published<\/a> today in the journal Frontiers in Mammal Science presents the first fossil evidence to suggest that a cynodont species gave birth.\u00a0Chiniquodon theotonicus lived roughly 236 million years ago, during the late Triassic period.\u00a0This discovery pushes the timeline of this evolutionary adaptation back by up to 95 million years, according to the researchers.<\/p>\n Stumbling upon a major discovery <\/p>\n
Co-author Maria Miceli Baro, a graduate student at the University of Buenos Aires in Argentina, was examining the bone microstructure of a fully grown C. theotonicus specimen when something surprising appeared.<\/p>\n
\u201cShe came with her samples, and we were looking at them, and we said, \u2018Hey, look, you have\u00a0embryonic tissue. This is very weird,\u00a0I have never seen this,’\u201d lead author Leandro Gaetano, a paleontologist at Argentina\u2019s National Scientific and Technical Research Council who is based at the University of Buenos Aires, told Gizmodo.\u00a0<\/p>\n
Data from living species helped Gaetano and his colleagues identify a neonatal line, a distinct growth ring that can be found in bones or teeth. It results from the strong growth-rate acceleration that occurs just after birth. The researchers realized this discovery could finally offer a way to test the universally accepted hypothesis that cynodonts laid eggs.<\/p>\n
\u201cWe started trying to figure out how we could use this new information to test the working hypothesis, and\u00a0we came up with this idea about using body size as a proxy,\u201d Gaetano explained.\u00a0<\/p>\n
Piecing together a reproductive puzzle <\/p>\n
The researchers measured the neonatal line and the specimen\u2019s outer surface to estimate its size and weight at birth and at death. They determined it weighed roughly 3.7 pounds (1.7 kilograms) at birth and 26.5 pounds (12 kg) when it died. That means the newborn C. theotonicus\u00a0weighed 14% of the mass it reached by the time of its death.<\/p>\n
The team then compared this newborn-adult body mass ratio to other groups of living animals to see which group\u00a0C. theotonicus most resembled. Present-day reptiles such as turtles, snakes, and crocodiles that weigh between 17.6 pounds (8 kg) and 32 pounds (14.5 kg) tend to produce hatchlings that weigh between 9 and 53 grams. This translates to very low newborn-adult body mass ratios of roughly 0.1% and 0.6%. Larger birds like some cranes, pelicans, and vultures also exhibit low newborn-adult body mass\u00a0ratios of around 1.3% to 4.5%.<\/p>\n
Those groups clearly weren\u2019t a good fit, but placental mammals\u2014which make up about 95% of all living mammal species\u2014have newborn-adult body mass ratios that closely align with that of C. theotonicus.\u00a0Those that weigh between 17.6 pounds (8 kg) and 33.1 pounds (15 kg) can have newborns that weigh between 35.5 grams and 4.1 pounds (1.87 kg), which translates to newborn-adult body mass ratios as high as 18.77%.<\/p>\n
Take the bay duiker antelope, for example. This African species gives birth to young that weigh roughly the same as a newborn C. theotonicus.\u00a0<\/p>\n
\u201cIn cynodonts, embryonic tissues were never observed before, let alone a neonatal line,\u201d Miceli Baro said in a statement. \u201cThrough its analysis, we found that a trait that is generally linked to evolutionary success was present in animals long before true mammals originated.\u201d<\/p>\n
While the researchers only studied a single cynodont species, Gaetano said his team\u2019s findings align with previous studies showing that some features of present-day placental mammals\u2014such as lactation, body hair, and brain size\u2014were already appearing in relatives of C. theotonicus.\u00a0Such traits are also linked to the genetic basis that underlies live birth, suggesting these changes may have emerged together.<\/p>\n
\u201cIt is very probable that there was a general shift from egg laying to live birth in these cynodonts,\u201d Gaetano said.<\/p>\n
He and his colleagues hope to look for embryonic tissues in other specimens of these animals to try and replicate their findings. Their future work could finally reveal the emergence of mammalian reproduction as we know it today.<\/p>\n","protected":false},"excerpt":{"rendered":"The vast majority of mammals alive today\u2014including us\u2014give birth to live young, but this reproductive mode isn\u2019t unique…\n","protected":false},"author":3,"featured_media":997607,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_share_on_mastodon":"0"},"categories":[8],"tags":[27613,173252,25054,159,67,132,68],"class_list":["post-997606","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-human-reproduction","tag-mammals","tag-paleontology","tag-science","tag-united-states","tag-unitedstates","tag-us"],"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@us\/117086800438991948","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/997606","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/comments?post=997606"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/997606\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media\/997607"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media?parent=997606"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/categories?post=997606"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/tags?post=997606"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}