#paleobiology

[smrow]

hatzegopteryx, for a friend

[shattersaurus]

More style explorations with Dilophosaurus

[o-craven-canto]

Forbidden phenotypes and the limits of evolution

Abstract. Evolution has produced an astonishing array of organisms, but does it have limits and, if so, how are these overcome and how have

An interesting paper (Vermeij, 2015) on the "empty phenotypic space", i.e. the forms and adaptations that we do not see in the living world, possibly relevant to the convergence vs. contingency debate.

Some examples:

Wheels: some curled-up arthropods can roll around, and bacterial flagella and some parts of weevil legs rotate on their axis, but macroscopic wheels with a free axle do not exist, probably because smooth surfaces on which they'd be useful are rare and it would be difficult to grow them through embryonal development.

Animal-provided pollination and dispersal do not exist in water, with the possible exception of one species of fish-pollinated seagrass (which is a descendant of terrestrial plants). Presumably water is already good enough at carrying gametes and propagules that buying the services of an animal is a useless expense.

Mineral reef-building does not occur on land nor, more surprisingly, in freshwater. The reason for the latter is not clear, since there are enough mineral ions in freshwater to build shells. Boring of rock, shells, and wood in freshwater is also extremely rare though common in the sea.

Gelatinous plankton like salps or jellyfish (with few exceptions of the latter) is also not found in freshwater, probably because they can't survive dispersal between separate water bodies.

Endothermy ("warm blood") is generally not found in small aquatic animals, probably because water leeches away heat much faster than air, so aquatic endotherms (tunas, sharks, seals, whales) need to be bulky. On land, however, endothermy is found among tiny vertebrates and even insects.

There is no passive air-floating plankton, since air is not dense enough to support living tissue or dissolved organic matter by buoyancy. For that reason filter-feeding is also rare outside of water, while carnivorous plants are not found in the ocean (the water already carries enough nutrient). Aquatic plants do not produce wood as buoyancy is enough to keep them upright.

Large terrestrial animals do not specialize as scavengers (all mammals famous for scavenging also hunt actively); large carcasses are too spread out. All specialist scavengers on land are either very small, or flying.

Herbivory is rare among active fliers, because plant matter has a low energy density and takes a long time to digest. Herbivorous birds and insects are poor fliers or flightless, and the best fliers, like geese, are the ones that can take shelter in water.

Many more examples are only excluded from specific groups (e.g. live-bearing, despite being very common in reptiles, never appeared in birds, probably because the bird egg-shell is too mineralized to be retained in the womb as transition toward full live-bearing).

Even though the author calls them "forbidden phenotypes", only some of them are actually impossible (because they cannot evolve in the first place, or because they cost more energy than they're worth), and others simply never happened to evolve. At the end of the paper there is a list of phenotypes that would have been "forbidden" in the aftermath of the Cambrian Explosion and Ordovician diversification, but which appeared later, and they include

cutins, suberins, lignins, flavonoids, alkaloids, vascular systems, roots, leaves, rigid frameworks of stems and branches, nutrition complemented by animal matter, and basal growth in land plants; nitrogen-fixing symbiosis on land; animal-mediated dispersal/pollination; silk-producing, sound-emitting, flying, eusocial, terrestrial herbivorous, wood-boring, terrestrial shell-bearing and endothermic animals; embryos nourished within the body of an animal or plant parent; mineralized phytoplankton; and rock-excavating marine herbivores. [...] photosymbiotic and chemosymbiotic molluscs, the bivalved condition in gastropods, terrestrial life in gastropods and vertebrates, complex septa within the phragmocone of externally shelled cephalopods, internalization and loss of the shell in cephalopods, cementation to the substratum with a glue of calcium carbonate and organic matrix in several animal groups (gastropods, brachiopods, bivalves and barnacles), spines on shells of several groups (brachiopods, bivalves and brachiopods), mineralized tubes in polychaete annelids, mobility in bryozoans and pelmatozoan echinoderms, jaws and teeth in vertebrates, and vascular systems in brown and red algae. A vast diversity of potent venoms also lay in the future as part of the defensive and aggressive arsenal of many gastropods, cephalopods, aculeate Hymenoptera, vertebrates and land plants.

He also mentions phenotypes that were lost, but every listed adaptation seems to have survived in some group (e.g. complex spiny shells disappeared among cephalopods but survived in gastropods).

[knuppitalism-with-ue]

I actually wanted to further talk about this sketch from last night a little, as it not only serves as an full body depiction of the animal but also a cheek in tongue critique of the paper describing Manipulonyx.

This animal, an alvarezsaur, is known from various bones, most importantly a complete hand that reveals novel structures for this group. Specifically osteoderms sitting on the side and palm of the hand. The authors speculated that these structures would have a specific, practical purpose and proposed that they would be used for grabbing, transporting and opening larger dinosaur eggs.

While this appears an interesting idea and I certainly think that occasional consumption of eggs wasn't off the table for this animals I doubt that they were specialized in this way. At least to the degree that it actively shaped their limbs.

And here is why I think that:

Eggs are a very seasonal treat. While certain areas with a stable climate can see a year long supply of eggs from different species, the Nemegt formation, where this animal was found, is unlikely to provide such a stable egg supply. The climate was quite seasonal, in winter maybe even reached freezing temperatures occasionally. Not ideal when you have to wait months for your main source of food to return.

Which brings us to the next point. Animals today, that are specialized in egg consumption are usually "cold blooded", as these are usually too rare of a treat to fuel more active creatures.

The fossils of Manipulonyx were indeed found in the vicinity of larger dinosaur eggs but being found together with them doesn't mean the animal predated on these. Beyond that the paper doesn't provide a taphonomic explanation for the locality, meaning: how did this fossils end up here? Were they preserved in situ or were the fossils maybe transported, how long did it take for the fossils to accumulate?

The limbs of Manipulonyx do not look like they would be great for transporting eggs. Especially the palmar osteoderm seems in the way when trying to hold anything, I wouldn't the surprised if the hand overall was actually quite rigid.

The idea of these animal would go after eggs that they can wrap their arms around begs the question what juvenile Manipulonyx would eat. Did smaller/younger individuals simply go for smaller eggs? Would there be ontogenetic niche shift? That seems, in my eyes, unlikely.

So what did they use their arms for? Please take everything you read here with a grain of salt, as an artist who hasn't seen the fossils personally I can only provide limited insight into this. Non of what you read here is peer reviewed research. Non the less I think there are some alternative ideas what is animal did that seem, for the moment, more likely to me.

Most prominently I see two possibility, both related and based on observations on modern birds:

Display, the age old argument, I know, but tons of spikes on really short arms just don't seem really practical. But with some flashy colors... who knows, I am not kink shaming.

Intraspecific combat. Many modern day birds have wing spurs, often times visible even in the bone. They might look weird but many birds are known for beating each other with their wings, the arms of Manipulonyx were short yes, but I think they would still allow for some wrestling matches. In birds they are also used for defense but given the arm length of Manipulonyx I think that's not as likely ;)

Ok rant over.

[sinosauropteryxjuice]

Short post of paleontologists absolutely slaying photo shoots with their discoveries. Please add more such images if you have them.

[makairodonx]

A pair of subadult male Diplodocus drink from one of the few reminding streams of water in the middle of the dry season; the coloration and color patterns are based off a groundbreaking study on the sauropod’s skin integuments from last year.

[banalcreature]

Let's be paleoart with mama

[mushrooms-and-millipedes]

YO NEW HELL ANT JUST DROPPED

IN THE SOUTHERN HEMISPHERE NO LESS

This is from a study just published a few days ago by Lepeco et al. (2025).

Hell ants (subfamily: Haidomyrmecinae) are super cool ants that possessed vertically closing jaws.

Below is a model of the ant's body/anatomy generated via micro-computed tomography

Vulcanidris cratensis is a new species discovered in Brazil. It dates back to the lower Cretaceous, and at the time of writing, is now the oldest known ant to science!