/04/11/a-case-of-mesozoic-misidentification/

Rubecula

I wonder what it mostly ate?

Adam Khor

Mostly fish and non-armored cephalopods which were probably captured by means of suction, if the similarity between the shastasaurid's toothless jaws* and those of modern beaked whales are anything to go by. 
Like beaked whales, shastasaurids had features of the skull and jaws (including large foramina) which suggest there was some sort of specialized soft tissue to aid during suction of prey. The jaws also seem adapted to open very forcefully and quickly, rather than snapping quickly as would be expected if they were catching prey like say, crocodiles do. Most interestingly, these short snouted ichthyosaurs also appear to have very small pectoral fins relative to the body which is a feature they share with beaked whales and sperm whales; the small fins reduce drag during deep diving. Last but not least, the size range of different species within genus Shastasaurus appears to be the same as in modern, suction feeding odontocetes (the largest being comparable or even superior in size to the sperm whale). 

*Juvenile shastasaurs apparently had teeth and lost them as they aged so the little ones probably were catching prey the way other, more typical ichthyosaurs did.

Rubecula

Adam Khor wrote: »

Mostly fish and non-armored cephalopods which were probably captured by means of suction, if the similarity between the shastasaurid's toothless jaws* and those of modern beaked whales are anything to go by. 
Like beaked whales, shastasaurids had features of the skull and jaws (including large foramina) which suggest there was some sort of specialized soft tissue to aid during suction of prey. The jaws also seem adapted to open very forcefully and quickly, rather than snapping quickly as would be expected if they were catching prey like say, crocodiles do. Most interestingly, these short snouted ichthyosaurs also appear to have very small pectoral fins relative to the body which is a feature they share with beaked whales and sperm whales; the small fins reduce drag during deep diving. Last but not least, the size range of different species within genus Shastasaurus appears to be the same as in modern, suction feeding odontocetes (the largest being comparable or even superior in size to the sperm whale). 

*Juvenile shastasaurs apparently had teeth and lost them as they aged so the little ones probably were catching prey the way other, more typical ichthyosaurs did.

How would you rate the intelligence Adam?

Adam Khor

Haha I don´t believe in rating animal intelligence :B I can imagine that, if they were alive, we would grossly underestimate them as we do most modern day creatures.

Adam Khor

https://www.livescience.com/62236-prehistoric-sea-monster-octomom.html

Capt'n Midnight

It wouldn't have to compete with dolphins, and given it's size a larger brain wouldn't be that much of an extra load.

Adam Khor

But even if we knew they had particularly large brains (which to my knowledge they didn´t), that wouldn´t necessarily relate to intelligence. Consider Troodon, popularly known as the smartest dinosaur due to its relatively large brain. Now we know the areas of the brain that were enlarged were due to its extra-developed senses of sight and hearing (comparable to those of owls). 

Ichtyosaurs had much smaller brains than cetaceans, but even if their brains were bigger than those of other reptiles (not saying they were- I haven´t read anything comparing ichthyosaur brain sizes), we should remember that they too had developed several senses (eyesight, smell, even mechanoreception apparently) beyond other reptiles, meaning certain areas of their brain would've been enlarged for this reason.

Rubecula

Brain size has been shown to not affect intelligence as much as neural links. for example crows are intelligent and they are modern dinosaurs.:)

Adam Khor

Paleopathology shows these ichthyosaurs led very rough lives.

https://blogs.plos.org/paleocomm/2018/10/29/its-a-hard-knock-life-for-an-ichthyosaur/

Adam Khor

https://www.livescience.com/63851-sea-monster-salt-glands.html

Adam Khor

http://blogs.discovermagazine.com/deadthings/2018/12/05/ichthyosaur-blubber/#.XAhwG2OZ21s



Not that there were many doubts about it by now.

Adam Khor

https://peerj.com/articles/6112/

Adam Khor

Interesting article on the maximum sizes estimated for both pliosaurs and ichthyosaurs.

http://markwitton-com.blogspot.com/2020/04/in-pursuit-of-giant-pliosaurids-and.html



Regarding ichthyosaurs:

This leaves the Shonisaurus species as the named record holders of ichthyosaur size, and by some margin. Both species are known from substantial remains that allow us to be fairly confident in our body length estimates. We can actually get a lot of data from simply measuring their articulated skeletons. Our best size predictions for these animals shake out to 13-15 m for Sho. popularis (McGowan and Motani 1999) and a whopping 21 m for Sho. sikanniensis (Nicholls and Manabe 2004). Using data from Gutarra et al. (2019), these equate to approximate body masses of 20-30 and 80 tonnes, respectively. The Shonisaurus species were huge animals, among the largest to ever swim the seas.

Adam Khor

Early, amphibious ichthyosaur Cartorhynchus looked like a "tadpole/seal hybrid" and had strange teeth to crush hard shelled prey.

https://www.9news.com.au/world/dinosaurs-fossil-study-ct-scan-uncovers-ichthyosaurs-reptilian-predator-dolphins-history/0380d093-4376-4fce-918f-0b0ad4c7ddc8#close

Adam Khor

Mixosaurus, one of the earliest known ichthyosaurs, is found to have been surprisingly advanced thanks to fossils preserving the outline of a dorsal and upper caudal fin lobe. The specimen even preserves traces of the intestine and gut content which shows it fed on small fish and cephalopods.

The finding makes Mixosaurus the earliest known amniote with a dorsal fin.

http://dml.cmnh.org/2020Jul/msg00008.html

Adam Khor

Voracious ichthyosaur preserved with its last meal. The ichthyosaur lacked any obvious adaptations to a macropredatory (large prey hunting) lifestyle, yet this find shows that they would at least attempt to swallow large prey whole, not unlike large fish today.

The ichthyosaur was a little under 5 m long, whereas the victim, another sea reptile known as a thalattosaur, was around 4 m. The completeness and articulation of the prey's remains strongly suggests it was preyed on and not scavenged. This would indicate that macropredatory ichthyosaurs did not necessarily have large, serrated teeth to cut and tear through flesh as was formerly believed, and instead could swallow considerably large prey whole or in large chunks.

(They could easily swallow a person of course, had they coexisted with us)

The main specimen (XNGM-WS-50-R4) likely represents the oldest direct record of megafaunal predation by marine tetrapods and also sets the record for the largest prey size of Mesozoic marine reptiles at 4 m (Table 2), which is larger than the previous record of 2.5 m (Everhart, 2004; Konishi et al., 2014).

The main specimen (XNGM-WS-50-R4) likely represents the oldest direct record of megafaunal predation by marine tetrapods and also sets the record for the largest prey size of Mesozoic marine reptiles at 4 m (Table 2), which is larger than the previous record of 2.5 m (Everhart, 2004; Konishi et al., 2014).

Two questions arise concerning how the individual of Xinpusaurus found its way to the stomach of Guizhouichthyosaurus: was it by predation or scavenging, and, if the latter, were the head and tail detached by the scavenger or through postmortem decay? The answer to the second question is simpler than that for the first. Forensic taphonomy in the marine context has shown that hands and feet are the first to be detached through postmortem decay of human remains at sea, followed by the head and then more proximal parts of the limbs, whereas the vertebral column is the last to disintegrate, being strongly reinforced by extensive connective tissues that take time to decay (Haglund, 1993; Mason et al., 1996). This tendency is expected to have been exaggerated in Xinpusaurus, which likely used its body axis for propulsion, whereas its small limbs were used as rudders without a role of body support; appendicular connective tissues must have been limited relative to those along the axial skeleton, allowing faster decay. Then the presence of at least one manus and some pedal elements in the absence of the head and tail therefore cannot be explained very well by the decay hypothesis.
Possibilities of predation versus scavenging merit careful consideration. We conclude that predation is more likely than scavenging for the following reasons. First, marine carrion usually results from partial predation rather than deaths due to other causes (Barrett-Lennard et al., 2011; Britton and Morton, 2004). If a predator other than Guizhouichthyosaurus killed the thalattosaur in question, then it would be strange for the nutritious trunk and limbs to be left intact by the predator. Second, ingestion likely took place at the sea surface where Guizhouichthyosaurus was able to breathe because swallowing of a large food item would have taken a long time, whether the food was ingested in one or a few pieces. This would limit the possibilities of scavenging because marine scavenging usually occurs at the seafloor (Britton and Morton, 2004; Whitehead and Reeves, 2005)—marine carrion usually do not stay afloat at the surface (Haglund, 1993; Mason et al., 1996). In addition, the specimen is from the subtropical region of the warm Middle Triassic period, so the decomposition would have been rapid, further narrowing the window of time when carcass would have been available at the sea surface. Third, marine carrions are rare (Britton and Morton, 2004), especially that of megafauna available within the diving depth of typical air-breathing predators like killer whales (Whitehead and Reeves, 2005) and Guizhouichthyosaurus.
Even in the unlikely case of the present bromalite representing scavenged prey, X. xingyiensis would still be on the list of prey actively hunted by Guizhouichthyosaurus. Obligate scavenging by large animals is rare in modern marine ecosystems (Beasley et al., 2012; Wilson and Wolkovich, 2011), instead, marine scavenging is almost always facultative (Britton and Morton, 2004; Hammerschlag et al., 2016). Modern megapredators, such as the great white shark (Carcharodon carcharias) (Tucker et al., 2019), tiger shark (Galeocerado cuvier) (Hammerschlag et al., 2016), and killer whale (O. orca) (Whitehead and Reeves, 2005), are known to scavenge when given opportunities, but they tend to scavenge the carrion of the species that they also hunt. The carrion that they scavenge is derived from predation by the same or another individual, unless it is human caused (Britton and Morton, 2004).
The isolated tail specimen (XNGM-WS2011-50-R6) also supports the predation hypothesis. The specimen witnesses, whether it belonged to the prey individual in the bromalite or not, that there was a mechanism to detach the tail of a large thalattosaur while it was intact—decay was probably not involved because the distal part of the tail is still articulated, whereas decay would have detached that region first because there is less connective tissue there. The specimen instead shows that the most proximal vertebra, which would be the last to decay, is halfway detached (Figure 2E). External forces would be necessary to cause such detachment, and it is difficult to find a source outside of a predator. Thus, there was at least a predator that could hunt Xinpusaurus, whereas Guizhouichthyosaurus was the only species larger than the prey in this and coeval localities in the region.
Circumstantial evidence suggests that the isolated tail belongs to the prey individual in the bromalite. The tail was only 23 m away from the ichthyosaur specimen on the same rock surface and has a size and completeness that are expected for the lost tail of the prey in the bromalite. Also, as stated above, its preservation suggests that the tail was detached from the body while it was intact. If it is from the prey individual, the predator likely died soon after ingesting the prey, and that may explain the lack of etching of the bone in the bromalite by the stomach acid, as well as the strange detachment of the neck of the predator. Unfortunately, it is impossible to test this hypothesis directly so a clear conclusion cannot be drawn on this issue.