Paleo-Myth Number 5: Cenozoic: The Age of Mammals?

Speak of the Cenozoic (New Life) and you implicitly speak of what is commonly referred to as "the Age of Mammals". Although mammals were around during the Mesozoic and were very diverse in small size guilds- its only in the Mesozoic do we see them expand into large and dominant carnivores, herbivores, and omnivores. We also see expansion into the marine realm and a certain aberrant, bipedal ape became especially dominant and widespread during the Holocene. Certainly when one looks across the breadth of mammalian diversity one is astounded by the myriad forms: from shrew to bat to giraffe to beaked whale they are all mammals.

And this post is not discounting the obvious success mammals have sustained during this time period. But what it is addressing is how this notion- how the Cenozoic became synonymous with "The Age of Mammals"- has distorted our view of the relative ecological importance of other vertebrates during this time period- namely birds.

Now some of you reading this might be well aware that the Cenozoic always represented a significant expansion of Aves and especially Neognathene passerines- this post and the Paleo-Myth series is not necessarily aimed at you but at those perhaps less conscious of the importance of birds in the Cenozoic.

Chances are wherever you are at on the planet right now as you read this, if you step outside and just start counting species you will see more of and greater diversity of birds than mammals.

Consider this:

Most estimates place the number of extant bird species at about 10,000. Mammals? roughly half the number of species as birds at about 5,500 species. And of the mammal species alive the vast majority are rodents, bats, and shrews (red, blue, and yellow in the graph below).

So basically about 75% of all mammals can be characterized as being small, primarily nocturnal, and insectivorous/omnivorous- they basically have not changed a bunch from the Mesozoic. And if you look at the largest order Rodentia it comprises a little less than 2,500 species- or roughly half the amount of species that compromise Passerines at roughly 5,000. This comparison is especially telling as rodents and passerines do share a lot in terms of ecological overlap. And this diversity among birds is not slowing down, if anything it is picking up!

Looking at species diversity offers us one perspective on the bird vs mammal question. It should be noted that the peculiar adaptations and specializations of many birds might have a way of inflating bird species counts compared to mammals. Also because birds can be quite mobile they are able to fly off to different areas and speciate- unlike rodents. But the sheer number of bird species, compared to mammals, can not be ignored.

But lets look at biomass, as this may offer another perspective on the issue.

Tsavo. (c) Antero Topp. The most abundant bird, red-billed Quelea, vs largest land mammal, African Elephant

Now biomass estimates are tenuous at best and it is hard to estimate the population of even people- but lets look at the most common bird in the world- Africas Red-Billed Quelea (Quelea quelea). Estimates for the population range from 3 billion to up to 10 billion- pretty respectable numbers. But here the mammals probably have the birds beat. Most experts believe the brown rat (Rattus norvegicus) to be the only land based vertebrate to come close to humans in terms of biomass. Some estimate New York City alone to have a population of rats at up to 100 million! Ok so mammals hold the #1 and #2 spot for terrestrial vertebrate biomass- who come in at #3? a bird, the common chicken (Gallus gallus domesticus).

Another point to be made with the rodent question is that birds of prey- owls, falcons, hawks- and also birds like corvids, herons, gulls, and shrikes are the most important predatory control on exponential rodent growth in many habitats. And, unlike mammal predators, can converge from long distance to exploit areas with rodent plagues. They thus serve as a last line of defense for rodent scourges. Another point for the birds.

Another avenue to explore in regards to the bird/mammal debate is extent of ecological niches. Both extant and extinct forms of birds show that they have made significant ecological inroads into niches of large terrestrial herbivore and carnivore traditionally occupied by mammals. Examples include modern flightless birds (ostriches, rheas etc) and in the past phorusrhachids, moas, and elephant birds. But mammals have not yet exploited many niches that are the exclusive domain of birds. There are no soaring mammals that scavenge carcasses (vultures, condors etc). There are no mammals that exploit shores/intertidal zones to the extent the myriad waders, shorebirds etc do. There are no filter feeding freshwater or brackish water mammals like ducks, flamingoes, anseriformes etc. Birds show a much greater diversity in their insectivorous forms than mammals. Although bats are important pollinators, seed dispersal agents in some areas they are less successful/diverse than the myriad birds that perform these same functions. And there are no bats that exploit marine resources, unlike the myriad diversity of marine birds.

In short birds can often do the same tasks that mammals do when given a chance- but mammals do not seem to succeed in the areas where birds do exceptionally well.

The Cenozoic: The Age of Mammals and Birds

(c) Flip Nicklin

Pertinencia

Along with Humans, Who Else is in the 7 Billion Club?

Global Diversity of Birds in Space and Time

Influence of Predation on Rodent Population

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To Go Where No Crustacean Has Gone Before

I want to talk about a particularly interesting little critter I stumbled upon while doing some research on detritivores. Since this guys's story was new to me perhaps it is new to you.

Hemilepistus reaumuri. wikipedia

Ok, so a freakin' pillbug (aka woodlouse) what is so special about them? Yes we are all familiar with pillbugs, rolly-pollies, sow-bug whatever name you know them by they are found or introduced all over the world- usually in dark/damp places and feed mainly on dead vegetation. They are crustaceans,  Isopods, and represent the most successful radiation of terrestrial crustaceans- the suborder Oniscidea. Now that is all fine and dandy- but what I want to talk about is the guy pictured above- Hemilepistus reaumuri- which "inhabits the driest habitat conquered by any species of crustacean".

Now I grew up in southern California and these guys were definitely part of my childhood urban fauna growing up. The crustacean in question most certainly is Armadillidium vulgare native to Europe including the British Isles. It thrives in coastal areas, especially with calcareous soils- so it does alright here. Despite being invasive it is considered relatively benign on the ecology, unlike the situation of our crayfish in British waters. In addition to  A. vulgare, southern California also hosts at least two sowbugs (the ones that can't roll up); the European woodlouse Oniscus asellus; and the rough woodlouse, Porcellio scaber. Both require somewhat wetter

conditions than the rollies to respire. In the pic to the left you can see the difference between the two with European woodlouse having the colored specks while the rough woodlouse is more textured. Interestingly these isopods are doing so well in the irrigated sections of California that their European native predator- the woodlouse Spider Dysdera crocata- came along too and is doing just fine here eating 100% sowbug al dente which it pierces their exoskeleton with those big ol' fangs it has. And its a good thing that spider is around to eat 'em as many spiders find them distasteful as they excrete ammonia gas and have blue blood due to the copper based blood- haemocycanin- that they utilize. Anyways, despite their familiarity as urban landscape critters they are quite interesting

and worthy of admiration. That being said the isopod at question, Hemilepistus reaumuri, departs from these other guys both in respect to the harsher environment that it thrives in and the sociality that this species has evolved.

Native to steppes, semideserts, salt lake shores and real deserts of North Africa and the Mediterranean this isopod not only survives but thrives in an extreme environment. Central to its success is its habit of burrowing. New burrows are only made in early spring by a single woodlouse which guards the entrance assiduously against other conspecifics. Only after a prolonged courtship does the desert woodlouse accept a member of the opposite sex. Once bonded the crustaceans form an alliance that is about as magnanimous as any in the animal kingdom. They both guard the entrance to the burrow, taking turns for foraging as needed, and reject intruders. Partners are recognized based on scent. When the female gives birth (woodlouse eggs hatch on the underside of their body so they appear to "give birth") to 50-100 young they actually stay and hang around for quite some time being fed by the parents. All the offspring develop a specific "scent badge" which allows the parents to identify them as kin and reject (or even consume) the young of other woodlouse. In this way only the offspring of the monogamously mated pair actually benefit from the refuge of the burrow in an environment that would otherwise fatally desiccate these crustaceans. The parents, in addition to their offspring, form a sort of colony and individuals will embark on provisioning trips for food which is brought back to the burrow. Over time a faecal embankment builds up around the colony which demarcates the extent of their territory. The pair only raise one brood and an individual only lives about 15 months max.

So what we have here is an isopod, a crustacean, that is dependent on some moisture to keep its tracheal lungs operating- living at the extreme edge of its ability and adapting to this environment with an advanced sociability, burrow construction, food provisioning, pair bonding, and child rearing. Cool. Oh yeah, it is also very successful at this lifestyle and biomass studies indicate it is often the most abundant critter in its environment- supporting a myriad of predators including being the primary prey for a species of scorpion, Scorpio maurus.

Negev Desert, natural habitat for desert woodlouse. 

Of course such an interesting juxtaposition of an intensely social crustacean setting up shop in the desert has stimulated much scientific conjecture. Do harsh environments encourage parental care strategies? How might such a system have evolved? Does this provide a model for how other social invertebrates (social insects) may have evolved their life strategies?

Anyways, pill-bugs rule.
Peace.

Pertinencia

K. Eduard Linsenmair (1974). "Some adaptations of the desert woodlouse Hemilepistus reaumuri (Isopoda, Oniscoidea) to desert environment" (PDF). Verhandlungen der Gesellschaft für Ökologie 4: 183–185. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2010/4448/pdf/Linsenmair_adaption_woodlouse.pdf.

The CaRE OF WOODLICE

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Jurassic Burglar Alarm Final Edition

So I've been working on a picture for a couple of weeks now in color pencil. And since I've been staring at it so much while working on it I have grown kind of sick of it. Anyways there are some things I like about it, some things I am not so happy with....

"Jurassic Burglar Alarm" Duane Nash. 2013

Of course what grabs your attention is the saurian carnage- and that is no mistake- and if you want to read about why the fleeing toddler sauropod is mauled and why that Torvo is ripping some huevos out of the Allosaurus- read my post here. On the heels of the recent "All Yesterdays" backlash maybe I should preface everything with a "highly speculative" label.

Anyways I don't want to talk too much about the beasties depicted, although I should mention that I got inspiration for the Allo from the Perentie monitor of Australia, but what I do want to talk about is my

my choices for the vegetation. As I outlined in one of my earliest posts (Mesozoic Big Three) conifers, cycads, and ferns, although doubtless important during the Mesozoic, are over represented in depictions of Mesozoic vegetation in my opinion. Artists will often choice from a palette of pines, auracarians, generic cycads, tree ferns and run of the mill groundcover ferns. That being said I consciously went for vegetation of a slightly different bent. And although I do use conifers, cycads, and ferns in this pic I did try to portray them in slightly untypical styles. Also I tried to add color to the landscape. It is a common sentiment that the Mesozoic vegetation was colorless due to the lack of flowering plants and this attitude prevails in much of the art depicting this period. But if you look at the full panoply of plants which may have existed in these habits there is actually much option for color; the strange cones of cycads; weird hues in the wood of conifers; sporangia on ferns and horsetails; the weird pseudo-flowers of gnetales and seed ferns- perhaps even colorful enough to attract insect pollinators- you have a lot of color to choose from. And also keep in mind that even in angiosperm dominated landscapes you don't necessarily see a riot of color everywhere you look- think about savanna grasslands or tropical jungles- you mainly see hues of green, browns, and tans.

I picture the environment depicted here as part of the upper reaches of the Morrison formation-perhaps alluvial fans emanating form the Eastern mountains, Late Jurassic North America. It is a semi-arid area, but recent showers have greened up the landscape. In texture and mode it feels like chapparal, or scrubby savanna. The ground has a reddish, oxidized hue to it.

The knarly twisted juniper-looking conifers is a hypothetical cheirolepidiacean conifer and they dominate the landscape. The groundcover is a mix of putative types- I draw them in discrete bunches implying a type of slow motion war between the plants as they clamber for space, sun, and water.

The Baby Blue Bronto is in a patch of Ephedra like plants. Ephedra is a
type of gnetale and I invoke them here as a quite successful plant of arid conditions-as they are today. We do have good evidence for members
of the Gnetophyta in the early Cretaceous- perhaps there were ghost lineages going back further? The plants behind the Bronto and underneath the Torvo are putative whisk ferns. Whisk ferns, although allied with ferns, are another  botanical anomaly- we don't really know much about where they came from or their fossil record. They lack true roots but instead rely on mycorrhizal fungi. They spread with rhizoidal structures and lack true leaves but have chlorophyl in their stems. Today they are found widely scattered around the globe, suggesting perhaps a more widespread distribution in the past. The cycads in the foreground I depicted with their trunks underground, forming underground stems like a few extant cycads (Bowenia, Strangeria). I drew both male/female varieties and gave them some

Whisk Fern. Psilotum nudum

color as well. Maybe they released weird toxins into the soil to inhibit other plants. Little spreading ferns exist in the north side of the conifers and spread little runners during the wet season. The dense, mat forming vegetation under the Allosaur is a clump of putative lycopsids. Like the Resurrection plant they go dormant during the dry and spring to life rapidly with the returns of the rains. Here I depict them forming almost a grass like thatch of growth, spreading indefinitely via rhizomes, cropped back by hungry dinos.

You will also notice that I gave some hue & color to the soil itself. This is to imply a sort of biological soil crust, common today in arid regions, composed of a diverse community of moss, lichens, fungi, cyanobacteria that I suggest were common in appropriate environments during the Mesozoic. Perhaps even some dinos regularly nibbled these crusts?

Today soil crusts suffer from trampling and take many years, sometimes centuries to recover. Perhaps a community of crusts, ideally adapted to the large- but spreading- feet of many dinos existed forming a unique aspect to Mesozoic ecosystems?

And finally to the right you can see a large, amorphous, ctulhu looking clump of vegetation in my pic. That is another putative gnetophyte- this time based off the strange Welwitschia of the Namib desert.

This guy grows only two leaves- but they just keep growing- and have weird reproductive propagules.

Anyways what I hoped to do with this piece is get your attention with the dino carnage but really draw you in to the vegetation/environment as well. Just as there is a fossil bias for verteberates, there is a fossil bias for plants as well. There are just so many facets of the past we may never know. However I do not think we should get too conservative in construing possibilities just because the evidence is not ideal.

Cheers!!

Welwitschia mirabilis. Rob Nicholls (C)

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