If the di­nosaurs hadn’t been wiped out in a mass ex­tinc­tion 66 mil­lion years ago, the world would look very dif­fer­ent to­day

Focus-Science and Technology - - Dinosaurs - Words: John Pick­rell Il­lus­tra­tions: James Gil­leard

“Given that arms were non-crit­i­cal for hunt­ing, it’s pos­si­ble a tyran­nosaur could have been arm­less”

Around 66 mil­lion years ago, a 14km-wide as­ter­oid smashed into our planet. An es­ti­mated 15 bil­lion tonnes of soot spread through the at­mos­phere, cre­at­ing one long night that lasted sev­eral years and made pho­to­syn­the­sis all but im­pos­si­ble. It her­alded an end­less win­ter that saw av­er­age tem­per­a­tures fall by as much as 28oC. These are the con­di­tions that the few wretched crea­tures that sur­vived the ini­tial im­pact had to en­dure – not to men­tion the earth­quakes, tsunamis, wild­fires and vol­canic erup­tions that swiftly fol­lowed in its wake.

Around three- quar­ters of all species went ex­tinct and no an­i­mal big­ger than a Labrador dog sur­vived. But ac­cord­ing to re­searchers at the Uni­ver­sity of Texas, things could have been very dif­fer­ent. They re­ported find­ings that had the as­ter­oid struck Earth just a few min­utes ear­lier, it would have hit the deep ocean rather than the shal­low sea of the Yu­catan Penin­sula in present-day Mex­ico.

Had that been the case, then the dam­age would have been more lo­calised. Some of the di­nosaurs far from the im­pact site might have sur­vived, and the world would be a dif­fer­ent place to­day. In our own his­tory, only the feath­ered thero­pod di­nosaurs (a group of bipedal di­nosaurs) we know as birds made it through the calamity, but how would things have turned out if their larger rel­a­tives had joined them? Would di­nosaurs still be alive to­day and could mam­mals such as hu­mans have evolved? What would our world look like if we shared it with the descendants of an­i­mals like T. rex and Tricer­atops?

“I’m sure a fairly nice di­ver­sity of non-avian di­nosaurs would still be here,” says Dr Stephen Brusatte, a palaeon­tol­o­gist at the Uni­ver­sity of Ed­in­burgh. “If there was no sud­den, cat­a­strophic shock of the as­ter­oid, I re­ally don’t see any­thing that’s hap­pened since – whether it was the spread of grass­lands; chang­ing ocean cur­rents; the sep­a­ra­tion of Antarc­tica

from South Amer­ica, which caused a cold snap; or the more re­cent Ice Ages – that would have knocked off the di­nosaurs.”

Over the years many have tried to imag­ine what kind of crea­tures di­nosaurs might have evolved into had they sur­vived. The most fa­mous at­tempt is a 1988 book called The New Di­nosaurs: An Al­ter­na­tive Evo­lu­tion, by Scot­tish ge­ol­o­gist and au­thor Dou­gal Dixon. For this mag­nif­i­cent work of spec­u­la­tive zo­ol­ogy, Dixon con­jured up crea­tures such as the ‘cut­lasstooth’ – a pack-hunt­ing, sabre-toothed preda­tor from South Amer­ica; the ‘cribrum’ – a flamingo-like, fil­ter-feed­ing thero­pod from Aus­tralia; and the ‘gour­mand’ – a rel­a­tive of T. rex that lost its front limbs en­tirely and de­vel­oped a dis­ten­si­ble jaw to al­low it to rapidly swal­low prey whole, much like a snake.

Per­haps this last idea isn’t en­tirely wide of the mark. Dr Tom Holtz, an ex­pert on thero­pod di­nosaurs at the Uni­ver­sity of Mary­land in the US, says that both tyran­nosaurs and abelisaurs, the two types of big meat- eater present in the Late Cre­ta­ceous, are no­table for their tiny fore­limbs. “Given that arms were non- crit­i­cal for hunt­ing, it’s pos­si­ble that a Ceno­zoic [cur­rent ge­o­log­i­cal era] tyran­nosaur could have been arm­less,” says Holtz.

The be­gin­ning of the Ceno­zoic Era (which spans the pe­riod from 66 mil­lion years ago un­til the present day) might es­sen­tially have been an eco­log­i­cal ex­ten­sion of the Late Cre­ta­ceous. Var­i­ous crea­tures such as ti­tanosaur sauropods ( huge, long- necked di­nosaurs like Ar­genti­nosaurus), hadrosaurs (duck­billed di­nosaurs like Ed­mon­tosaurus), cer­atop­sians ( horned, beaked di­nosaurs like Tricer­atops), and preda­tors such as the tyran­nosaurs would still have re­mained com­mon.

But as we head fur­ther from the Cre­ta­ceous to­wards the present day, there would likely have been sig­nif­i­cant changes, says Dr Andy Farke at the Ray­mond M. Alf Mu­seum of Pa­le­on­tol­ogy in Clare­mont, Cal­i­for­nia. “If di­nosaurs were still around to­day they’d be pretty dif­fer­ent to what we think of at the end of the age of the di­nosaurs – things like T. rex and Tricer­atops,” he ar­gues. “You might still recog­nise them as a di­nosaur, but who knows what kind of body shapes and body plans might have come up in the past 66 mil­lion years.”

Many of the mam­mals with which we’re fa­mil­iar might not have had the op­por­tu­nity to evolve. “You can’t un­der­es­ti­mate the im­por­tance of that ex­tinc­tion 66 mil­lion years ago in re­ally hit­ting the re­set but­ton for mam­mals and clear­ing the play­ing field,” adds Farke.


Al­ready in the Cre­ta­ceous there were nu­mer­ous fluffy, feath­ered theropods scam­per­ing in the trees. As­sum­ing that flow­er­ing plants con­tin­ued to spread and thrive as they did in our his­tory, then could pri­mate-like di­nosaurs have spe­cialised to take ad­van­tage of the fruit they pro­duced? Prof Matthew Bon­nan, a palaeo­bi­ol­o­gist at Stock­ton Uni­ver­sity in New Jer­sey, ar­gues that pri­mates evolved large, for­ward-fac­ing eyes with colour vi­sion to for­age for fruit.

“Is there a con­nec­tion be­tween be­ing fru­giv­o­rous [fruit- eat­ing] and hav­ing a larger brain? We don’t know, but one could imag­ine ar­bo­real di­nosaurs that formed a co- evo­lu­tion­ary re­la­tion­ship with flow­er­ing plants by eat­ing their fruits and dis­pers­ing the seeds,” he says. “Whether these fruit- eat­ing di­nosaurs would have evolved com­plex so­cial groups like pri­mates is pure spec­u­la­tion.”

Other eco­log­i­cal spa­ces lit­tle ex­plored by di­nosaurs were aquatic en­vi­ron­ments. “In mam­mals we’ve seen a return to the sea, in sev­eral dif­fer­ent it­er­a­tions,” says Farke. “We’ve had things like whales and man­a­tees that have gone back into the oceans, and things like ot­ters that spend a lot of time in the wa­ter. It’s cool to think about what di­nosaurs could have looked like if they’d gone in a cetacean direc­tion.”

But if their gi­ant marine rep­tile rel­a­tives – the mosasaurs and ple­siosaurs – had sur­vived, then di­nosaurs might have found it hard to get a foothold.

There could also have been other con­se­quences of di­nosaurs and their rep­til­ian rel­a­tives, such as the fly­ing pterosaurs, not pe­ter­ing out at the end of the Cre­ta­ceous. Al­though birds co- ex­isted with di­nosaurs for a long time in the Cre­ta­ceous, their di­ver­sity was low com­pared to to­day. “Mod­ern bird groups un­der­went an ex­plo­sive ra­di­a­tion af ter the mass ex­tinc­tion, maybe be­cause pterosaurs went ex­tinct and opened up new niches,” says Dr Vic­to­ria Ar­bour, a palaeon­tol­o­gist at the

“You can’t un­der­es­ti­mate the im­por­tance of that ex­tinc­tion re­ally hit­ting the re­set but­ton for mam­mals and clear­ing the play­ing field”

Royal On­tario Mu­seum in Toronto. “With­out the mass ex­tinc­tion, maybe birds wouldn’t be as di­verse and suc­cess­ful as they are to­day, and maybe we wouldn’t have things like song­birds, par­rots, hawks, or hum­ming­birds at all.”

Most ex­perts seem to agree that the largest land mam­mals such as ele­phants, mam­moths, gi­ant rel­a­tives of rhinos and sloths, and per­haps even horses and gi­raffes, prob­a­bly couldn’t have evolved if large di­nosaurs had re­mained to oc­cupy the niches they came to fill.

But per­haps smaller mam­mals such as ro­dents, bats and pri­mates would have been just as suc­cess­ful. If that had been the case, then some of those pri­mates could have climbed down from the trees onto the grass­lands and sa­van­nahs that even­tu­ally re­placed the thick forests of the Cre­ta­ceous, and evolved into ho­minids, as our an­ces­tors did.

“If we spec­u­late that hu­mans had evolved along­side di­nosaurs, then they prob­a­bly would have been able to co- ex­ist,” says Farke. “Hu­mans al­ready evolved in ecosys­tems that had large land an­i­mals and preda­tors. We prob­a­bly would have done okay.”

“Un­armed, soli­tary hu­mans are still easy tar­gets for large preda­tors like bears and lions,” agrees Ar­bour. “But over­all hu­mans are pretty good at sur­viv­ing along­side large, dan­ger­ous an­i­mals.”


Di­nosaurs might not have been so lucky though, as hu­mans seem to have a spe­cial skill for killing off large an­i­mals. Per­haps the biggest di­nosaurs would have gone the way of the mam­moth and the dodo. “Hu­mans are re­ally good at ex­tin­guish­ing megafauna – through hunt­ing, cli­mate change or habi­tat de­struc­tion,” Ar­bour says. “Di­nosaurs in the 21st Cen­tury, just like mod­ern an­i­mals, would prob­a­bly have re­duced pop­u­la­tions and face the threat of ex­tinc­tion.”

Big di­nosaurs would per­haps only per­sist in pro­tected re­serves, such as na­tional parks and wildlife refuges – mod­ern-day equiv­a­lents of Juras­sic Park.

“If we spec­u­late that hu­mans had evolved along­side di­nosaurs, then they prob­a­bly would have been able to co-ex­ist”

Smaller di­nosaurs that in­fringed on crops or live­stock would prob­a­bly be hunted as ‘nui­sance’ an­i­mals, as wolves and din­goes are to­day, adds Ar­bour. “It would be re­ally hard for large sauropods to sur­vive along­side us. They’re so big and would re­quire so much food, that I doubt we could set aside enough wild spa­ces for them to thrive.”


The di­nosaurs that might do par­tic­u­larly well in the mod­ern era are those that could learn to live and thrive along­side peo­ple. In our world to­day, the vast ma­jor­ity of an­i­mal biomass is made up of the species that we farm or have do­mes­ti­cated, or those that live around our cities and de­vel­op­ments – and so it would also have been in a re­al­ity where hu­mans and di­nosaurs co- ex­isted. There might have been di­nosaur equiv­a­lents of seag­ulls, pigeons, rats, rac­coons and foxes – all very well adapted to take ad­van­tage of the re­sources avail­able in ur­ban en­vi­ron­ments.

“Small, scrappy di­nosaurs might have been able to eke out a liv­ing on the mar­gins of hous­ing de­vel-

op­ments,” sug­gests Farke. You can just imag­ine lit­tle beaked her­biv­o­rous di­nosaurs nib­bling at the roses and hy­drangeas in your gar­den.

“An­i­mals that do well in ur­ban en­vi­ron­ments to­day tend to be those that are good at eat­ing what­ever we’re throw­ing away, and mak­ing use of the struc­tures we build,” agrees Ar­bour. “Small om­niv­o­rous or preda­tory theropods would per­haps have been lurk­ing around garbage cans.”

Ob­vi­ously, we might have do­mes­ti­cated di­nosaurs to ex­ploit for meat and eggs or agri­cul­tural labour, and we would very likely have taken them into our homes as pets – the feath­ery or scaly equiv­a­lents of dogs and cats.

Per­haps, though, the idea that hu­mans could have evolved in a world filled with di­nosaurs is sim­ply too far-fetched. “I have no doubt that we would not be here,” says Brusatte. “The as­ter­oid was one of those domi­noes that set in mo­tion a chain of events that led to us. With­out the di­nosaurs dis­ap­pear­ing, mam­mals would not have had the same op­por­tu­nity.”

He ar­gues that mam­mals had al­ready ex­isted with di­nosaurs for 160 mil­lion years or more when the as­ter­oid struck. But they were mostly “mar­ginal, shad­owy lit­tle crea­tures” and – had the as­ter­oid not caused a mass ex­tinc­tion – would likely re­main that way to­day.

As Brusatte points out: “What’s an­other 66 mil­lion years when it had al­ready been like that for 160 mil­lion years al­ready.”

“With­out the di­nosaurs dis­ap­pear­ing, mam­mals would not have had the same op­por­tu­nity”

Artist’s im­pres­sion of how di­nosaurs could have looked, if they had sur­vived

Cer­tain di­nosaurs might have gone back into the oceans, like the man­a­tee did

If di­nosaurs had sur­vived into the Ice Ages, could they have de­vel­oped thick pelts like mod­ern musk ox?

If all the di­nosaurs had sur­vived, their descendants could have given Mr Seag­ull some com­pe­ti­tion for your chips

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