WEBVTT 00:00:00.000 --> 00:00:03.040 I want you to imagine just for a second a dynasty 00:00:03.040 --> 00:00:05.940 of creatures that absolutely dominated the earth. 00:00:06.059 --> 00:00:08.740 Okay. We are talking about a reign that lasted 00:00:08.740 --> 00:00:12.929 for... Well over 190 million years. That is a 00:00:12.929 --> 00:00:15.150 staggering amount of time. Right. I mean, they 00:00:15.150 --> 00:00:17.449 watched the supercontinent Pangea fracture and 00:00:17.449 --> 00:00:20.710 drift apart. They survived the catastrophic KPG 00:00:20.710 --> 00:00:23.429 boundary. The literal asteroid impact. Exactly. 00:00:23.429 --> 00:00:26.609 The impact that famously wiped out the non -avian 00:00:26.609 --> 00:00:29.969 dinosaurs. They were survivors in the truest, 00:00:29.969 --> 00:00:32.090 most grueling sense of the word. They really 00:00:32.090 --> 00:00:35.210 were. And yet, despite that staggering record 00:00:35.210 --> 00:00:37.810 of resilience across multiple geological eras, 00:00:39.530 --> 00:00:42.189 massive group of animals was ultimately wiped 00:00:42.189 --> 00:00:45.670 out by a single word. Just one word. Obsolete. 00:00:45.750 --> 00:00:47.789 It is quite the dramatic twist, honestly. It 00:00:47.789 --> 00:00:50.689 really is. To survive the literal end of a world, 00:00:50.850 --> 00:00:52.850 you know, wading through the ash and ecological 00:00:52.850 --> 00:00:55.829 collapse that doomed the dinosaurs, only to be 00:00:55.829 --> 00:00:58.450 erased by the stroke of a taxonomist's pen millions 00:00:58.450 --> 00:01:00.909 of years later. And that is exactly what we are 00:01:00.909 --> 00:01:03.049 focusing our deep dive on today. We are looking 00:01:03.049 --> 00:01:05.760 at the history of Mesosuchia. This is an obsolete 00:01:05.760 --> 00:01:10.379 term for a truly massive ancient group of crocodile 00:01:10.379 --> 00:01:13.239 morph reptiles. And we're pulling a lot of this 00:01:13.239 --> 00:01:15.700 from a really comprehensive Wikipedia article 00:01:15.700 --> 00:01:17.719 on the topic. It's a great source for this. Yeah. 00:01:17.819 --> 00:01:20.959 So our mission today is to explore the history 00:01:20.959 --> 00:01:23.959 of these heavily armored sort of in -between 00:01:23.959 --> 00:01:27.920 crocodiles. We are going to unpack their incredibly 00:01:27.920 --> 00:01:31.269 bizarre anatomy. We'll look at how they conquered 00:01:31.269 --> 00:01:34.109 the globe and ultimately understand exactly why 00:01:34.109 --> 00:01:36.969 modern science had to completely rewrite their 00:01:36.969 --> 00:01:39.739 entire family tree. It serves as a perfect example 00:01:39.739 --> 00:01:41.959 of how our understanding of the natural world 00:01:41.959 --> 00:01:44.780 is, well, it's never truly static. We love to 00:01:44.780 --> 00:01:47.019 put things in neat little boxes. But the story 00:01:47.019 --> 00:01:49.500 of the Mesozoic shows us what happens when our 00:01:49.500 --> 00:01:52.400 rigid categories collide with the messy, sprawling 00:01:52.400 --> 00:01:55.340 reality of evolution. Nature doesn't care about 00:01:55.340 --> 00:01:57.659 our filing systems. OK, let's unpack this, because 00:01:57.659 --> 00:02:00.120 to really appreciate the Mesozoic, you have to 00:02:00.120 --> 00:02:01.859 understand the sheer scale of their timeline. 00:02:02.060 --> 00:02:04.900 You really do. These creatures existed from 199 00:02:04.900 --> 00:02:07.700 million years ago all the way down to roughly 00:02:07.700 --> 00:02:10.379 4 .57 million years ago. Which is just, it's 00:02:10.379 --> 00:02:12.800 hard to wrap your head around. It spans from 00:02:12.800 --> 00:02:15.099 the early Jurassic period right up to the late 00:02:15.099 --> 00:02:18.460 Miocene or even the early Pliocene. It is an 00:02:18.460 --> 00:02:21.620 almost incomprehensible amount of time to be 00:02:21.620 --> 00:02:24.139 successful on this planet. It truly is. I mean, 00:02:24.159 --> 00:02:26.879 when they first appeared, the world was a radically 00:02:26.879 --> 00:02:29.240 different place. The climate, the flora, the 00:02:29.240 --> 00:02:31.919 available prey. Everything was in flux. Everything. 00:02:32.139 --> 00:02:35.889 And yet. this group persisted through the entirety 00:02:35.889 --> 00:02:38.449 of the jurassic the entirety of the cretaceous 00:02:39.120 --> 00:02:42.199 crossed that apocalyptic threshold 66 million 00:02:42.199 --> 00:02:44.860 years ago and kept right on going. Through the 00:02:44.860 --> 00:02:46.560 Paleocene, the Eocene. Through the Volococene 00:02:46.560 --> 00:02:49.860 and into the Miocene. They were a constant dominant 00:02:49.860 --> 00:02:53.159 fixture across multiple major climatic upheavals. 00:02:53.400 --> 00:02:55.719 And their historical name actually reflects their 00:02:55.719 --> 00:02:57.939 place in that massive timeline, doesn't it? It 00:02:57.939 --> 00:02:59.840 does. Because the early scientific consensus 00:02:59.840 --> 00:03:02.759 seemed to view their evolution as a very simple 00:03:02.759 --> 00:03:05.340 three -act play. Right, a very linear progression. 00:03:05.819 --> 00:03:08.280 You had the quote -unquote first early crocodile. 00:03:08.430 --> 00:03:11.189 placed in a suborder called Protosuchia. Then 00:03:11.189 --> 00:03:14.009 you jump to the modern extant species, the ones 00:03:14.009 --> 00:03:15.550 you might see in a swamp today, which we call 00:03:15.550 --> 00:03:18.650 Eusachia. Which translates to true crocodiles. 00:03:18.810 --> 00:03:21.750 Exactly. True crocodiles. And right there in 00:03:21.750 --> 00:03:23.870 the middle, serving as this massive evolutionary 00:03:23.870 --> 00:03:27.370 bridge, was the Mesosuchia. The crocodiles in 00:03:27.370 --> 00:03:30.669 between. Precisely. It was a very neat, linear 00:03:30.669 --> 00:03:32.710 way of looking at their evolution, beginning, 00:03:32.949 --> 00:03:35.710 middle, and end. But nature is rarely that neat. 00:03:35.849 --> 00:03:38.530 No, never. What makes the Mesozoicians so compelling 00:03:38.530 --> 00:03:41.189 is that they were far more than just a transitional 00:03:41.189 --> 00:03:43.650 stepping stone waiting around to turn into modern 00:03:43.650 --> 00:03:46.969 crocodiles. Right. They were a wildly successful... 00:03:47.710 --> 00:03:50.569 dynamic, and incredibly diverse group of animals 00:03:50.569 --> 00:03:52.889 in their own right. Diverse might actually be 00:03:52.889 --> 00:03:55.210 underselling it a bit. Yeah. Because when you 00:03:55.210 --> 00:03:57.409 say the word crocodile to someone today, you 00:03:57.409 --> 00:03:59.449 immediately picture a very specific lifestyle. 00:03:59.770 --> 00:04:02.210 You picture a swamp. Yeah, a swamp -dwelling, 00:04:02.370 --> 00:04:04.770 semi -aquatic ambush predator lurking at the 00:04:04.770 --> 00:04:07.169 water's edge. Waiting for a zebra to drink. Exactly. 00:04:07.430 --> 00:04:09.889 Yeah. But these ancient creatures were not boxed 00:04:09.889 --> 00:04:12.530 into that one ecological niche. We're talking 00:04:12.530 --> 00:04:15.509 about... Terrestrial Mesozoans sprinting around 00:04:15.509 --> 00:04:18.160 on land. Running down prey. Yeah. We have the 00:04:18.160 --> 00:04:20.439 semi -aquatic ones, sure. But then there were 00:04:20.439 --> 00:04:23.759 fully aquatic, essentially marine crocodile morphs 00:04:23.759 --> 00:04:26.439 perfectly adapted for swimming in the open oceans. 00:04:26.540 --> 00:04:29.439 That diversity of lifestyle is exactly why they 00:04:29.439 --> 00:04:33.439 thrived for nearly 200 million years. They were 00:04:33.439 --> 00:04:35.740 everywhere. They didn't just survive. They adapted 00:04:35.740 --> 00:04:38.579 to exploit almost every available ecological 00:04:38.579 --> 00:04:42.600 niche left open by other predators. Wow. But 00:04:42.600 --> 00:04:44.800 here's the challenge for early paleontologists. 00:04:45.120 --> 00:04:56.689 A terrestrial crocodile... Right, longer legs 00:04:56.689 --> 00:05:00.620 versus... A paddle -like tail. Exactly. And yet 00:05:00.620 --> 00:05:03.019 beneath all those specialized adaptations, they 00:05:03.019 --> 00:05:05.500 shared a core set of defining anatomical features 00:05:05.500 --> 00:05:07.899 that allowed early scientists to group them together 00:05:07.899 --> 00:05:09.980 under that mezzosuchia banner. I really want 00:05:09.980 --> 00:05:11.920 to dig into that biological blueprint because 00:05:11.920 --> 00:05:14.259 looking at their anatomy, it becomes clear they 00:05:14.259 --> 00:05:15.980 were operating very differently from the crocodiles 00:05:15.980 --> 00:05:18.040 we know today. Very differently, yes. Let's start 00:05:18.040 --> 00:05:20.360 with the skull. One major differentiator is that 00:05:20.360 --> 00:05:23.079 mezzosuchians had a shorter secondary palate 00:05:23.079 --> 00:05:27.360 compared to modern usuchians. Functionally speaking, 00:05:27.620 --> 00:05:29.779 how did that change the way these animals operated? 00:05:30.000 --> 00:05:32.839 To understand the impact, let's visualize the 00:05:32.839 --> 00:05:35.540 secondary palate. It's essentially the bony roof 00:05:35.540 --> 00:05:38.139 of the mouth, which separates the nasal passage 00:05:38.139 --> 00:05:41.420 from the oral cavity. In Mesozoans, this palate 00:05:41.420 --> 00:05:44.899 is formed by three specific bones. The premaxillary, 00:05:45.079 --> 00:05:47.579 the maxillary, and the palatine bones. Spot on. 00:05:48.399 --> 00:05:50.879 Because it is physically shorter than what we 00:05:50.879 --> 00:05:53.959 see in modern crocodiles, it drastically shifts 00:05:53.959 --> 00:05:56.680 where the inner nostrils, the koani, are located. 00:05:56.980 --> 00:05:58.959 So where do they end up? In these ancient creatures, 00:05:59.100 --> 00:06:01.199 those inner nostrils are usually situated right 00:06:01.199 --> 00:06:03.579 between the palatine and pterygoid bones. And 00:06:03.579 --> 00:06:05.980 crucially, the text notes that Chorana is not 00:06:05.980 --> 00:06:08.839 surrounded by the medial pterygoid plate. Exactly. 00:06:08.899 --> 00:06:11.579 That is a major defining characteristic that 00:06:11.579 --> 00:06:13.740 separates them from modern forms. How does that 00:06:13.740 --> 00:06:16.879 compare to a modern crocodile? In modern Yusushians, 00:06:16.899 --> 00:06:19.300 that bony palate extends much further back. It 00:06:19.300 --> 00:06:21.600 completely surrounds the nasal opening. Which 00:06:21.600 --> 00:06:24.019 lets them do what? It allows a modern crocodile 00:06:24.019 --> 00:06:26.319 to breathe while its mouth is submerged or full 00:06:26.319 --> 00:06:28.779 of water, as long as the tip of its snout is 00:06:28.779 --> 00:06:31.759 above the surface. Oh, wow. So they can drown 00:06:31.759 --> 00:06:34.180 prey without drowning themselves. Precisely. 00:06:34.220 --> 00:06:36.939 The shorter palate of the Mississutians means 00:06:36.939 --> 00:06:39.480 their respiratory and feeding mechanics weren't 00:06:39.480 --> 00:06:42.100 quite as separated, which heavily influenced 00:06:42.100 --> 00:06:44.879 how they hunted and processed their prey, particularly 00:06:44.879 --> 00:06:47.360 in aquatic environments. That makes a lot of 00:06:47.360 --> 00:06:50.439 sense. And moving down from the skull, there 00:06:50.439 --> 00:06:53.939 is a fascinating detail about their spine. They 00:06:53.939 --> 00:06:56.379 possessed what's called an amphicoelum of the 00:06:56.379 --> 00:06:59.509 vertebrae. Yes, amphicoeolus vertebrae. How does 00:06:59.509 --> 00:07:02.230 that compare to the skeletal structure of a modern 00:07:02.230 --> 00:07:05.129 crocodile? An amphicoeolus vertebrae refers to 00:07:05.129 --> 00:07:07.250 the specific shape of the individual's spinal 00:07:07.250 --> 00:07:10.829 bones. They are concave on both ends. Okay. So 00:07:10.829 --> 00:07:13.550 if you were to isolate a single bone from a mesosucian 00:07:13.550 --> 00:07:16.230 spine, the main body of it would look a bit like 00:07:16.230 --> 00:07:18.870 an hourglass. Dented in on both the front and 00:07:18.870 --> 00:07:21.160 the back. Right. As opposed to the modern crocodile 00:07:21.160 --> 00:07:23.319 spine. Right. Modern crocodiles generally have 00:07:23.319 --> 00:07:25.680 percolous vertebrae, which are concave in the 00:07:25.680 --> 00:07:28.040 front and convex in the back. Kind of like a 00:07:28.040 --> 00:07:30.220 ball and socket joint. Exactly. More of a ball 00:07:30.220 --> 00:07:33.339 and socket arrangement. The amphicolelous structure 00:07:33.339 --> 00:07:36.220 in Mesozoans provided a very specific kind of 00:07:36.220 --> 00:07:38.160 flexibility and strength. It's an older design. 00:07:38.339 --> 00:07:40.800 It's an older Argosaurian design, but clearly 00:07:40.800 --> 00:07:43.579 it was incredibly effective given that it supported 00:07:43.579 --> 00:07:46.300 them from the early Jurassic all the way to the 00:07:46.300 --> 00:07:48.660 Miocene. Let's jump back to the skull architecture 00:07:48.660 --> 00:07:50.879 for a second. Sure. Because it sounds like they 00:07:50.879 --> 00:07:53.740 had incredibly robust, tightly packed heads. 00:07:54.079 --> 00:07:57.620 Their jawbones sometimes joined dorsally, which 00:07:57.620 --> 00:08:00.540 actually... push the nasal bones away from the 00:08:00.540 --> 00:08:03.879 premaxillary bones and their outer nostrils usually 00:08:03.879 --> 00:08:06.740 merge together. It paints a picture of a very 00:08:06.740 --> 00:08:10.779 specialized rigid snout. It does. And that rigidity 00:08:10.779 --> 00:08:13.060 is further supported by another key feature. 00:08:13.279 --> 00:08:16.779 They almost always lost the preorbital foramen. 00:08:17.100 --> 00:08:19.120 Remind me what that is. The preorbital foramen 00:08:19.120 --> 00:08:22.319 is a small opening or hole in the skull located 00:08:22.319 --> 00:08:25.120 just in front of the eye sockets. It's a common 00:08:25.120 --> 00:08:27.639 feature in many other archosaurs, including early 00:08:27.639 --> 00:08:31.360 dinosaurs. So losing that hole essentially solidifies 00:08:31.360 --> 00:08:34.340 the facial skeleton. Precisely. When you close 00:08:34.340 --> 00:08:37.759 up those fenestrae or windows in the skull, you 00:08:37.759 --> 00:08:40.259 are trading lightness for structural integrity. 00:08:40.559 --> 00:08:42.799 Making it much heavier. Heavier but much stronger. 00:08:43.120 --> 00:08:45.480 A solidifying of the facial skeleton means the 00:08:45.480 --> 00:08:47.879 skull can withstand immense stress and impact. 00:08:48.330 --> 00:08:50.929 Which ties perfectly into the next feature. Their 00:08:50.929 --> 00:08:53.990 superior temporal fossa was massive, and the 00:08:53.990 --> 00:08:56.210 frontal bone actually reached its edge. Yes. 00:08:56.269 --> 00:08:59.049 And functionally, the superior temporal fossa, 00:08:59.149 --> 00:09:01.269 those openings at the top of the skull behind 00:09:01.269 --> 00:09:04.029 the eyes, they accommodate the jaw muscles. So 00:09:04.029 --> 00:09:06.070 the larger hole means larger muscles. Exactly. 00:09:06.110 --> 00:09:08.570 The larger the fossa, the more space there is 00:09:08.570 --> 00:09:11.539 for massive muscle attachment. Wow. So a huge 00:09:11.539 --> 00:09:14.019 temporal fossa combined with a heavily solidified 00:09:14.019 --> 00:09:17.419 snout strongly suggests these animals had absolutely 00:09:17.419 --> 00:09:19.940 devastating bite forces. They were just built 00:09:19.940 --> 00:09:22.559 to clamp down on struggling prey and not let 00:09:22.559 --> 00:09:25.120 go. Absolute powerhouses. And just to add to 00:09:25.120 --> 00:09:27.779 that tough, rugged build, their postterminal 00:09:27.779 --> 00:09:29.980 arch was often located directly under the skin. 00:09:30.159 --> 00:09:32.429 Giving them a very distinct look. Right, so you'd 00:09:32.429 --> 00:09:35.370 have these pronounced bony ridges sitting right 00:09:35.370 --> 00:09:38.409 below the surface behind their eyes. Plus, there 00:09:38.409 --> 00:09:40.909 is a quirk in their hips. The pubis bone. Yeah, 00:09:40.929 --> 00:09:43.129 the pubis bone does not enter the acetabulum, 00:09:43.149 --> 00:09:45.850 which is the hip joint socket. That pelvic structure 00:09:45.850 --> 00:09:49.549 is a subtle but crucial differentiator. The way 00:09:49.549 --> 00:09:52.190 the femur articulates with the hip dictates an 00:09:52.190 --> 00:09:54.490 animal's gait and locomotion. So it changes how 00:09:54.490 --> 00:09:57.590 they walk? Very much so. The fact that the pubis 00:09:57.590 --> 00:09:59.850 is excluded from the acetabulum in these creatures 00:09:59.850 --> 00:10:03.250 is a distinct evolutionary signature. It influenced 00:10:03.250 --> 00:10:05.590 how efficiently those terrestrial mesosuchines 00:10:05.590 --> 00:10:08.149 could move on land compared to other reptile 00:10:08.149 --> 00:10:10.409 groups. They were just incredibly adapted machines. 00:10:11.159 --> 00:10:13.740 But my absolute favorite detail from this anatomical 00:10:13.740 --> 00:10:16.299 breakdown has to be the armor. The carapace. 00:10:16.320 --> 00:10:19.720 Yes. Their carapace was usually extremely well 00:10:19.720 --> 00:10:21.460 -developed. I really want you to picture this. 00:10:21.580 --> 00:10:23.740 We aren't just talking about thick, leathery 00:10:23.740 --> 00:10:25.860 reptilian skin. Yeah, not at all. We are talking 00:10:25.860 --> 00:10:29.259 about highly developed, heavy, bony armor plating. 00:10:29.659 --> 00:10:32.320 covering these creatures. Whether they were sprinting 00:10:32.320 --> 00:10:35.039 across the plains or swimming in the seas, they 00:10:35.039 --> 00:10:37.980 were essentially organic prehistoric tanks. The 00:10:37.980 --> 00:10:39.960 development of that carapace was undoubtedly 00:10:39.960 --> 00:10:42.500 a primary factor in their long -term survival. 00:10:43.480 --> 00:10:45.279 Think about the neighborhoods they lived in. 00:10:45.379 --> 00:10:48.039 Rough neighborhoods. Very rough. When you were 00:10:48.039 --> 00:10:51.039 sharing early ecosystems with massive theropod 00:10:51.039 --> 00:10:54.700 dinosaurs or navigating oceans filled with apex 00:10:54.700 --> 00:10:58.000 marine reptiles, having a well -developed suite 00:10:58.000 --> 00:11:02.139 of heavy bony armor is a distinct evolutionary 00:11:02.139 --> 00:11:05.059 advantage. It let them take a hit. It allowed 00:11:05.059 --> 00:11:07.200 them to hold their ground in highly competitive 00:11:07.200 --> 00:11:09.379 environments. Here's where it gets really interesting. 00:11:09.899 --> 00:11:12.500 Because they didn't just survive alongside those 00:11:12.500 --> 00:11:15.399 other massive predators. Right. In many cases, 00:11:15.419 --> 00:11:16.840 they were the top of the food chain themselves. 00:11:17.720 --> 00:11:20.860 There's an incredibly fascinating discovery that 00:11:20.860 --> 00:11:24.120 really proves how dominant they were long after 00:11:24.120 --> 00:11:26.460 the dinosaurs were gone. The Hispaniola find. 00:11:26.700 --> 00:11:28.820 Yes. A study published in the Proceedings of 00:11:28.820 --> 00:11:31.440 the Royal Society B details a creature called 00:11:31.440 --> 00:11:34.460 Sabicus ichirohinus. Fantastic paper. This is 00:11:34.460 --> 00:11:37.559 a South American sebicide discovered in the Miocene 00:11:37.559 --> 00:11:40.210 deposits of Hispaniola. That is a phenomenal 00:11:40.210 --> 00:11:42.409 piece of evidence, and it really changes the 00:11:42.409 --> 00:11:44.929 narrative. How so? Well, the Miocene Epoch is 00:11:44.929 --> 00:11:48.549 deep into the age of mammals. And finding Sabicus 00:11:48.549 --> 00:11:51.230 echiorhynus in Hispaniola, which is part of the 00:11:51.230 --> 00:11:54.669 Greater Antilles in the Caribbean, is incredibly 00:11:54.669 --> 00:11:57.230 significant from an ecological standpoint. I 00:11:57.230 --> 00:11:59.730 was struck by that location. How does a massive 00:11:59.730 --> 00:12:02.210 terrestrial predator end up dominating a Caribbean 00:12:02.210 --> 00:12:04.779 island? It speaks to their sheer adaptability 00:12:04.779 --> 00:12:07.379 and dispersal capabilities. Island ecosystems 00:12:07.379 --> 00:12:10.159 are fascinating because they are isolated. Right. 00:12:10.200 --> 00:12:12.639 It's hard to get there. Exactly. The species 00:12:12.639 --> 00:12:15.200 that manage to get there, often by rafting on 00:12:15.200 --> 00:12:17.960 vegetation or crossing narrow seaways, have to 00:12:17.960 --> 00:12:20.860 rapidly adapt to limited space and specific local 00:12:20.860 --> 00:12:24.820 prey. And they thrived. They did. The paper specifically 00:12:24.820 --> 00:12:28.059 documents these sebaceids as apex predators in 00:12:28.059 --> 00:12:30.240 those early West Indies environments. It completely 00:12:30.240 --> 00:12:32.399 shatters that old idea of them just... being 00:12:32.399 --> 00:12:34.480 a transitional middle group. Completely. This 00:12:34.480 --> 00:12:36.340 isn't a story of animals that barely scraped 00:12:36.340 --> 00:12:38.399 by in the shadows of the dinosaurs and then quietly 00:12:38.399 --> 00:12:41.299 faded away. No. This shows that millions of years 00:12:41.299 --> 00:12:44.019 after the dinosaur extinction, these Mesozoician 00:12:44.019 --> 00:12:46.639 descendants were still highly successful, dominant 00:12:46.639 --> 00:12:49.440 predators, conquering isolated island ecosystems. 00:12:50.080 --> 00:12:53.360 Exactly. They were the undisputed rulers of their 00:12:53.360 --> 00:12:56.480 domains. And when you look at the sheer sprawling 00:12:56.480 --> 00:12:58.970 diversity... of their broader classification, 00:12:59.549 --> 00:13:02.529 the scale is genuinely mind blowing. It really 00:13:02.529 --> 00:13:05.700 is. The list of subgroups within this classification 00:13:05.700 --> 00:13:09.500 is massive. It's huge. You have the Chartegasuchoidea 00:13:09.500 --> 00:13:12.940 group, which includes genera from Asia like Shantungasuchus 00:13:12.940 --> 00:13:15.799 and Sequanasuchus. Those particular Asian genera 00:13:15.799 --> 00:13:18.419 represent some of the fascinating, highly specialized 00:13:18.419 --> 00:13:22.600 branches of this lineage. It shows just how globally 00:13:22.600 --> 00:13:24.320 distributed the group was. They were everywhere. 00:13:24.519 --> 00:13:26.279 They weren't confined to one continent. They 00:13:26.279 --> 00:13:28.700 were a global phenomenon. Then you have the Metasuchia. 00:13:29.039 --> 00:13:31.080 Right. Which flits off into the Notosuchia and 00:13:31.080 --> 00:13:34.159 the Neosuchia. And the Neosuchians, which in 00:13:34.159 --> 00:13:37.340 this older classification explicitly excludes 00:13:37.340 --> 00:13:40.419 the modern true crocodiles, contains a staggering 00:13:40.419 --> 00:13:42.620 number of families. It really does. You've got 00:13:42.620 --> 00:13:45.460 the Oedipus sordae, the Goniophilitidae, the 00:13:45.460 --> 00:13:47.779 Paraligotoridae. And some amazing names in there. 00:13:47.840 --> 00:13:50.559 And, of course, the Thalatosuchia, those incredible 00:13:50.559 --> 00:13:53.120 open ocean marine crocodile morphs we talked 00:13:53.120 --> 00:13:55.360 about earlier. It's a wildly expansive family 00:13:55.360 --> 00:13:59.190 tree. It is a vast phylogenetic tree. And listening 00:13:59.190 --> 00:14:02.190 to that list of diverse families, you know, terrestrial 00:14:02.190 --> 00:14:05.350 runners, pelagic marine swimmers, heavy ambush 00:14:05.350 --> 00:14:08.950 predators, it highlights the incredible adaptive 00:14:08.950 --> 00:14:11.690 radiation of these animals. Adaptive radiation, 00:14:11.950 --> 00:14:13.570 meaning they spread out into different roles. 00:14:13.769 --> 00:14:16.190 Exactly. They filled nearly every conceivable 00:14:16.190 --> 00:14:19.289 ecological role available to a carnivore over 00:14:19.289 --> 00:14:21.909 a span of nearly 200 million years. Which brings 00:14:21.909 --> 00:14:24.409 us to the biggest plot twist of the entire deep 00:14:24.409 --> 00:14:27.580 dive. Yes. If they were this successful, if they 00:14:27.580 --> 00:14:30.200 lived for 190 million years, if they conquered 00:14:30.200 --> 00:14:33.039 the land, the sea and Caribbean islands, and 00:14:33.039 --> 00:14:35.139 if they were apex predators all the way into 00:14:35.139 --> 00:14:37.580 the Miocene. How did they lose the name? Exactly. 00:14:37.700 --> 00:14:41.220 Why on earth is the term Mesozoic now considered 00:14:41.220 --> 00:14:44.000 completely obsolete? How does a dynasty like 00:14:44.000 --> 00:14:46.440 that just get canceled by modern science? That 00:14:46.440 --> 00:14:48.419 is the crux of the issue. And it all comes down 00:14:48.419 --> 00:14:51.220 to the strict, unforgiving rules of modern taxonomy 00:14:51.220 --> 00:14:53.639 and cladistics. Our filing system again. Right. 00:14:53.779 --> 00:14:56.139 The term. Mesasuchia is no longer regarded as 00:14:56.139 --> 00:14:58.460 genuine because biologists realized it belongs 00:14:58.460 --> 00:15:01.039 to what we call a paraphyletic group. Okay, I 00:15:01.039 --> 00:15:03.159 think this is where human categorization really 00:15:03.159 --> 00:15:06.139 clashes with nature. Break down paraphyletic 00:15:06.139 --> 00:15:08.740 for us. What makes a group paraphyletic, and 00:15:08.740 --> 00:15:11.940 why is that invalid in modern evolutionary science? 00:15:12.340 --> 00:15:15.539 Let's use a family tree analogy. In modern taxonomy, 00:15:15.740 --> 00:15:19.240 a valid, genuine group, what we call a monophyletic 00:15:19.240 --> 00:15:25.500 group or a clade, All of its descendants. All 00:15:25.500 --> 00:15:28.399 of them. You cannot arbitrarily chop off a branch 00:15:28.399 --> 00:15:30.600 of the family tree just because those specific 00:15:30.600 --> 00:15:32.899 descendants evolved to look a little different 00:15:32.899 --> 00:15:36.129 over time. So if I start a defined family group, 00:15:36.190 --> 00:15:38.070 starting with my great -grandmother, I have to 00:15:38.070 --> 00:15:40.629 include all her kids, all her grandkids, and 00:15:40.629 --> 00:15:42.330 all her great -grandkids to be scientifically 00:15:42.330 --> 00:15:44.970 accurate. I can't just leave out my cousins because 00:15:44.970 --> 00:15:46.549 they moved to another country and changed their 00:15:46.549 --> 00:15:48.870 last name. Precisely. Now think back to that 00:15:48.870 --> 00:15:51.169 old linear classification we discussed earlier. 00:15:51.789 --> 00:15:54.029 Proto -Sushia is the first chapter. Right. Meso 00:15:54.029 --> 00:15:56.350 -Sushia is the middle chapter. And Yu -Sushia 00:15:56.350 --> 00:15:59.070 as the final chapter of modern crocodiles. Right. 00:15:59.289 --> 00:16:01.769 Meso -Sushia was specifically designed to be 00:16:01.769 --> 00:16:05.200 the middle group. The bridge. But as paleontologists 00:16:05.200 --> 00:16:08.259 mapped out the genetics and morphology more accurately, 00:16:08.519 --> 00:16:12.120 they realized a massive flaw in the filing system. 00:16:12.360 --> 00:16:14.639 What was it? The modern true crocodiles, the 00:16:14.639 --> 00:16:17.919 Usuchians, they didn't just replace the Mesosuchians. 00:16:17.980 --> 00:16:20.419 They actually evolved from within one of the 00:16:20.419 --> 00:16:23.860 Mesosuchian branches. Oh, so the modern crocodiles 00:16:23.860 --> 00:16:26.950 in our swamps today. are technically the direct 00:16:26.950 --> 00:16:29.710 evolutionary descendants of this middle group. 00:16:29.889 --> 00:16:32.690 What's fascinating here is that by creating a 00:16:32.690 --> 00:16:35.570 distinct box called Mesosuchia that deliberately 00:16:35.570 --> 00:16:38.990 excluded modern crocodiles, early scientists 00:16:38.990 --> 00:16:41.909 had created a textbook paraphyletic group. They 00:16:41.909 --> 00:16:44.090 cut out the cousins? They did. They had drawn 00:16:44.090 --> 00:16:46.610 a neat little circle around an ancient ancestor 00:16:46.610 --> 00:16:49.470 and most of its descendants, but purposely left 00:16:49.470 --> 00:16:52.009 the surviving modern descendants entirely out 00:16:52.009 --> 00:16:54.009 of the circle just to keep their categories clean. 00:16:54.230 --> 00:16:55.809 They were trying to force... nature into neat 00:16:55.809 --> 00:16:58.129 historical chapters. Which is very human of us 00:16:58.129 --> 00:17:00.549 to do. But nature doesn't work like that. It's 00:17:00.549 --> 00:17:03.830 a continuous, branching, messy tree. Very messy. 00:17:03.830 --> 00:17:05.609 You can't have a category that just abruptly 00:17:05.609 --> 00:17:08.009 stops simply because the animals successfully 00:17:08.009 --> 00:17:10.650 evolved into something that happens to still 00:17:10.650 --> 00:17:13.819 be alive today. Exactly. In modern phylogenetics, 00:17:13.859 --> 00:17:16.240 that makes the Mesozoic grouping artificial. 00:17:16.480 --> 00:17:19.619 It doesn't reflect the true evolutionary reality. 00:17:19.980 --> 00:17:22.940 So the scientific community had to fix the filing 00:17:22.940 --> 00:17:25.859 system. So what did they replace it with? How 00:17:25.859 --> 00:17:28.660 do you recategorize 190 million years of history? 00:17:28.839 --> 00:17:31.859 The obsolete term Mesozoic was replaced by its 00:17:31.859 --> 00:17:35.680 true phylogenetic equivalent. Mezucrocodilia. 00:17:36.200 --> 00:17:38.200 Mezucrocodilia. Yeah. That is a bit of a mouthful. 00:17:38.279 --> 00:17:40.700 It is, but it perfectly and accurately describes 00:17:40.700 --> 00:17:43.839 what the group actually is. This new classification 00:17:43.839 --> 00:17:46.539 contains all the original taxa that were housed 00:17:46.539 --> 00:17:49.559 in the old Mezosuchia, plus the crocodilia, which 00:17:49.559 --> 00:17:52.599 are the modern extant forms. Got it. And a variety 00:17:52.599 --> 00:17:54.660 of other allied forms that have been more recently 00:17:54.660 --> 00:17:57.319 discovered by paleontologists. So it brings everyone 00:17:57.319 --> 00:17:59.519 back to the reunion. It corrects the historical 00:17:59.519 --> 00:18:02.299 error by finally drawing the circle large enough 00:18:02.299 --> 00:18:04.829 to include the ancestor and... all of its descendants, 00:18:05.170 --> 00:18:08.089 whether they are fossilized in Miocene Rock or 00:18:08.089 --> 00:18:10.750 currently sunning themselves on a riverbank in 00:18:10.750 --> 00:18:13.569 Florida. That is brilliant. So the Mesozoans 00:18:13.569 --> 00:18:15.990 didn't actually disappear at all. They just got 00:18:15.990 --> 00:18:18.789 their modern grandkids legally added back into 00:18:18.789 --> 00:18:21.569 the family well. That is a very apt way to look 00:18:21.569 --> 00:18:24.049 at it. The animals themselves remain as magnificent, 00:18:24.390 --> 00:18:27.109 terrifying, and historically significant as ever. 00:18:27.250 --> 00:18:30.130 They didn't change. No. What changed wasn't the 00:18:30.130 --> 00:18:33.500 fossil record. What changed was our human methodology 00:18:33.500 --> 00:18:35.680 for understanding their relationships. That's 00:18:35.680 --> 00:18:38.059 incredible. It highlights the fact that scientific 00:18:38.059 --> 00:18:41.599 knowledge is a living, breathing process. As 00:18:41.599 --> 00:18:44.059 we uncover new fossils and better understand 00:18:44.059 --> 00:18:46.880 the intricate relationships of evolution, we 00:18:46.880 --> 00:18:49.140 must be willing to tear down our old assumptions 00:18:49.140 --> 00:18:52.079 and adapt our categories. It really is wild to 00:18:52.079 --> 00:18:53.880 think about. We build these entire scientific 00:18:53.880 --> 00:18:57.180 frameworks and then one realization about a family 00:18:57.180 --> 00:19:01.650 tree. forces us to relabel centuries of museum 00:19:01.650 --> 00:19:03.869 exhibits. If we connect this to the bigger picture, 00:19:04.089 --> 00:19:06.569 we just explored a phenomenally successful group 00:19:06.569 --> 00:19:09.609 of organisms. We are talking about heavily armored, 00:19:09.750 --> 00:19:12.569 highly diverse crocodilomorph. The organic tanks. 00:19:12.910 --> 00:19:16.009 Yes. They dominated terrestrial ecosystems with 00:19:16.009 --> 00:19:18.069 specialized hips and deep skulls. They waded 00:19:18.069 --> 00:19:20.150 into the open oceans and they survived global 00:19:20.150 --> 00:19:23.029 mass extinctions, reigning for nearly 200 million 00:19:23.029 --> 00:19:25.730 years. And yet. And yet their original scientific 00:19:25.730 --> 00:19:28.509 grouping was entirely... dismantled and rewritten 00:19:28.509 --> 00:19:31.470 simply because it was an artificial in -between 00:19:31.470 --> 00:19:34.509 category that failed to recognize their modern 00:19:34.509 --> 00:19:37.730 evolutionary descendants. It tells us as much 00:19:37.730 --> 00:19:40.430 about the evolution of human science as it does 00:19:40.430 --> 00:19:42.890 about the evolution of reptiles. So what does 00:19:42.890 --> 00:19:46.859 this all mean? I think it means that... Trying 00:19:46.859 --> 00:19:50.259 to understand the deep past requires a tremendous 00:19:50.259 --> 00:19:52.980 amount of humility. Absolutely. It means we have 00:19:52.980 --> 00:19:55.460 to be willing to completely change our labels 00:19:55.460 --> 00:19:59.019 and update our worldview when the evidence demands 00:19:59.019 --> 00:20:02.000 it. The Mesozoicians were ultimate survivors. 00:20:02.640 --> 00:20:04.980 adapting to everything the planet threw at them. 00:20:05.039 --> 00:20:07.640 But they couldn't survive a taxonomic update. 00:20:07.799 --> 00:20:09.779 Though it was an update that ultimately honored 00:20:09.779 --> 00:20:12.220 their true legacy by permanently connecting their 00:20:12.220 --> 00:20:14.319 ancient history directly to the animals that 00:20:14.319 --> 00:20:16.880 still swim in our rivers and swamps today. They 00:20:16.880 --> 00:20:18.740 aren't just an extinct middle chapter anymore. 00:20:18.960 --> 00:20:21.660 Exactly. They are part of an unbroken, ongoing 00:20:21.660 --> 00:20:24.599 story. That is beautifully put. And that leaves 00:20:24.599 --> 00:20:27.380 us with a really fascinating question to ponder. 00:20:27.799 --> 00:20:29.880 I want you to think about this. If a dominant 00:20:29.880 --> 00:20:34.319 190 million year dynasty of armored apex predators 00:20:34.319 --> 00:20:37.759 had its entire scientific classification rewritten 00:20:37.759 --> 00:20:40.059 just because it was a messy in -between category, 00:20:40.400 --> 00:20:43.660 what labels, definitions, or categories are we 00:20:43.660 --> 00:20:45.539 heavily relying on in our modern world right 00:20:45.539 --> 00:20:47.700 now that future generations will look back on 00:20:47.700 --> 00:20:49.579 and realize we're just an obsolete temporary 00:20:49.579 --> 00:20:50.579 state of understanding?